Clean Up Your ThreadLocals

Forgetting to clean up ThreadLocal variables might really hurt you. Let’s see how. I have several integration tests with Spring WebFlow and JSF and in one of them I have an setUp method like that:

 public void setUp() {
     RequestContextHolder.setRequestContext(new MockRequestContext());

I just create a MockRequestContext and put it into RequestContextHolder so that Webflow will think that it is a flow request. Everything was fine until I coded some other integration test using my own AbstractJsfTests clas which basically initializes FacesContext and executes lifecycle in standalone mode. At rendering phase, my test was failing with an exception;


javax.servlet.ServletException: The current state 'mockState' of this flow 'mockFlow' is not a view state - view scope not accessible

java.lang.RuntimeException: javax.servlet.ServletException: The current state 'mockState' of this flow 'mockFlow' is not a view state - view scope not accessible
 at org.speedyframework.web.view.jsf.test.AbstractJsfTests.createDocumentFromUIViewRoot(AbstractJsfTests.java:333)
 at org.speedyframework.web.view.jsf.component.builder.PageBuilderTests.processPageContent(PageBuilderTests.java:53)
 at org.speedyframework.web.view.jsf.component.builder.PageBuilderTests.testHtmlContentWithBodyOnly(PageBuilderTests.java:60)
 Caused by: javax.servlet.ServletException: The current state 'mockState' of this flow 'mockFlow' is not a view state - view scope not accessible
 at org.speedyframework.web.view.jsf.test.ErrorPageWriter.throwException(ErrorPageWriter.java:401)
 at org.speedyframework.web.view.jsf.test.ErrorPageWriter.handleException(ErrorPageWriter.java:353)
 at org.speedyframework.web.view.jsf.test.AbstractJsfTests.handleLifecycleException(AbstractJsfTests.java:287)
 at org.speedyframework.web.view.jsf.test.AbstractJsfTests.executeFacesLifecycle(AbstractJsfTests.java:171)
 at org.speedyframework.web.view.jsf.test.AbstractJsfTests.createDocumentFromUIViewRoot(AbstractJsfTests.java:320)
 Caused by: java.lang.IllegalStateException: The current state 'mockState' of this flow 'mockFlow' is not a view state - view scope not accessible
 at org.springframework.webflow.test.MockFlowSession.getViewScope(MockFlowSession.java:99)
 at org.springframework.webflow.test.MockRequestContext.getViewScope(MockRequestContext.java:147)
 at org.springframework.faces.webflow.FlowViewStateManager.saveView(FlowViewStateManager.java:149)
 at org.apache.myfaces.application.jsp.JspViewHandlerImpl.renderView(JspViewHandlerImpl.java:396)
 at org.speedyframework.web.view.jsf.handler.SpeedyFacesViewHandler.renderView(SpeedyFacesViewHandler.java:163)
 at org.springframework.faces.webflow.FlowViewHandler.renderView(FlowViewHandler.java:91)
 at org.apache.shale.validator.faces.ValidatorViewHandler.renderView(ValidatorViewHandler.java:130)
 at org.ajax4jsf.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:100)
 at org.ajax4jsf.application.AjaxViewHandler.renderView(AjaxViewHandler.java:176)
 at org.apache.myfaces.lifecycle.RenderResponseExecutor.execute(RenderResponseExecutor.java:41)
 at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:140)
 at org.speedyframework.web.view.jsf.test.AbstractJsfTests.executeFacesLifecycle(AbstractJsfTests.java:169)


The exception was implying that Webflow was in action during request processing. However my test was creating a mock http request which wasn’t triggering any flow execution. When I looked at FlowViewStateManager.saveView(FlowViewStateManager.java:149). I just realized that FlowViewStateManager instance was thinking that there is an active flow instance by first looking for an RequestContext instance bound at current thread context, and was finding one in it. But how could it have been possible if my request was a non-flow request. After all RequestControlContext instances are only put into current thread context by webflow during flow start or flow resume steps.

Then I just searched my source code base looking for any other calls to RequestContextHolder.setRequestContext(…) and found above block! Yeah that was the case two different tests were somehow executed in the same thread and the first one which is creating a RequestContext instance was not cleaning up its ThreadLocal variable when finished. As a result, the other test was affected and failed because of this side effect. Solution was simple;

 public void tearDown() {

Not cleaning up ThreadLocal variables is also a security threat for your application. Containers usually reuse threads to handle http requests accross different applications and sensitive information put into thread context by your application might be accessible when thread used processing your request is used to handle some other request arriving at a different application. Hence, it is always a good practice to clean up thread context at appropriate exit points in your application.

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