尝试从一个页面导航到另一个页面时，我收到NullPointerException。 我像往常一样在faces-config.xml
中定义了导航规则但由于某种原因，我的webapp无法导航到下一页。它保留在当前页面上，我看起来像是无限循环的堆栈错误消息。
我从Eclipse控制台获得的错误堆栈是：
SEVERE: Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
at javax.faces.component.UIViewRoot.getViewMap(UIViewRoot.java:657)
at javax.faces.component.UIViewRoot.getViewMap(UIViewRoot.java:645)
at org.apache.myfaces.renderkit.ErrorPageWriter._writeVariables(ErrorPageWriter.java:574)
at org.apache.myfaces.renderkit.ErrorPageWriter.debugHtml(ErrorPageWriter.java:288)
at org.apache.myfaces.renderkit.ErrorPageWriter.debugHtml(ErrorPageWriter.java:250)
at org.apache.myfaces.renderkit.ErrorPageWriter.handleThrowable(ErrorPageWriter.java:417)
at org.apache.myfaces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:274)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:191)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.myfaces.webapp.filter.ExtensionsFilter.doFilter(ExtensionsFilter.java:349)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:311)
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:116)
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:101)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:113)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilter(BasicAuthenticationFilter.java:150)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:182)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:173)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:259)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:662)
我已经阅读过其他论坛帖子，并提及包括（在web.xml中）：
<context-param>
<param-name>javax.faces.DEFAULT_SUFFIX</param-name>
<param-value>.jsp</param-value>
</context-param>
我已经这样做了，但没有运气。 需要强调的是，我之前一直在研究其他JSF项目，并且没有遇到麻烦，实现了页面导航。所以我认为这不是导航规则的问题。
我尝试导航到的页面名为“login.jsp”。导航规则如下所示：
<navigation-rule>
<display-name>Global Rule to Login Page</display-name>
<navigation-case>
<from-outcome>login</from-outcome>
<to-view-id>/login.jsf</to-view-id>
</navigation-case>
</navigation-rule>
非常感谢任何建议或意见。
非常感谢， 格伦
答案 0 :(得分：0)
看起来有一些异常抛出，MyFaces准备渲染相应的错误页面。 NullPointerException似乎在呈现错误页面期间发生。所以看起来原始错误是以某种方式隐藏的。
你可以尝试禁用MyFaces错误处理，看看你是否以某种方式找到了根本原因：
<context-param>
<param-name>org.apache.myfaces.ERROR_HANDLING</param-name>
<param-value>false</param-value>
</context-param>