Spring BlazeDS Integration Reference Guide

Spring has always aimed to be agnostic to the client technologies being used to access its core services, intentionally leaving options open and letting the community drive the demand for any new first-class integration solutions to be added to the Spring project portfolio. Spring BlazeDS Integration is an answer to the commmunity demand for a top-level solution for building Spring-powered Rich Internet Applications using Adobe Flex for the client-side technology.

BlazeDS is an open source project from Adobe that provides the remoting and messaging foundation for connecting a Flex-based front-end to Java back-end services. Though it has previously been possible to use BlazeDS to connect to Spring-managed services, it has not been in a way that feels "natural" to a Spring developer, requiring the extra burden of having to maintain a separate BlazeDS xml configuration. Spring BlazeDS Integration turns the tables by making the BlazeDS MessageBroker a Spring-managed object, opening up the pathways to a more extensive integration that follows "the Spring way".

Java 5

Spring 3.0

Adobe BlazeDS 4.0

Spring Security 3.0

Spring Integration 2.0

Hibernate 3.5

Professional from-the-source support on Spring BlazeDS Integration is available from SpringSource, the company behind Spring.

The central component that must be configured to use Spring BlazeDS Integration is the MessageBroker. HTTP messages from the Flex client will be routed through the Spring DispatcherServlet to the Spring-managed MessageBroker. There is no need to configure the BlazeDS MessageBrokerServlet when using the Spring-managed MessageBroker.

The DispatcherServlet must be configured as normal in web.xml to bootstrap a Spring WebApplicationContext. For example:

<!-- The front controller of this Spring Web application, responsible for handling all application 
requests -->
<servlet>
    <servlet-name>Spring MVC Dispatcher Servlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/config/web-application-config.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>
        

A simplified Spring XML config namespace is provided for configuring the MessageBroker in your WebApplicationContext. To use the namespace support you must add the schema location in your Spring XML config files. A typical config will look something like the following:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:flex="http://www.springframework.org/schema/flex"
       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-2.5.xsd
           http://www.springframework.org/schema/flex 
           http://www.springframework.org/schema/flex/spring-flex-1.0.xsd">
...
</beans>
         
        

This makes the Spring BlazeDS Integration configuration tags available under the flex namespace in your configuration files. The above setup will be assumed for the rest of the configuration examples to follow. For the full detail of every attribute and tag available in the config namespace, be sure to refer to the spring-flex-1.0.xsd as every element and attribute is fully documented there. Using an XSD-aware XML editor such as the one in Eclipse should bring up the documentation automatically as you type.

At a minimum, the MessageBrokerFactoryBean must be configured as a bean in your Spring WebApplicationContext in order to bootstrap the MessageBroker, along with a MessageBrokerHandlerAdapter and an appropriate HandlerMapping (usually a SimpleUrlHandlerMapping) to route incoming requests to the Spring-managed MessageBroker.

These beans will be registered automatically by using the provided message-broker tag in your bean definition file. For example, in its simplest form:

<flex:message-broker/>       
        

This will set up the MessageBroker and necessary supporting infrastructure using sensible defaults. The defaults can be overriden using the provided attributes of the message-broker tag and its associated child elements. For example, the default location of the BlazeDS XML configuration file (/WEB-INF/flex/services-config.xml) can be overridden using the services-config-path attribute. The MessageBrokerFactoryBean uses Spring's ResourceLoader abstraction, so that typical Spring resource paths may be used. For example, to load the configuration from the application's classpath:

<flex:message-broker services-config-path="classpath*:services-config.xml"       
        

The equivalent MessageBrokerFactoryBean definition using vanilla Spring configuration would be:

<!-- Bootstraps and exposes the BlazeDS MessageBroker -->
<bean id="_messageBroker" class="org.springframework.flex.core.MessageBrokerFactoryBean" >
    <property name="servicesConfigPath" value="classpath*:services-config.xml" />
</bean>      
        

Note especially that with the message-broker tag, it is not necessary to assign a custom id to the MessageBroker, and it is in fact discouraged so that you won't have to continually reference it later. The only reason you would ever need to provide a custom id is if you were bootstrapping more than one MessageBroker in the same WebApplicationContext.

To properly route incoming requests to the Spring-managed MessageBroker, request mapping must be configured in three places:

The simplest request mapping scenario is when the Flex front-end is the only client type for the application. In this case you can just map /messagebroker as the top-level path for requests. The mapping in web.xml would be:

<!-- Map all /messagbroker requests to the DispatcherServlet for handling -->
<servlet-mapping>
    <servlet-name>Spring MVC Dispatcher Servlet</servlet-name>
    <url-pattern>/messagebroker/*</url-pattern>
</servlet-mapping>    
        

When using the message-broker config tag, a SimpleUrlHandlerMapping is installed that by default maps all incoming DispatcherServlet requests to the Spring-managed MessageBroker using a /*path pattern. The default mapping can be overridden by providing one or more mapping child elements. If you want to provide your own HandlerMapping bean configuration, you can disable the default using the disable-default-mapping attribute of the message-broker tag. The order of the installed SimpleUrlHandlerMapping can be set (for complex scenarios where multiple handler mapping types are installed in the same context) using the mapping-order attribute.

The SimpleUrlHandlerMapping in the Spring WebApplicationContext maps all requests to the Spring-managed MessageBroker via the MessageBrokerHandlerAdapter. The default setup installed by the message-broker config tag is equivalent to the following bean definitions:

<!-- Maps request paths at /* to the BlazeDS MessageBroker -->
<bean class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
    <property name="mappings">
        <value>
            /*=_messageBroker
        </value>
    </property>
</bean>

<!-- Dispatches requests mapped to a MessageBroker -->
<bean class="org.springframework.flex.servlet.MessageBrokerHandlerAdapter"/>    
        

Channel definitions in the BlazeDS services-config.xml must correspond to the chosen mapping. For example, to set up a typical AMF channel in BlazeDS that matches the above mapping strategy:

<channel-definition id="my-amf" class="mx.messaging.channels.AMFChannel">
    <endpoint url="http://{server.name}:{server.port}/{context.root}/messagebroker/amf" 
        class="flex.messaging.endpoints.AMFEndpoint"/>
    <properties>
        <polling-enabled>false</polling-enabled>
    </properties>
</channel-definition>        
        

See the BlazeDS documentation for more information on configuring communication channels in services-config.xml.

It could often be the case that your application needs to serve more than just Flex-based clients. For example, you may be constructing a RESTful architecture that is meant to serve multiple client-types. You could potentially even be consuming RESTful endpoints using the Flex HTTPService component. Spring MVC's controller model provides a simple, flexible means to create such RESTful endpoints. In these sorts of hybrid web application secenarios, you will need to consider an alternate mapping strategy.

The simplest approach is to use a hierarchical application context with multiple DispatcherServlets. In this approach, you configure your main application layer (services, security, supporting infrastructure, etc) in a parent context loaded via the ContextLoaderListener, and then configure all aspects of your Spring MVC controllers in one child DispatcherServlet context, and all aspects specific to your Flex client in a separate child DispatcherServlet context. This approach could look as follows in web.xml:

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>
        /WEB-INF/spring/*-context.xml
    </param-value>
</context-param>

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

<servlet>
    <servlet-name>flex</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>flex</servlet-name>
    <url-pattern>/messagebroker/*</url-pattern>
</servlet-mapping>

<servlet>
    <servlet-name>spring-mvc</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>spring-mvc</servlet-name>
    <url-pattern>/spring/*</url-pattern>
</servlet-mapping>       
        

Here the parent application context is being assembled from a group of files ending in -context.xml contained in the /WEB-INF/spring/ directory. The child context for the Flex-specific setup would be built (by convention) from /WEB-INF/flex-servlet.xml, and the context for the Spring MVC controllers would be built from /WEB-INF/spring-mvc-servlet.xml. This approach provides a nice separation of concerns and will allow Spring 2.5+ annotated controllers to work using their default configuration.

An alternate approach is to keep things consolidated under one DispatcherServlet context. The down-side to this approach is that it requires some additional manual configuration, and you have to modify your mapping approach accordingly, such as mapping /spring/* to the DispatcherServlet, mapping /messagebroker/* to the Spring-managed MessageBroker via the mapping XML namespace config tag, and modifying any BlazeDS channel definitions accordingly. You would override the default mapping strategy of the message-broker tag as follows:

<flex:message-broker>
    <flex:mapping pattern="/messagebroker/*" />
</flex:message-broker>       
        

and you would have to account for the /spring/* mapping in your BlazeDS channel definitions. For example:

<channel-definition id="my-amf" class="mx.messaging.channels.AMFChannel">
    <endpoint url="http://{server.name}:{server.port}/{context.root}/spring/messagebroker/amf" 
        class="flex.messaging.endpoints.AMFEndpoint"/>
    <properties>
        <polling-enabled>false</polling-enabled>
    </properties>
</channel-definition>        
        

In addition to setting up the consolidated mapping strategy, you will also have to manually enable the correct HandlerMapping and HandlerAdapter for your Spring MVC controllers as described in the Spring MVC documentation, due to the fact that alternate HandlerMapping and HandlerAdapter beans are configured automatically when using the message-broker tag.

Explicit channel definition is a requirement when using dynamic destinations (meaning any destination that is added programmatically and not defined in the BlazeDS services-config.xml, i.e. the destinations created by the remoting-destination tag and the various *-message-destination tags). See Adobe's documentation for more detail.

The only way you don't have to explicitly define the ChannelSet on the client is if

Even if you weren't using dynamically created destinations it is debatable whether it is a good idea to ever compile your client against services-config.xml, thus coupling your client to your server configuration. It is often desirable to keep your flex client and your server side code as two distinct modules, but compiling against services-config.xml blurs the lines between those modules.

Our recommendation is that it is generally cleaner to keep the client-side configuration of ChannelSets explicitly contained within the client module. An excellent way to do this without having to hard-code the URLs in your client code is to use an ActionScript DI framework such as Spring ActionScript (a Spring Extensions project, formerly known as Prana).

If you choose to go the route of compiling your client against services-config.xml, note that you can at least keep the URL information out of the client code by using ServerConfig.getChannel as described in the referenced BlazeDS documentation.

The initialization of the MessageBroker by the MessageBrokerFactoryBean logically consists of two phases:

A special MessageBrokerConfigProcessor callback interface is provided that allows custom processing to be done on the newly created MessageBroker after each phase, before it is made available for request processing. This interface is used internally by Spring BlazeDS Integration, but is also available for general use in advanced programmatic introspection and customization of the MessageBroker. A custom MessageBrokerConfigProcessor can be configured as a Spring bean and then registered with the MessageBrokerFactoryBean via the config-processor tag. For example, given a trivial implementation to log some additional info about the MessageBroker:

package com.example;

import org.springframework.flex.config.MessageBrokerConfigProcessor;

import flex.messaging.MessageBroker;
import flex.messaging.services.RemotingService;

public class MyDestinationCountingConfigProcessor implements MessageBrokerConfigProcessor {

    public MessageBroker processAfterStartup(MessageBroker broker) {
        RemotingService remotingService = 
            (RemotingService) broker.getServiceByType(RemotingService.class.getName());
        if (remotingService.isStarted()) {
            System.out.println("The Remoting Service has been started with "
                    +remotingService.getDestinations().size()+" Destinations.");
        }
        return broker;
    }

    public MessageBroker processBeforeStartup(MessageBroker broker) {
        return broker;
    }
}        
        

This class could be configured and registered with the MessageBroker as follows:

<flex:message-broker>
    <flex:config-processor ref="myConfigProcessor" />
</flex:message-broker>

<bean id="myConfigProcessor" class="com.example.MyDestinationCountingConfigProcessor" />
        

In order to propagate useful information back to the Flex client when an exception occurs on the server, the original exception must be translated into an instance of flex.messaging.MessageException. If special translation logic is not applied, a generic "Server.Processing" error will propagate to the client that doesn't give the client the chance to reason on the real cause of the error to take appropriate action. Special exception translators are configured by default for transforming Spring Security exceptions into an appropriate MessageException, but it could also be useful to provide custom translation for your own application-level exceptions.

Custom exception translation logic can be provided through implementations of the org.springframework.flex.core.ExceptionTranslator interface. These implementations must be configured as Spring beans and then registered through the XML configuration namespace as follows:

<!-- Custom exception translator configured as a Spring bean -->
<bean id="myExceptionTranslator" class="com.foo.app.MyBusinessExceptionTranslator"/>

<flex:message-broker>
    <flex:exception-translator ref="myExceptionTranslator"/>
</flex:message-broker>           
        

Custom message interceptors may be used to apply special processing logic to incoming and outgoing AMF messages in their de-serialized Java form. For example, an interceptor can be used to inspect the contents of the incoming message, or to add extra information to the outgoing message.

Custom message processing logic is provided through implementations of the org.springframework.flex.core.MessageInterceptor interface. These implementations must be configured as Spring beans and then registered through the XML configuration namespace as follows:

<!-- Custom message interceptor configured as a Spring bean -->
<bean id="myMessageInterceptor" class="com.foo.app.MyMessageInterceptor"/>

<flex:message-broker>
    <flex:message-interceptor ref="myMessageInterceptor"/>
</flex:message-broker>           
        

Using the XML config namespace automatically installs the needed implementations of flex.messaging.services.ServiceAdapter for use with the Remoting and Message services. Third-party adapters (such as those provided by the dpHibernate or Gilead projects) can be configured using the org.springframework.flex.core.ManageableComponentFactoryBean. This factory bean implementation is able to process arbitrarily complex configuration metadata supplied in JSON format (instead of arbitrarily complex XML as in the native BlazeDS configuration) and honors the lifecycle semantics (such as proper invocation of the initialize method) of the ManageableComponent. These custom adapters may be used by Spring-managed Remoting and Message destinations by either setting its id as the default for the Remoting or Message service, or by setting the service-adapter attribute for a specific destination (see the Remoting and Messaging chapters for further detail).

For example, to use the special adapter provided by dpHibernate as the default adapter with the Remoting service, the configuration would be similar to the following:

<bean id="hibernate-object" class="org.springframework.flex.core.ManageableComponentFactoryBean">
<constructor-arg value="net.digitalprimates.persistence.hibernate.HibernateAdapter"/>
    <property name="properties">
        <value>
            {"hibernate" :
                {"sessionFactory" :
                    { "class" : "net.digitalprimates.persistence.hibernate.utils.HibernateUtil",
                      "getCurrentSessionMethod" : "getCurrentSession"
                    }
                }
            }
        </value>
    </property>
</bean> 

<flex:message-broker>
    <flex:remoting-service default-adapter-id="hibernate-object" />
</flex:message-broker>           
        

Using a Spring-managed MessageBroker enables Spring beans to be easily exported for direct remoting calls from a Flex client. This approach is quite similar to that taken with other remoting technologies in the core Spring Framework. Remoting is applied to existing Spring-managed beans as an external configuration concern. The MessageBroker transparently handles the process of serialization and deserialization between the Flex AMF data format and Java.

The BlazeDS RemotingService has traditionally been configured by the inclusion of a remoting-config.xml file in the BlazeDS XML configuration. When using only Spring-managed remoting destinations, this config file can be left out completely as the inclusion of the message-broker tag in your Spring configuration will cause the RemotingService to be configured with sensible defaults if none already exists at startup time. The end result is essentially equivalent to including the following minimal remoting-config.xml in your BlazeDS configuration:

<?xml version="1.0" encoding="UTF-8"?>
<service id="remoting-service"
    class="flex.messaging.services.RemotingService">

    <adapters>
        <adapter-definition id="java-object" 
            class="flex.messaging.services.remoting.adapters.JavaAdapter" 
            default="true"/>
    </adapters>

    <default-channels>
        <channel ref="my-amf"/>
    </default-channels>
    
</service>       
        

Note that this assumes that there is already an equivalent application-wide default-channels configuration. It is recommended that you set the desired service-specific channels (see example below) if not relying on an application-wide default setup. If no application-wide defaults exist, a best guess will be made by configuring the first available channel from the MessageBroker that uses an AMFEndpoint as the default for the RemotingService.

If you wish to have more explicit control over the defaults that will be set on the RemotingService, you can customize them via the remoting-service child element of the message-broker tag. For example:

<flex:message-broker>
    <flex:remoting-service default-adapter-id="my-default-remoting-adapter" 
        default-channels="my-amf, my-secure-amf" />
</flex:message-broker>
        

If you have an existing remoting-config.xml for a legacy BlazeDS application, the RemotingDestinationExporter will be able to work transparently with it, allowing you to gradually migrate to all Spring-managed remoting destinations.

The remoting-destination configuration tag can be used to export existing Spring-managed services for direct remoting from a Flex client. Given the following Spring bean definition for a productService bean:

    
<bean id="productService" class="flex.samples.product.ProductServiceImpl" />
        

and assuming the existance of a Spring-managed MessageBroker configured via the message-broker tag, the following top-level remoting-destination tag will expose the service for remoting to the Flex client as a remote service destination named productService:

<!-- Expose the productService bean for BlazeDS remoting -->
<flex:remoting-destination ref="productService" />
        

By default, the remote service destination exposed to the Flex client will use bean name of the bean being exported as the service id of the destination, but this may be overridden using the destination-id attribute on the remoting-destination tag.

An alternate way of using the remoting-destination tag is as a child element of an top-level bean definition. This is even more concise and works well if you don't have a need to keep your domain-layer bean definitions separate from infrastructure concerns such as Flex remoting. (Keep in mind that keeping them separate can lead to easier testability of the core domain layer.) The following achieves the equivalent result to the previous example:

    
<bean id="productService" class="flex.samples.product.ProductServiceImpl" >
    <flex:remoting-destination />
</bean>
        

The methods that are exposed to be called by the Flex client can be more tightly controlled through use of the include-methods and exclude-methods attributes of the remoting-destination tag. The BlazeDS channels over which the destination is exposed can also be controlled using the channels attribute. (These attributes are available whether using the top-level or the nested version.) A more extensively customized example would look something like:

<flex:remoting-destination ref="productService" 
    include-methods="read, update" 
    exclude-methods="create, delete" 
    channels="my-amf, my-secure-amf" />
        

The remoting-destination tag is transparently configuring a RemotingDestinationExporter bean instance for each bean being exported. The equivalent full bean syntax without the namespace support would be:

<!-- Expose the productService bean for BlazeDS remoting -->
<bean id="product" class="org.springframework.flex.remoting.RemotingDestinationExporter">
    <property name="messageBroker" ref="_messageBroker"/>
    <property name="service" ref="productService"/>
    <property name="destinationId" value="productService"/>
    <property name="includeMethods" value="read, update"/>
    <property name="excludeMethods" value="create, delete"/>
    <property name="channels" value="my-amf, my-secure-amf"/>
</bean>
        

The @RemotingDestination annotation may be used as an alternative to the XML remoting-destination tag when using annotation-based Spring configuration. @RemotingDestination is used at the type level to indicate the class being exported. @RemotingInclude and @RemotingExclude are used at the method level to mark the methods that should be included and excluded for remoting.

The following example illustrates the productService bean configured exclusively through annotations:

package flex.samples.product;

import org.springframework.flex.remoting.RemotingDestination;
import org.springframework.flex.remoting.RemotingExclude;
import org.springframework.flex.remoting.RemotingInclude;
import org.springframework.stereotype.Service;

@Service("productService")
@RemotingDestination(channels={"my-amf","my-secure-amf"})
public class ProductServiceImpl implements ProductService {

    @RemotingInclude
    public Product read(String id) {
        ...
    }
    
    @RemotingExclude
    public Product create(Product product){
        ...
    }
    
    @RemotingInclude
    public Product update(Product product){
        ...
    }
    
    @RemotingExclude
    public void delete(Product product) {
        ...
    }
}
        

package flex.samples.product;

import org.springframework.flex.remoting.RemotingDestination;
import org.springframework.flex.remoting.RemotingExclude;
import org.springframework.flex.remoting.RemotingInclude;
import org.springframework.stereotype.Service;

@Service("productService")
@RemotingDestination(channels={"${channel1}","${channel2}"})
public class ProductServiceImpl implements ProductService {
    ...
}
            

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="properties">
        <props>
            <prop key="channel1">my-amf</prop>
            <prop key="channel2">my-secure-amf, my-amf</prop>
        </props>
    </property>
</bean>      
            

Spring MVC 3 introduced support for building RESTful services using the @Controller programming model. This allows for serving multiple representations of the same content based on what the client has requested. For example, a single RESTful endpoint could be configured to serve HTML, XML, or JSON all from a single request handling Java method on the @Controller class. This approach allows a single service implementation to support a variety of different client types, automatically providing the representation that a particular client desires. In order to better support Flex as one of those client types, Spring BlazeDS Integration adds the necessary support to be able to support an AMF representation of a given RESTful resource.

AmfView and AmfHttpMessageConverter provide the foundation necessary to use AMF with Spring MVC @Controllers. The implementations are quite similar to MappingJacksonJsonView and MappingJacksonHttpMessageConverter which provide Spring's out-of-the-box JSON support. The basics of configuring these classes are shown throughout the rest of this chapter.

AmfView is a Spring MVC View implementation that is intended to be used in conjunction with Spring MVC's ContentNegotiatingViewResolver. In particular, it is expected that it will be configured as a "default" singleton view implementation that can render any MVC model as AMF, rather than needing to have a unique instance per logical view name.

The following example shows a simple configuration of ContentNegotiatingViewResolver to support both JSON and AMF representations:

        
<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
  <property name="mediaTypes">
    <map>
      <entry key="json" value="application/json"/>
      <entry key="amf" value="application/x-amf"/>
    </map>
  </property>
  <property name="defaultViews">
    <list>
      <bean class="org.springframework.web.servlet.view.json.MappingJacksonJsonView" />
      <bean class="org.springframework.flex.http.AmfView" />
    </list>
  </property>
</bean>        
        
        

The above example includes setting the mediaTypes property to map file extensions to media types. This is helpful for clients (such as Flex) that aren't always able to set an appropriate Accept header. So given the above configuration, and a simple controller such as the following:

        
@Controller
@RequestMapping("/contacts")
public class ContactsController {

    @Autowired
    private IContactDAO contactDAO;

    @RequestMapping(method=RequestMethod.GET)
    public List<Contact> find() {
        return contactDAO.findAll();
    }
}
        
        

an HTTP GET request issued to either http://localhost/myapp/contacts.amf without an appropriate Accept header or tohttp://localhost/myapp/contacts with an accept header of application/x-amf will return the list of contacts as an AMF message that may then be deserialized to an ArrayCollection of ActionScript objects on the Flex client.

AmfHttpMessageConverter is a HttpMessageConverter implementation that can convert to and from AMF. In order to be able to convert HTTP POST and PUT request message bodies from AMF to Java objects to be passed as a @RequestBody arguments to @Controller methods, it must be added to the converters used by Spring MVC's AnnotationMethodHandlerAdapter. In order to add AMF support while also leaving the framework's default HttpMessageConverters in place, a simple BeanPostProcessor such as the following example can be used:

        
package org.springframework.flex.samples.rest;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.flex.http.AmfHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.util.ObjectUtils;
import org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter;

public class HandlerAdapterPostProcessor implements BeanPostProcessor {

    public Object postProcessBeforeInitialization(Object bean, String beanName)
            throws BeansException {
        return bean;
    }

    public Object postProcessAfterInitialization(Object bean, String beanName)
            throws BeansException {
        if (bean instanceof AnnotationMethodHandlerAdapter) {
            AnnotationMethodHandlerAdapter adapter = (AnnotationMethodHandlerAdapter) bean;
            HttpMessageConverter<?>[] converters = adapter.getMessageConverters();
            adapter.setMessageConverters(
                (HttpMessageConverter<?>[]) ObjectUtils.
                addObjectToArray(converters, new AmfHttpMessageConverter()));
        }
        return bean;
    }

}
        
        

With this configuration in place, and a controller such as the following:

        
@Controller
@RequestMapping("/contacts")
public class ContactsController {

    @Autowired
    private IContactDAO contactDAO;

    @RequestMapping(method=RequestMethod.POST)
    public Contact create(@RequestBody Contact contact) {
        return contactDAO.create(contact);
    }
}
        
        

Effectively interacting with a RESTful service from the Flex client using AMF is generally a matter of dropping down to some lower-level Flash APIs such as flash.net.URLRequest and flash.net.URLStream. There are some limitations to how a Flash/Flex application can interact with a REST service from within the browser. These limitations are generally imposed by the host browser, and are similar to the limitations imposed on HTML pages. Fortunately, Spring MVC already accounts for such browser limitations and provides useable workarounds.

The first major limitation is that the Flash player is typically not able to set the Accept header for the request to application/x-amf when using URLRequest. Spring supports mapping file extensions to media types as an alternative (see the example Section 4.2, “Using AmfView” configuration for how this is achieved).

The second major limitation is the inability to properly send HTTP PUT and DELETE requests. Spring provides the HiddenHttpMethodFilter to help cope with this. With the filter configured, a DELETE request (for example) could be simulated by sending a POST request to a URL such as http://localhost/myapp/contacts/1.amf?_method=DELETE.

A complete insync-rest example of interacting with a Spring MVC @Controller is now provided in the Test Drive. This sample duplicates the full functionality of the complete inSync application that was originally built using BlazeDS Remoting. It shows in detail how to work around Flash player's limitations to use AMF to interact with a RESTful service that supports it.

While BlazeDS provides excellent support for serialization/deserialization between Java beans and AMF, there are certain limitations in the types of objects that can be handled out-of-the-box. For example, objects to be converted to/from AMF must have getter and setter methods and must have a public no-arg constructor. In order to allow for a more flexible approach, we have provided an extension mechanism for easily customizing the AMF type conversion process through Spring configuration.

                
@Entity
public class PackagePrivatePerson {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Integer id;

    @Version
    @Column(name = "version")
    Integer version;

    String name;
}
                
                

                
<flex:message-broker>
    <flex:config-processor ref="myJpaConfigProcessor" />
</flex:message-broker>

<bean id="myJpaConfigProcessor" class="org.springframework.flex.core.io.JpaConfigProcessor">
    <property name="useDirectFieldAccess" value="true" />
</bean>                
                
                

                
public class ImmutableValueObject {

    final String foo;

    final Integer zoo;

    @AmfCreator
    public ImmutableValueObject(@AmfProperty("foo") String foo, @AmfProperty("zoo") Integer zoo) {
        this.foo = foo;
        this.zoo = zoo;
    }

    public String getFoo() {
        return this.foo;
    }

    public Integer getZoo() {
        return this.zoo;
    }
}
                
                

                
public class IgnorablePropsObject {

    //Will be ignored on both serialization and deserialization
    private String foo;

    //Will be ignored only on serialization
    private String bar;

    //Will be ignored only on deserialization
    private String baz;

    @AmfIgnore
    public String getFoo() {
        return foo;
    }

    @AmfIgnore
    public void setFoo(String foo) {
        this.foo = foo;
    }

    @AmfIgnore
    public String getBar() {
        return bar;
    }

    public void setBar(String bar) {
        this.bar = bar;
    }

    public String getBaz() {
        return baz;
    }

    @AmfIgnore
    public void setBaz(String baz) {
        this.baz = baz;
    }
}                
                
                

                
public class IgnorableFieldsObject {

    //Will be ignored on both serialization and deserialization
    @AmfIgnoreField
    private String foo; 

    //Will be ignored only on serialization
    @AmfIgnoreField(onDeserialization=false)
    private String bar;

    //Will be ignored only on deserialization
    @AmfIgnoreField(onSerialization=false)
    private String baz;

}
                
                

                
package com.foo.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.convert.converter.ConverterRegistry;
import org.springframework.flex.core.io.ClassPathScanningAmfConversionServiceConfigProcessor;
import org.springframework.flex.core.io.HibernateProxyConverter;
import org.springframework.flex.core.io.PersistentCollectionConverterFactory;

@Configuration
public class CustomConverterConfiguration {

    @Bean
    public ClassPathScanningAmfConversionServiceConfigProcessor myConfigProcessor() {

        return new ClassPathScanningAmfConversionServiceConfigProcessor("com.foo.domain") {

            @Override
            protected void configureConverters(ConverterRegistry registry) {
                registry.addConverter(new HibernateProxyConverter());
                registry.addConverterFactory(new PersistentCollectionConverterFactory());
            }

        };
    }
}
                
                

                
<flex:message-broker>
    <flex:config-processor ref="myConfigProcessor" />
</flex:message-broker>                
                
                

Using Hibernate to handle persistence concerns is quite common in Spring applications. A common problem arises, though, when attempting to directly use Hibernate-loaded entities in AMF messages with BlazeDS. In essence, the default BlazeDS serialization mechanism tries to walk the entire object graph, forcing initialization of any lazily loaded associations that might be encountered. This generally leads either to LazyInitialization errors, or (if using a solution such as Spring's OpenSessionInViewFilter) the undesirable n+1 selects scenario. The other problem that arises is when associations are eagerly loaded, but still wrapped in a Hibernate-specific collection or proxy, which can cause unexpected results in the way the association gets serialized.

Spring BlazeDS Integration provides a simple solution that will allow the direct use of Hibernate entities in AMF messages. A few special Hibernate-aware Converters are automatically installed that understand how to properly convert Hibernate-specific types when they are encountered.

As an alternative to using the Hibernate Metadata API to find types to which the SpringPropertyProxy should be applied, a more general config processor implementation, org.springframework.flex.core.io.ClassPathScanningAmfConversionServiceConfigProcessor, is supplied as an alternative that will instead find types using Spring's internal classpath scanning support. The implementation scans recursively starting from a given base package, and all classes found in the scan will be registered to have the SpringPropertyProxy applied to them for AMF conversion. The scanning process may be customized further by configuring org.springframework.core.type.filter.TypeFilter implementations to either include or exclude matching types. For example, Spring provides out-of-the-box RegEx-based and Annotation-based TypeFilter implementations. The easiest way to configure this implementation is by using the Java config support provided in Spring 3+, as in the following example:

Spring Security provides an extremely flexible alternative to the container-based security support provided out-of-the-box with BlazeDS. Spring BlazeDS Integration provides explicit integration support for incorporating Spring Security smoothly into your Flex/BlazeDS application. Spring Security provides a wealth of different configuration options, but rather than go into the many different combinations here, we'll leave most of that to the Spring Security documentation.

<beans:beans xmlns="http://www.springframework.org/schema/security"
    xmlns:beans="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-3.0.xsd
                        http://www.springframework.org/schema/security 
                        http://www.springframework.org/schema/security/spring-security-3.0.xsd">

    <http entry-point-ref="entryPoint">
        <anonymous enabled="false"/>
    </http>
    
    <beans:bean id="entryPoint" 
        class="org.springframework.flex.security3.FlexAuthenticationEntryPoint"/>
    
    <authentication-manager>
       <authentication-provider>
           <user-service>
            <user name="john" password="john" authorities="ROLE_USER" />
            <user name="admin" password="admin" authorities="ROLE_USER, ROLE_ADMIN" />
            <user name="guest" password="guest" authorities="ROLE_GUEST" />
           </user-service>
       </authentication-provider>
    </authentication-manager>

</beans:beans>
        

<filter> 
    <filter-name>springSecurityFilterChain</filter-name> 
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class> 
</filter> 

<filter-mapping> 
    <filter-name>springSecurityFilterChain</filter-name> 
    <url-pattern>/*</url-pattern> 
</filter-mapping>           

            

We will assume the above configuration is in place for the remainder of the examples in this chapter. For additional details on the many options available in configuring and using Spring Security, please refer to that project's documentation.

Spring Security integration is enabled through the secured child element of the message-broker tag. The simplest possible configuration would be:

<flex:message-broker>
    <flex:secured />
</flex:message-broker>
        

This enables the basic security features. A special BlazeDS LoginCommand implementation is automatically installed that enables ChannelSet.login and ChannelSet.logout requests to integrate with Spring Security's Authorization mechanisms. Additionally, the special LoginCommand enables Spring Security granted authorities to be referenced in BlazeDS XML security constraints. For example, if we were using a traditional BlazeDS remoting destination defined in remoting-config.xml, we could have something like the following:

<destination id="productService">
    ...
    <security>
        <security-constraint>
            <auth-method>Custom</auth-method>
            <roles>
                <role>ROLE_USER</role>
            </roles>
        </security-constraint>
    </security>
</destination>       
        

As you can see, we are referencing the "ROLE_USER" authority from our simple Spring Security setup. The invocation of this remote destination would cause the provided LoginCommand to be invoked to both verify that the user is logged in and to check that they have the appropriate role. Violation of either will result in an exception being thrown by Spring Security.

The provided LoginCommand mimics as much as possible the functionality of Spring Security's AbstractAuthenticationProcessingFilter including taking the necessary actions to coordinate Spring Security's additional features such as, Remember Me, Session Fixation Protection, and Concurrent Session Management upon commencement of the authentication process. Additionally, it will invoke any configured LogoutHandlers as part of the logout process, including both those auto-configured by Spring Security, and any that might be supplied by the application developer.

<flex:message-broker>
    <flex:secured login-command="myLoginCommand"/>
</flex:message-broker>

<bean id="myLoginCommand" class="com.foo.app.security.CustomLoginCommand"/>
            

var token:AsyncToken = myChannelSet.login("jeremy","atlanta");
token.addResponder(
    new AsyncResponder(
        function(event:ResultEvent, token:Object = null):void {
            if (event.result.authorities.indexOf("ROLE_ADMIN") >= 0) {
                displayAdminPanel(event.result.name);
            } else {
                displayUserPanel(event.result.name);
            }
        },
        function(event:FaultEvent, token:Object = null):void {
            displayErrorMessage("Login Failed: "+event.fault.faultString);
        }
    )
);       
            

The Spring Security integration allows flexible control over how you secure your application. You can secure BlazeDS endpoints in a manner similar to Spring Security's traditional URL security, and you can secure your Spring services using the many existing object security mechanisms of Spring Security just as if you were writing a traditional web application.

<flex:message-broker>
    <flex:secured>
        <flex:secured-channel channel="my-amf" access="ROLE_USER" />
    </flex:secured>
</flex:message-broker>
            

<flex:message-broker>
    <flex:secured>
        <flex:secured-endpoint-path pattern="**/messagebroker/**" access="ROLE_USER" />
    </flex:secured>
</flex:message-broker>
            

6.3.3. Securing Exported Spring Services

Earlier in this chapter you saw an example of using the BlazeDS XML configuration to secure a BlazeDS-managed destination. Since most of the time you will instead be defining destinations by exporting Spring beans using the remoting-destinationtag, an alternate approach to securing destinations is needed. This is where Spring Security comes in, as all of its existing authorization mechanisms should "just work" when security integration is enabled using the secured tag.

Note

When securing destinations as in the examples shown below, it is important to keep in mind that this feature of Spring Security is using Spring AOP. By default, Spring AOP uses JDK dynamic proxies. As such, if you have need to secure methods on a class that are not part of an interface that the class implements, then you will need either factor those methods out into an interface, or configure Spring to use CGLIB-based proxies instead. See the following Spring documentation references for futher guidance: AOP Proxies Proxying Mechanisms

One of the major strengths of Spring Security is the multiple levels of granularity it provides you when securing your Spring services. You can go from securing your entire service layer in one concise statement:

<global-method-security>
    <protect-pointcut expression="execution(* com.mycompany.*Service.*(..))" access="ROLE_USER"/>
</global-method-security>
            

to controlling access in a more fine-grained manner at the method layer using XML:

<bean id="myService" class="com.mycompany.myapp.MyService">
    <flex:remoting-destination/>
    <security:intercept-methods>
        <security:protect method="set*" access="ROLE_ADMIN" />
        <security:protect method="get*" access="ROLE_ADMIN,ROLE_USER" />
        <security:protect method="doSomething" access="ROLE_USER" />
    </security:intercept-methods>
</bean>
            

to using a combination of XML and annotations:

<security:global-method-security secured-annotations="enabled" jsr250-annotations="enabled"/>
...
<flex:remoting-destination ref="myBankServiceImpl" />
  

            

public interface BankService {
  
    @Secured("IS_AUTHENTICATED_ANONYMOUSLY")
    public Account readAccount(Long id);
  
    @Secured("IS_AUTHENTICATED_ANONYMOUSLY")
    public Account[] findAccounts();
  
    @Secured("ROLE_TELLER")
    public Account post(Account account, double amount);
}

            

to even more fine-grained ACL-based domain object permissions. For more details on the options available, see the Spring Security documentation.

The BlazeDS MessageService provides a common abstraction for asynchronous messaging style communication that is ultimately agnostic to the messaging protocol being used on the server side. Messages can be passed exclusively between Flex clients, from Java POJOs to subscribed Flex clients, from Flex clients to POJO message handlers, or between just about any combination thereof. Using the Spring-managed MessageBroker enables support for using BlazeDS-native AMF messaging, JMS messaging based on Spring's proven and simple JMS abstractions, or messaging using Spring Integration's MessageChannel abstraction, all from a common programming model.

The same Consumer and Producer APIs are used to interact with message destinations from the Flex client, regardless of which underlying messaging protocol is being used on the server. As such, this chapter will focus mainly on setting up and using the various message destination types on the server side. For more details on how to use the Consumer and Producer APIs in the client, see the BlazeDS documentation.

The BlazeDS MessageService has traditionally been configured by the inclusion of a messaging-config.xml file in the BlazeDS XML configuration. When using only Spring-managed message destinations, this config file can be left out completely as the inclusion of the message-broker tag in your Spring configuration will cause the MessageService to be configured with sensible defaults if none already exists at startup time. The end result is essentially equivalent to including the following minimal messaging-config.xml in your BlazeDS configuration:

<?xml version="1.0" encoding="UTF-8"?>
<service id="message-service"
    class="flex.messaging.services.MessageService">

    <adapters>
        <adapter-definition id="actionscript" 
            class="flex.messaging.services.messaging.adapters.ActionScriptAdapter" 
            default="true"/>
    </adapters>

    <default-channels>
        <channel ref="my-polling-amf"/>
    </default-channels>
    
</service>       
        

Note that this assumes that there is already an equivalent application-wide default-channels configuration. It is recommended that you set the desired service-specific channels (see example below) if not relying on an application-wide default setup. If no application-wide defaults exist, a best guess will be made by configuring the first available channel from the MessageBroker that uses an AMFEndpoint with polling enabled as the default for the MessageService.

If you wish to have more explicit control over the defaults that will be set on the MessageService, you can customize them via the message-service child element of the message-broker tag. For example:

<flex:message-broker>
    <flex:message-service default-adapter-id="my-default-messaging-adapter" 
        default-channels="my-polling-amf" />
</flex:message-broker>
        

If you have an existing messaging-config.xml for a legacy BlazeDS application, the MessageDestinationFactory will be able to work transparently with it, allowing you to gradually migrate to all Spring-managed messaging destinations.

For simple messaging needs where there are no requirements for message durability, transaction support, or advanced routing logic, the BlazeDS-native AMF-based message destination is the ideal choice. These destinations can be fully configured in a Spring application context using the message-destination XML namespace tag. For example, assuming a Spring-managed MessageBroker has been configured, all that is needed to set up a basic destination named "event-bus" with default settings is the following:

<flex:message-destination id="event-bus" />      
        

This sets up a destination to use the BlazeDS ActionScriptAdapter to handle incoming messages. The settings of the destination can be further customized through the various attributes of the message-destination tag. Here is an example of the "event-bus" destination configured with most of the available attributes:

<flex:message-destination id="event-bus" 
    message-broker="messageServiceBroker"
    channels="my-polling-amf, my-secure-amf" 
    allow-subtopics="true" 
    cluster-message-routing="broadcast" 
    message-time-to-live="1" 
    send-security-constraint="fooConstraint" 
    subscribe-security-constraint="barConstraint" 
    subscription-timeout-minutes="1" 
    subtopic-separator="/" 
    throttle-inbound-max-frequency="500"
    throttle-inbound-policy="ERROR" 
    throttle-outbound-max-frequency="500" 
    throttle-outbound-policy="IGNORE" />     
        

The message-broker attribute is a reference to the id of a Spring-managed MessageBroker. The channels attribute allows you to specify a comma-delimited list of the BlazeDS channels to be used (in order of preference) for this destination. The remaining attributes correspond to the options available via the network and server settings when configuring a message destination in the BlazeDS-specific XML. Each of these additional attributes is documented in the XSD to provide live code-completion assistance. For additional details on their usage, see the BlazeDS documentation. The message-destination tag serves as a base for the jms-message-destination and integration-message-destination tags so that the same configuration options are available no matter the type of the underlying MessagingAdapter.

The only attribute available on the message-destination tag that is not available in the JMS and Spring Integration implementations is the service-adapter attribute, which can be used to provide a custom ServiceAdapter via a reference to a ManageableComponentFactoryBean. This can be used to provide integration with additional messaging protocols not directly supported by Spring BlazeDS Integration. See Providing Custom Service Adapters for additional information on using the ManageableComponentFactoryBean.

For integration with JMS, a special JmsAdapter is provided that internally makes use of Spring's JmsTemplate, DestinationResolver, DefaultMessageListenerContainer and other such JMS abstractions for simplified interaction with JMS resources. The jms-message-destination XML namespace tag is used to expose JMS destinations as BlazeDS message destinations. The minimal attributes that must be specified are the destination id and exactly one of jms-destination, queue-name, or topic-name. A JMS ConnectionFactory reference is also required, but does not have to be explicitly specified if there is already one configured in the current application context with an id of "connectionFactory". For example, to configure a BlazeDS message destination named "chatIn" that uses a Spring-managed ActiveMQ JMS queue with a local ActiveMQ installation:

<bean id="connectionFactory" class="org.apache.activemq.ActiveMQConnectionFactory">
    <property name="brokerURL" value="tcp://localhost:61616"/>
</bean>
    
<bean id="chatInQueue" class="org.apache.activemq.command.ActiveMQQueue">
    <constructor-arg value="queue.flex.chat.in"/>
</bean>

<flex:jms-message-destination id="chatIn" jms-destination="chatInQueue" />       
        

Using queue-name or topic-name will cause the destination to be resolved using a Spring DestinationResolver. The destination-resolver, message-converter, and transaction-manager attributes may be used to set custom references to a Spring-managed DestinationResolver, MessageConverter, or TransactionManager respectively.

For routing messages with Spring Integration, a special IntegrationAdapter is provided that is able to send/receive messages via a MessageChannel. This is especially useful when you have more complex routing needs for your messages, such as connecting to email or FTP endpoints. The integration-message-destination XML namespace tag is used to expose a Spring Integration MessageChannel as a BlazeDS message destination. For example, to configure a BlazeDS message destination named "chatOut" that uses a Spring Integration PublishSubscribeChannel:

<integration:publish-subscribe-channel id="chatOutPubSubChannel" />

<flex:integration-message-destination id="chatOut" message-channel="chatOutPubSubChannel" />
        

A convenient MessageTemplate helper class is provided that allows you to push messages to any BlazeDS MessageDestination from a simple POJO. This provides a nice abstraction over push style messaging that hides away the details of the underlying messaging protocol. Whether using a simple AMF based destination or full-blown JMS, etc., the use of the MessageTemplate stays the same. The only thing the MessageTemplate requires is a reference to a Spring-managed MessageBroker. If the MessageTemplate is configured as a Spring bean, it will try and auto-detect the MessageBroker from its application context.

As an example of how the MessageTemplate could be used, suppose we have a RESTful travel application that has a Flex-based admin console but also exposes an API over HTTP. To give the admin console a "live" view of the data, we want to push updates to it anytime a new hotel booking is created. Given the following setup in our application context:

<flex:message-broker />

<bean id="defaultMessageTemplate" class="org.springframework.flex.messaging.MessageTemplate" />

<flex:message-destination id="bookingUpdates" />
        

and assuming the Flex client is subscribed to the "bookingUpdates" destination, this could be achieved with the following controller code:

@Controller
public class BookingController {
    
    private MessageTemplate template;
    
    private BookingService bookingService;
    
    @RequestMapping(value="/bookings", method=RequestMethod.POST)
    public String createBooking(Booking booking){
        booking = bookingService.saveBooking(booking);
        template.send("bookingUpdates", booking);
        return "redirect:/bookings/"+booking.getId();
    }
    
    @Autowired
    public void setTemplate(MessageTemplate template) {
        this.template = template;
    }
    
    @Autowired
    public void setBookingService(BookingService bookingService) {
        this.bookingService = bookingService;
    }
}
        

Included in the project distribution is a collection of samples called the Spring BlazeDS Integration Test Drive. This samples project is set up to be built with Maven and either run via an embedded Tomcat instance using the Maven Tomcat plugin, or else imported into Eclipse for running via WTP.

MAVEN_OPTS="-Xms256m -Xmx512m -XX:PermSize=128m -XX:MaxPermSize=256m"

            

mvn clean install

            

mvn tomcat:run

            

<repository>
    <id>spring-external</id>
    <name>Spring External Repository</name>
    <url>http://maven.springframework.org/external</url>
    <releases>
        <enabled>true</enabled>
    </releases>
    <snapshots>
        <enabled>false</enabled>
    </snapshots>
</repository>