为什么FacesContext.getCurrentInstance（）。getExternalContext（）。dispatch（url）抛出异常

Question

如果条件为真，我正试图转发到另一页。这就是我的代码的样子

    public String handleBeforePhase(PhaseEvent phaseEvent){
    PhaseId phaseId = phaseEvent.getPhaseId();
    if(phaseId.equals(PhaseId.RENDER_RESPONSE)){
        if(!SecurityHelper.isAdmin()){              

            try {               
                  FacesContext.getCurrentInstance().getExternalContext().dispatch("notAdmin.xhtml");


            } catch (Exception e) {

                e.printStackTrace();
            }


        }
    }
    return null;
}

一切正常，它将它转发到下一页但在控制台中我看到下面的异常。我无法弄清楚为什么我会得到这个空指针异常。

 Root cause of ServletException
java.lang.NullPointerException
at javax.faces.component.UIViewRoot.getRendersChildren(UIViewRoot.java:1043)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1855)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:456)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:655)
at weblogic.servlet.internal.StubSecurityHelper$ServletServiceAction.run(StubSecurityHelper.java:280)
at weblogic.servlet.internal.StubSecurityHelper$ServletServiceAction.run(StubSecurityHelper.java:254)
at weblogic.servlet.internal.StubSecurityHelper.invokeServlet(StubSecurityHelper.java:136)
at weblogic.servlet.internal.ServletStubImpl.execute(ServletStubImpl.java:346)
at weblogic.servlet.internal.TailFilter.doFilter(TailFilter.java:25)
at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:79)
at gov.ny.health.hcs.fwrk.security.HCSSecurityFilter.redirectToFilterChain(HCSSecurityFilter.java:304)
at gov.ny.health.hcs.fwrk.security.HCSSecurityFilter.doFilter(HCSSecurityFilter.java:260)
at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:79)
at oracle.security.jps.ee.http.JpsAbsFilter$1.run(JpsAbsFilter.java:137)
at java.security.AccessController.doPrivileged(Native Method)
at oracle.security.jps.util.JpsSubject.doAsPrivileged(JpsSubject.java:315)
at oracle.security.jps.ee.util.JpsPlatformUtil.runJaasMode(JpsPlatformUtil.java:460)
at oracle.security.jps.ee.http.JpsAbsFilter.runJaasMode(JpsAbsFilter.java:120)
at oracle.security.jps.ee.http.JpsAbsFilter.doFilter(JpsAbsFilter.java:217)
at oracle.security.jps.ee.http.JpsFilter.doFilter(JpsFilter.java:81)
at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:79)
at oracle.dms.servlet.DMSServletFilter.doFilter(DMSServletFilter.java:220)
at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:79)
at weblogic.servlet.internal.RequestEventsFilter.doFilter(RequestEventsFilter.java:27)
at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:79)
at weblogic.servlet.internal.WebAppServletContext$ServletInvocationAction.wrapRun(WebAppServletContext.java:3436)
at weblogic.servlet.internal.WebAppServletContext$ServletInvocationAction.run(WebAppServletContext.java:3402)
at weblogic.security.acl.internal.AuthenticatedSubject.doAs(AuthenticatedSubject.java:321)
at weblogic.security.service.SecurityManager.runAs(SecurityManager.java:120)
at weblogic.servlet.provider.WlsSubjectHandle.run(WlsSubjectHandle.java:57)
at weblogic.servlet.internal.WebAppServletContext.doSecuredExecute(WebAppServletContext.java:2285)
at weblogic.servlet.internal.WebAppServletContext.securedExecute(WebAppServletContext.java:2201)
at weblogic.servlet.internal.WebAppServletContext.execute(WebAppServletContext.java:2179)
at weblogic.servlet.internal.ServletRequestImpl.run(ServletRequestImpl.java:1572)
at weblogic.servlet.provider.ContainerSupportProviderImpl$WlsRequestExecutor.run(ContainerSupportProviderImpl.java:255)
at weblogic.work.ExecuteThread.execute(ExecuteThread.java:311)
at weblogic.work.ExecuteThread.run(ExecuteThread.java:263)

以下是我正在使用的JSF jar的源代码。

       @Override
       public boolean getRendersChildren() {
       boolean value = super.getRendersChildren();

       FacesContext context = FacesContext.getCurrentInstance();

   if (context.getPartialViewContext().isAjaxRequest()) { //line 1043

        value = true;
    }
    return value;
}