JSF 导航期间的 NullPointerException (MyFaces)

Question

我在尝试从一个页面导航到另一个页面时遇到NullPointerException。我已经像往常一样在人脸配置中定义了导航规则.xml

但由于某种原因，我的网络应用程序无法导航到下一页。它停留在当前页面上，我得到看起来像堆栈错误消息的无限循环。

我从 Eclipse 控制台得到的错误堆栈是：

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)

我已经阅读了发生这种情况的其他论坛主题，他们提到包括（在网络中.xml）：

<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。只是为了强调，我之前一直在研究其他 JSF 项目，并且没有遇到任何问题地实现了页面导航。所以我认为这不是我的导航规则的问题。

我尝试导航到的页面称为"登录.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>

任何意见或建议将不胜感激。

非常感谢，幽谷

Answer 1

看起来抛出了一些异常，MyFaces准备呈现相应的错误页面。NullPointerException似乎发生在错误页面的呈现过程中。所以看起来原始错误以某种方式被隐藏了。

您可以尝试禁用MyFaces错误处理，以查看是否以某种方式找到根本原因：

<context-param>
  <param-name>org.apache.myfaces.ERROR_HANDLING</param-name>
  <param-value>false</param-value>
</context-param>