Integration

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:

Next we’ll have to expose our service using the RmiServiceExporter:

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.

Our client is a simple object using the AccountService to manage accounts:

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:

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.

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'):

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.

In the newly created application context called remoting-servlet.xml, we’ll create a HessianServiceExporter exporting your services:

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'):

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.

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:

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).

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.

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:

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'):

In addition, define a corresponding servlet for this exporter in 'web.xml', with the servlet name matching the bean name of the target exporter:

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:

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.

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:

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.

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.

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.

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:

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.

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):

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:

From the client code we can access the web service just as if it was a normal class:

On the server, you just need to expose the service object using the JmsInvokerServiceExporter.

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.

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.

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,

using variable-length arguments and

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.

The previous example using Apache HttpComponents HttpClient directly rewritten to use the RestTemplate is shown below

To use Apache HttpComponents instead of the native java.net functionality, construct the RestTemplate as follows:

The general callback interface is RequestCallback and is called when the execute method is invoked.

The RequestCallback interface is defined as

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.

Objects passed to and returned from the methods getForObject(), postForLocation(), and put() are converted to HTTP requests and from HTTP responses by HttpMessageConverters. The HttpMessageConverter interface is shown below to give you a better feel for its functionality

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.

The implementations of HttpMessageConverters 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

The AsyncRestTemplate is deprecated. Please use the WebClient instead.

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:

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.

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.

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:

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:

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:

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

This results in a message of the form:

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.

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.

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:

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).

Please refer to the Spring javadocs of the various message listener containers for a full description of the features supported by each implementation.

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.

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.

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.

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.

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.

The configuration of the attendant MessageListenerAdapter would look like this:

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:

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).

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.

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).

Then you just need to add it to our earlier container configuration. The container will take care of the rest.

To enable support for @JmsListener annotations add @EnableJms to one of your @Configuration classes.

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.

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.

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.

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:

These are the main elements you can inject in JMS listener endpoints:

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.

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:

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:

If you need to set additional headers in a transport-independent manner, you could return a Message instead, something like:

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:

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:

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:

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.

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:

For platforms/cases where the existing MBeanServer has a dynamic (or unknown) agentId which is retrieved through lookup methods, one should use factory-method:

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.

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:

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.

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:

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:

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.

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.

The example below shows the annotated version of the JmxTestBean class that you saw earlier:

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:

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.

The following source level metadata types are available for use in Spring JMX:

The following configuration parameters are available for use on these source-level metadata types:

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:

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.

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:

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:

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.

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:

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.

You can configure your own KeyNamingStrategy instance and configure it to read ObjectNames 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:

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.

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:

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.

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.

If you prefer XML based configuration the 'context:mbean-export' element serves the same purpose.

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.

To have Spring JMX create, start and expose a JSR-160 JMXConnectorServer use the following configuration:

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:

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:

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:

To create an MBeanServerConnection to a remote JSR-160 enabled MBeanServer use the MBeanServerConnectionFactoryBean as shown below:

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:

In the case of the above example, MX4J 3.0.0 was used; see the official MX4J documentation for more information.

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.

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:

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:

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:

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'.)