Injecting Seam component instances into Spring beans is accomplished using the <seam:instance/> namespace handler. To enable the Seam namespace handler, the Seam namespace must be added to the Spring beans definition file:

<beans xmlns="http://www.springframework.org/schema/beans"

    xmlns:seam="http://jboss.org/schema/seam/spring-seam"

    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-2.0.xsd

                        http://jboss.org/schema/seam/spring-seam

                        http://jboss.org/schema/seam/spring-seam-2.3.xsd">

Now any Seam component may be injected into any Spring bean:

<bean id="someSpringBean" class="SomeSpringBeanClass" scope="prototype">

    <property name="someProperty">

        <seam:instance name="someComponent"/>

    </property>

</bean>

An EL expression may be used instead of a component name:

<bean id="someSpringBean" class="SomeSpringBeanClass" scope="prototype">

    <property name="someProperty">

        <seam:instance name="#{someExpression}"/>

    </property>

</bean>

Seam component instances may even be made available for injection into Spring beans by a Spring bean id.

<seam:instance name="someComponent" id="someSeamComponentInstance"/>



<bean id="someSpringBean" class="SomeSpringBeanClass" scope="prototype">

    <property name="someProperty" ref="someSeamComponentInstance">

</bean>

Now for the caveat!

Seam was designed from the ground up to support a stateful component model with multiple contexts. Spring was not. Unlike Seam bijection, Spring injection does not occur at method invocation time. Instead, injection happens only when the Spring bean is instantiated. So the instance available when the bean is instantiated will be the same instance that the bean uses for the entire life of the bean. For example, if a Seam CONVERSATION-scoped component instance is directly injected into a singleton Spring bean, that singleton will hold a reference to the same instance long after the conversation is over! We call this problem scope impedance. Seam bijection ensures that scope impedance is maintained naturally as an invocation flows through the system. In Spring, we need to inject a proxy of the Seam component, and resolve the reference when the proxy is invoked.

The <seam:instance/> tag lets us automatically proxy the Seam component.

<seam:instance id="seamManagedEM" name="someManagedEMComponent" proxy="true"/>



<bean id="someSpringBean" class="SomeSpringBeanClass">

    <property name="entityManager" ref="seamManagedEM">

</bean>

This example shows one way to use a Seam-managed persistence context from a Spring bean. (For a more robust way to use Seam-managed persistence contexts as a replacement for the Spring OpenEntityManagerInView filter see section on Using a Seam Managed Persistence Context in Spring)

It is even easier to inject Spring beans into Seam component instances. Actually, there are two possible approaches:

We'll discuss the second option in the next section. The easiest approach is to access the Spring beans via EL.

The Spring DelegatingVariableResolver is an integration point Spring provides for integrating Spring with JSF. This VariableResolver makes all Spring beans available in EL by their bean id. You'll need to add the DelegatingVariableResolver to faces-config.xml:

<application>

    <variable-resolver>

        org.springframework.web.jsf.DelegatingVariableResolver

    </variable-resolver>

</application>

Then you can inject Spring beans using @In:

@In("#{bookingService}")

private BookingService bookingService;

The use of Spring beans in EL is not limited to injection. Spring beans may be used anywhere that EL expressions are used in Seam: process and pageflow definitions, working memory assertions, etc...

The <seam:component/> namespace handler can be used to make any Spring bean a Seam component. Just place the <seam:component/> tag within the declaration of the bean that you wish to be a Seam component:

<bean id="someSpringBean" class="SomeSpringBeanClass" scope="prototype">

    <seam:component/>

</bean>

By default, <seam:component/> will create a STATELESS Seam component with class and name provided in the bean definition. Occasionally, such as when a FactoryBean is used, the class of the Spring bean may not be the class appearing in the bean definition. In such cases the class should be explicitly specified. A Seam component name may be explicitly specified in cases where there is potential for a naming conflict.

The scope attribute of <seam:component/> may be used if you wish the Spring bean to be managed in a particular Seam scope. The Spring bean must be scoped to prototype if the Seam scope specified is anything other than STATELESS. Pre-existing Spring beans usually have a fundamentally stateless character, so this attribute is not usually needed.

The Seam integration package also lets you use Seam's contexts as Spring 2.0 style custom scopes. This lets you declare any Spring bean in any of Seam's contexts. However, note once again that Spring's component model was never architected to support statefulness, so please use this feature with great care. In particular, clustering of session or conversation scoped Spring beans is deeply problematic, and care must be taken when injecting a bean or component from a wider scope into a bean of a narrower scope.

By specifying <seam:configure-scopes/> once in a Spring bean factory configuration, all of the Seam scopes will be available to Spring beans as custom scopes. To associate a Spring bean with a particular Seam scope, specify the Seam scope in the scope attribute of the bean definition.

<!-- Only needs to be specified once per bean factory-->

<seam:configure-scopes/>



...



<bean id="someSpringBean" class="SomeSpringBeanClass" scope="seam.CONVERSATION"/>

The prefix of the scope name may be changed by specifying the prefix attribute in the configure-scopes definition. (The default prefix is seam.)

By default an instance of a Spring Component registered in this way is not automatically created when referenced using @In. To have an instance auto-created you must either specify @In(create=true) at the injection point to identify a specific bean to be auto created or you can use the default-auto-create attribute of configure-scopes to make all spring beans who use a seam scope auto created.

Seam-scoped Spring beans defined this way can be injected into other Spring beans without the use of <seam:instance/>. However, care must be taken to ensure scope impedance is maintained. The normal approach used in Spring is to specify <aop:scoped-proxy/> in the bean definition. However, Seam-scoped Spring beans are not compatible with <aop:scoped-proxy/>. So if you need to inject a Seam-scoped Spring bean into a singleton, <seam:instance/> must be used:

<bean id="someSpringBean" class="SomeSpringBeanClass" scope="seam.CONVERSATION"/>



...



<bean id="someSingleton">

    <property name="someSeamScopedSpringBean">

        <seam:instance name="someSpringBean" proxy="true"/>

    </property>

</bean>

Spring provides an extensible transaction management abstraction with support for many transaction APIs (JPA, Hibernate, JDO, and JTA) Spring also provides tight integrations with many application server TransactionManagers such as Websphere and Weblogic. Spring transaction management exposes support for many advanced features such as nested transactions and supports full Java EE transaction propagation rules like REQUIRES_NEW and NOT_SUPPORTED. For more information see the spring documentation here.

To configure Seam to use Spring transactions enable the SpringTransaction component like so:

<spring:spring-transaction platform-transaction-manager="#{transactionManager}"/>

The spring:spring-transaction component will utilize Springs transaction synchronization capabilities for synchronization callbacks.

One of the most powerful features of Seam is its conversation scope and the ability to have an EntityManager open for the life of a conversation. This eliminates many of the problems associated with the detachment and re-attachment of entities as well as mitigates occurrences of the dreaded LazyInitializationException. Spring does not provide a way to manage an persistence context beyond the scope of a single web request (OpenEntityManagerInViewFilter). So, it would be nice if Spring developers could have access to a Seam managed persistence context using all of the same tools Spring provides for integration with JPA(e.g. PersistenceAnnotationBeanPostProcessor, JpaTemplate, etc.)

Seam provides a way for Spring to access a Seam managed persistence context with Spring's provided JPA tools bringing conversation scoped persistence context capabilities to Spring applications.

This integration work provides the following functionality:

Spring's persistence context propagation model allows only one open EntityManager per EntityManagerFactory so the Seam integration works by wrapping an EntityManagerFactory around a Seam managed persistence context.

<bean id="seamEntityManagerFactory" class="org.jboss.seam.ioc.spring.SeamManagedEntityManagerFactoryBean">

    <property name="persistenceContextName" value="entityManager"/>

</bean>

Where 'persistenceContextName' is the name of the Seam managed persistence context component. By default this EntityManagerFactory has a unitName equal to the Seam component name or in this case 'entityManager'. If you wish to provide a different unitName you can do so by providing a persistenceUnitName like so:

<bean id="seamEntityManagerFactory" class="org.jboss.seam.ioc.spring.SeamManagedEntityManagerFactoryBean">

    <property name="persistenceContextName" value="entityManager"/>

    <property name="persistenceUnitName" value="bookingDatabase:extended"/>

</bean>

This EntityManagerFactory can then be used in any Spring provided tools. For example, using Spring's PersistenceAnnotationBeanPostProcessor is the exact same as before.

<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor"/>

If you define your real EntityManagerFactory in Spring but wish to use a Seam managed persistence context you can tell the PersistenceAnnotationBeanPostProcessor which persistenctUnitName you wish to use by default by specifying the defaultPersistenceUnitName property.

The applicationContext.xml might look like:

<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalEntityManagerFactoryBean">

    <property name="persistenceUnitName" value="bookingDatabase"/>

</bean>

<bean id="seamEntityManagerFactory" class="org.jboss.seam.ioc.spring.SeamManagedEntityManagerFactoryBean">

    <property name="persistenceContextName" value="entityManager"/>

    <property name="persistenceUnitName" value="bookingDatabase:extended"/>

</bean>

<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor">

    <property name="defaultPersistenceUnitName" value="bookingDatabase:extended"/>

</bean>

The component.xml might look like:

<persistence:managed-persistence-context name="entityManager"

    auto-create="true" entity-manager-factory="#{entityManagerFactory}"/>

JpaTemplate and JpaDaoSupport are configured the same way for a Seam managed persistence context as they would be fore a Seam managed persistence context.

<bean id="bookingService" class="org.jboss.seam.example.spring.BookingService">

    <property name="entityManagerFactory" ref="seamEntityManagerFactory"/>

</bean>

The Seam Spring integration also provides support for complete access to a Seam managed Hibernate session using spring's tools. This integration is very similar to the JPA integration.

Like Spring's JPA integration spring's propagation model allows only one open EntityManager per EntityManagerFactory per transaction??? to be available to spring tools. So, the Seam Session integration works by wrapping a proxy SessionFactory around a Seam managed Hibernate session context.

<bean id="seamSessionFactory" class="org.jboss.seam.ioc.spring.SeamManagedSessionFactoryBean">

    <property name="sessionName" value="hibernateSession"/>

</bean>

Where 'sessionName' is the name of the persistence:managed-hibernate-session component. This SessionFactory can then be used in any Spring provided tools. The integration also provides support for calls to SessionFactory.getCurrentInstance() as long as you call getCurrentInstance() on the SeamManagedSessionFactory.

Although it is possible to use the Spring ContextLoaderListener to start your application's Spring ApplicationContext there are a couple of limitations.

To overcome these two limitations the Spring integration includes a Seam component that will start a Spring ApplicationContext. To use this Seam component place the <spring:context-loader/> definition in the components.xml. Specify your Spring context file location in the config-locations attribute. If more than one config file is needed you can place them in the nested <spring:config-locations/> element following standard components.xml multi value practices.

<components xmlns="http://jboss.org/schema/seam/components"

            xmlns:spring="http://jboss.org/schema/seam/spring"

            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

            xsi:schemaLocation="http://jboss.org/schema/seam/components

                                http://jboss.org/schema/seam/components-2.3.xsd

                                http://jboss.org/schema/seam/spring

                                http://jboss.org/schema/seam/spring-2.3.xsd">



    <spring:context-loader config-locations="/WEB-INF/applicationContext.xml"/>



</components>

Spring provides an abstraction for executing code asynchronously called a TaskExecutor. The Spring Seam integration allows for the use of a Spring TaskExecutor for executing immediate @Asynchronous method calls. To enable this functionality install the SpringTaskExecutorDispatchor and provide a spring bean defined taskExecutor like so:

<spring:task-executor-dispatcher task-executor="#{springThreadPoolTaskExecutor}"/>

Because a Spring TaskExecutor does not support scheduling of an asynchronous event a fallback Seam Dispatcher can be provided to handle scheduled asynchronous event like so:

            <!-- Install a ThreadPoolDispatcher to handle scheduled asynchronous event -->

<core:thread-pool-dispatcher name="threadPoolDispatcher"/>



<!-- Install the SpringDispatcher as default -->

<spring:task-executor-dispatcher task-executor="#{springThreadPoolTaskExecutor}" schedule-dispatcher="#{threadPoolDispatcher}"/>