Google App Engine中的ConcurrentModificationException-Struts 2会话

Question

I'm using Struts2 in Google App Engine.

My Action for Logout:

public String logout(){     
    ActionContext.getContext().getSession().clear();
    return SUCCESS;
}

In my appengine-web.xml:

<sessions-enabled>true</sessions-enabled>
<async-session-persistence enabled="true" />

When deployed, I got the error below when trying to logout:

java.util.ConcurrentModificationException
      java.util.HashMap$HashIterator.nextEntry(HashMap.java:810)
      java.util.HashMap$KeyIterator.next(HashMap.java:845)
      java.util.Collections$2.nextElement(Collections.java:3647)
      org.apache.struts2.dispatcher.SessionMap.clear(SessionMap.java:91)
      dating.dating.LogAction.logout(LogAction.java:80)
      sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
      sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      java.lang.reflect.Method.invoke(Method.java:43)
      com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:453)
      com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:292)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:255)
      org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176)
      com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265)
      org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
      com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:211)
      com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:211)
      com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:90)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)
      com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:192)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187)
      com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)
      org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)
      org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:510)
      org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
      org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
      org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
      org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
      org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
      org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
      org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
      org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
      org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
      org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
      org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
      org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
      org.mortbay.jetty.Server.handle(Server.java:326)
      org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
      org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
      org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
      com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:449)
      com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:455)
      com.google.tracing.TraceContext.runInContext(TraceContext.java:695)
      com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:333)
      com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:325)
      com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:453)
      java.lang.Thread.run(Thread.java:679)

Answer 1

使用会话感知界面，然后在会话映射上使用session.remove（Object key）