似乎无法从 ViewScoped 构造函数重定向答案

【问题标题】：Can't seem to redirect from a ViewScoped constructor似乎无法从 ViewScoped 构造函数重定向
【发布时间】：2010-07-19 10:22:06
【问题描述】：

如果我们没有相关页面所需的信息，我无法从视图范围的 bean 进行重定向。 @PostContruct 中的日志条目在与尝试呈现自身而不是遵循我的重定向的视图相关的 NPE 之前的日志中可见。为什么会忽略重定向？

这是我的代码：

@ManagedBean
public class WelcomeView {

    private String sParam;
    private String aParam;

    public WelcomeView() {
        super();

        sParam = getURL_Param("surveyName");
        aParam = getURL_Param("accountName");

        project = fetchProject(sParam, aParam);

    }

    @PostConstruct
    public void redirectWithoutProject() {
        if (null == project) {
            try {
                logger.warn("NO project [" + sParam + "] for account [" + aParam + "]");
                FacesContext fc = FacesContext.getCurrentInstance();
                fc.getExternalContext().redirect("/errors/noSurvey.jsf");
                return;
            } catch (Exception e) {
                e.printStackTrace();
            }
        }        
    }

    ....

    public boolean getAuthenticated() {
        if (project.getPasswordProtected()) {
            return enteredPassword.equals(project.getLoginPassword());
        } else return true;
    }

}

这是堆栈跟踪：

SEVERE: Error Rendering View[/participant/welcome.xhtml]
javax.el.ELException: /templates/participant/welcome.xhtml @80,70 rendered="#{welcomeView.authenticated}": Error reading 'authenticated' on type com.MYCODE.general.controllers.participant.WelcomeView
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:107)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:190)
    at javax.faces.component.UIComponentBase.isRendered(UIComponentBase.java:416)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1607)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1616)
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:168)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:848)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1613)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1616)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1616)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:380)
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:126)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:127)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:313)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at com.MYCODE.general.filters.StatsFilter.doFilter(StatsFilter.java:28)
    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.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:433)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:568)
    at org.apache.catalina.authenticator.SingleSignOn.invoke(SingleSignOn.java:421)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
    at java.lang.Thread.run(Thread.java:637)
Caused by: java.lang.NullPointerException
    at com.MYCODE.general.controllers.participant.WelcomeView$$M$863c205f.getAuthenticated(WelcomeView.java:127)
    at com.MYCODE.general.controllers.participant.WelcomeView$$A$863c205f.getAuthenticated(<generated>)
    at com.MYCODE.general.controllers.participant.WelcomeView.getAuthenticated(WelcomeView.java:125)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:62)
    at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:53)
    at com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:72)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:118)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186)
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:102)
    ... 33 more

【问题讨论】：

注意，我已经尝试将相同的功能直接放入构造函数而不是@PostConstruct。我也尝试过 dispatch 和 sendRedirect。
请更新您的问题以包含 NPE 的堆栈跟踪。
我添加了一个堆栈跟踪。它指的是getAuthenticated方法，NPE是因为项目为空，所以我也添加了它。所以我从你想要看到从构造函数重定向的堆栈是一个有效的事情，我的代码很好，那么问题出在其他地方吗？

标签： java jsf jsf-2

【解决方案1】：

已解决！问题是我没有意识到无论我的重定向如何，页面都会被完全编译，因此 null 项目实际上是一个问题。对 getAuthenticated 的调用（实际上应该是 isAuthenticated，但这不会造成任何真正的麻烦）失败，因为 project 为 null（如预期的那样），我的逻辑是，如果重定向发生在构造函数中，则不应调用它。这是谎言。可以在构造函数中调用重定向，但 bean 和视图都是在重定向实际发生之前构建的。

【讨论】：