{"id":840,"date":"2012-01-11T21:03:00","date_gmt":"2012-01-11T21:03:00","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/2012\/10\/simulating-cdis-session-and-request-scope-in-a-j2se-app.html"},"modified":"2012-10-21T22:47:35","modified_gmt":"2012-10-21T22:47:35","slug":"simulating-cdis-session-and-request","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2012\/01\/simulating-cdis-session-and-request.html","title":{"rendered":"Simulating CDI’s Session and Request Scope in a J2SE app"},"content":{"rendered":"
We\u2019re currently considering refactoring the Naked Objects framework to use JSR-330 (dependency injection) and EE-oriented big brother, JSR-299 (CDI). Using vanilla JSR-330 is a no-brainer, but there are also some nice features in JSR-299 that we\u2019d like to exploit (such as events and decorators). The snag? The Naked Objects must also run transparently in J2SE environments.<\/p>\n

Now JSR-299 (at least, the Weld reference implementation) can run on J2SE, but it isn\u2019t possible to use beans that are annotated as either @SessionScoped or @RequestScoped\u2026 not surprising really, because there is no HttpSession or HttpServletRequest to hook into. On the other hand, at least in the Naked Objects framework in a J2SE context, we do have the ability to map these concepts onto its own internal lifecycle \u2026 eg, for a client-side app, the user is always in deemed to be running in one long session.<\/p>\n

How, then, to setup contexts for these scopes, and make them automatically active when running in J2SE?<\/p>\n

First, let\u2019s look at the code we want to run:<\/p>\n

package org.nakedobjects.experiments.cdi;\r\n\r\nimport java.util.List;\r\nimport javax.enterprise.context.RequestScoped;\r\nimport javax.enterprise.event.Observes;\r\nimport org.jboss.weld.environment.se.bindings.Parameters;\r\nimport org.jboss.weld.environment.se.events.ContainerInitialized;\r\n\r\n@RequestScoped\r\npublic class HelloWorld {\r\n    public static void main(String[] args) {\r\n        \/\/ bootstrap\r\n        org.jboss.weld.environment.se.StartMain.main(new String[]{\"JSR\",\"299\"});\r\n    }\r\n    public void printHello(@Observes ContainerInitialized event, @Parameters List<String> args) {\r\n        System.out.println(\"Hello \" + args);\r\n        System.out.flush();\r\n    }\r\n}\r\n<\/pre>\n
Because this is a CDI bean, we need an empty META-INF\/beans.xml.<\/span>
 
<\/div> <\/div><\/p>\n
The above class would print out \u201cHello [JSR, 299]\u201d if annotated as @ApplicationScoped<\/span>, but not with it being annotated as @RequestScoped<\/span>. What we therefore need to do is write an extension. It\u2019s a bit hacky, but it works:<\/p>\n
package org.jboss.weld.manager; \/\/ required for visibility to BeanManagerImpl#getContexts()\r\n\r\nimport java.lang.annotation.Annotation;\r\n\r\nimport javax.enterprise.context.RequestScoped;\r\nimport javax.enterprise.context.SessionScoped;\r\nimport javax.enterprise.event.Observes;\r\nimport javax.enterprise.inject.spi.AfterDeploymentValidation;\r\nimport javax.enterprise.inject.spi.BeanManager;\r\nimport javax.enterprise.inject.spi.Extension;\r\n\r\nimport org.jboss.weld.context.AbstractThreadLocalMapContext;\r\nimport org.jboss.weld.context.beanstore.HashMapBeanStore;\r\n\r\npublic class WeldServletScopesSupportForSe implements Extension {\r\n\r\n public void afterDeployment(@Observes AfterDeploymentValidation event,\r\n   BeanManager beanManager) {\r\n\r\n  setContextActive(beanManager, SessionScoped.class);\r\n  setContextActive(beanManager, RequestScoped.class);\r\n }\r\n\r\n private void setContextActive(BeanManager beanManager,\r\n   Class<? extends Annotation> cls) {\r\n  BeanManagerImpl beanManagerImpl = (BeanManagerImpl) beanManager;\r\n  AbstractThreadLocalMapContext context = (AbstractThreadLocalMapContext) beanManagerImpl\r\n    .getContexts().get(cls).get(0);\r\n  context.setBeanStore(new HashMapBeanStore());\r\n  context.setActive(true);\r\n }\r\n}\r\n<\/pre>\n
Like all Weld extensions, this needs to be registered in META-INF\/services<\/span>, in this case in a file called javax.enterprise.inject.spi.Extension<\/span> containing the fully-qualified class name.<\/p>\n
Now, when we run the application, the session and request scopes will both be set up, and our HelloWorld bean will fire.<\/p>\n
For developers writing apps in Naked Objects they will need to include a dependency to an additional module, if deploying a client (-t client<\/span> or a server on a non-web backend (-t server<\/span> with socket-level remoting, say). For the latter, we\u2019ll need to include some smarts to figure out whether we are running in a webapp or not, and only set up the Contexts if we determine that we\u2019re not (eg can\u2019t find javax.servlet<\/span> classes on the classpath.<\/p>\n
If you want to try out the code, you can check it out using<\/p>\n
svn co https:\/\/nakedobjects.svn.sourceforge.net\/svnroot\/nakedobjects\/framework\/trunk\/experiments .\r\n<\/pre>\n
Reference: <\/i><\/strong>Simulating CDI’s Session and Request Scope in a J2SE app<\/a> from our JCG partner<\/a> Dan Haywood at the Dan Haywood blog<\/a>.<\/p>\n
Related Articles :<\/i><\/strong><\/p>\n