Spring Web Flow Bean Scopes and JSF
I've recently finished up an interesting issue in Spring Web Flow. This issue (SWF-163) dealt with adding Spring 2.0 bean scoping support for Spring Web Flow's internal scopes. The implementation isn't really that interesting (the Scope interface is pretty easy to implement after all), but I wanted to mention exactly how you would use something like this in your application.
Spring 2.0 Scoping
In Spring 1.x, we had the idea of singleton and prototype bean scopes, but the notation was fixed and not especially descriptive with singleton="[true | false]". So in Spring 2.0, this notation was removed from the XSD style of configuration and now you see a notation that is more clear with scope="[singleton | prototype | …]". Spring itself adds three more bean scopes; request, session, and globalSession which are related to web applications.
With the latest snapshots of Spring Web Flow 1.1, we now see bean scopes for the three major Web Flow scopes, flash, flow, and conversation.
<bean id="sale" class="org.springframework.webflow.samples.sellitem.Sale" scope="flow"/>
<bean id="sale" class="org.springframework.webflow.samples.sellitem.Sale" scope="conversation"/>
To utilize these bean scopes you'll need to leverage the a new 1.1 version of the configuration (included in the Web Flow jar) and add a single element to your bean definition.
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:flow="http://www.springframework.org/schema/webflow-config"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
http://www.springframework.org/schema/webflow-config
http://www.springframework.org/schema/webflow-config/spring-webflow-config-1.1.xsd">
<flow:enable-scopes/>
<bean id="sale" class="org.springframework.webflow.samples.sellitem.Sale" scope="conversation"/>
</beans>
The <enable-scopes/> tag only needs to exist once in a given application context and will allow you to use any of the three scopes contributed by Spring Web Flow.
Scoped Beans and JSF
Right now the most compelling use of these new scopes is in JSF. By using the scope notation in a standard Spring bean definition file instead of the <var/> notation in a flow definition, the experience for JSF users is much closer to standard JSF behavior. To add this ability to JSF you register the standard Spring JSF DelegatingVariableResolver. The other definitions (FlowNavigationHandler, and FlowPhaseListener) are standard for using JSF with Spring.
<!DOCTYPE faces-config PUBLIC
"-//Sun Microsystems, Inc.//DTD JavaServer Faces Config 1.0//EN"
"http://java.sun.com/dtd/web-facesconfig_1_0.dtd">
<faces-config>
<application>
<navigation-handler>
org.springframework.webflow.executor.jsf.FlowNavigationHandler
</navigation-handler>
<variable-resolver>
org.springframework.web.jsf.DelegatingVariableResolver
</variable-resolver>
</application>
<lifecycle>
<phase-listener>
org.springframework.webflow.executor.jsf.FlowPhaseListener
</phase-listener>
</lifecycle>
</faces-config>
The major change from the previous Web Flow enabled configuration is that now the variable resolver is the one from Spring and not Spring Web Flow. When a JSP page looks for a sale variable, JSF will delegate to Spring for bean resolution and the bean instance will be scoped according to the scope attribute on its definition.
Conclusion
The end result of this is that now JSF users can now use a syntax similar to the built-in style but in a container that is much more powerful.
If you'd like to use this new functionality, it will be coming shortly with the Spring Web Flow 1.1-m1 release, or you can get a preview by downloading the latest Spring Web Flow 1.1-m1 nightly snapshot.
About Mark Fisher
Mark Fisher is an engineer within the SpringSource division of VMware and lead of the Spring Integration project. He is also a committer on the core Spring Framework and the Spring BlazeDS Integration project. Mark has provided consulting services for clients across numerous industries, and he has trained hundreds of developers how to use the Spring Framework and related projects effectively. Mark speaks regularly at conferences and user groups in America and Europe.
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