This part of the reference documentation covers the Spring Framework’s integration with a number of Java EE (and related) technologies.
1. Remoting and web services using Spring
1.1. Introduction
Spring features integration classes for remoting support using various technologies. The remoting support eases the development of remote-enabled services, implemented by your usual (Spring) POJOs. Currently, Spring supports the following remoting technologies:
-
Remote Method Invocation (RMI). Through the use of the
RmiProxyFactoryBean
and theRmiServiceExporter
Spring supports both traditional RMI (withjava.rmi.Remote
interfaces andjava.rmi.RemoteException
) and transparent remoting via RMI invokers (with any Java interface). -
Spring’s HTTP invoker. Spring provides a special remoting strategy which allows for Java serialization via HTTP, supporting any Java interface (just like the RMI invoker). The corresponding support classes are
HttpInvokerProxyFactoryBean
andHttpInvokerServiceExporter
. -
Hessian. By using Spring’s
HessianProxyFactoryBean
and theHessianServiceExporter
you can transparently expose your services using the lightweight binary HTTP-based protocol provided by Caucho. -
JAX-WS. Spring provides remoting support for web services via JAX-WS (the successor of JAX-RPC, as introduced in Java EE 5 and Java 6).
-
JMS. Remoting using JMS as the underlying protocol is supported via the
JmsInvokerServiceExporter
andJmsInvokerProxyFactoryBean
classes. -
AMQP. Remoting using AMQP as the underlying protocol is supported by the Spring AMQP project.
While discussing the remoting capabilities of Spring, we’ll use the following domain model and corresponding services:
public class Account implements Serializable{
private String name;
public String getName(){
return name;
}
public void setName(String name) {
this.name = name;
}
}
public interface AccountService {
public void insertAccount(Account account);
public List<Account> getAccounts(String name);
}
// the implementation doing nothing at the moment
public class AccountServiceImpl implements AccountService {
public void insertAccount(Account acc) {
// do something...
}
public List<Account> getAccounts(String name) {
// do something...
}
}
We will start exposing the service to a remote client by using RMI and talk a bit about the drawbacks of using RMI. We’ll then continue to show an example using Hessian as the protocol.
1.2. Exposing services using RMI
Using Spring’s support for RMI, you can transparently expose your services through the RMI infrastructure. After having this set up, you basically have a configuration similar to remote EJBs, except for the fact that there is no standard support for security context propagation or remote transaction propagation. Spring does provide hooks for such additional invocation context when using the RMI invoker, so you can for example plug in security frameworks or custom security credentials here.
1.2.1. Exporting the service using the RmiServiceExporter
Using the RmiServiceExporter
, we can expose the interface of our AccountService object
as RMI object. The interface can be accessed by using RmiProxyFactoryBean
, or via
plain RMI in case of a traditional RMI service. The RmiServiceExporter
explicitly
supports the exposing of any non-RMI services via RMI invokers.
Of course, we first have to set up our service in the Spring container:
<bean id="accountService" class="example.AccountServiceImpl">
<!-- any additional properties, maybe a DAO? -->
</bean>
Next we’ll have to expose our service using the RmiServiceExporter
:
<bean class="org.springframework.remoting.rmi.RmiServiceExporter">
<!-- does not necessarily have to be the same name as the bean to be exported -->
<property name="serviceName" value="AccountService"/>
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
<!-- defaults to 1099 -->
<property name="registryPort" value="1199"/>
</bean>
As you can see, we’re overriding the port for the RMI registry. Often, your application
server also maintains an RMI registry and it is wise to not interfere with that one.
Furthermore, the service name is used to bind the service under. So right now, the
service will be bound at 'rmi://HOST:1199/AccountService'
. We’ll use the URL later on
to link in the service at the client side.
The |
1.2.2. Linking in the service at the client
Our client is a simple object using the AccountService
to manage accounts:
public class SimpleObject {
private AccountService accountService;
public void setAccountService(AccountService accountService) {
this.accountService = accountService;
}
// additional methods using the accountService
}
To link in the service on the client, we’ll create a separate Spring container, containing the simple object and the service linking configuration bits:
<bean class="example.SimpleObject">
<property name="accountService" ref="accountService"/>
</bean>
<bean id="accountService" class="org.springframework.remoting.rmi.RmiProxyFactoryBean">
<property name="serviceUrl" value="rmi://HOST:1199/AccountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>
That’s all we need to do to support the remote account service on the client. Spring
will transparently create an invoker and remotely enable the account service through the
RmiServiceExporter
. At the client we’re linking it in using the RmiProxyFactoryBean
.
1.3. Using Hessian to remotely call services via HTTP
Hessian offers a binary HTTP-based remoting protocol. It is developed by Caucho and more information about Hessian itself can be found at http://www.caucho.com.
1.3.1. Wiring up the DispatcherServlet for Hessian and co.
Hessian communicates via HTTP and does so using a custom servlet. Using Spring’s
DispatcherServlet
principles, as known from Spring Web MVC usage, you can easily wire
up such a servlet exposing your services. First we’ll have to create a new servlet in
your application (this is an excerpt from 'web.xml'
):
<servlet>
<servlet-name>remoting</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>remoting</servlet-name>
<url-pattern>/remoting/*</url-pattern>
</servlet-mapping>
You’re probably familiar with Spring’s DispatcherServlet
principles and if so, you
know that now you’ll have to create a Spring container configuration resource named
'remoting-servlet.xml'
(after the name of your servlet) in the 'WEB-INF'
directory.
The application context will be used in the next section.
Alternatively, consider the use of Spring’s simpler HttpRequestHandlerServlet
. This
allows you to embed the remote exporter definitions in your root application context (by
default in 'WEB-INF/applicationContext.xml'
), with individual servlet definitions
pointing to specific exporter beans. Each servlet name needs to match the bean name of
its target exporter in this case.
1.3.2. Exposing your beans by using the HessianServiceExporter
In the newly created application context called remoting-servlet.xml
, we’ll create a
HessianServiceExporter
exporting your services:
<bean id="accountService" class="example.AccountServiceImpl">
<!-- any additional properties, maybe a DAO? -->
</bean>
<bean name="/AccountService" class="org.springframework.remoting.caucho.HessianServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>
Now we’re ready to link in the service at the client. No explicit handler mapping is
specified, mapping request URLs onto services, so BeanNameUrlHandlerMapping
will be
used: Hence, the service will be exported at the URL indicated through its bean name
within the containing DispatcherServlet
's mapping (as defined above):
'http://HOST:8080/remoting/AccountService'
.
Alternatively, create a HessianServiceExporter
in your root application context (e.g.
in 'WEB-INF/applicationContext.xml'
):
<bean name="accountExporter" class="org.springframework.remoting.caucho.HessianServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>
In the latter case, define a corresponding servlet for this exporter in 'web.xml'
,
with the same end result: The exporter getting mapped to the request path
/remoting/AccountService
. Note that the servlet name needs to match the bean name of
the target exporter.
<servlet>
<servlet-name>accountExporter</servlet-name>
<servlet-class>org.springframework.web.context.support.HttpRequestHandlerServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>accountExporter</servlet-name>
<url-pattern>/remoting/AccountService</url-pattern>
</servlet-mapping>
1.3.3. Linking in the service on the client
Using the HessianProxyFactoryBean
we can link in the service at the client. The same
principles apply as with the RMI example. We’ll create a separate bean factory or
application context and mention the following beans where the SimpleObject
is using
the AccountService
to manage accounts:
<bean class="example.SimpleObject">
<property name="accountService" ref="accountService"/>
</bean>
<bean id="accountService" class="org.springframework.remoting.caucho.HessianProxyFactoryBean">
<property name="serviceUrl" value="http://remotehost:8080/remoting/AccountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>
1.3.4. Applying HTTP basic authentication to a service exposed through Hessian
One of the advantages of Hessian is that we can easily apply HTTP basic authentication,
because both protocols are HTTP-based. Your normal HTTP server security mechanism can
easily be applied through using the web.xml
security features, for example. Usually,
you don’t use per-user security credentials here, but rather shared credentials defined
at the HessianProxyFactoryBean
level (similar to a JDBC DataSource
).
<bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping">
<property name="interceptors" ref="authorizationInterceptor"/>
</bean>
<bean id="authorizationInterceptor"
class="org.springframework.web.servlet.handler.UserRoleAuthorizationInterceptor">
<property name="authorizedRoles" value="administrator,operator"/>
</bean>
This is an example where we explicitly mention the BeanNameUrlHandlerMapping
and set
an interceptor allowing only administrators and operators to call the beans mentioned in
this application context.
Of course, this example doesn’t show a flexible kind of security infrastructure. For more options as far as security is concerned, have a look at the Spring Security project at http://projects.spring.io/spring-security/. |
1.4. Exposing services using HTTP invokers
As opposed to Hessian, which are both lightweight protocols using their own slim serialization mechanisms, Spring HTTP invokers use the standard Java serialization mechanism to expose services through HTTP. This has a huge advantage if your arguments and return types are complex types that cannot be serialized using the serialization mechanisms Hessian uses (refer to the next section for more considerations when choosing a remoting technology).
Under the hood, Spring uses either the standard facilities provided by the JDK or
Apache HttpComponents
to perform HTTP calls. Use the latter if you need more
advanced and easier-to-use functionality. Refer to
hc.apache.org/httpcomponents-client-ga/
for more information.
Be aware of vulnerabilities due to unsafe Java deserialization: Manipulated input streams could lead to unwanted code execution on the server during the deserialization step. As a consequence, do not expose HTTP invoker endpoints to untrusted clients but rather just between your own services. In general, we strongly recommend any other message format (e.g. JSON) instead. If you are concerned about security vulnerabilities due to Java serialization, consider the general-purpose serialization filter mechanism at the core JVM level, originally developed for JDK 9 but backported to JDK 8, 7 and 6 in the meantime: https://blogs.oracle.com/java-platform-group/entry/incoming_filter_serialization_data_a http://openjdk.java.net/jeps/290 |
1.4.1. Exposing the service object
Setting up the HTTP invoker infrastructure for a service object resembles closely the
way you would do the same using Hessian. Just as Hessian support provides the
HessianServiceExporter
, Spring’s HttpInvoker support provides the
org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter
.
To expose the AccountService
(mentioned above) within a Spring Web MVC
DispatcherServlet
, the following configuration needs to be in place in the
dispatcher’s application context:
<bean name="/AccountService" class="org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>
Such an exporter definition will be exposed through the DispatcherServlet
's standard
mapping facilities, as explained in the section on Hessian.
Alternatively, create an HttpInvokerServiceExporter
in your root application context
(e.g. in 'WEB-INF/applicationContext.xml'
):
<bean name="accountExporter" class="org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>
In addition, define a corresponding servlet for this exporter in 'web.xml'
, with the
servlet name matching the bean name of the target exporter:
<servlet>
<servlet-name>accountExporter</servlet-name>
<servlet-class>org.springframework.web.context.support.HttpRequestHandlerServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>accountExporter</servlet-name>
<url-pattern>/remoting/AccountService</url-pattern>
</servlet-mapping>
If you are running outside of a servlet container and are using Oracle’s Java 6, then you
can use the built-in HTTP server implementation. You can configure the
SimpleHttpServerFactoryBean
together with a SimpleHttpInvokerServiceExporter
as is
shown in this example:
<bean name="accountExporter"
class="org.springframework.remoting.httpinvoker.SimpleHttpInvokerServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>
<bean id="httpServer"
class="org.springframework.remoting.support.SimpleHttpServerFactoryBean">
<property name="contexts">
<util:map>
<entry key="/remoting/AccountService" value-ref="accountExporter"/>
</util:map>
</property>
<property name="port" value="8080" />
</bean>
1.4.2. Linking in the service at the client
Again, linking in the service from the client much resembles the way you would do it when using Hessian. Using a proxy, Spring will be able to translate your calls to HTTP POST requests to the URL pointing to the exported service.
<bean id="httpInvokerProxy" class="org.springframework.remoting.httpinvoker.HttpInvokerProxyFactoryBean">
<property name="serviceUrl" value="http://remotehost:8080/remoting/AccountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>
As mentioned before, you can choose what HTTP client you want to use. By default, the
HttpInvokerProxy
uses the JDK’s HTTP functionality, but you can also use the Apache
HttpComponents
client by setting the httpInvokerRequestExecutor
property:
<property name="httpInvokerRequestExecutor">
<bean class="org.springframework.remoting.httpinvoker.HttpComponentsHttpInvokerRequestExecutor"/>
</property>
1.5. Web services
Spring provides full support for standard Java web services APIs:
-
Exposing web services using JAX-WS
-
Accessing web services using JAX-WS
In addition to stock support for JAX-WS in Spring Core, the Spring portfolio also features Spring Web Services, a solution for contract-first, document-driven web services - highly recommended for building modern, future-proof web services.
1.5.1. Exposing servlet-based web services using JAX-WS
Spring provides a convenient base class for JAX-WS servlet endpoint implementations -
SpringBeanAutowiringSupport
. To expose our AccountService
we extend Spring’s
SpringBeanAutowiringSupport
class and implement our business logic here, usually
delegating the call to the business layer. We’ll simply use Spring’s @Autowired
annotation for expressing such dependencies on Spring-managed beans.
/**
* JAX-WS compliant AccountService implementation that simply delegates
* to the AccountService implementation in the root web application context.
*
* This wrapper class is necessary because JAX-WS requires working with dedicated
* endpoint classes. If an existing service needs to be exported, a wrapper that
* extends SpringBeanAutowiringSupport for simple Spring bean autowiring (through
* the @Autowired annotation) is the simplest JAX-WS compliant way.
*
* This is the class registered with the server-side JAX-WS implementation.
* In the case of a Java EE 5 server, this would simply be defined as a servlet
* in web.xml, with the server detecting that this is a JAX-WS endpoint and reacting
* accordingly. The servlet name usually needs to match the specified WS service name.
*
* The web service engine manages the lifecycle of instances of this class.
* Spring bean references will just be wired in here.
*/
import org.springframework.web.context.support.SpringBeanAutowiringSupport;
@WebService(serviceName="AccountService")
public class AccountServiceEndpoint extends SpringBeanAutowiringSupport {
@Autowired
private AccountService biz;
@WebMethod
public void insertAccount(Account acc) {
biz.insertAccount(acc);
}
@WebMethod
public Account[] getAccounts(String name) {
return biz.getAccounts(name);
}
}
Our AccountServiceEndpoint
needs to run in the same web application as the Spring
context to allow for access to Spring’s facilities. This is the case by default in Java
EE 5 environments, using the standard contract for JAX-WS servlet endpoint deployment.
See Java EE 5 web service tutorials for details.
1.5.2. Exporting standalone web services using JAX-WS
The built-in JAX-WS provider that comes with Oracle’s JDK supports exposure of web
services using the built-in HTTP server that’s included in the JDK as well. Spring’s
SimpleJaxWsServiceExporter
detects all @WebService
annotated beans in the Spring
application context, exporting them through the default JAX-WS server (the JDK HTTP
server).
In this scenario, the endpoint instances are defined and managed as Spring beans
themselves; they will be registered with the JAX-WS engine but their lifecycle will be
up to the Spring application context. This means that Spring functionality like explicit
dependency injection may be applied to the endpoint instances. Of course,
annotation-driven injection through @Autowired
will work as well.
<bean class="org.springframework.remoting.jaxws.SimpleJaxWsServiceExporter">
<property name="baseAddress" value="http://localhost:8080/"/>
</bean>
<bean id="accountServiceEndpoint" class="example.AccountServiceEndpoint">
...
</bean>
...
The AccountServiceEndpoint
may derive from Spring’s SpringBeanAutowiringSupport
but
doesn’t have to since the endpoint is a fully Spring-managed bean here. This means that
the endpoint implementation may look like as follows, without any superclass declared -
and Spring’s @Autowired
configuration annotation still being honored:
@WebService(serviceName="AccountService")
public class AccountServiceEndpoint {
@Autowired
private AccountService biz;
@WebMethod
public void insertAccount(Account acc) {
biz.insertAccount(acc);
}
@WebMethod
public List<Account> getAccounts(String name) {
return biz.getAccounts(name);
}
}
1.5.3. Exporting web services using the JAX-WS RI’s Spring support
Oracle’s JAX-WS RI, developed as part of the GlassFish project, ships Spring support as part of its JAX-WS Commons project. This allows for defining JAX-WS endpoints as Spring-managed beans, similar to the standalone mode discussed in the previous section - but this time in a Servlet environment. Note that this is not portable in a Java EE 5 environment; it is mainly intended for non-EE environments such as Tomcat, embedding the JAX-WS RI as part of the web application.
The difference to the standard style of exporting servlet-based endpoints is that the
lifecycle of the endpoint instances themselves will be managed by Spring here, and that
there will be only one JAX-WS servlet defined in web.xml
. With the standard Java EE 5
style (as illustrated above), you’ll have one servlet definition per service endpoint,
with each endpoint typically delegating to Spring beans (through the use of
@Autowired
, as shown above).
Check out https://jax-ws-commons.java.net/spring/ for details on setup and usage style.
1.5.4. Accessing web services using JAX-WS
Spring provides two factory beans to create JAX-WS web service proxies, namely
LocalJaxWsServiceFactoryBean
and JaxWsPortProxyFactoryBean
. The former can only
return a JAX-WS service class for us to work with. The latter is the full-fledged
version that can return a proxy that implements our business service interface. In this
example we use the latter to create a proxy for the AccountService
endpoint (again):
<bean id="accountWebService" class="org.springframework.remoting.jaxws.JaxWsPortProxyFactoryBean">
<property name="serviceInterface" value="example.AccountService"/>
<property name="wsdlDocumentUrl" value="http://localhost:8888/AccountServiceEndpoint?WSDL"/>
<property name="namespaceUri" value="http://example/"/>
<property name="serviceName" value="AccountService"/>
<property name="portName" value="AccountServiceEndpointPort"/>
</bean>
Where serviceInterface
is our business interface the clients will use.
wsdlDocumentUrl
is the URL for the WSDL file. Spring needs this a startup time to
create the JAX-WS Service. namespaceUri
corresponds to the targetNamespace in the
.wsdl file. serviceName
corresponds to the service name in the .wsdl file. portName
corresponds to the port name in the .wsdl file.
Accessing the web service is now very easy as we have a bean factory for it that will
expose it as AccountService
interface. We can wire this up in Spring:
<bean id="client" class="example.AccountClientImpl">
...
<property name="service" ref="accountWebService"/>
</bean>
From the client code we can access the web service just as if it was a normal class:
public class AccountClientImpl {
private AccountService service;
public void setService(AccountService service) {
this.service = service;
}
public void foo() {
service.insertAccount(...);
}
}
The above is slightly simplified in that JAX-WS requires endpoint interfaces
and implementation classes to be annotated with |
1.6. JMS
It is also possible to expose services transparently using JMS as the underlying
communication protocol. The JMS remoting support in the Spring Framework is pretty basic
- it sends and receives on the same thread
and in the same non-transactional
Session
, and as such throughput will be very implementation dependent. Note that these
single-threaded and non-transactional constraints apply only to Spring’s JMS
remoting support. See JMS (Java Message Service) for information on Spring’s rich support for JMS-based
messaging.
The following interface is used on both the server and the client side.
package com.foo;
public interface CheckingAccountService {
public void cancelAccount(Long accountId);
}
The following simple implementation of the above interface is used on the server-side.
package com.foo;
public class SimpleCheckingAccountService implements CheckingAccountService {
public void cancelAccount(Long accountId) {
System.out.println("Cancelling account [" + accountId + "]");
}
}
This configuration file contains the JMS-infrastructure beans that are shared on both the client and server.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="connectionFactory" class="org.apache.activemq.ActiveMQConnectionFactory">
<property name="brokerURL" value="tcp://ep-t43:61616"/>
</bean>
<bean id="queue" class="org.apache.activemq.command.ActiveMQQueue">
<constructor-arg value="mmm"/>
</bean>
</beans>
1.6.1. Server-side configuration
On the server, you just need to expose the service object using the
JmsInvokerServiceExporter
.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="checkingAccountService"
class="org.springframework.jms.remoting.JmsInvokerServiceExporter">
<property name="serviceInterface" value="com.foo.CheckingAccountService"/>
<property name="service">
<bean class="com.foo.SimpleCheckingAccountService"/>
</property>
</bean>
<bean class="org.springframework.jms.listener.SimpleMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="queue"/>
<property name="concurrentConsumers" value="3"/>
<property name="messageListener" ref="checkingAccountService"/>
</bean>
</beans>
package com.foo;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Server {
public static void main(String[] args) throws Exception {
new ClassPathXmlApplicationContext(new String[]{"com/foo/server.xml", "com/foo/jms.xml"});
}
}
1.6.2. Client-side configuration
The client merely needs to create a client-side proxy that will implement the agreed
upon interface ( CheckingAccountService
). The resulting object created off the back of
the following bean definition can be injected into other client side objects, and the
proxy will take care of forwarding the call to the server-side object via JMS.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="checkingAccountService"
class="org.springframework.jms.remoting.JmsInvokerProxyFactoryBean">
<property name="serviceInterface" value="com.foo.CheckingAccountService"/>
<property name="connectionFactory" ref="connectionFactory"/>
<property name="queue" ref="queue"/>
</bean>
</beans>
package com.foo;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Client {
public static void main(String[] args) throws Exception {
ApplicationContext ctx = new ClassPathXmlApplicationContext(
new String[] {"com/foo/client.xml", "com/foo/jms.xml"});
CheckingAccountService service = (CheckingAccountService) ctx.getBean("checkingAccountService");
service.cancelAccount(new Long(10));
}
}
1.7. AMQP
Refer to the Spring AMQP Reference Document 'Spring Remoting with AMQP' section for more information.
1.8. Auto-detection is not implemented for remote interfaces
The main reason why auto-detection of implemented interfaces does not occur for remote
interfaces is to avoid opening too many doors to remote callers. The target object might
implement internal callback interfaces like InitializingBean
or DisposableBean
which
one would not want to expose to callers.
Offering a proxy with all interfaces implemented by the target usually does not matter in the local case. But when exporting a remote service, you should expose a specific service interface, with specific operations intended for remote usage. Besides internal callback interfaces, the target might implement multiple business interfaces, with just one of them intended for remote exposure. For these reasons, we require such a service interface to be specified.
This is a trade-off between configuration convenience and the risk of accidental exposure of internal methods. Always specifying a service interface is not too much effort, and puts you on the safe side regarding controlled exposure of specific methods.
1.9. Considerations when choosing a technology
Each and every technology presented here has its drawbacks. You should carefully consider your needs, the services you are exposing and the objects you’ll be sending over the wire when choosing a technology.
When using RMI, it’s not possible to access the objects through the HTTP protocol, unless you’re tunneling the RMI traffic. RMI is a fairly heavy-weight protocol in that it supports full-object serialization which is important when using a complex data model that needs serialization over the wire. However, RMI-JRMP is tied to Java clients: It is a Java-to-Java remoting solution.
Spring’s HTTP invoker is a good choice if you need HTTP-based remoting but also rely on Java serialization. It shares the basic infrastructure with RMI invokers, just using HTTP as transport. Note that HTTP invokers are not only limited to Java-to-Java remoting but also to Spring on both the client and server side. (The latter also applies to Spring’s RMI invoker for non-RMI interfaces.)
Hessian might provide significant value when operating in a heterogeneous environment, because they explicitly allow for non-Java clients. However, non-Java support is still limited. Known issues include the serialization of Hibernate objects in combination with lazily-initialized collections. If you have such a data model, consider using RMI or HTTP invokers instead of Hessian.
JMS can be useful for providing clusters of services and allowing the JMS broker to take care of load balancing, discovery and auto-failover. By default: Java serialization is used when using JMS remoting but the JMS provider could use a different mechanism for the wire formatting, such as XStream to allow servers to be implemented in other technologies.
Last but not least, EJB has an advantage over RMI in that it supports standard role-based authentication and authorization and remote transaction propagation. It is possible to get RMI invokers or HTTP invokers to support security context propagation as well, although this is not provided by core Spring: There are just appropriate hooks for plugging in third-party or custom solutions here.
1.10. Accessing REST endpoints
The Spring Framework has two choices for client-side access to REST endpoints:
-
RestTemplate — the original Spring REST client with an API similar to other template classes in Spring such as
JdbcTemplate
,JmsTemplate
and others.RestTemplate
has a synchronous API and relies on blocking I/O which is okay for client scenarios with low concurrency. -
WebClient — reactive client with a functional, fluent API from the
spring-webflux
module. It relies on non-blocking I/O which allows it to support high concurrency more efficiently (i.e. using a small number of threads) than theRestTemplate
.WebClient
is a natural fit for streaming scenarios.
1.10.1. RestTemplate
The RestTemplate
provides a higher level API over HTTP client libraries with methods
that correspond to each of the six main HTTP methods that make invoking many RESTful
services a one-liner and enforce REST best practices.
HTTP Method | RestTemplate Method |
---|---|
DELETE |
|
GET |
|
HEAD |
|
OPTIONS |
|
POST |
postForLocation(String url, Object request, String… uriVariables) postForObject(String url, Object request, Class<T> responseType, String… uriVariables) |
PUT |
|
PATCH and others |
The names of RestTemplate
methods follow a naming convention, the first part indicates
what HTTP method is being invoked and the second part indicates what is returned. For
example, the method getForObject()
will perform a GET, convert the HTTP response into
an object type of your choice and return that object. The method postForLocation()
will do a POST, converting the given object into a HTTP request and return the response
HTTP Location header where the newly created object can be found. In case of an
exception processing the HTTP request, an exception of the type RestClientException
will be thrown; this behavior can be changed by plugging in another
ResponseErrorHandler
implementation into the RestTemplate
.
The exchange
and execute
methods are generalized versions of the more
specific methods listed above them and can support additional combinations and methods,
like HTTP PATCH. However, note that the underlying HTTP library must also support the
desired combination. The JDK HttpURLConnection
does not support the PATCH
method, but
Apache HttpComponents HttpClient version 4.2 or later does. They also enable
RestTemplate
to read an HTTP response to a generic type (e.g. List<Account>
), using a
ParameterizedTypeReference
, a new class that enables capturing and passing generic
type info.
Objects passed to and returned from these methods are converted to and from HTTP
messages by HttpMessageConverter
instances. Converters for the main mime types are
registered by default, but you can also write your own converter and register it via the
messageConverters()
bean property. The default converter instances registered with the
template are ByteArrayHttpMessageConverter
, StringHttpMessageConverter
,
FormHttpMessageConverter
and SourceHttpMessageConverter
. You can override these
defaults using the messageConverters()
bean property as would be required if using the
MarshallingHttpMessageConverter
or MappingJackson2HttpMessageConverter
.
Each method takes URI template arguments in two forms, either as a String
variable-length argument or a Map<String,String>
. For example,
String result = restTemplate.getForObject(
"http://example.com/hotels/{hotel}/bookings/{booking}", String.class,"42", "21");
using variable-length arguments and
Map<String, String> vars = Collections.singletonMap("hotel", "42");
String result = restTemplate.getForObject(
"http://example.com/hotels/{hotel}/rooms/{hotel}", String.class, vars);
using a Map<String,String>
.
To create an instance of RestTemplate
you can simply call the default no-arg
constructor. This will use standard Java classes from the java.net
package as the
underlying implementation to create HTTP requests. This can be overridden by specifying
an implementation of ClientHttpRequestFactory
. Spring provides the implementation
HttpComponentsClientHttpRequestFactory
that uses the Apache HttpComponents
HttpClient
to create requests. HttpComponentsClientHttpRequestFactory
is configured
using an instance of org.apache.http.client.HttpClient
which can in turn be configured
with credentials information or connection pooling functionality.
Note that the |
The previous example using Apache HttpComponents HttpClient
directly rewritten to use
the RestTemplate
is shown below
uri = "http://example.com/hotels/{id}/bookings";
RestTemplate template = new RestTemplate();
Booking booking = // create booking object
URI location = template.postForLocation(uri, booking, "1");
To use Apache HttpComponents instead of the native java.net
functionality, construct
the RestTemplate
as follows:
RestTemplate template = new RestTemplate(new HttpComponentsClientHttpRequestFactory());
Apache HttpClient supports gzip encoding. To use it,
construct a
|
The general callback interface is RequestCallback
and is called when the execute
method is invoked.
public <T> T execute(String url, HttpMethod method, RequestCallback requestCallback,
ResponseExtractor<T> responseExtractor, String... uriVariables)
// also has an overload with uriVariables as a Map<String, String>.
The RequestCallback
interface is defined as
public interface RequestCallback {
void doWithRequest(ClientHttpRequest request) throws IOException;
}
and allows you to manipulate the request headers and write to the request body. When using the execute method you do not have to worry about any resource management, the template will always close the request and handle any errors. Refer to the API documentation for more information on using the execute method and the meaning of its other method arguments.
Working with the URI
For each of the main HTTP methods, the RestTemplate
provides two variants that take
either a String URI template or java.net.URI
as the first argument. When using a String
URI template, encoding is automatically applied:
restTemplate.getForObject("http://example.com/hotel list", String.class);
The resulting target URI is "http://example.com/hotel%20list". Alternatively you can
provide an already prepared java.net.URI
that will be used as is. For more information
on preparing URIs or customizing how the RestTemplate
expands URI templates, see
URI Links in the "Web Servlet" section.
Dealing with request and response headers
Besides the methods described above, the RestTemplate
also has the exchange()
method, which can be used for arbitrary HTTP method execution based on the HttpEntity
class.
Perhaps most importantly, the exchange()
method can be used to add request headers and
read response headers. For example:
HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.set("MyRequestHeader", "MyValue");
HttpEntity<?> requestEntity = new HttpEntity(requestHeaders);
HttpEntity<String> response = template.exchange(
"http://example.com/hotels/{hotel}",
HttpMethod.GET, requestEntity, String.class, "42");
String responseHeader = response.getHeaders().getFirst("MyResponseHeader");
String body = response.getBody();
In the above example, we first prepare a request entity that contains the
MyRequestHeader
header. We then retrieve the response, and read the MyResponseHeader
and body.
Jackson JSON Views support
It is possible to specify a Jackson JSON View to serialize only a subset of the object properties. For example:
MappingJacksonValue value = new MappingJacksonValue(new User("eric", "7!jd#h23"));
value.setSerializationView(User.WithoutPasswordView.class);
HttpEntity<MappingJacksonValue> entity = new HttpEntity<MappingJacksonValue>(value);
String s = template.postForObject("http://example.com/user", entity, String.class);
1.10.2. HTTP Message Converters
The spring-web
module contains the HttpMessageConverter
contract for reading and
writing the body of HTTP requests and responses via InputStream
and OutputStream
.
HttpMessageConverter
's are used on the client side, e.g. in the RestTemplate
, and
also on the server side, e.g. in Spring MVC REST controllers.
Concrete implementations for the main media (mime) types are provided in the framework
and are registered by default with the RestTemplate
on the client-side and with
RequestMethodHandlerAdapter
on the server-side (see
Configuring Message Converters).
The implementations of HttpMessageConverter
s are described in the following sections.
For all converters a default media type is used but can be overridden by setting the
supportedMediaTypes
bean property
StringHttpMessageConverter
An HttpMessageConverter
implementation that can read and write Strings from the HTTP
request and response. By default, this converter supports all text media types (
text/*
), and writes with a Content-Type
of text/plain
.
FormHttpMessageConverter
An HttpMessageConverter
implementation that can read and write form data from the HTTP
request and response. By default, this converter reads and writes the media type
application/x-www-form-urlencoded
. Form data is read from and written into a
MultiValueMap<String, String>
.
ByteArrayHttpMessageConverter
An HttpMessageConverter
implementation that can read and write byte arrays from the
HTTP request and response. By default, this converter supports all media types ( */*
),
and writes with a Content-Type
of application/octet-stream
. This can be overridden
by setting the supportedMediaTypes
property, and overriding getContentType(byte[])
.
MarshallingHttpMessageConverter
An HttpMessageConverter
implementation that can read and write XML using Spring’s
Marshaller
and Unmarshaller
abstractions from the org.springframework.oxm
package.
This converter requires a Marshaller
and Unmarshaller
before it can be used. These
can be injected via constructor or bean properties. By default this converter supports (
text/xml
) and ( application/xml
).
MappingJackson2HttpMessageConverter
An HttpMessageConverter
implementation that can read and write JSON using Jackson’s
ObjectMapper
. JSON mapping can be customized as needed through the use of Jackson’s
provided annotations. When further control is needed, a custom ObjectMapper
can be
injected through the ObjectMapper
property for cases where custom JSON
serializers/deserializers need to be provided for specific types. By default this
converter supports ( application/json
).
MappingJackson2XmlHttpMessageConverter
An HttpMessageConverter
implementation that can read and write XML using
Jackson XML extension’s
XmlMapper
. XML mapping can be customized as needed through the use of JAXB
or Jackson’s provided annotations. When further control is needed, a custom XmlMapper
can be injected through the ObjectMapper
property for cases where custom XML
serializers/deserializers need to be provided for specific types. By default this
converter supports ( application/xml
).
1.10.3. Async RestTemplate
The AsyncRestTemplate
is deprecated.
Please use the WebClient instead.
2. Enterprise JavaBeans (EJB) integration
2.1. Introduction
As a lightweight container, Spring is often considered an EJB replacement. We do believe that for many if not most applications and use cases, Spring as a container, combined with its rich supporting functionality in the area of transactions, ORM and JDBC access, is a better choice than implementing equivalent functionality via an EJB container and EJBs.
However, it is important to note that using Spring does not prevent you from using EJBs. In fact, Spring makes it much easier to access EJBs and implement EJBs and functionality within them. Additionally, using Spring to access services provided by EJBs allows the implementation of those services to later transparently be switched between local EJB, remote EJB, or POJO (plain old Java object) variants, without the client code having to be changed.
In this chapter, we look at how Spring can help you access and implement EJBs. Spring provides particular value when accessing stateless session beans (SLSBs), so we’ll begin by discussing this.
2.2. Accessing EJBs
2.2.1. Concepts
To invoke a method on a local or remote stateless session bean, client code must normally perform a JNDI lookup to obtain the (local or remote) EJB Home object, then use a 'create' method call on that object to obtain the actual (local or remote) EJB object. One or more methods are then invoked on the EJB.
To avoid repeated low-level code, many EJB applications use the Service Locator and Business Delegate patterns. These are better than spraying JNDI lookups throughout client code, but their usual implementations have significant disadvantages. For example:
-
Typically code using EJBs depends on Service Locator or Business Delegate singletons, making it hard to test.
-
In the case of the Service Locator pattern used without a Business Delegate, application code still ends up having to invoke the create() method on an EJB home, and deal with the resulting exceptions. Thus it remains tied to the EJB API and the complexity of the EJB programming model.
-
Implementing the Business Delegate pattern typically results in significant code duplication, where we have to write numerous methods that simply call the same method on the EJB.
The Spring approach is to allow the creation and use of proxy objects, normally configured inside a Spring container, which act as codeless business delegates. You do not need to write another Service Locator, another JNDI lookup, or duplicate methods in a hand-coded Business Delegate unless you are actually adding real value in such code.
2.2.2. Accessing local SLSBs
Assume that we have a web controller that needs to use a local EJB. We’ll follow best
practice and use the EJB Business Methods Interface pattern, so that the EJB’s local
interface extends a non EJB-specific business methods interface. Let’s call this
business methods interface MyComponent
.
public interface MyComponent {
...
}
One of the main reasons to use the Business Methods Interface pattern is to ensure that
synchronization between method signatures in local interface and bean implementation
class is automatic. Another reason is that it later makes it much easier for us to
switch to a POJO (plain old Java object) implementation of the service if it makes sense
to do so. Of course we’ll also need to implement the local home interface and provide an
implementation class that implements SessionBean
and the MyComponent
business
methods interface. Now the only Java coding we’ll need to do to hook up our web tier
controller to the EJB implementation is to expose a setter method of type MyComponent
on the controller. This will save the reference as an instance variable in the
controller:
private MyComponent myComponent;
public void setMyComponent(MyComponent myComponent) {
this.myComponent = myComponent;
}
We can subsequently use this instance variable in any business method in the controller.
Now assuming we are obtaining our controller object out of a Spring container, we can
(in the same context) configure a LocalStatelessSessionProxyFactoryBean
instance,
which will be the EJB proxy object. The configuration of the proxy, and setting of the
myComponent
property of the controller is done with a configuration entry such as:
<bean id="myComponent"
class="org.springframework.ejb.access.LocalStatelessSessionProxyFactoryBean">
<property name="jndiName" value="ejb/myBean"/>
<property name="businessInterface" value="com.mycom.MyComponent"/>
</bean>
<bean id="myController" class="com.mycom.myController">
<property name="myComponent" ref="myComponent"/>
</bean>
There’s a lot of work happening behind the scenes, courtesy of the Spring AOP framework,
although you aren’t forced to work with AOP concepts to enjoy the results. The
myComponent
bean definition creates a proxy for the EJB, which implements the business
method interface. The EJB local home is cached on startup, so there’s only a single JNDI
lookup. Each time the EJB is invoked, the proxy invokes the classname
method on the
local EJB and invokes the corresponding business method on the EJB.
The myController
bean definition sets the myComponent
property of the controller
class to the EJB proxy.
Alternatively (and preferably in case of many such proxy definitions), consider using
the <jee:local-slsb>
configuration element in Spring’s "jee" namespace:
<jee:local-slsb id="myComponent" jndi-name="ejb/myBean"
business-interface="com.mycom.MyComponent"/>
<bean id="myController" class="com.mycom.myController">
<property name="myComponent" ref="myComponent"/>
</bean>
This EJB access mechanism delivers huge simplification of application code: the web tier
code (or other EJB client code) has no dependence on the use of EJB. If we want to
replace this EJB reference with a POJO or a mock object or other test stub, we could
simply change the myComponent
bean definition without changing a line of Java code.
Additionally, we haven’t had to write a single line of JNDI lookup or other EJB plumbing
code as part of our application.
Benchmarks and experience in real applications indicate that the performance overhead of this approach (which involves reflective invocation of the target EJB) is minimal, and is typically undetectable in typical use. Remember that we don’t want to make fine-grained calls to EJBs anyway, as there’s a cost associated with the EJB infrastructure in the application server.
There is one caveat with regards to the JNDI lookup. In a bean container, this class is
normally best used as a singleton (there simply is no reason to make it a prototype).
However, if that bean container pre-instantiates singletons (as do the various XML
ApplicationContext
variants) you may have a problem if the bean container is loaded
before the EJB container loads the target EJB. That is because the JNDI lookup will be
performed in the init()
method of this class and then cached, but the EJB will not
have been bound at the target location yet. The solution is to not pre-instantiate this
factory object, but allow it to be created on first use. In the XML containers, this is
controlled via the lazy-init
attribute.
Although this will not be of interest to the majority of Spring users, those doing
programmatic AOP work with EJBs may want to look at LocalSlsbInvokerInterceptor
.
2.2.3. Accessing remote SLSBs
Accessing remote EJBs is essentially identical to accessing local EJBs, except that the
SimpleRemoteStatelessSessionProxyFactoryBean
or <jee:remote-slsb>
configuration
element is used. Of course, with or without Spring, remote invocation semantics apply; a
call to a method on an object in another VM in another computer does sometimes have to
be treated differently in terms of usage scenarios and failure handling.
Spring’s EJB client support adds one more advantage over the non-Spring approach.
Normally it is problematic for EJB client code to be easily switched back and forth
between calling EJBs locally or remotely. This is because the remote interface methods
must declare that they throw RemoteException
, and client code must deal with this,
while the local interface methods don’t. Client code written for local EJBs which needs
to be moved to remote EJBs typically has to be modified to add handling for the remote
exceptions, and client code written for remote EJBs which needs to be moved to local
EJBs, can either stay the same but do a lot of unnecessary handling of remote
exceptions, or needs to be modified to remove that code. With the Spring remote EJB
proxy, you can instead not declare any thrown RemoteException
in your Business Method
Interface and implementing EJB code, have a remote interface which is identical except
that it does throw RemoteException
, and rely on the proxy to dynamically treat the two
interfaces as if they were the same. That is, client code does not have to deal with the
checked RemoteException
class. Any actual RemoteException
that is thrown during the
EJB invocation will be re-thrown as the non-checked RemoteAccessException
class, which
is a subclass of RuntimeException
. The target service can then be switched at will
between a local EJB or remote EJB (or even plain Java object) implementation, without
the client code knowing or caring. Of course, this is optional; there is nothing
stopping you from declaring RemoteExceptions
in your business interface.
2.2.4. Accessing EJB 2.x SLSBs versus EJB 3 SLSBs
Accessing EJB 2.x Session Beans and EJB 3 Session Beans via Spring is largely
transparent. Spring’s EJB accessors, including the <jee:local-slsb>
and
<jee:remote-slsb>
facilities, transparently adapt to the actual component at runtime.
They handle a home interface if found (EJB 2.x style), or perform straight component
invocations if no home interface is available (EJB 3 style).
Note: For EJB 3 Session Beans, you could effectively use a JndiObjectFactoryBean
/
<jee:jndi-lookup>
as well, since fully usable component references are exposed for
plain JNDI lookups there. Defining explicit <jee:local-slsb>
/ <jee:remote-slsb>
lookups simply provides consistent and more explicit EJB access configuration.
3. JMS (Java Message Service)
3.1. Introduction
Spring provides a JMS integration framework that simplifies the use of the JMS API much like Spring’s integration does for the JDBC API.
JMS can be roughly divided into two areas of functionality, namely the production and
consumption of messages. The JmsTemplate
class is used for message production and
synchronous message reception. For asynchronous reception similar to Java EE’s
message-driven bean style, Spring provides a number of message listener containers that
are used to create Message-Driven POJOs (MDPs). Spring also provides a declarative way
of creating message listeners.
The package org.springframework.jms.core
provides the core functionality for using
JMS. It contains JMS template classes that simplify the use of the JMS by handling the
creation and release of resources, much like the JdbcTemplate
does for JDBC. The
design principle common to Spring template classes is to provide helper methods to
perform common operations and for more sophisticated usage, delegate the essence of the
processing task to user implemented callback interfaces. The JMS template follows the
same design. The classes offer various convenience methods for the sending of messages,
consuming a message synchronously, and exposing the JMS session and message producer to
the user.
The package org.springframework.jms.support
provides JMSException
translation
functionality. The translation converts the checked JMSException
hierarchy to a
mirrored hierarchy of unchecked exceptions. If there are any provider specific
subclasses of the checked javax.jms.JMSException
, this exception is wrapped in the
unchecked UncategorizedJmsException
.
The package org.springframework.jms.support.converter
provides a MessageConverter
abstraction to convert between Java objects and JMS messages.
The package org.springframework.jms.support.destination
provides various strategies
for managing JMS destinations, such as providing a service locator for destinations
stored in JNDI.
The package org.springframework.jms.annotation
provides the necessary infrastructure
to support annotation-driven listener endpoints using @JmsListener
.
The package org.springframework.jms.config
provides the parser implementation for the
jms
namespace as well the java config support to configure listener containers and
create listener endpoints.
Finally, the package org.springframework.jms.connection
provides an implementation of
the ConnectionFactory
suitable for use in standalone applications. It also contains an
implementation of Spring’s PlatformTransactionManager
for JMS (the cunningly named
JmsTransactionManager
). This allows for seamless integration of JMS as a transactional
resource into Spring’s transaction management mechanisms.
3.2. Using Spring JMS
3.2.1. JmsTemplate
The JmsTemplate
class is the central class in the JMS core package. It simplifies the
use of JMS since it handles the creation and release of resources when sending or
synchronously receiving messages.
Code that uses the JmsTemplate
only needs to implement callback interfaces giving them
a clearly defined high level contract. The MessageCreator
callback interface creates a
message given a Session
provided by the calling code in JmsTemplate
. In order to
allow for more complex usage of the JMS API, the callback SessionCallback
provides the
user with the JMS session and the callback ProducerCallback
exposes a Session
and
MessageProducer
pair.
The JMS API exposes two types of send methods, one that takes delivery mode, priority,
and time-to-live as Quality of Service (QOS) parameters and one that takes no QOS
parameters which uses default values. Since there are many send methods in
JmsTemplate
, the setting of the QOS parameters have been exposed as bean properties to
avoid duplication in the number of send methods. Similarly, the timeout value for
synchronous receive calls is set using the property setReceiveTimeout
.
Some JMS providers allow the setting of default QOS values administratively through the
configuration of the ConnectionFactory
. This has the effect that a call to
MessageProducer
's send method send(Destination destination, Message message)
will
use different QOS default values than those specified in the JMS specification. In order
to provide consistent management of QOS values, the JmsTemplate
must therefore be
specifically enabled to use its own QOS values by setting the boolean property
isExplicitQosEnabled
to true
.
For convenience, JmsTemplate
also exposes a basic request-reply operation that allows
to send a message and wait for a reply on a temporary queue that is created as part of
the operation.
Instances of the |
As of Spring Framework 4.1, JmsMessagingTemplate
is built on top of JmsTemplate
and provides an integration with the messaging abstraction, i.e.
org.springframework.messaging.Message
. This allows you to create the message to
send in generic manner.
3.2.2. Connections
The JmsTemplate
requires a reference to a ConnectionFactory
. The ConnectionFactory
is part of the JMS specification and serves as the entry point for working with JMS. It
is used by the client application as a factory to create connections with the JMS
provider and encapsulates various configuration parameters, many of which are vendor
specific such as SSL configuration options.
When using JMS inside an EJB, the vendor provides implementations of the JMS interfaces
so that they can participate in declarative transaction management and perform pooling
of connections and sessions. In order to use this implementation, Java EE containers
typically require that you declare a JMS connection factory as a resource-ref
inside
the EJB or servlet deployment descriptors. To ensure the use of these features with the
JmsTemplate
inside an EJB, the client application should ensure that it references the
managed implementation of the ConnectionFactory
.
Caching Messaging Resources
The standard API involves creating many intermediate objects. To send a message the following 'API' walk is performed
ConnectionFactory->Connection->Session->MessageProducer->send
Between the ConnectionFactory and the Send operation there are three intermediate
objects that are created and destroyed. To optimise the resource usage and increase
performance two implementations of ConnectionFactory
are provided.
SingleConnectionFactory
Spring provides an implementation of the ConnectionFactory
interface,
SingleConnectionFactory
, that will return the same Connection
on all
createConnection()
calls and ignore calls to close()
. This is useful for testing and
standalone environments so that the same connection can be used for multiple
JmsTemplate
calls that may span any number of transactions. SingleConnectionFactory
takes a reference to a standard ConnectionFactory
that would typically come from JNDI.
CachingConnectionFactory
The CachingConnectionFactory
extends the functionality of SingleConnectionFactory
and adds the caching of Sessions, MessageProducers, and MessageConsumers. The initial
cache size is set to 1, use the property sessionCacheSize
to increase the number of
cached sessions. Note that the number of actual cached sessions will be more than that
number as sessions are cached based on their acknowledgment mode, so there can be up to
4 cached session instances when sessionCacheSize
is set to one, one for each
acknowledgment mode. MessageProducers and MessageConsumers are cached within their
owning session and also take into account the unique properties of the producers and
consumers when caching. MessageProducers are cached based on their destination.
MessageConsumers are cached based on a key composed of the destination, selector,
noLocal delivery flag, and the durable subscription name (if creating durable consumers).
3.2.3. Destination Management
Destinations, like ConnectionFactories, are JMS administered objects that can be stored
and retrieved in JNDI. When configuring a Spring application context you can use the
JNDI factory class JndiObjectFactoryBean
/ <jee:jndi-lookup>
to perform dependency
injection on your object’s references to JMS destinations. However, often this strategy
is cumbersome if there are a large number of destinations in the application or if there
are advanced destination management features unique to the JMS provider. Examples of
such advanced destination management would be the creation of dynamic destinations or
support for a hierarchical namespace of destinations. The JmsTemplate
delegates the
resolution of a destination name to a JMS destination object to an implementation of the
interface DestinationResolver
. DynamicDestinationResolver
is the default
implementation used by JmsTemplate
and accommodates resolving dynamic destinations. A
JndiDestinationResolver
is also provided that acts as a service locator for
destinations contained in JNDI and optionally falls back to the behavior contained in
DynamicDestinationResolver
.
Quite often the destinations used in a JMS application are only known at runtime and
therefore cannot be administratively created when the application is deployed. This is
often because there is shared application logic between interacting system components
that create destinations at runtime according to a well-known naming convention. Even
though the creation of dynamic destinations is not part of the JMS specification, most
vendors have provided this functionality. Dynamic destinations are created with a name
defined by the user which differentiates them from temporary destinations and are often
not registered in JNDI. The API used to create dynamic destinations varies from provider
to provider since the properties associated with the destination are vendor specific.
However, a simple implementation choice that is sometimes made by vendors is to
disregard the warnings in the JMS specification and to use the TopicSession
method
createTopic(String topicName)
or the QueueSession
method createQueue(String
queueName)
to create a new destination with default destination properties. Depending
on the vendor implementation, DynamicDestinationResolver
may then also create a
physical destination instead of only resolving one.
The boolean property pubSubDomain
is used to configure the JmsTemplate
with
knowledge of what JMS domain is being used. By default the value of this property is
false, indicating that the point-to-point domain, Queues, will be used. This property
used by JmsTemplate
determines the behavior of dynamic destination resolution via
implementations of the DestinationResolver
interface.
You can also configure the JmsTemplate
with a default destination via the property
defaultDestination
. The default destination will be used with send and receive
operations that do not refer to a specific destination.
3.2.4. Message Listener Containers
One of the most common uses of JMS messages in the EJB world is to drive message-driven
beans (MDBs). Spring offers a solution to create message-driven POJOs (MDPs) in a way
that does not tie a user to an EJB container. (See Asynchronous reception: Message-Driven POJOs
for detailed coverage of Spring’s MDP support.) As from Spring Framework 4.1, endpoint
methods can be simply annotated using @JmsListener
see Annotation-driven listener endpoints for more
details.
A message listener container is used to receive messages from a JMS message queue and
drive the MessageListener
that is injected into it. The listener container is
responsible for all threading of message reception and dispatches into the listener for
processing. A message listener container is the intermediary between an MDP and a
messaging provider, and takes care of registering to receive messages, participating in
transactions, resource acquisition and release, exception conversion and suchlike. This
allows you as an application developer to write the (possibly complex) business logic
associated with receiving a message (and possibly responding to it), and delegates
boilerplate JMS infrastructure concerns to the framework.
There are two standard JMS message listener containers packaged with Spring, each with its specialised feature set.
SimpleMessageListenerContainer
This message listener container is the simpler of the two standard flavors. It creates a
fixed number of JMS sessions and consumers at startup, registers the listener using the
standard JMS MessageConsumer.setMessageListener()
method, and leaves it up the JMS
provider to perform listener callbacks. This variant does not allow for dynamic adaption
to runtime demands or for participation in externally managed transactions.
Compatibility-wise, it stays very close to the spirit of the standalone JMS
specification - but is generally not compatible with Java EE’s JMS restrictions.
While The default 'AUTO_ACKNOWLEDGE' mode does not provide proper reliability guarantees. Messages may get lost when listener execution fails (since the provider will automatically acknowledge each message after listener invocation, with no exceptions to be propagated to the provider) or when the listener container shuts down (this may be configured through the 'acceptMessagesWhileStopping' flag). Make sure to use transacted sessions in case of reliability needs, e.g. for reliable queue handling and durable topic subscriptions. |
DefaultMessageListenerContainer
This message listener container is the one used in most cases. In contrast to
SimpleMessageListenerContainer
, this container variant allows for dynamic adaptation
to runtime demands and is able to participate in externally managed transactions. Each
received message is registered with an XA transaction when configured with a
JtaTransactionManager
; so processing may take advantage of XA transaction semantics.
This listener container strikes a good balance between low requirements on the JMS
provider, advanced functionality such as the participation in externally managed
transactions, and compatibility with Java EE environments.
The cache level of the container can be customized. Note that when no caching is enabled, a new connection and a new session is created for each message reception. Combining this with a non durable subscription with high loads may lead to message lost. Make sure to use a proper cache level in such case.
This container also has recoverable capabilities when the broker goes down. By default,
a simple BackOff
implementation retries every 5 seconds. It is possible to specify
a custom BackOff
implementation for more fine-grained recovery options, see
ExponentialBackOff
for an example.
Like its sibling The default 'AUTO_ACKNOWLEDGE' mode does not provide proper reliability guarantees. Messages may get lost when listener execution fails (since the provider will automatically acknowledge each message before listener invocation) or when the listener container shuts down (this may be configured through the 'acceptMessagesWhileStopping' flag). Make sure to use transacted sessions in case of reliability needs, e.g. for reliable queue handling and durable topic subscriptions. |
3.2.5. Transaction management
Spring provides a JmsTransactionManager
that manages transactions for a single JMS
ConnectionFactory
. This allows JMS applications to leverage the managed transaction
features of Spring as described in Transaction Management.
The JmsTransactionManager
performs local resource transactions, binding a JMS
Connection/Session pair from the specified ConnectionFactory
to the thread.
JmsTemplate
automatically detects such transactional resources and operates
on them accordingly.
In a Java EE environment, the ConnectionFactory
will pool Connections and Sessions, so
those resources are efficiently reused across transactions. In a standalone environment,
using Spring’s SingleConnectionFactory
will result in a shared JMS Connection
, with
each transaction having its own independent Session
. Alternatively, consider the use
of a provider-specific pooling adapter such as ActiveMQ’s PooledConnectionFactory
class.
JmsTemplate
can also be used with the JtaTransactionManager
and an XA-capable JMS
ConnectionFactory
for performing distributed transactions. Note that this requires the
use of a JTA transaction manager as well as a properly XA-configured ConnectionFactory!
(Check your Java EE server’s / JMS provider’s documentation.)
Reusing code across a managed and unmanaged transactional environment can be confusing
when using the JMS API to create a Session
from a Connection
. This is because the
JMS API has only one factory method to create a Session
and it requires values for the
transaction and acknowledgment modes. In a managed environment, setting these values is
the responsibility of the environment’s transactional infrastructure, so these values
are ignored by the vendor’s wrapper to the JMS Connection. When using the JmsTemplate
in an unmanaged environment you can specify these values through the use of the
properties sessionTransacted
and sessionAcknowledgeMode
. When using a
PlatformTransactionManager
with JmsTemplate
, the template will always be given a
transactional JMS Session
.
3.3. Sending a Message
The JmsTemplate
contains many convenience methods to send a message. There are send
methods that specify the destination using a javax.jms.Destination
object and those
that specify the destination using a string for use in a JNDI lookup. The send method
that takes no destination argument uses the default destination.
import javax.jms.ConnectionFactory;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.Queue;
import javax.jms.Session;
import org.springframework.jms.core.MessageCreator;
import org.springframework.jms.core.JmsTemplate;
public class JmsQueueSender {
private JmsTemplate jmsTemplate;
private Queue queue;
public void setConnectionFactory(ConnectionFactory cf) {
this.jmsTemplate = new JmsTemplate(cf);
}
public void setQueue(Queue queue) {
this.queue = queue;
}
public void simpleSend() {
this.jmsTemplate.send(this.queue, new MessageCreator() {
public Message createMessage(Session session) throws JMSException {
return session.createTextMessage("hello queue world");
}
});
}
}
This example uses the MessageCreator
callback to create a text message from the
supplied Session
object. The JmsTemplate
is constructed by passing a reference to a
ConnectionFactory
. As an alternative, a zero argument constructor and
connectionFactory
is provided and can be used for constructing the instance in
JavaBean style (using a BeanFactory or plain Java code). Alternatively, consider
deriving from Spring’s JmsGatewaySupport
convenience base class, which provides
pre-built bean properties for JMS configuration.
The method send(String destinationName, MessageCreator creator)
lets you send a
message using the string name of the destination. If these names are registered in JNDI,
you should set the destinationResolver
property of the template to an instance of
JndiDestinationResolver
.
If you created the JmsTemplate
and specified a default destination, the
send(MessageCreator c)
sends a message to that destination.
3.3.1. Using Message Converters
In order to facilitate the sending of domain model objects, the JmsTemplate
has
various send methods that take a Java object as an argument for a message’s data
content. The overloaded methods convertAndSend()
and receiveAndConvert()
in
JmsTemplate
delegate the conversion process to an instance of the MessageConverter
interface. This interface defines a simple contract to convert between Java objects and
JMS messages. The default implementation SimpleMessageConverter
supports conversion
between String
and TextMessage
, byte[]
and BytesMesssage
, and java.util.Map
and MapMessage
. By using the converter, you and your application code can focus on the
business object that is being sent or received via JMS and not be concerned with the
details of how it is represented as a JMS message.
The sandbox currently includes a MapMessageConverter
which uses reflection to convert
between a JavaBean and a MapMessage
. Other popular implementation choices you might
implement yourself are Converters that use an existing XML marshalling package, such as
JAXB, Castor or XStream, to create a TextMessage
representing the object.
To accommodate the setting of a message’s properties, headers, and body that can not be
generically encapsulated inside a converter class, the MessagePostProcessor
interface
gives you access to the message after it has been converted, but before it is sent. The
example below demonstrates how to modify a message header and a property after a
java.util.Map
is converted to a message.
public void sendWithConversion() {
Map map = new HashMap();
map.put("Name", "Mark");
map.put("Age", new Integer(47));
jmsTemplate.convertAndSend("testQueue", map, new MessagePostProcessor() {
public Message postProcessMessage(Message message) throws JMSException {
message.setIntProperty("AccountID", 1234);
message.setJMSCorrelationID("123-00001");
return message;
}
});
}
This results in a message of the form:
MapMessage={ Header={ ... standard headers ... CorrelationID={123-00001} } Properties={ AccountID={Integer:1234} } Fields={ Name={String:Mark} Age={Integer:47} } }
3.3.2. SessionCallback and ProducerCallback
While the send operations cover many common usage scenarios, there are cases when you
want to perform multiple operations on a JMS Session
or MessageProducer
. The
SessionCallback
and ProducerCallback
expose the JMS Session
and Session
/
MessageProducer
pair respectively. The execute()
methods on JmsTemplate
execute
these callback methods.
3.4. Receiving a message
3.4.1. Synchronous reception
While JMS is typically associated with asynchronous processing, it is possible to
consume messages synchronously. The overloaded receive(..)
methods provide this
functionality. During a synchronous receive, the calling thread blocks until a message
becomes available. This can be a dangerous operation since the calling thread can
potentially be blocked indefinitely. The property receiveTimeout
specifies how long
the receiver should wait before giving up waiting for a message.
3.4.2. Asynchronous reception: Message-Driven POJOs
Spring also supports annotated-listener endpoints through the use of the |
In a fashion similar to a Message-Driven Bean (MDB) in the EJB world, the Message-Driven
POJO (MDP) acts as a receiver for JMS messages. The one restriction (but see also below
for the discussion of the MessageListenerAdapter
class) on an MDP is that it must
implement the javax.jms.MessageListener
interface. Please also be aware that in the
case where your POJO will be receiving messages on multiple threads, it is important to
ensure that your implementation is thread-safe.
Below is a simple implementation of an MDP:
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.jms.TextMessage;
public class ExampleListener implements MessageListener {
public void onMessage(Message message) {
if (message instanceof TextMessage) {
try {
System.out.println(((TextMessage) message).getText());
}
catch (JMSException ex) {
throw new RuntimeException(ex);
}
}
else {
throw new IllegalArgumentException("Message must be of type TextMessage");
}
}
}
Once you’ve implemented your MessageListener
, it’s time to create a message listener
container.
Find below an example of how to define and configure one of the message listener
containers that ships with Spring (in this case the DefaultMessageListenerContainer
).
<!-- this is the Message Driven POJO (MDP) -->
<bean id="messageListener" class="jmsexample.ExampleListener" />
<!-- and this is the message listener container -->
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="destination"/>
<property name="messageListener" ref="messageListener" />
</bean>
Please refer to the Spring javadocs of the various message listener containers for a full description of the features supported by each implementation.
3.4.3. SessionAwareMessageListener interface
The SessionAwareMessageListener
interface is a Spring-specific interface that provides
a similar contract to the JMS MessageListener
interface, but also provides the message
handling method with access to the JMS Session
from which the Message
was received.
package org.springframework.jms.listener;
public interface SessionAwareMessageListener {
void onMessage(Message message, Session session) throws JMSException;
}
You can choose to have your MDPs implement this interface (in preference to the standard
JMS MessageListener
interface) if you want your MDPs to be able to respond to any
received messages (using the Session
supplied in the onMessage(Message, Session)
method). All of the message listener container implementations that ship with Spring
have support for MDPs that implement either the MessageListener
or
SessionAwareMessageListener
interface. Classes that implement the
SessionAwareMessageListener
come with the caveat that they are then tied to Spring
through the interface. The choice of whether or not to use it is left entirely up to you
as an application developer or architect.
Please note that the 'onMessage(..)'
method of the SessionAwareMessageListener
interface throws JMSException
. In contrast to the standard JMS MessageListener
interface, when using the SessionAwareMessageListener
interface, it is the
responsibility of the client code to handle any exceptions thrown.
3.4.4. MessageListenerAdapter
The MessageListenerAdapter
class is the final component in Spring’s asynchronous
messaging support: in a nutshell, it allows you to expose almost any class as a MDP
(there are of course some constraints).
Consider the following interface definition. Notice that although the interface extends
neither the MessageListener
nor SessionAwareMessageListener
interfaces, it can still
be used as a MDP via the use of the MessageListenerAdapter
class. Notice also how the
various message handling methods are strongly typed according to the contents of the
various Message
types that they can receive and handle.
public interface MessageDelegate {
void handleMessage(String message);
void handleMessage(Map message);
void handleMessage(byte[] message);
void handleMessage(Serializable message);
}
public class DefaultMessageDelegate implements MessageDelegate {
// implementation elided for clarity...
}
In particular, note how the above implementation of the MessageDelegate
interface (the
above DefaultMessageDelegate
class) has no JMS dependencies at all. It truly is a
POJO that we will make into an MDP via the following configuration.
<!-- this is the Message Driven POJO (MDP) -->
<bean id="messageListener" class="org.springframework.jms.listener.adapter.MessageListenerAdapter">
<constructor-arg>
<bean class="jmsexample.DefaultMessageDelegate"/>
</constructor-arg>
</bean>
<!-- and this is the message listener container... -->
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="destination"/>
<property name="messageListener" ref="messageListener" />
</bean>
Below is an example of another MDP that can only handle the receiving of JMS
TextMessage
messages. Notice how the message handling method is actually called
'receive'
(the name of the message handling method in a MessageListenerAdapter
defaults to 'handleMessage'
), but it is configurable (as you will see below). Notice
also how the 'receive(..)'
method is strongly typed to receive and respond only to JMS
TextMessage
messages.
public interface TextMessageDelegate {
void receive(TextMessage message);
}
public class DefaultTextMessageDelegate implements TextMessageDelegate {
// implementation elided for clarity...
}
The configuration of the attendant MessageListenerAdapter
would look like this:
<bean id="messageListener" class="org.springframework.jms.listener.adapter.MessageListenerAdapter">
<constructor-arg>
<bean class="jmsexample.DefaultTextMessageDelegate"/>
</constructor-arg>
<property name="defaultListenerMethod" value="receive"/>
<!-- we don't want automatic message context extraction -->
<property name="messageConverter">
<null/>
</property>
</bean>
Please note that if the above 'messageListener'
receives a JMS Message
of a type
other than TextMessage
, an IllegalStateException
will be thrown (and subsequently
swallowed). Another of the capabilities of the MessageListenerAdapter
class is the
ability to automatically send back a response Message
if a handler method returns a
non-void value. Consider the interface and class:
public interface ResponsiveTextMessageDelegate {
// notice the return type...
String receive(TextMessage message);
}
public class DefaultResponsiveTextMessageDelegate implements ResponsiveTextMessageDelegate {
// implementation elided for clarity...
}
If the above DefaultResponsiveTextMessageDelegate
is used in conjunction with a
MessageListenerAdapter
then any non-null value that is returned from the execution of
the 'receive(..)'
method will (in the default configuration) be converted into a
TextMessage
. The resulting TextMessage
will then be sent to the Destination
(if
one exists) defined in the JMS Reply-To property of the original Message
, or the
default Destination
set on the MessageListenerAdapter
(if one has been configured);
if no Destination
is found then an InvalidDestinationException
will be thrown (and
please note that this exception will not be swallowed and will propagate up the
call stack).
3.4.5. Processing messages within transactions
Invoking a message listener within a transaction only requires reconfiguration of the listener container.
Local resource transactions can simply be activated through the sessionTransacted
flag
on the listener container definition. Each message listener invocation will then operate
within an active JMS transaction, with message reception rolled back in case of listener
execution failure. Sending a response message (via SessionAwareMessageListener
) will
be part of the same local transaction, but any other resource operations (such as
database access) will operate independently. This usually requires duplicate message
detection in the listener implementation, covering the case where database processing
has committed but message processing failed to commit.
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="destination"/>
<property name="messageListener" ref="messageListener"/>
<property name="sessionTransacted" value="true"/>
</bean>
For participating in an externally managed transaction, you will need to configure a
transaction manager and use a listener container which supports externally managed
transactions: typically DefaultMessageListenerContainer
.
To configure a message listener container for XA transaction participation, you’ll want
to configure a JtaTransactionManager
(which, by default, delegates to the Java EE
server’s transaction subsystem). Note that the underlying JMS ConnectionFactory needs to
be XA-capable and properly registered with your JTA transaction coordinator! (Check your
Java EE server’s configuration of JNDI resources.) This allows message reception as well
as e.g. database access to be part of the same transaction (with unified commit
semantics, at the expense of XA transaction log overhead).
<bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager"/>
Then you just need to add it to our earlier container configuration. The container will take care of the rest.
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="destination"/>
<property name="messageListener" ref="messageListener"/>
<property name="transactionManager" ref="transactionManager"/>
</bean>
3.5. Support for JCA Message Endpoints
Beginning with version 2.5, Spring also provides support for a JCA-based
MessageListener
container. The JmsMessageEndpointManager
will attempt to
automatically determine the ActivationSpec
class name from the provider’s
ResourceAdapter
class name. Therefore, it is typically possible to just provide
Spring’s generic JmsActivationSpecConfig
as shown in the following example.
<bean class="org.springframework.jms.listener.endpoint.JmsMessageEndpointManager">
<property name="resourceAdapter" ref="resourceAdapter"/>
<property name="activationSpecConfig">
<bean class="org.springframework.jms.listener.endpoint.JmsActivationSpecConfig">
<property name="destinationName" value="myQueue"/>
</bean>
</property>
<property name="messageListener" ref="myMessageListener"/>
</bean>
Alternatively, you may set up a JmsMessageEndpointManager
with a given
ActivationSpec
object. The ActivationSpec
object may also come from a JNDI lookup
(using <jee:jndi-lookup>
).
<bean class="org.springframework.jms.listener.endpoint.JmsMessageEndpointManager">
<property name="resourceAdapter" ref="resourceAdapter"/>
<property name="activationSpec">
<bean class="org.apache.activemq.ra.ActiveMQActivationSpec">
<property name="destination" value="myQueue"/>
<property name="destinationType" value="javax.jms.Queue"/>
</bean>
</property>
<property name="messageListener" ref="myMessageListener"/>
</bean>
Using Spring’s ResourceAdapterFactoryBean
, the target ResourceAdapter
may be
configured locally as depicted in the following example.
<bean id="resourceAdapter" class="org.springframework.jca.support.ResourceAdapterFactoryBean">
<property name="resourceAdapter">
<bean class="org.apache.activemq.ra.ActiveMQResourceAdapter">
<property name="serverUrl" value="tcp://localhost:61616"/>
</bean>
</property>
<property name="workManager">
<bean class="org.springframework.jca.work.SimpleTaskWorkManager"/>
</property>
</bean>
The specified WorkManager
may also point to an environment-specific thread pool -
typically through SimpleTaskWorkManager
's "asyncTaskExecutor" property. Consider
defining a shared thread pool for all your ResourceAdapter
instances if you happen to
use multiple adapters.
In some environments (e.g. WebLogic 9 or above), the entire ResourceAdapter
object may
be obtained from JNDI instead (using <jee:jndi-lookup>
). The Spring-based message
listeners can then interact with the server-hosted ResourceAdapter
, also using the
server’s built-in WorkManager
.
Please consult the javadoc for JmsMessageEndpointManager
, JmsActivationSpecConfig
,
and ResourceAdapterFactoryBean
for more details.
Spring also provides a generic JCA message endpoint manager which is not tied to JMS:
org.springframework.jca.endpoint.GenericMessageEndpointManager
. This component allows
for using any message listener type (e.g. a CCI MessageListener) and any
provider-specific ActivationSpec object. Check out your JCA provider’s documentation to
find out about the actual capabilities of your connector, and consult
GenericMessageEndpointManager
's javadoc for the Spring-specific configuration details.
JCA-based message endpoint management is very analogous to EJB 2.1 Message-Driven Beans; it uses the same underlying resource provider contract. Like with EJB 2.1 MDBs, any message listener interface supported by your JCA provider can be used in the Spring context as well. Spring nevertheless provides explicit 'convenience' support for JMS, simply because JMS is the most common endpoint API used with the JCA endpoint management contract. |
3.6. Annotation-driven listener endpoints
The easiest way to receive a message asynchronously is to use the annotated listener endpoint infrastructure. In a nutshell, it allows you to expose a method of a managed bean as a JMS listener endpoint.
@Component
public class MyService {
@JmsListener(destination = "myDestination")
public void processOrder(String data) { ... }
}
The idea of the example above is that whenever a message is available on the
javax.jms.Destination
"myDestination", the processOrder
method is invoked
accordingly (in this case, with the content of the JMS message similarly to
what the MessageListenerAdapter
provides).
The annotated endpoint infrastructure creates a message listener container
behind the scenes for each annotated method, using a JmsListenerContainerFactory
.
Such a container is not registered against the application context but can be easily
located for management purposes using the JmsListenerEndpointRegistry
bean.
|
3.6.1. Enable listener endpoint annotations
To enable support for @JmsListener
annotations add @EnableJms
to one of
your @Configuration
classes.
@Configuration
@EnableJms
public class AppConfig {
@Bean
public DefaultJmsListenerContainerFactory jmsListenerContainerFactory() {
DefaultJmsListenerContainerFactory factory = new DefaultJmsListenerContainerFactory();
factory.setConnectionFactory(connectionFactory());
factory.setDestinationResolver(destinationResolver());
factory.setSessionTransacted(true);
factory.setConcurrency("3-10");
return factory;
}
}
By default, the infrastructure looks for a bean named jmsListenerContainerFactory
as the source for the factory to use to create message listener containers. In this
case, and ignoring the JMS infrastructure setup, the processOrder
method can be
invoked with a core poll size of 3 threads and a maximum pool size of 10 threads.
It is possible to customize the listener container factory to use per annotation or
an explicit default can be configured by implementing the JmsListenerConfigurer
interface. The default is only required if at least one endpoint is registered
without a specific container factory. See the javadoc for full details and examples.
If you prefer XML configuration use the <jms:annotation-driven>
element.
<jms:annotation-driven/>
<bean id="jmsListenerContainerFactory"
class="org.springframework.jms.config.DefaultJmsListenerContainerFactory">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destinationResolver" ref="destinationResolver"/>
<property name="sessionTransacted" value="true"/>
<property name="concurrency" value="3-10"/>
</bean>
3.6.2. Programmatic endpoints registration
JmsListenerEndpoint
provides a model of an JMS endpoint and is responsible for configuring
the container for that model. The infrastructure allows you to configure endpoints
programmatically in addition to the ones that are detected by the JmsListener
annotation.
@Configuration
@EnableJms
public class AppConfig implements JmsListenerConfigurer {
@Override
public void configureJmsListeners(JmsListenerEndpointRegistrar registrar) {
SimpleJmsListenerEndpoint endpoint = new SimpleJmsListenerEndpoint();
endpoint.setId("myJmsEndpoint");
endpoint.setDestination("anotherQueue");
endpoint.setMessageListener(message -> {
// processing
});
registrar.registerEndpoint(endpoint);
}
}
In the example above, we used SimpleJmsListenerEndpoint
which provides the actual
MessageListener
to invoke but you could just as well build your own endpoint variant
describing a custom invocation mechanism.
It should be noted that you could just as well skip the use of @JmsListener
altogether
and only register your endpoints programmatically through JmsListenerConfigurer
.
3.6.3. Annotated endpoint method signature
So far, we have been injecting a simple String
in our endpoint but it can actually
have a very flexible method signature. Let’s rewrite it to inject the Order
with
a custom header:
@Component
public class MyService {
@JmsListener(destination = "myDestination")
public void processOrder(Order order, @Header("order_type") String orderType) {
...
}
}
These are the main elements you can inject in JMS listener endpoints:
-
The raw
javax.jms.Message
or any of its subclasses (provided of course that it matches the incoming message type). -
The
javax.jms.Session
for optional access to the native JMS API e.g. for sending a custom reply. -
The
org.springframework.messaging.Message
representing the incoming JMS message. Note that this message holds both the custom and the standard headers (as defined byJmsHeaders
). -
@Header
-annotated method arguments to extract a specific header value, including standard JMS headers. -
@Headers
-annotated argument that must also be assignable tojava.util.Map
for getting access to all headers. -
A non-annotated element that is not one of the supported types (i.e.
Message
andSession
) is considered to be the payload. You can make that explicit by annotating the parameter with@Payload
. You can also turn on validation by adding an extra@Valid
.
The ability to inject Spring’s Message
abstraction is particularly useful to benefit
from all the information stored in the transport-specific message without relying on
transport-specific API.
@JmsListener(destination = "myDestination")
public void processOrder(Message<Order> order) { ... }
Handling of method arguments is provided by DefaultMessageHandlerMethodFactory
which can be
further customized to support additional method arguments. The conversion and validation
support can be customized there as well.
For instance, if we want to make sure our Order
is valid before processing it, we can
annotate the payload with @Valid
and configure the necessary validator as follows:
@Configuration
@EnableJms
public class AppConfig implements JmsListenerConfigurer {
@Override
public void configureJmsListeners(JmsListenerEndpointRegistrar registrar) {
registrar.setMessageHandlerMethodFactory(myJmsHandlerMethodFactory());
}
@Bean
public DefaultMessageHandlerMethodFactory myHandlerMethodFactory() {
DefaultMessageHandlerMethodFactory factory = new DefaultMessageHandlerMethodFactory();
factory.setValidator(myValidator());
return factory;
}
}
3.6.4. Response management
The existing support in MessageListenerAdapter
already allows your method to have a non-void
return type. When that’s the case, the result of
the invocation is encapsulated in a javax.jms.Message
sent either in the destination specified
in the JMSReplyTo
header of the original message or in the default destination configured on
the listener. That default destination can now be set using the @SendTo
annotation of the
messaging abstraction.
Assuming our processOrder
method should now return an OrderStatus
, it is possible to write it
as follow to automatically send a response:
@JmsListener(destination = "myDestination")
@SendTo("status")
public OrderStatus processOrder(Order order) {
// order processing
return status;
}
If you have several |
If you need to set additional headers in a transport-independent manner, you could return a
Message
instead, something like:
@JmsListener(destination = "myDestination")
@SendTo("status")
public Message<OrderStatus> processOrder(Order order) {
// order processing
return MessageBuilder
.withPayload(status)
.setHeader("code", 1234)
.build();
}
If you need to compute the response destination at runtime, you can encapsulate your response
in a JmsResponse
instance that also provides the destination to use at runtime. The previous
example can be rewritten as follows:
@JmsListener(destination = "myDestination")
public JmsResponse<Message<OrderStatus>> processOrder(Order order) {
// order processing
Message<OrderStatus> response = MessageBuilder
.withPayload(status)
.setHeader("code", 1234)
.build();
return JmsResponse.forQueue(response, "status");
}
Finally if you need to specify some QoS values for the response such as the priority or
the time to live, you can configure the JmsListenerContainerFactory
accordingly:
@Configuration
@EnableJms
public class AppConfig {
@Bean
public DefaultJmsListenerContainerFactory jmsListenerContainerFactory() {
DefaultJmsListenerContainerFactory factory = new DefaultJmsListenerContainerFactory();
factory.setConnectionFactory(connectionFactory());
QosSettings replyQosSettings = new ReplyQosSettings();
replyQosSettings.setPriority(2);
replyQosSettings.setTimeToLive(10000);
factory.setReplyQosSettings(replyQosSettings);
return factory;
}
}
3.7. JMS namespace support
Spring provides an XML namespace for simplifying JMS configuration. To use the JMS namespace elements you will need to reference the JMS schema:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jms="http://www.springframework.org/schema/jms"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/jms http://www.springframework.org/schema/jms/spring-jms.xsd">
<!-- bean definitions here -->
</beans>
The namespace consists of three top-level elements: <annotation-driven/>
, <listener-container/>
and <jca-listener-container/>
. <annotation-driven
enables the use of annotation-driven listener endpoints. <listener-container/>
and <jca-listener-container/>
defines shared listener container configuration and may contain <listener/>
child elements. Here
is an example of a basic configuration for two listeners.
<jms:listener-container>
<jms:listener destination="queue.orders" ref="orderService" method="placeOrder"/>
<jms:listener destination="queue.confirmations" ref="confirmationLogger" method="log"/>
</jms:listener-container>
The example above is equivalent to creating two distinct listener container bean
definitions and two distinct MessageListenerAdapter
bean definitions as demonstrated
in MessageListenerAdapter. In addition to the attributes shown
above, the listener
element may contain several optional ones. The following table
describes all available attributes:
Attribute | Description |
---|---|
id |
A bean name for the hosting listener container. If not specified, a bean name will be automatically generated. |
destination (required) |
The destination name for this listener, resolved through the |
ref (required) |
The bean name of the handler object. |
method |
The name of the handler method to invoke. If the |
response-destination |
The name of the default response destination to send response messages to. This will be applied in case of a request message that does not carry a "JMSReplyTo" field. The type of this destination will be determined by the listener-container’s "response-destination-type" attribute. Note: This only applies to a listener method with a return value, for which each result object will be converted into a response message. |
subscription |
The name of the durable subscription, if any. |
selector |
An optional message selector for this listener. |
concurrency |
The number of concurrent sessions/consumers to start for this listener. Can either be a simple number indicating the maximum number (e.g. "5") or a range indicating the lower as well as the upper limit (e.g. "3-5"). Note that a specified minimum is just a hint and might be ignored at runtime. Default is the value provided by the container |
The <listener-container/>
element also accepts several optional attributes. This
allows for customization of the various strategies (for example, taskExecutor
and
destinationResolver
) as well as basic JMS settings and resource references. Using
these attributes, it is possible to define highly-customized listener containers while
still benefiting from the convenience of the namespace.
Such settings can be automatically exposed as a JmsListenerContainerFactory
by
specifying the id of the bean to expose through the factory-id
attribute.
<jms:listener-container connection-factory="myConnectionFactory"
task-executor="myTaskExecutor"
destination-resolver="myDestinationResolver"
transaction-manager="myTransactionManager"
concurrency="10">
<jms:listener destination="queue.orders" ref="orderService" method="placeOrder"/>
<jms:listener destination="queue.confirmations" ref="confirmationLogger" method="log"/>
</jms:listener-container>
The following table describes all available attributes. Consult the class-level javadocs
of the AbstractMessageListenerContainer
and its concrete subclasses for more details
on the individual properties. The javadocs also provide a discussion of transaction
choices and message redelivery scenarios.
Attribute | Description |
---|---|
container-type |
The type of this listener container. Available options are: |
container-class |
A custom listener container implementation class as fully qualified class name.
Default is Spring’s standard |
factory-id |
Exposes the settings defined by this element as a |
connection-factory |
A reference to the JMS |
task-executor |
A reference to the Spring |
destination-resolver |
A reference to the |
message-converter |
A reference to the |
error-handler |
A reference to an |
destination-type |
The JMS destination type for this listener: |
response-destination-type |
The JMS destination type for responses: "queue", "topic". Default is the value of the "destination-type" attribute. |
client-id |
The JMS client id for this listener container. Needs to be specified when using durable subscriptions. |
cache |
The cache level for JMS resources: |
acknowledge |
The native JMS acknowledge mode: |
transaction-manager |
A reference to an external |
concurrency |
The number of concurrent sessions/consumers to start for each listener. Can either be a simple number indicating the maximum number (e.g. "5") or a range indicating the lower as well as the upper limit (e.g. "3-5"). Note that a specified minimum is just a hint and might be ignored at runtime. Default is 1; keep concurrency limited to 1 in case of a topic listener or if queue ordering is important; consider raising it for general queues. |
prefetch |
The maximum number of messages to load into a single session. Note that raising this number might lead to starvation of concurrent consumers! |
receive-timeout |
The timeout to use for receive calls (in milliseconds). The default is |
back-off |
Specify the |
recovery-interval |
Specify the interval between recovery attempts, in milliseconds. Convenience
way to create a |
phase |
The lifecycle phase within which this container should start and stop. The lower the
value the earlier this container will start and the later it will stop. The default is
|
Configuring a JCA-based listener container with the "jms" schema support is very similar.
<jms:jca-listener-container resource-adapter="myResourceAdapter"
destination-resolver="myDestinationResolver"
transaction-manager="myTransactionManager"
concurrency="10">
<jms:listener destination="queue.orders" ref="myMessageListener"/>
</jms:jca-listener-container>
The available configuration options for the JCA variant are described in the following table:
Attribute | Description |
---|---|
factory-id |
Exposes the settings defined by this element as a |
resource-adapter |
A reference to the JCA |
activation-spec-factory |
A reference to the |
destination-resolver |
A reference to the |
message-converter |
A reference to the |
destination-type |
The JMS destination type for this listener: |
response-destination-type |
The JMS destination type for responses: "queue", "topic". Default is the value of the "destination-type" attribute. |
client-id |
The JMS client id for this listener container. Needs to be specified when using durable subscriptions. |
acknowledge |
The native JMS acknowledge mode: |
transaction-manager |
A reference to a Spring |
concurrency |
The number of concurrent sessions/consumers to start for each listener. Can either be a simple number indicating the maximum number (e.g. "5") or a range indicating the lower as well as the upper limit (e.g. "3-5"). Note that a specified minimum is just a hint and will typically be ignored at runtime when using a JCA listener container. Default is 1. |
prefetch |
The maximum number of messages to load into a single session. Note that raising this number might lead to starvation of concurrent consumers! |
4. JMX
4.1. Introduction
The JMX support in Spring provides you with the features to easily and transparently integrate your Spring application into a JMX infrastructure.
Specifically, Spring’s JMX support provides four core features:
-
The automatic registration of any Spring bean as a JMX MBean
-
A flexible mechanism for controlling the management interface of your beans
-
The declarative exposure of MBeans over remote, JSR-160 connectors
-
The simple proxying of both local and remote MBean resources
These features are designed to work without coupling your application components to either Spring or JMX interfaces and classes. Indeed, for the most part your application classes need not be aware of either Spring or JMX in order to take advantage of the Spring JMX features.
4.2. Exporting your beans to JMX
The core class in Spring’s JMX framework is the MBeanExporter
. This class is
responsible for taking your Spring beans and registering them with a JMX MBeanServer
.
For example, consider the following class:
package org.springframework.jmx;
public class JmxTestBean implements IJmxTestBean {
private String name;
private int age;
private boolean isSuperman;
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
public int add(int x, int y) {
return x + y;
}
public void dontExposeMe() {
throw new RuntimeException();
}
}
To expose the properties and methods of this bean as attributes and operations of an
MBean you simply configure an instance of the MBeanExporter
class in your
configuration file and pass in the bean as shown below:
<beans>
<!-- this bean must not be lazily initialized if the exporting is to happen -->
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter" lazy-init="false">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>
The pertinent bean definition from the above configuration snippet is the exporter
bean. The beans
property tells the MBeanExporter
exactly which of your beans must be
exported to the JMX MBeanServer
. In the default configuration, the key of each entry
in the beans
Map
is used as the ObjectName
for the bean referenced by the
corresponding entry value. This behavior can be changed as described in Controlling the ObjectNames for your beans.
With this configuration the testBean
bean is exposed as an MBean under the
ObjectName
bean:name=testBean1
. By default, all public properties of the bean
are exposed as attributes and all public methods (bar those inherited from the
Object
class) are exposed as operations.
|
4.2.1. Creating an MBeanServer
The above configuration assumes that the application is running in an environment that
has one (and only one) MBeanServer
already running. In this case, Spring will attempt
to locate the running MBeanServer
and register your beans with that server (if any).
This behavior is useful when your application is running inside a container such as
Tomcat or IBM WebSphere that has its own MBeanServer
.
However, this approach is of no use in a standalone environment, or when running inside
a container that does not provide an MBeanServer
. To address this you can create an
MBeanServer
instance declaratively by adding an instance of the
org.springframework.jmx.support.MBeanServerFactoryBean
class to your configuration.
You can also ensure that a specific MBeanServer
is used by setting the value of the
MBeanExporter
's server
property to the MBeanServer
value returned by an
MBeanServerFactoryBean
; for example:
<beans>
<bean id="mbeanServer" class="org.springframework.jmx.support.MBeanServerFactoryBean"/>
<!--
this bean needs to be eagerly pre-instantiated in order for the exporting to occur;
this means that it must not be marked as lazily initialized
-->
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="server" ref="mbeanServer"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>
Here an instance of MBeanServer
is created by the MBeanServerFactoryBean
and is
supplied to the MBeanExporter
via the server property. When you supply your own
MBeanServer
instance, the MBeanExporter
will not attempt to locate a running
MBeanServer
and will use the supplied MBeanServer
instance. For this to work
correctly, you must (of course) have a JMX implementation on your classpath.
4.2.2. Reusing an existing MBeanServer
If no server is specified, the MBeanExporter
tries to automatically detect a running
MBeanServer
. This works in most environment where only one MBeanServer
instance is
used, however when multiple instances exist, the exporter might pick the wrong server.
In such cases, one should use the MBeanServer
agentId
to indicate which instance to
be used:
<beans>
<bean id="mbeanServer" class="org.springframework.jmx.support.MBeanServerFactoryBean">
<!-- indicate to first look for a server -->
<property name="locateExistingServerIfPossible" value="true"/>
<!-- search for the MBeanServer instance with the given agentId -->
<property name="agentId" value="MBeanServer_instance_agentId>"/>
</bean>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="server" ref="mbeanServer"/>
...
</bean>
</beans>
For platforms/cases where the existing MBeanServer
has a dynamic (or unknown)
agentId
which is retrieved through lookup methods, one should use
factory-method:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="server">
<!-- Custom MBeanServerLocator -->
<bean class="platform.package.MBeanServerLocator" factory-method="locateMBeanServer"/>
</property>
</bean>
<!-- other beans here -->
</beans>
4.2.3. Lazy-initialized MBeans
If you configure a bean with the MBeanExporter
that is also configured for lazy
initialization, then the MBeanExporter
will not break this contract and will avoid
instantiating the bean. Instead, it will register a proxy with the MBeanServer
and
will defer obtaining the bean from the container until the first invocation on the proxy
occurs.
4.2.4. Automatic registration of MBeans
Any beans that are exported through the MBeanExporter
and are already valid MBeans are
registered as-is with the MBeanServer
without further intervention from Spring. MBeans
can be automatically detected by the MBeanExporter
by setting the autodetect
property to true
:
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="autodetect" value="true"/>
</bean>
<bean name="spring:mbean=true" class="org.springframework.jmx.export.TestDynamicMBean"/>
Here, the bean called spring:mbean=true
is already a valid JMX MBean and will be
automatically registered by Spring. By default, beans that are autodetected for JMX
registration have their bean name used as the ObjectName
. This behavior can be
overridden as detailed in Controlling the ObjectNames for your beans.
4.2.5. Controlling the registration behavior
Consider the scenario where a Spring MBeanExporter
attempts to register an MBean
with an MBeanServer
using the ObjectName
'bean:name=testBean1'
. If an MBean
instance has already been registered under that same ObjectName
, the default behavior
is to fail (and throw an InstanceAlreadyExistsException
).
It is possible to control the behavior of exactly what happens when an MBean
is
registered with an MBeanServer
. Spring’s JMX support allows for three different
registration behaviors to control the registration behavior when the registration
process finds that an MBean
has already been registered under the same ObjectName
;
these registration behaviors are summarized on the following table:
Registration behavior | Explanation |
---|---|
|
This is the default registration behavior. If an |
|
If an |
|
If an |
The above values are defined as constants on the MBeanRegistrationSupport
class (the
MBeanExporter
class derives from this superclass). If you want to change the default
registration behavior, you simply need to set the value of the
registrationBehaviorName
property on your MBeanExporter
definition to one of those
values.
The following example illustrates how to effect a change from the default registration
behavior to the REGISTRATION_REPLACE_EXISTING
behavior:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="registrationBehaviorName" value="REGISTRATION_REPLACE_EXISTING"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>
4.3. Controlling the management interface of your beans
In the previous example, you had little control over the management interface of your bean; all of the public properties and methods of each exported bean was exposed as JMX attributes and operations respectively. To exercise finer-grained control over exactly which properties and methods of your exported beans are actually exposed as JMX attributes and operations, Spring JMX provides a comprehensive and extensible mechanism for controlling the management interfaces of your beans.
4.3.1. MBeanInfoAssembler interface
Behind the scenes, the MBeanExporter
delegates to an implementation of the
org.springframework.jmx.export.assembler.MBeanInfoAssembler
interface which is
responsible for defining the management interface of each bean that is being exposed.
The default implementation,
org.springframework.jmx.export.assembler.SimpleReflectiveMBeanInfoAssembler
, simply
defines a management interface that exposes all public properties and methods (as you
saw in the previous examples). Spring provides two additional implementations of the
MBeanInfoAssembler
interface that allow you to control the generated management
interface using either source-level metadata or any arbitrary interface.
4.3.2. Using source-level metadata: Java annotations
Using the MetadataMBeanInfoAssembler
you can define the management interfaces for your
beans using source level metadata. The reading of metadata is encapsulated by the
org.springframework.jmx.export.metadata.JmxAttributeSource
interface. Spring JMX
provides a default implementation which uses Java annotations, namely
org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource
. The
MetadataMBeanInfoAssembler
must be configured with an implementation instance of
the JmxAttributeSource
interface for it to function correctly (there is no
default).
To mark a bean for export to JMX, you should annotate the bean class with the
ManagedResource
annotation. Each method you wish to expose as an operation must be
marked with the ManagedOperation
annotation and each property you wish to expose must
be marked with the ManagedAttribute
annotation. When marking properties you can omit
either the annotation of the getter or the setter to create a write-only or read-only
attribute respectively.
A ManagedResource annotated bean must be public as well as the methods exposing
an operation or an attribute.
|
The example below shows the annotated version of the JmxTestBean
class that you saw
earlier:
package org.springframework.jmx;
import org.springframework.jmx.export.annotation.ManagedResource;
import org.springframework.jmx.export.annotation.ManagedOperation;
import org.springframework.jmx.export.annotation.ManagedAttribute;
@ManagedResource(
objectName="bean:name=testBean4",
description="My Managed Bean",
log=true,
logFile="jmx.log",
currencyTimeLimit=15,
persistPolicy="OnUpdate",
persistPeriod=200,
persistLocation="foo",
persistName="bar")
public class AnnotationTestBean implements IJmxTestBean {
private String name;
private int age;
@ManagedAttribute(description="The Age Attribute", currencyTimeLimit=15)
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@ManagedAttribute(description="The Name Attribute",
currencyTimeLimit=20,
defaultValue="bar",
persistPolicy="OnUpdate")
public void setName(String name) {
this.name = name;
}
@ManagedAttribute(defaultValue="foo", persistPeriod=300)
public String getName() {
return name;
}
@ManagedOperation(description="Add two numbers")
@ManagedOperationParameters({
@ManagedOperationParameter(name = "x", description = "The first number"),
@ManagedOperationParameter(name = "y", description = "The second number")})
public int add(int x, int y) {
return x + y;
}
public void dontExposeMe() {
throw new RuntimeException();
}
}
Here you can see that the JmxTestBean
class is marked with the ManagedResource
annotation and that this ManagedResource
annotation is configured with a set of
properties. These properties can be used to configure various aspects of the MBean that
is generated by the MBeanExporter
, and are explained in greater detail later in
section entitled Source-level metadata types.
You will also notice that both the age
and name
properties are annotated with the
ManagedAttribute
annotation, but in the case of the age
property, only the getter is
marked. This will cause both of these properties to be included in the management
interface as attributes, but the age
attribute will be read-only.
Finally, you will notice that the add(int, int)
method is marked with the
ManagedOperation
attribute whereas the dontExposeMe()
method is not. This will cause
the management interface to contain only one operation, add(int, int)
, when using the
MetadataMBeanInfoAssembler
.
The configuration below shows how you configure the MBeanExporter
to use the
MetadataMBeanInfoAssembler
:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="assembler" ref="assembler"/>
<property name="namingStrategy" ref="namingStrategy"/>
<property name="autodetect" value="true"/>
</bean>
<bean id="jmxAttributeSource"
class="org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource"/>
<!-- will create management interface using annotation metadata -->
<bean id="assembler"
class="org.springframework.jmx.export.assembler.MetadataMBeanInfoAssembler">
<property name="attributeSource" ref="jmxAttributeSource"/>
</bean>
<!-- will pick up the ObjectName from the annotation -->
<bean id="namingStrategy"
class="org.springframework.jmx.export.naming.MetadataNamingStrategy">
<property name="attributeSource" ref="jmxAttributeSource"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.AnnotationTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>
Here you can see that an MetadataMBeanInfoAssembler
bean has been configured with an
instance of the AnnotationJmxAttributeSource
class and passed to the MBeanExporter
through the assembler property. This is all that is required to take advantage of
metadata-driven management interfaces for your Spring-exposed MBeans.
4.3.3. Source-level metadata types
The following source level metadata types are available for use in Spring JMX:
Purpose | Annotation | Annotation Type |
---|---|---|
Mark all instances of a |
|
Class |
Mark a method as a JMX operation |
|
Method |
Mark a getter or setter as one half of a JMX attribute |
|
Method (only getters and setters) |
Define descriptions for operation parameters |
|
Method |
The following configuration parameters are available for use on these source-level metadata types:
Parameter | Description | Applies to |
---|---|---|
|
Used by |
|
|
Sets the friendly description of the resource, attribute or operation |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the display name of an operation parameter |
|
|
Sets the index of an operation parameter |
|
4.3.4. AutodetectCapableMBeanInfoAssembler interface
To simplify configuration even further, Spring introduces the
AutodetectCapableMBeanInfoAssembler
interface which extends the MBeanInfoAssembler
interface to add support for autodetection of MBean resources. If you configure the
MBeanExporter
with an instance of AutodetectCapableMBeanInfoAssembler
then it is
allowed to "vote" on the inclusion of beans for exposure to JMX.
Out of the box, the only implementation of the AutodetectCapableMBeanInfo
interface is
the MetadataMBeanInfoAssembler
which will vote to include any bean which is marked
with the ManagedResource
attribute. The default approach in this case is to use the
bean name as the ObjectName
which results in a configuration like this:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<!-- notice how no 'beans' are explicitly configured here -->
<property name="autodetect" value="true"/>
<property name="assembler" ref="assembler"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
<bean id="assembler" class="org.springframework.jmx.export.assembler.MetadataMBeanInfoAssembler">
<property name="attributeSource">
<bean class="org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource"/>
</property>
</bean>
</beans>
Notice that in this configuration no beans are passed to the MBeanExporter
; however,
the JmxTestBean
will still be registered since it is marked with the ManagedResource
attribute and the MetadataMBeanInfoAssembler
detects this and votes to include it. The
only problem with this approach is that the name of the JmxTestBean
now has business
meaning. You can address this issue by changing the default behavior for ObjectName
creation as defined in Controlling the ObjectNames for your beans.
4.3.5. Defining management interfaces using Java interfaces
In addition to the MetadataMBeanInfoAssembler
, Spring also includes the
InterfaceBasedMBeanInfoAssembler
which allows you to constrain the methods and
properties that are exposed based on the set of methods defined in a collection of
interfaces.
Although the standard mechanism for exposing MBeans is to use interfaces and a simple
naming scheme, the InterfaceBasedMBeanInfoAssembler
extends this functionality by
removing the need for naming conventions, allowing you to use more than one interface
and removing the need for your beans to implement the MBean interfaces.
Consider this interface that is used to define a management interface for the
JmxTestBean
class that you saw earlier:
public interface IJmxTestBean {
public int add(int x, int y);
public long myOperation();
public int getAge();
public void setAge(int age);
public void setName(String name);
public String getName();
}
This interface defines the methods and properties that will be exposed as operations and attributes on the JMX MBean. The code below shows how to configure Spring JMX to use this interface as the definition for the management interface:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean5" value-ref="testBean"/>
</map>
</property>
<property name="assembler">
<bean class="org.springframework.jmx.export.assembler.InterfaceBasedMBeanInfoAssembler">
<property name="managedInterfaces">
<value>org.springframework.jmx.IJmxTestBean</value>
</property>
</bean>
</property>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>
Here you can see that the InterfaceBasedMBeanInfoAssembler
is configured to use the
IJmxTestBean
interface when constructing the management interface for any bean. It is
important to understand that beans processed by the InterfaceBasedMBeanInfoAssembler
are not required to implement the interface used to generate the JMX management
interface.
In the case above, the IJmxTestBean
interface is used to construct all management
interfaces for all beans. In many cases this is not the desired behavior and you may
want to use different interfaces for different beans. In this case, you can pass
InterfaceBasedMBeanInfoAssembler
a Properties
instance via the interfaceMappings
property, where the key of each entry is the bean name and the value of each entry is a
comma-separated list of interface names to use for that bean.
If no management interface is specified through either the managedInterfaces
or
interfaceMappings
properties, then the InterfaceBasedMBeanInfoAssembler
will reflect
on the bean and use all of the interfaces implemented by that bean to create the
management interface.
4.3.6. Using MethodNameBasedMBeanInfoAssembler
The MethodNameBasedMBeanInfoAssembler
allows you to specify a list of method names
that will be exposed to JMX as attributes and operations. The code below shows a sample
configuration for this:
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean5" value-ref="testBean"/>
</map>
</property>
<property name="assembler">
<bean class="org.springframework.jmx.export.assembler.MethodNameBasedMBeanInfoAssembler">
<property name="managedMethods">
<value>add,myOperation,getName,setName,getAge</value>
</property>
</bean>
</property>
</bean>
Here you can see that the methods add
and myOperation
will be exposed as JMX
operations and getName()
, setName(String)
and getAge()
will be exposed as the
appropriate half of a JMX attribute. In the code above, the method mappings apply to
beans that are exposed to JMX. To control method exposure on a bean-by-bean basis, use
the methodMappings
property of MethodNameMBeanInfoAssembler
to map bean names to
lists of method names.
4.4. Controlling the ObjectNames for your beans
Behind the scenes, the MBeanExporter
delegates to an implementation of the
ObjectNamingStrategy
to obtain ObjectName
s for each of the beans it is registering.
The default implementation, KeyNamingStrategy
, will, by default, use the key of the
beans
Map
as the ObjectName
. In addition, the KeyNamingStrategy
can map the key
of the beans
Map
to an entry in a Properties
file (or files) to resolve the
ObjectName
. In addition to the KeyNamingStrategy
, Spring provides two additional
ObjectNamingStrategy
implementations: the IdentityNamingStrategy
that builds an
ObjectName
based on the JVM identity of the bean and the MetadataNamingStrategy
that
uses source level metadata to obtain the ObjectName
.
4.4.1. Reading ObjectNames from Properties
You can configure your own KeyNamingStrategy
instance and configure it to read
ObjectName
s from a Properties
instance rather than use bean key. The
KeyNamingStrategy
will attempt to locate an entry in the Properties
with a key
corresponding to the bean key. If no entry is found or if the Properties
instance is
null
then the bean key itself is used.
The code below shows a sample configuration for the KeyNamingStrategy
:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="testBean" value-ref="testBean"/>
</map>
</property>
<property name="namingStrategy" ref="namingStrategy"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
<bean id="namingStrategy" class="org.springframework.jmx.export.naming.KeyNamingStrategy">
<property name="mappings">
<props>
<prop key="testBean">bean:name=testBean1</prop>
</props>
</property>
<property name="mappingLocations">
<value>names1.properties,names2.properties</value>
</property>
</bean>
</beans>
Here an instance of KeyNamingStrategy
is configured with a Properties
instance that
is merged from the Properties
instance defined by the mapping property and the
properties files located in the paths defined by the mappings property. In this
configuration, the testBean
bean will be given the ObjectName
bean:name=testBean1
since this is the entry in the Properties
instance that has a key corresponding to the
bean key.
If no entry in the Properties
instance can be found then the bean key name is used as
the ObjectName
.
4.4.2. Using the MetadataNamingStrategy
The MetadataNamingStrategy
uses the objectName
property of the ManagedResource
attribute on each bean to create the ObjectName
. The code below shows the
configuration for the MetadataNamingStrategy
:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="testBean" value-ref="testBean"/>
</map>
</property>
<property name="namingStrategy" ref="namingStrategy"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
<bean id="namingStrategy" class="org.springframework.jmx.export.naming.MetadataNamingStrategy">
<property name="attributeSource" ref="attributeSource"/>
</bean>
<bean id="attributeSource"
class="org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource"/>
</beans>
If no objectName
has been provided for the ManagedResource
attribute, then an
ObjectName
will be created with the following
format:[fully-qualified-package-name]:type=[short-classname],name=[bean-name]. For
example, the generated ObjectName
for the following bean would be:
com.foo:type=MyClass,name=myBean.
<bean id="myBean" class="com.foo.MyClass"/>
4.4.3. Configuring annotation based MBean export
If you prefer using the annotation based approach to define
your management interfaces, then a convenience subclass of MBeanExporter
is available:
AnnotationMBeanExporter
. When defining an instance of this subclass, the
namingStrategy
, assembler
, and attributeSource
configuration is no longer needed,
since it will always use standard Java annotation-based metadata (autodetection is
always enabled as well). In fact, rather than defining an MBeanExporter
bean, an even
simpler syntax is supported by the @EnableMBeanExport
@Configuration
annotation.
@Configuration
@EnableMBeanExport
public class AppConfig {
}
If you prefer XML based configuration the 'context:mbean-export'
element serves the
same purpose.
<context:mbean-export/>
You can provide a reference to a particular MBean server
if necessary, and the
defaultDomain
attribute (a property of AnnotationMBeanExporter
) accepts an alternate
value for the generated MBean `ObjectNames’ domains. This would be used in place of the
fully qualified package name as described in the previous section on
MetadataNamingStrategy.
@EnableMBeanExport(server="myMBeanServer", defaultDomain="myDomain")
@Configuration
ContextConfiguration {
}
<context:mbean-export server="myMBeanServer" default-domain="myDomain"/>
Do not use interface-based AOP proxies in combination with autodetection of JMX
annotations in your bean classes. Interface-based proxies 'hide' the target class, which
also hides the JMX managed resource annotations. Hence, use target-class proxies in that
case: through setting the 'proxy-target-class' flag on |
4.5. JSR-160 Connectors
For remote access, Spring JMX module offers two FactoryBean
implementations inside the
org.springframework.jmx.support
package for creating both server- and client-side
connectors.
4.5.1. Server-side connectors
To have Spring JMX create, start and expose a JSR-160 JMXConnectorServer
use the
following configuration:
<bean id="serverConnector" class="org.springframework.jmx.support.ConnectorServerFactoryBean"/>
By default ConnectorServerFactoryBean
creates a JMXConnectorServer
bound to
"service:jmx:jmxmp://localhost:9875"
. The serverConnector
bean thus exposes the
local MBeanServer
to clients through the JMXMP protocol on localhost, port 9875. Note
that the JMXMP protocol is marked as optional by the JSR 160 specification: currently,
the main open-source JMX implementation, MX4J, and the one provided with the JDK
do not support JMXMP.
To specify another URL and register the JMXConnectorServer
itself with the
MBeanServer
use the serviceUrl
and ObjectName
properties respectively:
<bean id="serverConnector"
class="org.springframework.jmx.support.ConnectorServerFactoryBean">
<property name="objectName" value="connector:name=rmi"/>
<property name="serviceUrl"
value="service:jmx:rmi://localhost/jndi/rmi://localhost:1099/myconnector"/>
</bean>
If the ObjectName
property is set Spring will automatically register your connector
with the MBeanServer
under that ObjectName
. The example below shows the full set of
parameters which you can pass to the ConnectorServerFactoryBean
when creating a
JMXConnector:
<bean id="serverConnector"
class="org.springframework.jmx.support.ConnectorServerFactoryBean">
<property name="objectName" value="connector:name=iiop"/>
<property name="serviceUrl"
value="service:jmx:iiop://localhost/jndi/iiop://localhost:900/myconnector"/>
<property name="threaded" value="true"/>
<property name="daemon" value="true"/>
<property name="environment">
<map>
<entry key="someKey" value="someValue"/>
</map>
</property>
</bean>
Note that when using a RMI-based connector you need the lookup service (tnameserv or rmiregistry) to be started in order for the name registration to complete. If you are using Spring to export remote services for you via RMI, then Spring will already have constructed an RMI registry. If not, you can easily start a registry using the following snippet of configuration:
<bean id="registry" class="org.springframework.remoting.rmi.RmiRegistryFactoryBean">
<property name="port" value="1099"/>
</bean>
4.5.2. Client-side connectors
To create an MBeanServerConnection
to a remote JSR-160 enabled MBeanServer
use the
MBeanServerConnectionFactoryBean
as shown below:
<bean id="clientConnector" class="org.springframework.jmx.support.MBeanServerConnectionFactoryBean">
<property name="serviceUrl" value="service:jmx:rmi://localhost/jndi/rmi://localhost:1099/jmxrmi"/>
</bean>
4.5.3. JMX over Hessian or SOAP
JSR-160 permits extensions to the way in which communication is done between the client and the server. The examples above are using the mandatory RMI-based implementation required by the JSR-160 specification (IIOP and JRMP) and the (optional) JMXMP. By using other providers or JMX implementations (such as MX4J) you can take advantage of protocols like SOAP or Hessian over simple HTTP or SSL and others:
<bean id="serverConnector" class="org.springframework.jmx.support.ConnectorServerFactoryBean">
<property name="objectName" value="connector:name=burlap"/>
<property name="serviceUrl" value="service:jmx:burlap://localhost:9874"/>
</bean>
In the case of the above example, MX4J 3.0.0 was used; see the official MX4J documentation for more information.
4.6. Accessing MBeans via proxies
Spring JMX allows you to create proxies that re-route calls to MBeans registered in a
local or remote MBeanServer
. These proxies provide you with a standard Java interface
through which you can interact with your MBeans. The code below shows how to configure a
proxy for an MBean running in a local MBeanServer
:
<bean id="proxy" class="org.springframework.jmx.access.MBeanProxyFactoryBean">
<property name="objectName" value="bean:name=testBean"/>
<property name="proxyInterface" value="org.springframework.jmx.IJmxTestBean"/>
</bean>
Here you can see that a proxy is created for the MBean registered under the
ObjectName
: bean:name=testBean
. The set of interfaces that the proxy will implement
is controlled by the proxyInterfaces
property and the rules for mapping methods and
properties on these interfaces to operations and attributes on the MBean are the same
rules used by the InterfaceBasedMBeanInfoAssembler
.
The MBeanProxyFactoryBean
can create a proxy to any MBean that is accessible via an
MBeanServerConnection
. By default, the local MBeanServer
is located and used, but
you can override this and provide an MBeanServerConnection
pointing to a remote
MBeanServer
to cater for proxies pointing to remote MBeans:
<bean id="clientConnector"
class="org.springframework.jmx.support.MBeanServerConnectionFactoryBean">
<property name="serviceUrl" value="service:jmx:rmi://remotehost:9875"/>
</bean>
<bean id="proxy" class="org.springframework.jmx.access.MBeanProxyFactoryBean">
<property name="objectName" value="bean:name=testBean"/>
<property name="proxyInterface" value="org.springframework.jmx.IJmxTestBean"/>
<property name="server" ref="clientConnector"/>
</bean>
Here you can see that we create an MBeanServerConnection
pointing to a remote machine
using the MBeanServerConnectionFactoryBean
. This MBeanServerConnection
is then
passed to the MBeanProxyFactoryBean
via the server
property. The proxy that is
created will forward all invocations to the MBeanServer
via this
MBeanServerConnection
.
4.7. Notifications
Spring’s JMX offering includes comprehensive support for JMX notifications.
4.7.1. Registering listeners for notifications
Spring’s JMX support makes it very easy to register any number of
NotificationListeners
with any number of MBeans (this includes MBeans exported by
Spring’s MBeanExporter
and MBeans registered via some other mechanism). By way of an
example, consider the scenario where one would like to be informed (via a
Notification
) each and every time an attribute of a target MBean changes.
package com.example;
import javax.management.AttributeChangeNotification;
import javax.management.Notification;
import javax.management.NotificationFilter;
import javax.management.NotificationListener;
public class ConsoleLoggingNotificationListener
implements NotificationListener, NotificationFilter {
public void handleNotification(Notification notification, Object handback) {
System.out.println(notification);
System.out.println(handback);
}
public boolean isNotificationEnabled(Notification notification) {
return AttributeChangeNotification.class.isAssignableFrom(notification.getClass());
}
}
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="notificationListenerMappings">
<map>
<entry key="bean:name=testBean1">
<bean class="com.example.ConsoleLoggingNotificationListener"/>
</entry>
</map>
</property>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>
With the above configuration in place, every time a JMX Notification
is broadcast from
the target MBean ( bean:name=testBean1
), the ConsoleLoggingNotificationListener
bean
that was registered as a listener via the notificationListenerMappings
property will
be notified. The ConsoleLoggingNotificationListener
bean can then take whatever action
it deems appropriate in response to the Notification
.
You can also use straight bean names as the link between exported beans and listeners:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="notificationListenerMappings">
<map>
<entry key="testBean">
<bean class="com.example.ConsoleLoggingNotificationListener"/>
</entry>
</map>
</property>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>
If one wants to register a single NotificationListener
instance for all of the beans
that the enclosing MBeanExporter
is exporting, one can use the special wildcard '*'
(sans quotes) as the key for an entry in the notificationListenerMappings
property
map; for example:
<property name="notificationListenerMappings">
<map>
<entry key="*">
<bean class="com.example.ConsoleLoggingNotificationListener"/>
</entry>
</map>
</property>
If one needs to do the inverse (that is, register a number of distinct listeners against
an MBean), then one has to use the notificationListeners
list property instead (and in
preference to the notificationListenerMappings
property). This time, instead of
configuring simply a NotificationListener
for a single MBean, one configures
NotificationListenerBean
instances… a NotificationListenerBean
encapsulates a
NotificationListener
and the ObjectName
(or ObjectNames
) that it is to be
registered against in an MBeanServer
. The NotificationListenerBean
also encapsulates
a number of other properties such as a NotificationFilter
and an arbitrary handback
object that can be used in advanced JMX notification scenarios.
The configuration when using NotificationListenerBean
instances is not wildly
different to what was presented previously:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="notificationListeners">
<list>
<bean class="org.springframework.jmx.export.NotificationListenerBean">
<constructor-arg>
<bean class="com.example.ConsoleLoggingNotificationListener"/>
</constructor-arg>
<property name="mappedObjectNames">
<list>
<value>bean:name=testBean1</value>
</list>
</property>
</bean>
</list>
</property>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>
The above example is equivalent to the first notification example. Lets assume then that
we want to be given a handback object every time a Notification
is raised, and that
additionally we want to filter out extraneous Notifications
by supplying a
NotificationFilter
. (For a full discussion of just what a handback object is, and
indeed what a NotificationFilter
is, please do consult that section of the JMX
specification (1.2) entitled 'The JMX Notification Model'.)
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean1"/>
<entry key="bean:name=testBean2" value-ref="testBean2"/>
</map>
</property>
<property name="notificationListeners">
<list>
<bean class="org.springframework.jmx.export.NotificationListenerBean">
<constructor-arg ref="customerNotificationListener"/>
<property name="mappedObjectNames">
<list>
<!-- handles notifications from two distinct MBeans -->
<value>bean:name=testBean1</value>
<value>bean:name=testBean2</value>
</list>
</property>
<property name="handback">
<bean class="java.lang.String">
<constructor-arg value="This could be anything..."/>
</bean>
</property>
<property name="notificationFilter" ref="customerNotificationListener"/>
</bean>
</list>
</property>
</bean>
<!-- implements both the NotificationListener and NotificationFilter interfaces -->
<bean id="customerNotificationListener" class="com.example.ConsoleLoggingNotificationListener"/>
<bean id="testBean1" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
<bean id="testBean2" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="ANOTHER TEST"/>
<property name="age" value="200"/>
</bean>
</beans>
4.7.2. Publishing Notifications
Spring provides support not just for registering to receive Notifications
, but also
for publishing Notifications
.
Please note that this section is really only relevant to Spring managed beans that have
been exposed as MBeans via an |
The key interface in Spring’s JMX notification publication support is the
NotificationPublisher
interface (defined in the
org.springframework.jmx.export.notification
package). Any bean that is going to be
exported as an MBean via an MBeanExporter
instance can implement the related
NotificationPublisherAware
interface to gain access to a NotificationPublisher
instance. The NotificationPublisherAware
interface simply supplies an instance of a
NotificationPublisher
to the implementing bean via a simple setter method, which the
bean can then use to publish Notifications
.
As stated in the javadocs of the NotificationPublisher
class, managed beans that are
publishing events via the NotificationPublisher
mechanism are not responsible for
the state management of any notification listeners and the like … Spring’s JMX support
will take care of handling all the JMX infrastructure issues. All one need do as an
application developer is implement the NotificationPublisherAware
interface and start
publishing events using the supplied NotificationPublisher
instance. Note that the
NotificationPublisher
will be set after the managed bean has been registered with
an MBeanServer
.
Using a NotificationPublisher
instance is quite straightforward… one simply creates
a JMX Notification
instance (or an instance of an appropriate Notification
subclass), populates the notification with the data pertinent to the event that is to be
published, and one then invokes the sendNotification(Notification)
on the
NotificationPublisher
instance, passing in the Notification
.
Find below a simple example… in this scenario, exported instances of the JmxTestBean
are going to publish a NotificationEvent
every time the add(int, int)
operation is
invoked.
package org.springframework.jmx;
import org.springframework.jmx.export.notification.NotificationPublisherAware;
import org.springframework.jmx.export.notification.NotificationPublisher;
import javax.management.Notification;
public class JmxTestBean implements IJmxTestBean, NotificationPublisherAware {
private String name;
private int age;
private boolean isSuperman;
private NotificationPublisher publisher;
// other getters and setters omitted for clarity
public int add(int x, int y) {
int answer = x + y;
this.publisher.sendNotification(new Notification("add", this, 0));
return answer;
}
public void dontExposeMe() {
throw new RuntimeException();
}
public void setNotificationPublisher(NotificationPublisher notificationPublisher) {
this.publisher = notificationPublisher;
}
}
The NotificationPublisher
interface and the machinery to get it all working is one of
the nicer features of Spring’s JMX support. It does however come with the price tag of
coupling your classes to both Spring and JMX; as always, the advice here is to be
pragmatic… if you need the functionality offered by the NotificationPublisher
and
you can accept the coupling to both Spring and JMX, then do so.
4.8. Further resources
This section contains links to further resources about JMX.
-
The JMX homepage at Oracle
-
The JMX specification (JSR-000003)
-
The JMX Remote API specification (JSR-000160)
-
The MX4J homepage (an Open Source implementation of various JMX specs)
5. JCA CCI
5.1. Introduction
Java EE provides a specification to standardize access to enterprise information systems (EIS): the JCA (Java EE Connector Architecture). This specification is divided into several different parts:
-
SPI (Service provider interfaces) that the connector provider must implement. These interfaces constitute a resource adapter which can be deployed on a Java EE application server. In such a scenario, the server manages connection pooling, transaction and security (managed mode). The application server is also responsible for managing the configuration, which is held outside the client application. A connector can be used without an application server as well; in this case, the application must configure it directly (non-managed mode).
-
CCI (Common Client Interface) that an application can use to interact with the connector and thus communicate with an EIS. An API for local transaction demarcation is provided as well.
The aim of the Spring CCI support is to provide classes to access a CCI connector in typical Spring style, leveraging the Spring Framework’s general resource and transaction management facilities.
The client side of connectors doesn’t alway use CCI. Some connectors expose their own APIs, only providing JCA resource adapter to use the system contracts of a Java EE container (connection pooling, global transactions, security). Spring does not offer special support for such connector-specific APIs. |
5.2. Configuring CCI
5.2.1. Connector configuration
The base resource to use JCA CCI is the ConnectionFactory
interface. The connector
used must provide an implementation of this interface.
To use your connector, you can deploy it on your application server and fetch the
ConnectionFactory
from the server’s JNDI environment (managed mode). The connector
must be packaged as a RAR file (resource adapter archive) and contain a ra.xml
file to
describe its deployment characteristics. The actual name of the resource is specified
when you deploy it. To access it within Spring, simply use Spring’s
JndiObjectFactoryBean
/ <jee:jndi-lookup>
fetch the factory by its JNDI name.
Another way to use a connector is to embed it in your application (non-managed mode),
not using an application server to deploy and configure it. Spring offers the
possibility to configure a connector as a bean, through a provided FactoryBean
(
LocalConnectionFactoryBean
). In this manner, you only need the connector library in
the classpath (no RAR file and no ra.xml
descriptor needed). The library must be
extracted from the connector’s RAR file, if necessary.
Once you have got access to your ConnectionFactory
instance, you can inject it into
your components. These components can either be coded against the plain CCI API or
leverage Spring’s support classes for CCI access (e.g. CciTemplate
).
When you use a connector in non-managed mode, you can’t use global transactions because the resource is never enlisted / delisted in the current global transaction of the current thread. The resource is simply not aware of any global Java EE transactions that might be running. |
5.2.2. ConnectionFactory configuration in Spring
In order to make connections to the EIS, you need to obtain a ConnectionFactory
from
the application server if you are in a managed mode, or directly from Spring if you are
in a non-managed mode.
In a managed mode, you access a ConnectionFactory
from JNDI; its properties will be
configured in the application server.
<jee:jndi-lookup id="eciConnectionFactory" jndi-name="eis/cicseci"/>
In non-managed mode, you must configure the ConnectionFactory
you want to use in the
configuration of Spring as a JavaBean. The LocalConnectionFactoryBean
class offers
this setup style, passing in the ManagedConnectionFactory
implementation of your
connector, exposing the application-level CCI ConnectionFactory
.
<bean id="eciManagedConnectionFactory" class="com.ibm.connector2.cics.ECIManagedConnectionFactory">
<property name="serverName" value="TXSERIES"/>
<property name="connectionURL" value="tcp://localhost/"/>
<property name="portNumber" value="2006"/>
</bean>
<bean id="eciConnectionFactory" class="org.springframework.jca.support.LocalConnectionFactoryBean">
<property name="managedConnectionFactory" ref="eciManagedConnectionFactory"/>
</bean>
You can’t directly instantiate a specific |
5.2.3. Configuring CCI connections
JCA CCI allow the developer to configure the connections to the EIS using the
ConnectionSpec
implementation of your connector. In order to configure its properties,
you need to wrap the target connection factory with a dedicated adapter,
ConnectionSpecConnectionFactoryAdapter
. So, the dedicated ConnectionSpec
can be
configured with the property connectionSpec
(as an inner bean).
This property is not mandatory because the CCI ConnectionFactory
interface defines two
different methods to obtain a CCI connection. Some of the ConnectionSpec
properties
can often be configured in the application server (in managed mode) or on the
corresponding local ManagedConnectionFactory
implementation.
public interface ConnectionFactory implements Serializable, Referenceable {
...
Connection getConnection() throws ResourceException;
Connection getConnection(ConnectionSpec connectionSpec) throws ResourceException;
...
}
Spring provides a ConnectionSpecConnectionFactoryAdapter
that allows for specifying a
ConnectionSpec
instance to use for all operations on a given factory. If the adapter’s
connectionSpec
property is specified, the adapter uses the getConnection
variant
with the ConnectionSpec
argument, otherwise the variant without argument.
<bean id="managedConnectionFactory"
class="com.sun.connector.cciblackbox.CciLocalTxManagedConnectionFactory">
<property name="connectionURL" value="jdbc:hsqldb:hsql://localhost:9001"/>
<property name="driverName" value="org.hsqldb.jdbcDriver"/>
</bean>
<bean id="targetConnectionFactory"
class="org.springframework.jca.support.LocalConnectionFactoryBean">
<property name="managedConnectionFactory" ref="managedConnectionFactory"/>
</bean>
<bean id="connectionFactory"
class="org.springframework.jca.cci.connection.ConnectionSpecConnectionFactoryAdapter">
<property name="targetConnectionFactory" ref="targetConnectionFactory"/>
<property name="connectionSpec">
<bean class="com.sun.connector.cciblackbox.CciConnectionSpec">
<property name="user" value="sa"/>
<property name="password" value=""/>
</bean>
</property>
</bean>
5.2.4. Using a single CCI connection
If you want to use a single CCI connection, Spring provides a further
ConnectionFactory
adapter to manage this. The SingleConnectionFactory
adapter class
will open a single connection lazily and close it when this bean is destroyed at
application shutdown. This class will expose special Connection
proxies that behave
accordingly, all sharing the same underlying physical connection.
<bean id="eciManagedConnectionFactory"
class="com.ibm.connector2.cics.ECIManagedConnectionFactory">
<property name="serverName" value="TEST"/>
<property name="connectionURL" value="tcp://localhost/"/>
<property name="portNumber" value="2006"/>
</bean>
<bean id="targetEciConnectionFactory"
class="org.springframework.jca.support.LocalConnectionFactoryBean">
<property name="managedConnectionFactory" ref="eciManagedConnectionFactory"/>
</bean>
<bean id="eciConnectionFactory"
class="org.springframework.jca.cci.connection.SingleConnectionFactory">
<property name="targetConnectionFactory" ref="targetEciConnectionFactory"/>
</bean>
This |
5.3. Using Spring’s CCI access support
5.3.1. Record conversion
One of the aims of the JCA CCI support is to provide convenient facilities for
manipulating CCI records. The developer can specify the strategy to create records and
extract datas from records, for use with Spring’s CciTemplate
. The following
interfaces will configure the strategy to use input and output records if you don’t want
to work with records directly in your application.
In order to create an input Record
, the developer can use a dedicated implementation
of the RecordCreator
interface.
public interface RecordCreator {
Record createRecord(RecordFactory recordFactory) throws ResourceException, DataAccessException;
}
As you can see, the createRecord(..)
method receives a RecordFactory
instance as
parameter, which corresponds to the RecordFactory
of the ConnectionFactory
used.
This reference can be used to create IndexedRecord
or MappedRecord
instances. The
following sample shows how to use the RecordCreator
interface and indexed/mapped
records.
public class MyRecordCreator implements RecordCreator {
public Record createRecord(RecordFactory recordFactory) throws ResourceException {
IndexedRecord input = recordFactory.createIndexedRecord("input");
input.add(new Integer(id));
return input;
}
}
An output Record
can be used to receive data back from the EIS. Hence, a specific
implementation of the RecordExtractor
interface can be passed to Spring’s
CciTemplate
for extracting data from the output Record
.
public interface RecordExtractor {
Object extractData(Record record) throws ResourceException, SQLException, DataAccessException;
}
The following sample shows how to use the RecordExtractor
interface.
public class MyRecordExtractor implements RecordExtractor {
public Object extractData(Record record) throws ResourceException {
CommAreaRecord commAreaRecord = (CommAreaRecord) record;
String str = new String(commAreaRecord.toByteArray());
String field1 = string.substring(0,6);
String field2 = string.substring(6,1);
return new OutputObject(Long.parseLong(field1), field2);
}
}
5.3.2. CciTemplate
The CciTemplate
is the central class of the core CCI support package (
org.springframework.jca.cci.core
). It simplifies the use of CCI since it handles the
creation and release of resources. This helps to avoid common errors like forgetting to
always close the connection. It cares for the lifecycle of connection and interaction
objects, letting application code focus on generating input records from application
data and extracting application data from output records.
The JCA CCI specification defines two distinct methods to call operations on an EIS. The
CCI Interaction
interface provides two execute method signatures:
public interface javax.resource.cci.Interaction {
...
boolean execute(InteractionSpec spec, Record input, Record output) throws ResourceException;
Record execute(InteractionSpec spec, Record input) throws ResourceException;
...
}
Depending on the template method called, CciTemplate
will know which execute
method
to call on the interaction. In any case, a correctly initialized InteractionSpec
instance is mandatory.
CciTemplate.execute(..)
can be used in two ways:
-
With direct
Record
arguments. In this case, you simply need to pass the CCI input record in, and the returned object be the corresponding CCI output record. -
With application objects, using record mapping. In this case, you need to provide corresponding
RecordCreator
andRecordExtractor
instances.
With the first approach, the following methods of the template will be used. These
methods directly correspond to those on the Interaction
interface.
public class CciTemplate implements CciOperations {
public Record execute(InteractionSpec spec, Record inputRecord)
throws DataAccessException { ... }
public void execute(InteractionSpec spec, Record inputRecord, Record outputRecord)
throws DataAccessException { ... }
}
With the second approach, we need to specify the record creation and record extraction
strategies as arguments. The interfaces used are those describe in the previous section
on record conversion. The corresponding CciTemplate
methods are the following:
public class CciTemplate implements CciOperations {
public Record execute(InteractionSpec spec,
RecordCreator inputCreator) throws DataAccessException {
// ...
}
public Object execute(InteractionSpec spec, Record inputRecord,
RecordExtractor outputExtractor) throws DataAccessException {
// ...
}
public Object execute(InteractionSpec spec, RecordCreator creator,
RecordExtractor extractor) throws DataAccessException {
// ...
}
}
Unless the outputRecordCreator
property is set on the template (see the following
section), every method will call the corresponding execute
method of the CCI
Interaction
with two parameters: InteractionSpec
and input Record
, receiving an
output Record
as return value.
CciTemplate
also provides methods to create IndexRecord
and MappedRecord
outside a
RecordCreator
implementation, through its createIndexRecord(..)
and
createMappedRecord(..)
methods. This can be used within DAO implementations to create
Record
instances to pass into corresponding CciTemplate.execute(..)
methods.
public class CciTemplate implements CciOperations {
public IndexedRecord createIndexedRecord(String name) throws DataAccessException { ... }
public MappedRecord createMappedRecord(String name) throws DataAccessException { ... }
}
5.3.3. DAO support
Spring’s CCI support provides a abstract class for DAOs, supporting injection of a
ConnectionFactory
or a CciTemplate
instances. The name of the class is
CciDaoSupport
: It provides simple setConnectionFactory
and setCciTemplate
methods.
Internally, this class will create a CciTemplate
instance for a passed-in
ConnectionFactory
, exposing it to concrete data access implementations in subclasses.
public abstract class CciDaoSupport {
public void setConnectionFactory(ConnectionFactory connectionFactory) {
// ...
}
public ConnectionFactory getConnectionFactory() {
// ...
}
public void setCciTemplate(CciTemplate cciTemplate) {
// ...
}
public CciTemplate getCciTemplate() {
// ...
}
}
5.3.4. Automatic output record generation
If the connector used only supports the Interaction.execute(..)
method with input and
output records as parameters (that is, it requires the desired output record to be
passed in instead of returning an appropriate output record), you can set the
outputRecordCreator
property of the CciTemplate
to automatically generate an output
record to be filled by the JCA connector when the response is received. This record will
be then returned to the caller of the template.
This property simply holds an implementation of the RecordCreator
interface, used for
that purpose. The RecordCreator
interface has already been discussed in
Record conversion. The outputRecordCreator
property must be directly specified on
the CciTemplate
. This could be done in the application code like so:
cciTemplate.setOutputRecordCreator(new EciOutputRecordCreator());
Or (recommended) in the Spring configuration, if the CciTemplate
is configured as a
dedicated bean instance:
<bean id="eciOutputRecordCreator" class="eci.EciOutputRecordCreator"/>
<bean id="cciTemplate" class="org.springframework.jca.cci.core.CciTemplate">
<property name="connectionFactory" ref="eciConnectionFactory"/>
<property name="outputRecordCreator" ref="eciOutputRecordCreator"/>
</bean>
As the |
5.3.5. Summary
The following table summarizes the mechanisms of the CciTemplate
class and the
corresponding methods called on the CCI Interaction
interface:
CciTemplate method signature | CciTemplate outputRecordCreator property | execute method called on the CCI Interaction |
---|---|---|
Record execute(InteractionSpec, Record) |
not set |
Record execute(InteractionSpec, Record) |
Record execute(InteractionSpec, Record) |
set |
boolean execute(InteractionSpec, Record, Record) |
void execute(InteractionSpec, Record, Record) |
not set |
void execute(InteractionSpec, Record, Record) |
void execute(InteractionSpec, Record, Record) |
set |
void execute(InteractionSpec, Record, Record) |
Record execute(InteractionSpec, RecordCreator) |
not set |
Record execute(InteractionSpec, Record) |
Record execute(InteractionSpec, RecordCreator) |
set |
void execute(InteractionSpec, Record, Record) |
Record execute(InteractionSpec, Record, RecordExtractor) |
not set |
Record execute(InteractionSpec, Record) |
Record execute(InteractionSpec, Record, RecordExtractor) |
set |
void execute(InteractionSpec, Record, Record) |
Record execute(InteractionSpec, RecordCreator, RecordExtractor) |
not set |
Record execute(InteractionSpec, Record) |
Record execute(InteractionSpec, RecordCreator, RecordExtractor) |
set |
void execute(InteractionSpec, Record, Record) |
5.3.6. Using a CCI Connection and Interaction directly
CciTemplate
also offers the possibility to work directly with CCI connections and
interactions, in the same manner as JdbcTemplate
and JmsTemplate
. This is useful
when you want to perform multiple operations on a CCI connection or interaction, for
example.
The interface ConnectionCallback
provides a CCI Connection
as argument, in order to
perform custom operations on it, plus the CCI ConnectionFactory
which the Connection
was created with. The latter can be useful for example to get an associated
RecordFactory
instance and create indexed/mapped records, for example.
public interface ConnectionCallback {
Object doInConnection(Connection connection, ConnectionFactory connectionFactory)
throws ResourceException, SQLException, DataAccessException;
}
The interface InteractionCallback
provides the CCI Interaction
, in order to perform
custom operations on it, plus the corresponding CCI ConnectionFactory
.
public interface InteractionCallback {
Object doInInteraction(Interaction interaction, ConnectionFactory connectionFactory)
throws ResourceException, SQLException, DataAccessException;
}
|
5.3.7. Example for CciTemplate usage
In this section, the usage of the CciTemplate
will be shown to acces to a CICS with
ECI mode, with the IBM CICS ECI connector.
Firstly, some initializations on the CCI InteractionSpec
must be done to specify which
CICS program to access and how to interact with it.
ECIInteractionSpec interactionSpec = new ECIInteractionSpec();
interactionSpec.setFunctionName("MYPROG");
interactionSpec.setInteractionVerb(ECIInteractionSpec.SYNC_SEND_RECEIVE);
Then the program can use CCI via Spring’s template and specify mappings between custom
objects and CCI Records
.
public class MyDaoImpl extends CciDaoSupport implements MyDao {
public OutputObject getData(InputObject input) {
ECIInteractionSpec interactionSpec = ...;
OutputObject output = (ObjectOutput) getCciTemplate().execute(interactionSpec,
new RecordCreator() {
public Record createRecord(RecordFactory recordFactory) throws ResourceException {
return new CommAreaRecord(input.toString().getBytes());
}
},
new RecordExtractor() {
public Object extractData(Record record) throws ResourceException {
CommAreaRecord commAreaRecord = (CommAreaRecord)record;
String str = new String(commAreaRecord.toByteArray());
String field1 = string.substring(0,6);
String field2 = string.substring(6,1);
return new OutputObject(Long.parseLong(field1), field2);
}
});
return output;
}
}
As discussed previously, callbacks can be used to work directly on CCI connections or interactions.
public class MyDaoImpl extends CciDaoSupport implements MyDao {
public OutputObject getData(InputObject input) {
ObjectOutput output = (ObjectOutput) getCciTemplate().execute(
new ConnectionCallback() {
public Object doInConnection(Connection connection,
ConnectionFactory factory) throws ResourceException {
// do something...
}
});
}
return output;
}
}
With a |
For a more specific callback, you can implement an InteractionCallback
. The passed-in
Interaction
will be managed and closed by the CciTemplate
in this case.
public class MyDaoImpl extends CciDaoSupport implements MyDao {
public String getData(String input) {
ECIInteractionSpec interactionSpec = ...;
String output = (String) getCciTemplate().execute(interactionSpec,
new InteractionCallback() {
public Object doInInteraction(Interaction interaction,
ConnectionFactory factory) throws ResourceException {
Record input = new CommAreaRecord(inputString.getBytes());
Record output = new CommAreaRecord();
interaction.execute(holder.getInteractionSpec(), input, output);
return new String(output.toByteArray());
}
});
return output;
}
}
For the examples above, the corresponding configuration of the involved Spring beans could look like this in non-managed mode:
<bean id="managedConnectionFactory" class="com.ibm.connector2.cics.ECIManagedConnectionFactory">
<property name="serverName" value="TXSERIES"/>
<property name="connectionURL" value="local:"/>
<property name="userName" value="CICSUSER"/>
<property name="password" value="CICS"/>
</bean>
<bean id="connectionFactory" class="org.springframework.jca.support.LocalConnectionFactoryBean">
<property name="managedConnectionFactory" ref="managedConnectionFactory"/>
</bean>
<bean id="component" class="mypackage.MyDaoImpl">
<property name="connectionFactory" ref="connectionFactory"/>
</bean>
In managed mode (that is, in a Java EE environment), the configuration could look as follows:
<jee:jndi-lookup id="connectionFactory" jndi-name="eis/cicseci"/>
<bean id="component" class="MyDaoImpl">
<property name="connectionFactory" ref="connectionFactory"/>
</bean>
5.4. Modeling CCI access as operation objects
The org.springframework.jca.cci.object
package contains support classes that allow you
to access the EIS in a different style: through reusable operation objects, analogous to
Spring’s JDBC operation objects (see JDBC chapter). This will usually encapsulate the
CCI API: an application-level input object will be passed to the operation object, so it
can construct the input record and then convert the received record data to an
application-level output object and return it.
This approach is internally based on the |
5.4.1. MappingRecordOperation
MappingRecordOperation
essentially performs the same work as CciTemplate
, but
represents a specific, pre-configured operation as an object. It provides two template
methods to specify how to convert an input object to a input record, and how to convert
an output record to an output object (record mapping):
-
createInputRecord(..)
to specify how to convert an input object to an inputRecord
-
extractOutputData(..)
to specify how to extract an output object from an outputRecord
Here are the signatures of these methods:
public abstract class MappingRecordOperation extends EisOperation {
...
protected abstract Record createInputRecord(RecordFactory recordFactory,
Object inputObject) throws ResourceException, DataAccessException {
// ...
}
protected abstract Object extractOutputData(Record outputRecord)
throws ResourceException, SQLException, DataAccessException {
// ...
}
...
}
Thereafter, in order to execute an EIS operation, you need to use a single execute method, passing in an application-level input object and receiving an application-level output object as result:
public abstract class MappingRecordOperation extends EisOperation {
...
public Object execute(Object inputObject) throws DataAccessException {
}
...
}
As you can see, contrary to the CciTemplate
class, this execute(..)
method does not
have an InteractionSpec
as argument. Instead, the InteractionSpec
is global to the
operation. The following constructor must be used to instantiate an operation object
with a specific InteractionSpec
:
InteractionSpec spec = ...;
MyMappingRecordOperation eisOperation = new MyMappingRecordOperation(getConnectionFactory(), spec);
...
5.4.2. MappingCommAreaOperation
Some connectors use records based on a COMMAREA which represents an array of bytes
containing parameters to send to the EIS and data returned by it. Spring provides a
special operation class for working directly on COMMAREA rather than on records. The
MappingCommAreaOperation
class extends the MappingRecordOperation
class to provide
such special COMMAREA support. It implicitly uses the CommAreaRecord
class as input
and output record type, and provides two new methods to convert an input object into an
input COMMAREA and the output COMMAREA into an output object.
public abstract class MappingCommAreaOperation extends MappingRecordOperation {
...
protected abstract byte[] objectToBytes(Object inObject)
throws IOException, DataAccessException;
protected abstract Object bytesToObject(byte[] bytes)
throws IOException, DataAccessException;
...
}
5.4.3. Automatic output record generation
As every MappingRecordOperation
subclass is based on CciTemplate internally, the same
way to automatically generate output records as with CciTemplate
is available. Every
operation object provides a corresponding setOutputRecordCreator(..)
method. For
further information, see Automatic output record generation.
5.4.4. Summary
The operation object approach uses records in the same manner as the CciTemplate
class.
MappingRecordOperation method signature | MappingRecordOperation outputRecordCreator property | execute method called on the CCI Interaction |
---|---|---|
Object execute(Object) |
not set |
Record execute(InteractionSpec, Record) |
Object execute(Object) |
set |
boolean execute(InteractionSpec, Record, Record) |
5.4.5. Example for MappingRecordOperation usage
In this section, the usage of the MappingRecordOperation
will be shown to access a
database with the Blackbox CCI connector.
The original version of this connector is provided by the Java EE SDK (version 1.3), available from Oracle. |
Firstly, some initializations on the CCI InteractionSpec
must be done to specify which
SQL request to execute. In this sample, we directly define the way to convert the
parameters of the request to a CCI record and the way to convert the CCI result record
to an instance of the Person
class.
public class PersonMappingOperation extends MappingRecordOperation {
public PersonMappingOperation(ConnectionFactory connectionFactory) {
setConnectionFactory(connectionFactory);
CciInteractionSpec interactionSpec = new CciConnectionSpec();
interactionSpec.setSql("select * from person where person_id=?");
setInteractionSpec(interactionSpec);
}
protected Record createInputRecord(RecordFactory recordFactory,
Object inputObject) throws ResourceException {
Integer id = (Integer) inputObject;
IndexedRecord input = recordFactory.createIndexedRecord("input");
input.add(new Integer(id));
return input;
}
protected Object extractOutputData(Record outputRecord)
throws ResourceException, SQLException {
ResultSet rs = (ResultSet) outputRecord;
Person person = null;
if (rs.next()) {
Person person = new Person();
person.setId(rs.getInt("person_id"));
person.setLastName(rs.getString("person_last_name"));
person.setFirstName(rs.getString("person_first_name"));
}
return person;
}
}
Then the application can execute the operation object, with the person identifier as argument. Note that operation object could be set up as shared instance, as it is thread-safe.
public class MyDaoImpl extends CciDaoSupport implements MyDao {
public Person getPerson(int id) {
PersonMappingOperation query = new PersonMappingOperation(getConnectionFactory());
Person person = (Person) query.execute(new Integer(id));
return person;
}
}
The corresponding configuration of Spring beans could look as follows in non-managed mode:
<bean id="managedConnectionFactory"
class="com.sun.connector.cciblackbox.CciLocalTxManagedConnectionFactory">
<property name="connectionURL" value="jdbc:hsqldb:hsql://localhost:9001"/>
<property name="driverName" value="org.hsqldb.jdbcDriver"/>
</bean>
<bean id="targetConnectionFactory"
class="org.springframework.jca.support.LocalConnectionFactoryBean">
<property name="managedConnectionFactory" ref="managedConnectionFactory"/>
</bean>
<bean id="connectionFactory"
class="org.springframework.jca.cci.connection.ConnectionSpecConnectionFactoryAdapter">
<property name="targetConnectionFactory" ref="targetConnectionFactory"/>
<property name="connectionSpec">
<bean class="com.sun.connector.cciblackbox.CciConnectionSpec">
<property name="user" value="sa"/>
<property name="password" value=""/>
</bean>
</property>
</bean>
<bean id="component" class="MyDaoImpl">
<property name="connectionFactory" ref="connectionFactory"/>
</bean>
In managed mode (that is, in a Java EE environment), the configuration could look as follows:
<jee:jndi-lookup id="targetConnectionFactory" jndi-name="eis/blackbox"/>
<bean id="connectionFactory"
class="org.springframework.jca.cci.connection.ConnectionSpecConnectionFactoryAdapter">
<property name="targetConnectionFactory" ref="targetConnectionFactory"/>
<property name="connectionSpec">
<bean class="com.sun.connector.cciblackbox.CciConnectionSpec">
<property name="user" value="sa"/>
<property name="password" value=""/>
</bean>
</property>
</bean>
<bean id="component" class="MyDaoImpl">
<property name="connectionFactory" ref="connectionFactory"/>
</bean>
5.4.6. Example for MappingCommAreaOperation usage
In this section, the usage of the MappingCommAreaOperation
will be shown: accessing a
CICS with ECI mode with the IBM CICS ECI connector.
Firstly, the CCI InteractionSpec
needs to be initialized to specify which CICS program
to access and how to interact with it.
public abstract class EciMappingOperation extends MappingCommAreaOperation {
public EciMappingOperation(ConnectionFactory connectionFactory, String programName) {
setConnectionFactory(connectionFactory);
ECIInteractionSpec interactionSpec = new ECIInteractionSpec(),
interactionSpec.setFunctionName(programName);
interactionSpec.setInteractionVerb(ECIInteractionSpec.SYNC_SEND_RECEIVE);
interactionSpec.setCommareaLength(30);
setInteractionSpec(interactionSpec);
setOutputRecordCreator(new EciOutputRecordCreator());
}
private static class EciOutputRecordCreator implements RecordCreator {
public Record createRecord(RecordFactory recordFactory) throws ResourceException {
return new CommAreaRecord();
}
}
}
The abstract EciMappingOperation
class can then be subclassed to specify mappings
between custom objects and Records
.
public class MyDaoImpl extends CciDaoSupport implements MyDao {
public OutputObject getData(Integer id) {
EciMappingOperation query = new EciMappingOperation(getConnectionFactory(), "MYPROG") {
protected abstract byte[] objectToBytes(Object inObject) throws IOException {
Integer id = (Integer) inObject;
return String.valueOf(id);
}
protected abstract Object bytesToObject(byte[] bytes) throws IOException;
String str = new String(bytes);
String field1 = str.substring(0,6);
String field2 = str.substring(6,1);
String field3 = str.substring(7,1);
return new OutputObject(field1, field2, field3);
}
});
return (OutputObject) query.execute(new Integer(id));
}
}
The corresponding configuration of Spring beans could look as follows in non-managed mode:
<bean id="managedConnectionFactory" class="com.ibm.connector2.cics.ECIManagedConnectionFactory">
<property name="serverName" value="TXSERIES"/>
<property name="connectionURL" value="local:"/>
<property name="userName" value="CICSUSER"/>
<property name="password" value="CICS"/>
</bean>
<bean id="connectionFactory" class="org.springframework.jca.support.LocalConnectionFactoryBean">
<property name="managedConnectionFactory" ref="managedConnectionFactory"/>
</bean>
<bean id="component" class="MyDaoImpl">
<property name="connectionFactory" ref="connectionFactory"/>
</bean>
In managed mode (that is, in a Java EE environment), the configuration could look as follows:
<jee:jndi-lookup id="connectionFactory" jndi-name="eis/cicseci"/>
<bean id="component" class="MyDaoImpl">
<property name="connectionFactory" ref="connectionFactory"/>
</bean>
5.5. Transactions
JCA specifies several levels of transaction support for resource adapters. The kind of
transactions that your resource adapter supports is specified in its ra.xml
file.
There are essentially three options: none (for example with CICS EPI connector), local
transactions (for example with a CICS ECI connector), global transactions (for example
with an IMS connector).
<connector>
<resourceadapter>
<!-- <transaction-support>NoTransaction</transaction-support> -->
<!-- <transaction-support>LocalTransaction</transaction-support> -->
<transaction-support>XATransaction</transaction-support>
<resourceadapter>
<connector>
For global transactions, you can use Spring’s generic transaction infrastructure to
demarcate transactions, with JtaTransactionManager
as backend (delegating to the Java
EE server’s distributed transaction coordinator underneath).
For local transactions on a single CCI ConnectionFactory
, Spring provides a specific
transaction management strategy for CCI, analogous to the DataSourceTransactionManager
for JDBC. The CCI API defines a local transaction object and corresponding local
transaction demarcation methods. Spring’s CciLocalTransactionManager
executes such
local CCI transactions, fully compliant with Spring’s generic
PlatformTransactionManager
abstraction.
<jee:jndi-lookup id="eciConnectionFactory" jndi-name="eis/cicseci"/>
<bean id="eciTransactionManager"
class="org.springframework.jca.cci.connection.CciLocalTransactionManager">
<property name="connectionFactory" ref="eciConnectionFactory"/>
</bean>
Both transaction strategies can be used with any of Spring’s transaction demarcation
facilities, be it declarative or programmatic. This is a consequence of Spring’s generic
PlatformTransactionManager
abstraction, which decouples transaction demarcation from
the actual execution strategy. Simply switch between JtaTransactionManager
and
CciLocalTransactionManager
as needed, keeping your transaction demarcation as-is.
For more information on Spring’s transaction facilities, see the chapter entitled Transaction Management.
6. Email
6.1. Introduction
The Spring Framework provides a helpful utility library for sending email that shields the user from the specifics of the underlying mailing system and is responsible for low level resource handling on behalf of the client.
The org.springframework.mail
package is the root level package for the Spring
Framework’s email support. The central interface for sending emails is the MailSender
interface; a simple value object encapsulating the properties of a simple mail such as
from and to (plus many others) is the SimpleMailMessage
class. This package
also contains a hierarchy of checked exceptions which provide a higher level of
abstraction over the lower level mail system exceptions with the root exception being
MailException
. Please refer to the javadocs for more information on the rich mail
exception hierarchy.
The org.springframework.mail.javamail.JavaMailSender
interface adds specialized
JavaMail features such as MIME message support to the MailSender
interface (from
which it inherits). JavaMailSender
also provides a callback interface for preparation
of JavaMail MIME messages, called
org.springframework.mail.javamail.MimeMessagePreparator
6.2. Usage
Let’s assume there is a business interface called OrderManager
:
public interface OrderManager {
void placeOrder(Order order);
}
Let us also assume that there is a requirement stating that an email message with an order number needs to be generated and sent to a customer placing the relevant order.
6.2.1. Basic MailSender and SimpleMailMessage usage
import org.springframework.mail.MailException;
import org.springframework.mail.MailSender;
import org.springframework.mail.SimpleMailMessage;
public class SimpleOrderManager implements OrderManager {
private MailSender mailSender;
private SimpleMailMessage templateMessage;
public void setMailSender(MailSender mailSender) {
this.mailSender = mailSender;
}
public void setTemplateMessage(SimpleMailMessage templateMessage) {
this.templateMessage = templateMessage;
}
public void placeOrder(Order order) {
// Do the business calculations...
// Call the collaborators to persist the order...
// Create a thread safe "copy" of the template message and customize it
SimpleMailMessage msg = new SimpleMailMessage(this.templateMessage);
msg.setTo(order.getCustomer().getEmailAddress());
msg.setText(
"Dear " + order.getCustomer().getFirstName()
+ order.getCustomer().getLastName()
+ ", thank you for placing order. Your order number is "
+ order.getOrderNumber());
try{
this.mailSender.send(msg);
}
catch (MailException ex) {
// simply log it and go on...
System.err.println(ex.getMessage());
}
}
}
Find below the bean definitions for the above code:
<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
<property name="host" value="mail.mycompany.com"/>
</bean>
<!-- this is a template message that we can pre-load with default state -->
<bean id="templateMessage" class="org.springframework.mail.SimpleMailMessage">
<property name="from" value="[email protected]"/>
<property name="subject" value="Your order"/>
</bean>
<bean id="orderManager" class="com.mycompany.businessapp.support.SimpleOrderManager">
<property name="mailSender" ref="mailSender"/>
<property name="templateMessage" ref="templateMessage"/>
</bean>
6.2.2. Using the JavaMailSender and the MimeMessagePreparator
Here is another implementation of OrderManager
using the MimeMessagePreparator
callback interface. Please note in this case that the mailSender
property is of type
JavaMailSender
so that we are able to use the JavaMail MimeMessage
class:
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMessage;
import org.springframework.mail.MailException;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.MimeMessagePreparator;
public class SimpleOrderManager implements OrderManager {
private JavaMailSender mailSender;
public void setMailSender(JavaMailSender mailSender) {
this.mailSender = mailSender;
}
public void placeOrder(final Order order) {
// Do the business calculations...
// Call the collaborators to persist the order...
MimeMessagePreparator preparator = new MimeMessagePreparator() {
public void prepare(MimeMessage mimeMessage) throws Exception {
mimeMessage.setRecipient(Message.RecipientType.TO,
new InternetAddress(order.getCustomer().getEmailAddress()));
mimeMessage.setFrom(new InternetAddress("[email protected]"));
mimeMessage.setText(
"Dear " + order.getCustomer().getFirstName() + " "
+ order.getCustomer().getLastName()
+ ", thank you for placing order. Your order number is "
+ order.getOrderNumber());
}
};
try {
this.mailSender.send(preparator);
}
catch (MailException ex) {
// simply log it and go on...
System.err.println(ex.getMessage());
}
}
}
The mail code is a crosscutting concern and could well be a candidate for refactoring
into a custom Spring AOP aspect, which then could be executed at appropriate
joinpoints on the |
The Spring Framework’s mail support ships with the standard JavaMail implementation. Please refer to the relevant javadocs for more information.
6.3. Using the JavaMail MimeMessageHelper
A class that comes in pretty handy when dealing with JavaMail messages is the
org.springframework.mail.javamail.MimeMessageHelper
class, which shields you from
having to use the verbose JavaMail API. Using the MimeMessageHelper
it is pretty easy
to create a MimeMessage
:
// of course you would use DI in any real-world cases
JavaMailSenderImpl sender = new JavaMailSenderImpl();
sender.setHost("mail.host.com");
MimeMessage message = sender.createMimeMessage();
MimeMessageHelper helper = new MimeMessageHelper(message);
helper.setTo("[email protected]");
helper.setText("Thank you for ordering!");
sender.send(message);
6.3.1. Sending attachments and inline resources
Multipart email messages allow for both attachments and inline resources. Examples of inline resources would be images or a stylesheet you want to use in your message, but that you don’t want displayed as an attachment.
Attachments
The following example shows you how to use the MimeMessageHelper
to send an email
along with a single JPEG image attachment.
JavaMailSenderImpl sender = new JavaMailSenderImpl();
sender.setHost("mail.host.com");
MimeMessage message = sender.createMimeMessage();
// use the true flag to indicate you need a multipart message
MimeMessageHelper helper = new MimeMessageHelper(message, true);
helper.setTo("[email protected]");
helper.setText("Check out this image!");
// let's attach the infamous windows Sample file (this time copied to c:/)
FileSystemResource file = new FileSystemResource(new File("c:/Sample.jpg"));
helper.addAttachment("CoolImage.jpg", file);
sender.send(message);
Inline resources
The following example shows you how to use the MimeMessageHelper
to send an email
along with an inline image.
JavaMailSenderImpl sender = new JavaMailSenderImpl();
sender.setHost("mail.host.com");
MimeMessage message = sender.createMimeMessage();
// use the true flag to indicate you need a multipart message
MimeMessageHelper helper = new MimeMessageHelper(message, true);
helper.setTo("[email protected]");
// use the true flag to indicate the text included is HTML
helper.setText("<html><body><img src='cid:identifier1234'></body></html>", true);
// let's include the infamous windows Sample file (this time copied to c:/)
FileSystemResource res = new FileSystemResource(new File("c:/Sample.jpg"));
helper.addInline("identifier1234", res);
sender.send(message);
Inline resources are added to the mime message using the specified |
6.3.2. Creating email content using a templating library
The code in the previous examples explicitly created the content of the email message,
using methods calls such as message.setText(..)
. This is fine for simple cases, and it
is okay in the context of the aforementioned examples, where the intent was to show you
the very basics of the API.
In your typical enterprise application though, you are not going to create the content of your emails using the above approach for a number of reasons.
-
Creating HTML-based email content in Java code is tedious and error prone
-
There is no clear separation between display logic and business logic
-
Changing the display structure of the email content requires writing Java code, recompiling, redeploying…
Typically the approach taken to address these issues is to use a template library such as FreeMarker to define the display structure of email content. This leaves your code tasked only with creating the data that is to be rendered in the email template and sending the email. It is definitely a best practice for when the content of your emails becomes even moderately complex, and with the Spring Framework’s support classes for FreeMarker becomes quite easy to do.
7. Task Execution and Scheduling
7.1. Introduction
The Spring Framework provides abstractions for asynchronous execution and scheduling of
tasks with the TaskExecutor
and TaskScheduler
interfaces, respectively. Spring also
features implementations of those interfaces that support thread pools or delegation to
CommonJ within an application server environment. Ultimately the use of these
implementations behind the common interfaces abstracts away the differences between Java
SE 5, Java SE 6 and Java EE environments.
Spring also features integration classes for supporting scheduling with the Timer
,
part of the JDK since 1.3, and the Quartz Scheduler ( http://quartz-scheduler.org).
Both of those schedulers are set up using a FactoryBean
with optional references to
Timer
or Trigger
instances, respectively. Furthermore, a convenience class for both
the Quartz Scheduler and the Timer
is available that allows you to invoke a method of
an existing target object (analogous to the normal MethodInvokingFactoryBean
operation).
7.2. The Spring TaskExecutor abstraction
Executors are the JDK name for the concept of thread pools. The "executor" naming is due to the fact that there is no guarantee that the underlying implementation is actually a pool; an executor may be single-threaded or even synchronous. Spring’s abstraction hides implementation details between Java SE and Java EE environments.
Spring’s TaskExecutor
interface is identical to the java.util.concurrent.Executor
interface. In fact, originally, its primary reason for existence was to abstract away
the need for Java 5 when using thread pools. The interface has a single method
execute(Runnable task)
that accepts a task for execution based on the semantics
and configuration of the thread pool.
The TaskExecutor
was originally created to give other Spring components an abstraction
for thread pooling where needed. Components such as the ApplicationEventMulticaster
,
JMS’s AbstractMessageListenerContainer
, and Quartz integration all use the
TaskExecutor
abstraction to pool threads. However, if your beans need thread pooling
behavior, it is possible to use this abstraction for your own needs.
7.2.1. TaskExecutor types
There are a number of pre-built implementations of TaskExecutor
included with the
Spring distribution. In all likelihood, you shouldn’t ever need to implement your own.
-
SimpleAsyncTaskExecutor
This implementation does not reuse any threads, rather it starts up a new thread for each invocation. However, it does support a concurrency limit which will block any invocations that are over the limit until a slot has been freed up. If you are looking for true pooling, see the discussions ofSimpleThreadPoolTaskExecutor
andThreadPoolTaskExecutor
below. -
SyncTaskExecutor
This implementation doesn’t execute invocations asynchronously. Instead, each invocation takes place in the calling thread. It is primarily used in situations where multi-threading isn’t necessary such as simple test cases. -
ConcurrentTaskExecutor
This implementation is an adapter for ajava.util.concurrent.Executor
object. There is an alternative,ThreadPoolTaskExecutor
, that exposes theExecutor
configuration parameters as bean properties. It is rare to need to use theConcurrentTaskExecutor
, but if theThreadPoolTaskExecutor
isn’t flexible enough for your needs, theConcurrentTaskExecutor
is an alternative. -
SimpleThreadPoolTaskExecutor
This implementation is actually a subclass of Quartz’sSimpleThreadPool
which listens to Spring’s lifecycle callbacks. This is typically used when you have a thread pool that may need to be shared by both Quartz and non-Quartz components. -
ThreadPoolTaskExecutor
This implementation is the most commonly used one. It exposes bean properties for configuring ajava.util.concurrent.ThreadPoolExecutor
and wraps it in aTaskExecutor
. If you need to adapt to a different kind ofjava.util.concurrent.Executor
, it is recommended that you use aConcurrentTaskExecutor
instead. -
WorkManagerTaskExecutor
This implementation uses the CommonJ
WorkManager
as its backing implementation and is the central convenience class for setting up a CommonJWorkManager
reference in a Spring context. Similar to theSimpleThreadPoolTaskExecutor
, this class implements theWorkManager
interface and therefore can be used directly as aWorkManager
as well.
7.2.2. Using a TaskExecutor
Spring’s TaskExecutor
implementations are used as simple JavaBeans. In the example
below, we define a bean that uses the ThreadPoolTaskExecutor
to asynchronously print
out a set of messages.
import org.springframework.core.task.TaskExecutor;
public class TaskExecutorExample {
private class MessagePrinterTask implements Runnable {
private String message;
public MessagePrinterTask(String message) {
this.message = message;
}
public void run() {
System.out.println(message);
}
}
private TaskExecutor taskExecutor;
public TaskExecutorExample(TaskExecutor taskExecutor) {
this.taskExecutor = taskExecutor;
}
public void printMessages() {
for(int i = 0; i < 25; i++) {
taskExecutor.execute(new MessagePrinterTask("Message" + i));
}
}
}
As you can see, rather than retrieving a thread from the pool and executing yourself,
you add your Runnable
to the queue and the TaskExecutor
uses its internal rules to
decide when the task gets executed.
To configure the rules that the TaskExecutor
will use, simple bean properties have
been exposed.
<bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
<property name="corePoolSize" value="5" />
<property name="maxPoolSize" value="10" />
<property name="queueCapacity" value="25" />
</bean>
<bean id="taskExecutorExample" class="TaskExecutorExample">
<constructor-arg ref="taskExecutor" />
</bean>
7.3. The Spring TaskScheduler abstraction
In addition to the TaskExecutor
abstraction, Spring 3.0 introduces a TaskScheduler
with a variety of methods for scheduling tasks to run at some point in the future.
public interface TaskScheduler {
ScheduledFuture schedule(Runnable task, Trigger trigger);
ScheduledFuture schedule(Runnable task, Date startTime);
ScheduledFuture scheduleAtFixedRate(Runnable task, Date startTime, long period);
ScheduledFuture scheduleAtFixedRate(Runnable task, long period);
ScheduledFuture scheduleWithFixedDelay(Runnable task, Date startTime, long delay);
ScheduledFuture scheduleWithFixedDelay(Runnable task, long delay);
}
The simplest method is the one named 'schedule' that takes a Runnable
and Date
only.
That will cause the task to run once after the specified time. All of the other methods
are capable of scheduling tasks to run repeatedly. The fixed-rate and fixed-delay
methods are for simple, periodic execution, but the method that accepts a Trigger is
much more flexible.
7.3.1. Trigger interface
The Trigger
interface is essentially inspired by JSR-236, which, as of Spring 3.0, has
not yet been officially implemented. The basic idea of the Trigger
is that execution
times may be determined based on past execution outcomes or even arbitrary conditions.
If these determinations do take into account the outcome of the preceding execution,
that information is available within a TriggerContext
. The Trigger
interface itself
is quite simple:
public interface Trigger {
Date nextExecutionTime(TriggerContext triggerContext);
}
As you can see, the TriggerContext
is the most important part. It encapsulates all of
the relevant data, and is open for extension in the future if necessary. The
TriggerContext
is an interface (a SimpleTriggerContext
implementation is used by
default). Here you can see what methods are available for Trigger
implementations.
public interface TriggerContext {
Date lastScheduledExecutionTime();
Date lastActualExecutionTime();
Date lastCompletionTime();
}
7.3.2. Trigger implementations
Spring provides two implementations of the Trigger
interface. The most interesting one
is the CronTrigger
. It enables the scheduling of tasks based on cron expressions. For
example, the following task is being scheduled to run 15 minutes past each hour but only
during the 9-to-5 "business hours" on weekdays.
scheduler.schedule(task, new CronTrigger("0 15 9-17 * * MON-FRI"));
The other out-of-the-box implementation is a PeriodicTrigger
that accepts a fixed
period, an optional initial delay value, and a boolean to indicate whether the period
should be interpreted as a fixed-rate or a fixed-delay. Since the TaskScheduler
interface already defines methods for scheduling tasks at a fixed-rate or with a
fixed-delay, those methods should be used directly whenever possible. The value of the
PeriodicTrigger
implementation is that it can be used within components that rely on
the Trigger
abstraction. For example, it may be convenient to allow periodic triggers,
cron-based triggers, and even custom trigger implementations to be used interchangeably.
Such a component could take advantage of dependency injection so that such Triggers
could be configured externally and therefore easily modified or extended.
7.3.3. TaskScheduler implementations
As with Spring’s TaskExecutor
abstraction, the primary benefit of the TaskScheduler
is that code relying on scheduling behavior need not be coupled to a particular
scheduler implementation. The flexibility this provides is particularly relevant when
running within Application Server environments where threads should not be created
directly by the application itself. For such cases, Spring provides a
TimerManagerTaskScheduler
that delegates to a CommonJ TimerManager instance, typically
configured with a JNDI-lookup.
A simpler alternative, the ThreadPoolTaskScheduler
, can be used whenever external
thread management is not a requirement. Internally, it delegates to a
ScheduledExecutorService
instance. ThreadPoolTaskScheduler
actually implements
Spring’s TaskExecutor
interface as well, so that a single instance can be used for
asynchronous execution as soon as possible as well as scheduled, and potentially
recurring, executions.
7.4. Annotation Support for Scheduling and Asynchronous Execution
Spring provides annotation support for both task scheduling and asynchronous method execution.
7.4.1. Enable scheduling annotations
To enable support for @Scheduled
and @Async
annotations add @EnableScheduling
and
@EnableAsync
to one of your @Configuration
classes:
@Configuration
@EnableAsync
@EnableScheduling
public class AppConfig {
}
You are free to pick and choose the relevant annotations for your application. For
example, if you only need support for @Scheduled
, simply omit @EnableAsync
. For more
fine-grained control you can additionally implement the SchedulingConfigurer
and/or
AsyncConfigurer
interfaces. See the javadocs for full details.
If you prefer XML configuration use the <task:annotation-driven>
element.
<task:annotation-driven executor="myExecutor" scheduler="myScheduler"/>
<task:executor id="myExecutor" pool-size="5"/>
<task:scheduler id="myScheduler" pool-size="10"/>
Notice with the above XML that an executor reference is provided for handling those
tasks that correspond to methods with the @Async
annotation, and the scheduler
reference is provided for managing those methods annotated with @Scheduled
.
The default advice mode for processing |
7.4.2. The @Scheduled annotation
The @Scheduled
annotation can be added to a method along with trigger metadata. For
example, the following method would be invoked every 5 seconds with a fixed delay,
meaning that the period will be measured from the completion time of each preceding
invocation.
@Scheduled(fixedDelay=5000)
public void doSomething() {
// something that should execute periodically
}
If a fixed rate execution is desired, simply change the property name specified within the annotation. The following would be executed every 5 seconds measured between the successive start times of each invocation.
@Scheduled(fixedRate=5000)
public void doSomething() {
// something that should execute periodically
}
For fixed-delay and fixed-rate tasks, an initial delay may be specified indicating the number of milliseconds to wait before the first execution of the method.
@Scheduled(initialDelay=1000, fixedRate=5000)
public void doSomething() {
// something that should execute periodically
}
If simple periodic scheduling is not expressive enough, then a cron expression may be provided. For example, the following will only execute on weekdays.
@Scheduled(cron="*/5 * * * * MON-FRI")
public void doSomething() {
// something that should execute on weekdays only
}
You can additionally use the |
Notice that the methods to be scheduled must have void returns and must not expect any arguments. If the method needs to interact with other objects from the Application Context, then those would typically have been provided through dependency injection.
As of Spring Framework 4.3, Make sure that you are not initializing multiple instances of the same |
7.4.3. The @Async annotation
The @Async
annotation can be provided on a method so that invocation of that method
will occur asynchronously. In other words, the caller will return immediately upon
invocation and the actual execution of the method will occur in a task that has been
submitted to a Spring TaskExecutor
. In the simplest case, the annotation may be
applied to a void
-returning method.
@Async
void doSomething() {
// this will be executed asynchronously
}
Unlike the methods annotated with the @Scheduled
annotation, these methods can expect
arguments, because they will be invoked in the "normal" way by callers at runtime rather
than from a scheduled task being managed by the container. For example, the following is
a legitimate application of the @Async
annotation.
@Async
void doSomething(String s) {
// this will be executed asynchronously
}
Even methods that return a value can be invoked asynchronously. However, such methods
are required to have a Future
typed return value. This still provides the benefit of
asynchronous execution so that the caller can perform other tasks prior to calling
get()
on that Future.
@Async
Future<String> returnSomething(int i) {
// this will be executed asynchronously
}
|
@Async
can not be used in conjunction with lifecycle callbacks such as
@PostConstruct
. To asynchronously initialize Spring beans you currently have to use
a separate initializing Spring bean that invokes the @Async
annotated method on the
target then.
public class SampleBeanImpl implements SampleBean {
@Async
void doSomething() {
// ...
}
}
public class SampleBeanInitializer {
private final SampleBean bean;
public SampleBeanInitializer(SampleBean bean) {
this.bean = bean;
}
@PostConstruct
public void initialize() {
bean.doSomething();
}
}
There is no direct XML equivalent for |
7.4.4. Executor qualification with @Async
By default when specifying @Async
on a method, the executor that will be used is the
one supplied to the 'annotation-driven' element as described above. However, the value
attribute of the @Async
annotation can be used when needing to indicate that an
executor other than the default should be used when executing a given method.
@Async("otherExecutor")
void doSomething(String s) {
// this will be executed asynchronously by "otherExecutor"
}
In this case, "otherExecutor" may be the name of any Executor
bean in the Spring
container, or may be the name of a qualifier associated with any Executor
, e.g. as
specified with the <qualifier>
element or Spring’s @Qualifier
annotation.
7.4.5. Exception management with @Async
When an @Async
method has a Future
typed return value, it is easy to manage
an exception that was thrown during the method execution as this exception will
be thrown when calling get
on the Future
result. With a void return type
however, the exception is uncaught and cannot be transmitted. For those cases, an
AsyncUncaughtExceptionHandler
can be provided to handle such exceptions.
public class MyAsyncUncaughtExceptionHandler implements AsyncUncaughtExceptionHandler {
@Override
public void handleUncaughtException(Throwable ex, Method method, Object... params) {
// handle exception
}
}
By default, the exception is simply logged. A custom AsyncUncaughtExceptionHandler
can
be defined via AsyncConfigurer
or the task:annotation-driven
XML element.
7.5. The task namespace
Beginning with Spring 3.0, there is an XML namespace for configuring TaskExecutor
and
TaskScheduler
instances. It also provides a convenient way to configure tasks to be
scheduled with a trigger.
7.5.1. The 'scheduler' element
The following element will create a ThreadPoolTaskScheduler
instance with the
specified thread pool size.
<task:scheduler id="scheduler" pool-size="10"/>
The value provided for the 'id' attribute will be used as the prefix for thread names within the pool. The 'scheduler' element is relatively straightforward. If you do not provide a 'pool-size' attribute, the default thread pool will only have a single thread. There are no other configuration options for the scheduler.
7.5.2. The 'executor' element
The following will create a ThreadPoolTaskExecutor
instance:
<task:executor id="executor" pool-size="10"/>
As with the scheduler above, the value provided for the 'id' attribute will be used as
the prefix for thread names within the pool. As far as the pool size is concerned, the
'executor' element supports more configuration options than the 'scheduler' element. For
one thing, the thread pool for a ThreadPoolTaskExecutor
is itself more configurable.
Rather than just a single size, an executor’s thread pool may have different values for
the core and the max size. If a single value is provided then the executor will
have a fixed-size thread pool (the core and max sizes are the same). However, the
'executor' element’s 'pool-size' attribute also accepts a range in the form of "min-max".
<task:executor
id="executorWithPoolSizeRange"
pool-size="5-25"
queue-capacity="100"/>
As you can see from that configuration, a 'queue-capacity' value has also been provided. The configuration of the thread pool should also be considered in light of the executor’s queue capacity. For the full description of the relationship between pool size and queue capacity, consult the documentation for ThreadPoolExecutor. The main idea is that when a task is submitted, the executor will first try to use a free thread if the number of active threads is currently less than the core size. If the core size has been reached, then the task will be added to the queue as long as its capacity has not yet been reached. Only then, if the queue’s capacity has been reached, will the executor create a new thread beyond the core size. If the max size has also been reached, then the executor will reject the task.
By default, the queue is unbounded, but this is rarely the desired configuration,
because it can lead to OutOfMemoryErrors
if enough tasks are added to that queue while
all pool threads are busy. Furthermore, if the queue is unbounded, then the max size has
no effect at all. Since the executor will always try the queue before creating a new
thread beyond the core size, a queue must have a finite capacity for the thread pool to
grow beyond the core size (this is why a fixed size pool is the only sensible case
when using an unbounded queue).
In a moment, we will review the effects of the keep-alive setting which adds yet another
factor to consider when providing a pool size configuration. First, let’s consider the
case, as mentioned above, when a task is rejected. By default, when a task is rejected,
a thread pool executor will throw a TaskRejectedException
. However, the rejection
policy is actually configurable. The exception is thrown when using the default
rejection policy which is the AbortPolicy
implementation. For applications where some
tasks can be skipped under heavy load, either the DiscardPolicy
or
DiscardOldestPolicy
may be configured instead. Another option that works well for
applications that need to throttle the submitted tasks under heavy load is the
CallerRunsPolicy
. Instead of throwing an exception or discarding tasks, that policy
will simply force the thread that is calling the submit method to run the task itself.
The idea is that such a caller will be busy while running that task and not able to
submit other tasks immediately. Therefore it provides a simple way to throttle the
incoming load while maintaining the limits of the thread pool and queue. Typically this
allows the executor to "catch up" on the tasks it is handling and thereby frees up some
capacity on the queue, in the pool, or both. Any of these options can be chosen from an
enumeration of values available for the 'rejection-policy' attribute on the 'executor'
element.
<task:executor
id="executorWithCallerRunsPolicy"
pool-size="5-25"
queue-capacity="100"
rejection-policy="CALLER_RUNS"/>
Finally, the keep-alive
setting determines the time limit (in seconds) for which threads
may remain idle before being terminated. If there are more than the core number of threads
currently in the pool, after waiting this amount of time without processing a task, excess
threads will get terminated. A time value of zero will cause excess threads to terminate
immediately after executing a task without remaining follow-up work in the task queue.
<task:executor
id="executorWithKeepAlive"
pool-size="5-25"
keep-alive="120"/>
7.5.3. The 'scheduled-tasks' element
The most powerful feature of Spring’s task namespace is the support for configuring tasks to be scheduled within a Spring Application Context. This follows an approach similar to other "method-invokers" in Spring, such as that provided by the JMS namespace for configuring Message-driven POJOs. Basically a "ref" attribute can point to any Spring-managed object, and the "method" attribute provides the name of a method to be invoked on that object. Here is a simple example.
<task:scheduled-tasks scheduler="myScheduler">
<task:scheduled ref="beanA" method="methodA" fixed-delay="5000"/>
</task:scheduled-tasks>
<task:scheduler id="myScheduler" pool-size="10"/>
As you can see, the scheduler is referenced by the outer element, and each individual task includes the configuration of its trigger metadata. In the preceding example, that metadata defines a periodic trigger with a fixed delay indicating the number of milliseconds to wait after each task execution has completed. Another option is 'fixed-rate', indicating how often the method should be executed regardless of how long any previous execution takes. Additionally, for both fixed-delay and fixed-rate tasks an 'initial-delay' parameter may be specified indicating the number of milliseconds to wait before the first execution of the method. For more control, a "cron" attribute may be provided instead. Here is an example demonstrating these other options.
<task:scheduled-tasks scheduler="myScheduler">
<task:scheduled ref="beanA" method="methodA" fixed-delay="5000" initial-delay="1000"/>
<task:scheduled ref="beanB" method="methodB" fixed-rate="5000"/>
<task:scheduled ref="beanC" method="methodC" cron="*/5 * * * * MON-FRI"/>
</task:scheduled-tasks>
<task:scheduler id="myScheduler" pool-size="10"/>
7.6. Using the Quartz Scheduler
Quartz uses Trigger
, Job
and JobDetail
objects to realize scheduling of all kinds
of jobs. For the basic concepts behind Quartz, have a look at
http://quartz-scheduler.org. For convenience purposes, Spring offers a couple of
classes that simplify the usage of Quartz within Spring-based applications.
7.6.1. Using the JobDetailFactoryBean
Quartz JobDetail
objects contain all information needed to run a job. Spring provides a
JobDetailFactoryBean
which provides bean-style properties for XML configuration purposes.
Let’s have a look at an example:
<bean name="exampleJob" class="org.springframework.scheduling.quartz.JobDetailFactoryBean">
<property name="jobClass" value="example.ExampleJob"/>
<property name="jobDataAsMap">
<map>
<entry key="timeout" value="5"/>
</map>
</property>
</bean>
The job detail configuration has all information it needs to run the job (ExampleJob
).
The timeout is specified in the job data map. The job data map is available through the
JobExecutionContext
(passed to you at execution time), but the JobDetail
also gets
its properties from the job data mapped to properties of the job instance. So in this
case, if the ExampleJob
contains a bean property named timeout
, the JobDetail
will have it applied automatically:
package example;
public class ExampleJob extends QuartzJobBean {
private int timeout;
/**
* Setter called after the ExampleJob is instantiated
* with the value from the JobDetailFactoryBean (5)
*/
public void setTimeout(int timeout) {
this.timeout = timeout;
}
protected void executeInternal(JobExecutionContext ctx) throws JobExecutionException {
// do the actual work
}
}
All additional properties from the job data map are of course available to you as well.
Using the |
7.6.2. Using the MethodInvokingJobDetailFactoryBean
Often you just need to invoke a method on a specific object. Using the
MethodInvokingJobDetailFactoryBean
you can do exactly this:
<bean id="jobDetail" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean">
<property name="targetObject" ref="exampleBusinessObject"/>
<property name="targetMethod" value="doIt"/>
</bean>
The above example will result in the doIt
method being called on the
exampleBusinessObject
method (see below):
public class ExampleBusinessObject {
// properties and collaborators
public void doIt() {
// do the actual work
}
}
<bean id="exampleBusinessObject" class="examples.ExampleBusinessObject"/>
Using the MethodInvokingJobDetailFactoryBean
, you don’t need to create one-line jobs
that just invoke a method, and you only need to create the actual business object and
wire up the detail object.
By default, Quartz Jobs are stateless, resulting in the possibility of jobs interfering
with each other. If you specify two triggers for the same JobDetail
, it might be
possible that before the first job has finished, the second one will start. If
JobDetail
classes implement the Stateful
interface, this won’t happen. The second
job will not start before the first one has finished. To make jobs resulting from the
MethodInvokingJobDetailFactoryBean
non-concurrent, set the concurrent
flag to
false
.
<bean id="jobDetail" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean">
<property name="targetObject" ref="exampleBusinessObject"/>
<property name="targetMethod" value="doIt"/>
<property name="concurrent" value="false"/>
</bean>
By default, jobs will run in a concurrent fashion. |
7.6.3. Wiring up jobs using triggers and the SchedulerFactoryBean
We’ve created job details and jobs. We’ve also reviewed the convenience bean that allows
you to invoke a method on a specific object. Of course, we still need to schedule the
jobs themselves. This is done using triggers and a SchedulerFactoryBean
. Several
triggers are available within Quartz and Spring offers two Quartz FactoryBean
implementations with convenient defaults: CronTriggerFactoryBean
and
SimpleTriggerFactoryBean
.
Triggers need to be scheduled. Spring offers a SchedulerFactoryBean
that exposes
triggers to be set as properties. SchedulerFactoryBean
schedules the actual jobs with
those triggers.
Find below a couple of examples:
<bean id="simpleTrigger" class="org.springframework.scheduling.quartz.SimpleTriggerFactoryBean">
<!-- see the example of method invoking job above -->
<property name="jobDetail" ref="jobDetail"/>
<!-- 10 seconds -->
<property name="startDelay" value="10000"/>
<!-- repeat every 50 seconds -->
<property name="repeatInterval" value="50000"/>
</bean>
<bean id="cronTrigger" class="org.springframework.scheduling.quartz.CronTriggerFactoryBean">
<property name="jobDetail" ref="exampleJob"/>
<!-- run every morning at 6 AM -->
<property name="cronExpression" value="0 0 6 * * ?"/>
</bean>
Now we’ve set up two triggers, one running every 50 seconds with a starting delay of 10
seconds and one every morning at 6 AM. To finalize everything, we need to set up the
SchedulerFactoryBean
:
<bean class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
<property name="triggers">
<list>
<ref bean="cronTrigger"/>
<ref bean="simpleTrigger"/>
</list>
</property>
</bean>
More properties are available for the SchedulerFactoryBean
for you to set, such as the
calendars used by the job details, properties to customize Quartz with, etc. Have a look
at the
SchedulerFactoryBean
javadocs for more information.
8. Cache Abstraction
8.1. Introduction
Since version 3.1, Spring Framework provides support for transparently adding caching into an existing Spring application. Similar to the transaction support, the caching abstraction allows consistent use of various caching solutions with minimal impact on the code.
As from Spring 4.1, the cache abstraction has been significantly improved with the support of JSR-107 annotations and more customization options.
8.2. Understanding the cache abstraction
At its core, the abstraction applies caching to Java methods, reducing thus the number of executions based on the information available in the cache. That is, each time a targeted method is invoked, the abstraction will apply a caching behavior checking whether the method has been already executed for the given arguments. If it has, then the cached result is returned without having to execute the actual method; if it has not, then method is executed, the result cached and returned to the user so that, the next time the method is invoked, the cached result is returned. This way, expensive methods (whether CPU or IO bound) can be executed only once for a given set of parameters and the result reused without having to actually execute the method again. The caching logic is applied transparently without any interference to the invoker.
Obviously this approach works only for methods that are guaranteed to return the same output (result) for a given input (or arguments) no matter how many times it is being executed. |
Other cache-related operations are provided by the abstraction such as the ability to update the content of the cache or remove one of all entries. These are useful if the cache deals with data that can change during the course of the application.
Just like other services in the Spring Framework, the caching service is an
abstraction (not a cache implementation) and requires the use of an actual storage to
store the cache data - that is, the abstraction frees the developer from having to write
the caching logic but does not provide the actual stores. This abstraction is
materialized by the org.springframework.cache.Cache
and
org.springframework.cache.CacheManager
interfaces.
There are a few implementations of that abstraction
available out of the box: JDK java.util.concurrent.ConcurrentMap
based caches,
Ehcache 2.x, Gemfire cache,
Caffeine and JSR-107 compliant
caches (e.g. Ehcache 3.x). See Plugging-in different back-end caches for more information on plugging in
other cache stores/providers.
The caching abstraction has no special handling of multi-threaded and multi-process environments as such features are handled by the cache implementation. . |
If you have a multi-process environment (i.e. an application deployed on several nodes), you will need to configure your cache provider accordingly. Depending on your use cases, a copy of the same data on several nodes may be enough but if you change the data during the course of the application, you may need to enable other propagation mechanisms.
Caching a particular item is a direct equivalent of the typical get-if-not-found-then- proceed-and-put-eventually code blocks found with programmatic cache interaction: no locks are applied and several threads may try to load the same item concurrently. The same applies to eviction: if several threads are trying to update or evict data concurrently, you may use stale data. Certain cache providers offer advanced features in that area, refer to the documentation of the cache provider that you are using for more details.
To use the cache abstraction, the developer needs to take care of two aspects:
-
caching declaration - identify the methods that need to be cached and their policy
-
cache configuration - the backing cache where the data is stored and read from
8.3. Declarative annotation-based caching
For caching declaration, the abstraction provides a set of Java annotations:
-
@Cacheable
triggers cache population -
@CacheEvict
triggers cache eviction -
@CachePut
updates the cache without interfering with the method execution -
@Caching
regroups multiple cache operations to be applied on a method -
@CacheConfig
shares some common cache-related settings at class-level
Let us take a closer look at each annotation:
8.3.1. @Cacheable annotation
As the name implies, @Cacheable
is used to demarcate methods that are cacheable - that
is, methods for whom the result is stored into the cache so on subsequent invocations
(with the same arguments), the value in the cache is returned without having to actually
execute the method. In its simplest form, the annotation declaration requires the name
of the cache associated with the annotated method:
@Cacheable("books")
public Book findBook(ISBN isbn) {...}
In the snippet above, the method findBook
is associated with the cache named books
.
Each time the method is called, the cache is checked to see whether the invocation has
been already executed and does not have to be repeated. While in most cases, only one
cache is declared, the annotation allows multiple names to be specified so that more
than one cache are being used. In this case, each of the caches will be checked before
executing the method - if at least one cache is hit, then the associated value will be
returned:
All the other caches that do not contain the value will be updated as well even though the cached method was not actually executed. |
@Cacheable({"books", "isbns"})
public Book findBook(ISBN isbn) {...}
Default Key Generation
Since caches are essentially key-value stores, each invocation of a cached method needs
to be translated into a suitable key for cache access. Out of the box, the caching
abstraction uses a simple KeyGenerator
based on the following algorithm:
-
If no params are given, return
SimpleKey.EMPTY
. -
If only one param is given, return that instance.
-
If more the one param is given, return a
SimpleKey
containing all parameters.
This approach works well for most use-cases; As long as parameters have natural keys
and implement valid hashCode()
and equals()
methods. If that is not the case then the
strategy needs to be changed.
To provide a different default key generator, one needs to implement the
org.springframework.cache.interceptor.KeyGenerator
interface.
The default key generation strategy changed with the release of Spring 4.0. Earlier
versions of Spring used a key generation strategy that, for multiple key parameters,
only considered the If you want to keep using the previous key strategy, you can configure the deprecated
|
Custom Key Generation Declaration
Since caching is generic, it is quite likely the target methods have various signatures that cannot be simply mapped on top of the cache structure. This tends to become obvious when the target method has multiple arguments out of which only some are suitable for caching (while the rest are used only by the method logic). For example:
@Cacheable("books")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
At first glance, while the two boolean
arguments influence the way the book is found,
they are no use for the cache. Further more what if only one of the two is important
while the other is not?
For such cases, the @Cacheable
annotation allows the user to specify how the key is
generated through its key
attribute. The developer can use SpEL to
pick the arguments of interest (or their nested properties), perform operations or even
invoke arbitrary methods without having to write any code or implement any interface.
This is the recommended approach over the
default generator since methods tend to be
quite different in signatures as the code base grows; while the default strategy might
work for some methods, it rarely does for all methods.
Below are some examples of various SpEL declarations - if you are not familiar with it, do yourself a favor and read Spring Expression Language:
@Cacheable(cacheNames="books", key="#isbn")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
@Cacheable(cacheNames="books", key="#isbn.rawNumber")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
@Cacheable(cacheNames="books", key="T(someType).hash(#isbn)")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
The snippets above show how easy it is to select a certain argument, one of its properties or even an arbitrary (static) method.
If the algorithm responsible to generate the key is too specific or if it needs
to be shared, you may define a custom keyGenerator
on the operation. To do
this, specify the name of the KeyGenerator
bean implementation to use:
@Cacheable(cacheNames="books", keyGenerator="myKeyGenerator")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
The |
Default Cache Resolution
Out of the box, the caching abstraction uses a simple CacheResolver
that
retrieves the cache(s) defined at the operation level using the configured
CacheManager
.
To provide a different default cache resolver, one needs to implement the
org.springframework.cache.interceptor.CacheResolver
interface.
Custom cache resolution
The default cache resolution fits well for applications working with a
single CacheManager
and with no complex cache resolution requirements.
For applications working with several cache managers, it is possible
to set the cacheManager
to use per operation:
@Cacheable(cacheNames="books", cacheManager="anotherCacheManager")
public Book findBook(ISBN isbn) {...}
It is also possible to replace the CacheResolver
entirely in a similar
fashion as for key generation. The
resolution is requested for every cache operation, giving a chance to
the implementation to actually resolve the cache(s) to use based on
runtime arguments:
@Cacheable(cacheResolver="runtimeCacheResolver")
public Book findBook(ISBN isbn) {...}
Since Spring 4.1, the Similarly to |
Synchronized caching
In a multi-threaded environment, certain operations might be concurrently invoked for the same argument (typically on startup). By default, the cache abstraction does not lock anything and the same value may be computed several times, defeating the purpose of caching.
For those particular cases, the sync
attribute can be used to instruct the underlying
cache provider to lock the cache entry while the value is being computed. As a result,
only one thread will be busy computing the value while the others are blocked until the
entry is updated in the cache.
@Cacheable(cacheNames="foos", sync=true)
public Foo executeExpensiveOperation(String id) {...}
This is an optional feature and your favorite cache library may not support it. All
|
Conditional caching
Sometimes, a method might not be suitable for caching all the time (for example, it
might depend on the given arguments). The cache annotations support such functionality
through the condition
parameter which takes a SpEL
expression that is evaluated to
either true
or false
. If true
, the method is cached - if not, it behaves as if the
method is not cached, that is executed every time no matter what values are in the cache
or what arguments are used. A quick example - the following method will be cached only
if the argument name
has a length shorter than 32:
@Cacheable(cacheNames="book", condition="#name.length() < 32")
public Book findBook(String name)
In addition the condition
parameter, the unless
parameter can be used to veto the
adding of a value to the cache. Unlike condition
, unless
expressions are evaluated
after the method has been called. Expanding on the previous example - perhaps we
only want to cache paperback books:
@Cacheable(cacheNames="book", condition="#name.length() < 32", unless="#result.hardback")
public Book findBook(String name)
The cache abstraction supports java.util.Optional
, using its content as cached value
only if it present. #result
always refers to the business entity and never on a
supported wrapper so the previous example can be rewritten as follows:
@Cacheable(cacheNames="book", condition="#name.length() < 32", unless="#result?.hardback")
public Optional<Book> findBook(String name)
Note that result
still refers to Book
and not Optional
. As it might be null
, we
should use the safe navigation operator.
Available caching SpEL evaluation context
Each SpEL
expression evaluates again a dedicated
context
. In addition to the build in parameters, the
framework provides dedicated caching related metadata such as the argument names. The
next table lists the items made available to the context so one can use them for key and
conditional computations:
Name | Location | Description | Example |
---|---|---|---|
methodName |
root object |
The name of the method being invoked |
|
method |
root object |
The method being invoked |
|
target |
root object |
The target object being invoked |
|
targetClass |
root object |
The class of the target being invoked |
|
args |
root object |
The arguments (as array) used for invoking the target |
|
caches |
root object |
Collection of caches against which the current method is executed |
|
argument name |
evaluation context |
Name of any of the method arguments. If for some reason the names are not available
(e.g. no debug information), the argument names are also available under the |
|
result |
evaluation context |
The result of the method call (the value to be cached). Only available in |
|
8.3.2. @CachePut annotation
For cases where the cache needs to be updated without interfering with the method
execution, one can use the @CachePut
annotation. That is, the method will always be
executed and its result placed into the cache (according to the @CachePut
options). It
supports the same options as @Cacheable
and should be used for cache population rather
than method flow optimization:
@CachePut(cacheNames="book", key="#isbn")
public Book updateBook(ISBN isbn, BookDescriptor descriptor)
Note that using |
8.3.3. @CacheEvict annotation
The cache abstraction allows not just population of a cache store but also eviction.
This process is useful for removing stale or unused data from the cache. Opposed to
@Cacheable
, annotation @CacheEvict
demarcates methods that perform cache
eviction, that is methods that act as triggers for removing data from the cache.
Just like its sibling, @CacheEvict
requires specifying one (or multiple) caches
that are affected by the action, allows a custom cache and key resolution or a
condition to be specified but in addition, features an extra parameter
allEntries
which indicates whether a cache-wide eviction needs to be performed
rather then just an entry one (based on the key):
@CacheEvict(cacheNames="books", allEntries=true)
public void loadBooks(InputStream batch)
This option comes in handy when an entire cache region needs to be cleared out - rather then evicting each entry (which would take a long time since it is inefficient), all the entries are removed in one operation as shown above. Note that the framework will ignore any key specified in this scenario as it does not apply (the entire cache is evicted not just one entry).
One can also indicate whether the eviction should occur after (the default) or before
the method executes through the beforeInvocation
attribute. The former provides the
same semantics as the rest of the annotations - once the method completes successfully,
an action (in this case eviction) on the cache is executed. If the method does not
execute (as it might be cached) or an exception is thrown, the eviction does not occur.
The latter ( beforeInvocation=true
) causes the eviction to occur always, before the
method is invoked - this is useful in cases where the eviction does not need to be tied
to the method outcome.
It is important to note that void methods can be used with @CacheEvict
- as the
methods act as triggers, the return values are ignored (as they don’t interact with the
cache) - this is not the case with @Cacheable
which adds/updates data into the cache
and thus requires a result.
8.3.4. @Caching annotation
There are cases when multiple annotations of the same type, such as @CacheEvict
or
@CachePut
need to be specified, for example because the condition or the key
expression is different between different caches. @Caching
allows multiple nested
@Cacheable
, @CachePut
and @CacheEvict
to be used on the same method:
@Caching(evict = { @CacheEvict("primary"), @CacheEvict(cacheNames="secondary", key="#p0") })
public Book importBooks(String deposit, Date date)
8.3.5. @CacheConfig annotation
So far we have seen that caching operations offered many customization options and
these can be set on an operation basis. However, some of the customization options
can be tedious to configure if they apply to all operations of the class. For
instance, specifying the name of the cache to use for every cache operation of the
class could be replaced by a single class-level definition. This is where @CacheConfig
comes into play.
@CacheConfig("books")
public class BookRepositoryImpl implements BookRepository {
@Cacheable
public Book findBook(ISBN isbn) {...}
}
@CacheConfig
is a class-level annotation that allows to share the cache names, the custom
KeyGenerator
, the custom CacheManager
and finally the custom CacheResolver
. Placing
this annotation on the class does not turn on any caching operation.
An operation-level customization will always override a customization set on @CacheConfig
. This
gives therefore three levels of customizations per cache operation:
-
Globally configured, available for
CacheManager
,KeyGenerator
-
At class level, using
@CacheConfig
-
At the operation level
8.3.6. Enable caching annotations
It is important to note that even though declaring the cache annotations does not automatically trigger their actions - like many things in Spring, the feature has to be declaratively enabled (which means if you ever suspect caching is to blame, you can disable it by removing only one configuration line rather than all the annotations in your code).
To enable caching annotations add the annotation @EnableCaching
to one of your
@Configuration
classes:
@Configuration
@EnableCaching
public class AppConfig {
}
Alternatively for XML configuration use the cache:annotation-driven
element:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:cache="http://www.springframework.org/schema/cache"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache.xsd">
<cache:annotation-driven />
</beans>
Both the cache:annotation-driven
element and @EnableCaching
annotation allow various
options to be specified that influence the way the caching behavior is added to the
application through AOP. The configuration is intentionally similar with that of
@Transactional
:
The default advice mode for processing caching annotations is "proxy" which allows for interception of calls through the proxy only; local calls within the same class cannot get intercepted that way. For a more advanced mode of interception, consider switching to "aspectj" mode in combination with compile-time or load-time weaving. |
Advanced customizations using Java config require to implement |
XML Attribute | Annotation Attribute | Default | Description |
---|---|---|---|
|
N/A (See |
cacheManager |
Name of cache manager to use. A default |
|
N/A (See |
A |
The bean name of the CacheResolver that is to be used to resolve the backing caches. This attribute is not required, and only needs to be specified as an alternative to the 'cache-manager' attribute. |
|
N/A (See |
|
Name of the custom key generator to use. |
|
N/A (See |
|
Name of the custom cache error handler to use. By default, any exception throw during a cache related operations are thrown back at the client. |
|
|
proxy |
The default mode "proxy" processes annotated beans to be proxied using Spring’s AOP framework (following proxy semantics, as discussed above, applying to method calls coming in through the proxy only). The alternative mode "aspectj" instead weaves the affected classes with Spring’s AspectJ caching aspect, modifying the target class byte code to apply to any kind of method call. AspectJ weaving requires spring-aspects.jar in the classpath as well as load-time weaving (or compile-time weaving) enabled. (See Spring configuration for details on how to set up load-time weaving.) |
|
|
false |
Applies to proxy mode only. Controls what type of caching proxies are created for
classes annotated with the |
|
|
Ordered.LOWEST_PRECEDENCE |
Defines the order of the cache advice that is applied to beans annotated with
|
|
Spring recommends that you only annotate concrete classes (and methods of concrete
classes) with the |
In proxy mode (which is the default), only external method calls coming in through the
proxy are intercepted. This means that self-invocation, in effect, a method within the
target object calling another method of the target object, will not lead to an actual
caching at runtime even if the invoked method is marked with |
8.3.7. Using custom annotations
The caching abstraction allows you to use your own annotations to identify what method
triggers cache population or eviction. This is quite handy as a template mechanism as it
eliminates the need to duplicate cache annotation declarations (especially useful if the
key or condition are specified) or if the foreign imports (org.springframework
) are
not allowed in your code base. Similar to the rest of the
stereotype annotations, @Cacheable
, @CachePut
,
@CacheEvict
and @CacheConfig
can be used as meta-annotations,
that is annotations that can annotate other annotations. To wit, let us replace a common
@Cacheable
declaration with our own, custom annotation:
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
@Cacheable(cacheNames="books", key="#isbn")
public @interface SlowService {
}
Above, we have defined our own SlowService
annotation which itself is annotated with
@Cacheable
- now we can replace the following code:
@Cacheable(cacheNames="books", key="#isbn")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
with:
@SlowService
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
Even though @SlowService
is not a Spring annotation, the container automatically picks
up its declaration at runtime and understands its meaning. Note that as mentioned
above, the annotation-driven behavior needs to be enabled.
8.4. JCache (JSR-107) annotations
Since the Spring Framework 4.1, the caching abstraction fully supports the JCache
standard annotations: these are @CacheResult
, @CachePut
, @CacheRemove
and
@CacheRemoveAll
as well as the @CacheDefaults
, @CacheKey
and @CacheValue
companions. These annotations can be used right the way without migrating your
cache store to JSR-107: the internal implementation uses Spring’s caching abstraction
and provides default CacheResolver
and KeyGenerator
implementations that are
compliant with the specification. In other words, if you are already using Spring’s
caching abstraction, you can switch to these standard annotations without changing
your cache storage (or configuration, for that matter).
8.4.1. Feature summary
For those who are familiar with Spring’s caching annotations, the following table describes the main differences between the Spring annotations and the JSR-107 counterpart:
Spring | JSR-107 | Remark |
---|---|---|
|
|
Fairly similar. |
|
|
While Spring updates the cache with the result of the method invocation, JCache
requires to pass it as an argument that is annotated with |
|
|
Fairly similar. |
|
|
See |
|
|
Allows to configure the same concepts, in a similar fashion. |
JCache has the notion of javax.cache.annotation.CacheResolver
that is identical
to the Spring’s CacheResolver
interface, except that JCache only supports a single
cache. By default, a simple implementation retrieves the cache to use based on
the name declared on the annotation. It should be noted that if no cache name
is specified on the annotation, a default is automatically generated, check the
javadoc of @CacheResult#cacheName()
for more information.
CacheResolver
instances are retrieved by a CacheResolverFactory
. It is
possible to customize the factory per cache operation:
@CacheResult(cacheNames="books", cacheResolverFactory=MyCacheResolverFactory.class)
public Book findBook(ISBN isbn)
For all referenced classes, Spring tries to locate a bean with the given type. If more than one match exists, a new instance is created and can use the regular bean lifecycle callbacks such as dependency injection. |
Keys are generated by a javax.cache.annotation.CacheKeyGenerator
that serves the
same purpose as Spring’s KeyGenerator
. By default, all method arguments are taken
into account unless at least one parameter is annotated with @CacheKey
. This is
similar to Spring’s custom key generation
declaration. For instance these are identical operations, one using Spring’s
abstraction and the other with JCache:
@Cacheable(cacheNames="books", key="#isbn")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
@CacheResult(cacheName="books")
public Book findBook(@CacheKey ISBN isbn, boolean checkWarehouse, boolean includeUsed)
The CacheKeyResolver
to use can also be specified on the operation, in a similar
fashion as the CacheResolverFactory
.
JCache can manage exceptions thrown by annotated methods: this can prevent an update of
the cache but it can also cache the exception as an indicator of the failure instead of
calling the method again. Let’s assume that InvalidIsbnNotFoundException
is thrown if
the structure of the ISBN is invalid. This is a permanent failure, no book could ever be
retrieved with such parameter. The following caches the exception so that further calls
with the same, invalid ISBN, throws the cached exception directly instead of invoking
the method again.
@CacheResult(cacheName="books", exceptionCacheName="failures"
cachedExceptions = InvalidIsbnNotFoundException.class)
public Book findBook(ISBN isbn)
8.4.2. Enabling JSR-107 support
Nothing specific needs to be done to enable the JSR-107 support alongside Spring’s
declarative annotation support. Both @EnableCaching
and the
cache:annotation-driven
element will enable automatically the JCache support
if both the JSR-107 API and the spring-context-support
module are present in
the classpath.
Depending of your use case, the choice is basically yours. You can even mix and match services using the JSR-107 API and others using Spring’s own annotations. Be aware however that if these services are impacting the same caches, a consistent and identical key generation implementation should be used. |
8.5. Declarative XML-based caching
If annotations are not an option (no access to the sources or no external code), one can use XML for declarative caching. So instead of annotating the methods for caching, one specifies the target method and the caching directives externally (similar to the declarative transaction management advice). The previous example can be translated into:
<!-- the service we want to make cacheable -->
<bean id="bookService" class="x.y.service.DefaultBookService"/>
<!-- cache definitions -->
<cache:advice id="cacheAdvice" cache-manager="cacheManager">
<cache:caching cache="books">
<cache:cacheable method="findBook" key="#isbn"/>
<cache:cache-evict method="loadBooks" all-entries="true"/>
</cache:caching>
</cache:advice>
<!-- apply the cacheable behavior to all BookService interfaces -->
<aop:config>
<aop:advisor advice-ref="cacheAdvice" pointcut="execution(* x.y.BookService.*(..))"/>
</aop:config>
<!-- cache manager definition omitted -->
In the configuration above, the bookService
is made cacheable. The caching semantics
to apply are encapsulated in the cache:advice
definition which instructs method
findBooks
to be used for putting data into the cache while method loadBooks
for
evicting data. Both definitions are working against the books
cache.
The aop:config
definition applies the cache advice to the appropriate points in the
program by using the AspectJ pointcut expression (more information is available in
Aspect Oriented Programming with Spring).
In the example above, all methods from the BookService
are considered and
the cache advice applied to them.
The declarative XML caching supports all of the annotation-based model so moving between
the two should be fairly easy - further more both can be used inside the same
application. The XML based approach does not touch the target code however it is
inherently more verbose; when dealing with classes with overloaded methods that are
targeted for caching, identifying the proper methods does take an extra effort since the
method
argument is not a good discriminator - in these cases, the AspectJ pointcut can
be used to cherry pick the target methods and apply the appropriate caching
functionality. However through XML, it is easier to apply a package/group/interface-wide
caching (again due to the AspectJ pointcut) and to create template-like definitions (as
we did in the example above by defining the target cache through the cache:definitions
cache
attribute).
8.6. Configuring the cache storage
Out of the box, the cache abstraction provides several storage integration. To use
them, one needs to simply declare an appropriate CacheManager
- an entity that
controls and manages Cache
s and can be used to retrieve these for storage.
8.6.1. JDK ConcurrentMap-based Cache
The JDK-based Cache
implementation resides under
org.springframework.cache.concurrent
package. It allows one to use ConcurrentHashMap
as a backing Cache
store.
<!-- simple cache manager -->
<bean id="cacheManager" class="org.springframework.cache.support.SimpleCacheManager">
<property name="caches">
<set>
<bean class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean" p:name="default"/>
<bean class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean" p:name="books"/>
</set>
</property>
</bean>
The snippet above uses the SimpleCacheManager
to create a CacheManager
for the two
nested ConcurrentMapCache
instances named default and books. Note that the
names are configured directly for each cache.
As the cache is created by the application, it is bound to its lifecycle, making it suitable for basic use cases, tests or simple applications. The cache scales well and is very fast but it does not provide any management or persistence capabilities nor eviction contracts.
8.6.2. Ehcache-based Cache
Ehcache 3.x is fully JSR-107 compliant and no dedicated support is required for it. |
The Ehcache 2.x implementation is located under org.springframework.cache.ehcache
package.
Again, to use it, one simply needs to declare the appropriate CacheManager
:
<bean id="cacheManager"
class="org.springframework.cache.ehcache.EhCacheCacheManager" p:cache-manager-ref="ehcache"/>
<!-- EhCache library setup -->
<bean id="ehcache"
class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean" p:config-location="ehcache.xml"/>
This setup bootstraps the ehcache library inside Spring IoC (through the ehcache
bean) which
is then wired into the dedicated CacheManager
implementation. Note the entire
ehcache-specific configuration is read from ehcache.xml
.
8.6.3. Caffeine Cache
Caffeine is a Java 8 rewrite of Guava’s cache and its implementation is located under
org.springframework.cache.caffeine
package and provides access to several features
of Caffeine.
Configuring a CacheManager
that creates the cache on demand is straightforward:
<bean id="cacheManager"
class="org.springframework.cache.caffeine.CaffeineCacheManager"/>
It is also possible to provide the caches to use explicitly. In that case, only those will be made available by the manager:
<bean id="cacheManager" class="org.springframework.cache.caffeine.CaffeineCacheManager">
<property name="caches">
<set>
<value>default</value>
<value>books</value>
</set>
</property>
</bean>
The Caffeine CacheManager
also supports customs Caffeine
and CacheLoader
. See
the Caffeine documentation for more
information about those.
8.6.4. GemFire-based Cache
GemFire is a memory-oriented/disk-backed, elastically scalable, continuously available, active (with built-in pattern-based subscription notifications), globally replicated database and provides fully-featured edge caching. For further information on how to use GemFire as a CacheManager (and more), please refer to the Spring Data GemFire reference documentation.
8.6.5. JSR-107 Cache
JSR-107 compliant caches can also be used by Spring’s caching abstraction. The JCache
implementation is located under org.springframework.cache.jcache
package.
Again, to use it, one simply needs to declare the appropriate CacheManager
:
<bean id="cacheManager"
class="org.springframework.cache.jcache.JCacheCacheManager"
p:cache-manager-ref="jCacheManager"/>
<!-- JSR-107 cache manager setup -->
<bean id="jCacheManager" .../>
8.6.6. Dealing with caches without a backing store
Sometimes when switching environments or doing testing, one might have cache declarations without an actual backing cache configured. As this is an invalid configuration, at runtime an exception will be thrown since the caching infrastructure is unable to find a suitable store. In situations like this, rather then removing the cache declarations (which can prove tedious), one can wire in a simple, dummy cache that performs no caching - that is, forces the cached methods to be executed every time:
<bean id="cacheManager" class="org.springframework.cache.support.CompositeCacheManager">
<property name="cacheManagers">
<list>
<ref bean="jdkCache"/>
<ref bean="gemfireCache"/>
</list>
</property>
<property name="fallbackToNoOpCache" value="true"/>
</bean>
The CompositeCacheManager
above chains multiple CacheManager
s and additionally,
through the fallbackToNoOpCache
flag, adds a no op cache that for all the
definitions not handled by the configured cache managers. That is, every cache
definition not found in either jdkCache
or gemfireCache
(configured above) will be
handled by the no op cache, which will not store any information causing the target
method to be executed every time.
8.7. Plugging-in different back-end caches
Clearly there are plenty of caching products out there that can be used as a backing
store. To plug them in, one needs to provide a CacheManager
and Cache
implementation
since unfortunately there is no available standard that we can use instead. This may
sound harder than it is since in practice, the classes tend to be simple
adapters that map the caching abstraction
framework on top of the storage API as the ehcache
classes can show. Most
CacheManager
classes can use the classes in org.springframework.cache.support
package, such as AbstractCacheManager
which takes care of the boiler-plate code
leaving only the actual mapping to be completed. We hope that in time, the libraries
that provide integration with Spring can fill in this small configuration gap.
8.8. How can I set the TTL/TTI/Eviction policy/XXX feature?
Directly through your cache provider. The cache abstraction is… well, an abstraction
not a cache implementation. The solution you are using might support various data
policies and different topologies which other solutions do not (take for example the JDK
ConcurrentHashMap
) - exposing that in the cache abstraction would be useless simply
because there would no backing support. Such functionality should be controlled directly
through the backing cache, when configuring it or through its native API.
9. Appendix
9.1. XML Schemas
This part of the appendix lists XML schemas related to integration technologies.
9.1.1. The jee schema
The jee
tags deal with Java EE (Java Enterprise Edition)-related configuration issues,
such as looking up a JNDI object and defining EJB references.
To use the tags in the jee
schema, you need to have the following preamble at the top
of your Spring XML configuration file; the text in the following snippet references the
correct schema so that the tags in the jee
namespace are available to you.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jee="http://www.springframework.org/schema/jee" xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee.xsd"> <!-- bean definitions here -->
</beans>
<jee:jndi-lookup/> (simple)
Before…
<bean id="dataSource" class="org.springframework.jndi.JndiObjectFactoryBean">
<property name="jndiName" value="jdbc/MyDataSource"/>
</bean>
<bean id="userDao" class="com.foo.JdbcUserDao">
<!-- Spring will do the cast automatically (as usual) -->
<property name="dataSource" ref="dataSource"/>
</bean>
After…
<jee:jndi-lookup id="dataSource" jndi-name="jdbc/MyDataSource"/>
<bean id="userDao" class="com.foo.JdbcUserDao">
<!-- Spring will do the cast automatically (as usual) -->
<property name="dataSource" ref="dataSource"/>
</bean>
<jee:jndi-lookup/> (with single JNDI environment setting)
Before…
<bean id="simple" class="org.springframework.jndi.JndiObjectFactoryBean">
<property name="jndiName" value="jdbc/MyDataSource"/>
<property name="jndiEnvironment">
<props>
<prop key="foo">bar</prop>
</props>
</property>
</bean>
After…
<jee:jndi-lookup id="simple" jndi-name="jdbc/MyDataSource">
<jee:environment>foo=bar</jee:environment>
</jee:jndi-lookup>
<jee:jndi-lookup/> (with multiple JNDI environment settings)
Before…
<bean id="simple" class="org.springframework.jndi.JndiObjectFactoryBean">
<property name="jndiName" value="jdbc/MyDataSource"/>
<property name="jndiEnvironment">
<props>
<prop key="foo">bar</prop>
<prop key="ping">pong</prop>
</props>
</property>
</bean>
After…
<jee:jndi-lookup id="simple" jndi-name="jdbc/MyDataSource">
<!-- newline-separated, key-value pairs for the environment (standard Properties format) -->
<jee:environment>
foo=bar
ping=pong
</jee:environment>
</jee:jndi-lookup>
<jee:jndi-lookup/> (complex)
Before…
<bean id="simple" class="org.springframework.jndi.JndiObjectFactoryBean">
<property name="jndiName" value="jdbc/MyDataSource"/>
<property name="cache" value="true"/>
<property name="resourceRef" value="true"/>
<property name="lookupOnStartup" value="false"/>
<property name="expectedType" value="com.myapp.DefaultFoo"/>
<property name="proxyInterface" value="com.myapp.Foo"/>
</bean>
After…
<jee:jndi-lookup id="simple"
jndi-name="jdbc/MyDataSource"
cache="true"
resource-ref="true"
lookup-on-startup="false"
expected-type="com.myapp.DefaultFoo"
proxy-interface="com.myapp.Foo"/>
<jee:local-slsb/> (simple)
The <jee:local-slsb/>
tag configures a reference to an EJB Stateless SessionBean.
Before…
<bean id="simple"
class="org.springframework.ejb.access.LocalStatelessSessionProxyFactoryBean">
<property name="jndiName" value="ejb/RentalServiceBean"/>
<property name="businessInterface" value="com.foo.service.RentalService"/>
</bean>
After…
<jee:local-slsb id="simpleSlsb" jndi-name="ejb/RentalServiceBean"
business-interface="com.foo.service.RentalService"/>
<jee:local-slsb/> (complex)
<bean id="complexLocalEjb"
class="org.springframework.ejb.access.LocalStatelessSessionProxyFactoryBean">
<property name="jndiName" value="ejb/RentalServiceBean"/>
<property name="businessInterface" value="com.foo.service.RentalService"/>
<property name="cacheHome" value="true"/>
<property name="lookupHomeOnStartup" value="true"/>
<property name="resourceRef" value="true"/>
</bean>
After…
<jee:local-slsb id="complexLocalEjb"
jndi-name="ejb/RentalServiceBean"
business-interface="com.foo.service.RentalService"
cache-home="true"
lookup-home-on-startup="true"
resource-ref="true">
<jee:remote-slsb/>
The <jee:remote-slsb/>
tag configures a reference to a remote
EJB Stateless
SessionBean.
Before…
<bean id="complexRemoteEjb"
class="org.springframework.ejb.access.SimpleRemoteStatelessSessionProxyFactoryBean">
<property name="jndiName" value="ejb/MyRemoteBean"/>
<property name="businessInterface" value="com.foo.service.RentalService"/>
<property name="cacheHome" value="true"/>
<property name="lookupHomeOnStartup" value="true"/>
<property name="resourceRef" value="true"/>
<property name="homeInterface" value="com.foo.service.RentalService"/>
<property name="refreshHomeOnConnectFailure" value="true"/>
</bean>
After…
<jee:remote-slsb id="complexRemoteEjb"
jndi-name="ejb/MyRemoteBean"
business-interface="com.foo.service.RentalService"
cache-home="true"
lookup-home-on-startup="true"
resource-ref="true"
home-interface="com.foo.service.RentalService"
refresh-home-on-connect-failure="true">
9.1.2. The jms schema
The jms
tags deal with configuring JMS-related beans such as Spring’s
MessageListenerContainers. These tags are detailed in the
section of the JMS chapter entitled JMS namespace support. Please do consult that chapter for full details on this support
and the jms
tags themselves.
In the interest of completeness, to use the tags in the jms
schema, you need to have
the following preamble at the top of your Spring XML configuration file; the text in the
following snippet references the correct schema so that the tags in the jms
namespace
are available to you.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jms="http://www.springframework.org/schema/jms" xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/jms http://www.springframework.org/schema/jms/spring-jms.xsd"> <!-- bean definitions here -->
</beans>
9.1.3. <context:mbean-export/>
This element is detailed in Configuring annotation based MBean export.
9.1.4. The cache schema
The cache
tags can be used to enable support for Spring’s @CacheEvict
, @CachePut
and @Caching
annotations. It it also supports declarative XML-based caching. See
Enable caching annotations and
Declarative XML-based caching for details.
To use the tags in the cache
schema, you need to have the following preamble at the
top of your Spring XML configuration file; the text in the following snippet references
the correct schema so that the tags in the cache
namespace are available to you.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:cache="http://www.springframework.org/schema/cache" xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache.xsd"> <!-- bean definitions here -->
</beans>