我们在org.apache.catalina.connector.Request中的parseParemeters期间间歇性地执行NPE。在线用户越多，NPE发生的越多。在JBoss重启后，NPE会消失一段时间。在24小时内，我们会收到一到四百多名NPE。调用哪个服务并不重要。任何服务请求都可以在此NPE中结束。
java.lang.NullPointerException
at org.apache.catalina.connector.Request.parseParameters(Request.java:2517)
at org.apache.catalina.connector.Request.getParameterNames(Request.java:1102)
at org.apache.catalina.connector.Request.getParameterMap(Request.java:1082)
at org.apache.catalina.connector.RequestFacade.getParameterMap(RequestFacade.java:414)
at javax.servlet.ServletRequestWrapper.getParameterMap(ServletRequestWrapper.java:166)
at org.jboss.seam.mock.MockExternalContext.getRequestParameterValuesMap(MockExternalContext.java:307)
at org.jboss.seam.faces.Parameters.getRequestParameters(Parameters.java:61)
at org.jboss.seam.Component.injectParameters(Component.java:1586)
at org.jboss.seam.Component.inject(Component.java:1556)
at org.jboss.seam.core.BijectionInterceptor.aroundInvoke(BijectionInterceptor.java:61)
at org.jboss.seam.intercept.SeamInvocationContext.proceed(SeamInvocationContext.java:68)
at org.jboss.seam.transaction.TransactionInterceptor$1.work(TransactionInterceptor.java:97)
at org.jboss.seam.util.Work.workInTransaction(Work.java:61)
at org.jboss.seam.transaction.TransactionInterceptor.aroundInvoke(TransactionInterceptor.java:91)
at org.jboss.seam.intercept.SeamInvocationContext.proceed(SeamInvocationContext.java:68)
at org.jboss.seam.core.MethodContextInterceptor.aroundInvoke(MethodContextInterceptor.java:44)
at org.jboss.seam.intercept.SeamInvocationContext.proceed(SeamInvocationContext.java:68)
at org.jboss.seam.security.SecurityInterceptor.aroundInvoke(SecurityInterceptor.java:163)
at org.jboss.seam.intercept.SeamInvocationContext.proceed(SeamInvocationContext.java:68)
at ExceptionInterceptor.aroundInvoke(ExceptionInterceptor.java:51)
at sun.reflect.GeneratedMethodAccessor289.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.jboss.seam.util.Reflections.invoke(Reflections.java:22)
at org.jboss.seam.intercept.Interceptor.aroundInvoke(Interceptor.java:187)
at org.jboss.seam.intercept.SeamInvocationContext.proceed(SeamInvocationContext.java:72)
at org.jboss.seam.intercept.RootInterceptor.invoke(RootInterceptor.java:107)
at org.jboss.seam.intercept.JavaBeanInterceptor.interceptInvocation(JavaBeanInterceptor.java:185)
at org.jboss.seam.intercept.JavaBeanInterceptor.invoke(JavaBeanInterceptor.java:103)
at TaskService_$$_javassist_seam_7.getNumberOfUpdatedTasks(TaskService_$$_javassist_seam_7.java)
at sun.reflect.GeneratedMethodAccessor319.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.jboss.seam.remoting.gwt.GWTToSeamAdapter.callWebRemoteMethod(GWTToSeamAdapter.java:100)
at org.jboss.seam.remoting.gwt.GWTService.RPC_invokeAndEncodeResponse(GWTService.java:550)
at org.jboss.seam.remoting.gwt.GWTService.processCall(GWTService.java:206)
at org.jboss.seam.remoting.gwt.GWTService$1.process(GWTService.java:120)
at org.jboss.seam.servlet.ContextualHttpServletRequest.run(ContextualHttpServletRequest.java:53)
at org.jboss.seam.remoting.gwt.GWTService.getResource(GWTService.java:105)
at org.jboss.seam.servlet.SeamResourceServlet.service(SeamResourceServlet.java:80)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:83)
at org.jboss.seam.web.LoggingFilter.doFilter(LoggingFilter.java:60)
at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
at org.jboss.seam.web.ExceptionFilter.doFilter(ExceptionFilter.java:64)
at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
at org.jboss.seam.web.RedirectFilter.doFilter(RedirectFilter.java:45)
at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
at org.jboss.seam.web.IdentityFilter.doFilter(IdentityFilter.java:40)
at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:73)
at org.jboss.seam.servlet.SeamFilter.doFilter(SeamFilter.java:158)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:190)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:433)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:92)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.process(SecurityContextEstablishmentValve.java:126)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:70)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:330)
at org.apache.coyote.ajp.AjpProcessor.process(AjpProcessor.java:436)
at org.apache.coyote.ajp.AjpProtocol$AjpConnectionHandler.process(AjpProtocol.java:384)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:619)
我们使用JBoss AS 5.1.0.GA，Seam 2.2.0.GA和GWT 2.0.3。 JBoss通过mod_jk接收来自Apache 2的请求。提供的行号（Request.java:2517）表示请求的方法为null，尽管firebug（client），Apache和mod_jk的日志显示该方法是POST。
目前，我们既不知道可能是NPE的根本原因，也不知道我们如何能够解决这个问题。我们猜测问题是否与此有关：
我们可以做些什么来找到这个问题的原因？有没有可能解决这个问题？
非常感谢任何帮助或建议。
谢谢！
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我们很幸运，能够在NPE期间调试堆栈跟踪。我们发现MockExternalContext中的请求对象并不总是与SeamResourceServlet收到的请求对象匹配。有时，MockExternalContext中的请求对象是新的，包含org.apache.coyote.Request的全新实例，所有字段都设置为null。如果可以处理请求，则SeamResourceServlet收到的请求对象与MockExternalContext中的请求对象相同。
任何Seam专家都可以帮助我们并告诉我们在上面的堆栈跟踪中何时何地创建MockExternalContext使用的org.jboss.seam.faces.Parameters？ Seam在哪些情况下使用新的请求对象而不是MockExternalContext提供的对象初始化SeamResourceServlet？
我已在Seam forum中交叉发布此问题。
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更新
与此同时，我们找到了NPE的原因：
由于我们在客户端使用GWT，所有客户端 - 服务器通信都是通过GWT-RPC异步完成的。很少，注销调用会导致另一个仍在处理的RPC。注销调用使会话无效，因此其他RPC无法正常完成，这导致ServletLifecycle.endRequest（request）期间出现异常;在ContextualHttpServletRequest中。此异常由Seam的ExceptionFilter处理。不幸的是，由于会话失效导致以下错误，ExceptionFilter也无法正常完成：
ERROR [Seam Resource Servlet].error: Servlet.service() for servlet Seam Resource Servlet threw exception
java.lang.IllegalStateException: Cannot create a session after the response has been committed
at org.apache.catalina.connector.Request.doGetSession(Request.java:2338)
at org.apache.catalina.connector.Request.getSession(Request.java:2094)
at org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:833)
at javax.servlet.http.HttpServletRequestWrapper.getSession(HttpServletRequestWrapper.java:216)
at org.jboss.seam.mock.MockExternalContext.getSessionMap(MockExternalContext.java:357)
at org.jboss.seam.contexts.FacesLifecycle.beginExceptionRecovery(FacesLifecycle.java:86)
at org.jboss.seam.web.ExceptionFilter.endWebRequestAfterException(ExceptionFilter.java:96)
at org.jboss.seam.web.ExceptionFilter.doFilter(ExceptionFilter.java:70)
at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
at org.jboss.seam.web.RedirectFilter.doFilter(RedirectFilter.java:45)
at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
at org.jboss.seam.web.IdentityFilter.doFilter(IdentityFilter.java:40)
at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:73)
at org.jboss.seam.servlet.SeamFilter.doFilter(SeamFilter.java:158)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:190)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:433)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:92)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.process(SecurityContextEstablishmentValve.java:126)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:70)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:330)
at org.apache.coyote.ajp.AjpProcessor.process(AjpProcessor.java:436)
at org.apache.coyote.ajp.AjpProtocol$AjpConnectionHandler.process(AjpProtocol.java:384)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:619)
在ExceptionFilter中创建的MockExternalContext，“以某种方式”保留在应用程序上下文中，并且“有时”用于处理请求。它甚至可以在我们的应用程序的重新部署中存活下来，因此我们必须重新启动JBoss才能摆脱NPE。
答案 0 :(得分：1)
非常感谢这篇文章。这个错误是我们几个星期的噩梦。我们的配置是：GWT 2.0.4，Seam 2.2.1 CR2，JBoss AS 5.1.0。我们在我们的应用程序中修补了注销机制，但它仍然返回（尽管很少）。现在看来，当事务在EJB层中持续太长时间时会发生这种情况。现在我们已经准备好摆脱Seam，它会导致比我们处理的问题更多的问题。
<强>更新 当“ServiceImpl”组件的范围从“SESSION”更改为默认值时，这个奇怪的bug完全消失了。还添加了注释@BypassInterceptors。同时我为我们的app准备了Seam-GWT桥的替代品。这是Guice + gwt-dispatch。非常快速可靠的解决方案。