Outcommented Facelets代码仍调用#{bean.action()}之类的EL表达式,并在#{bean.action}上导致javax.el.PropertyNotFoundException

Question

我的Facelet中有以下代码片段:

<h:commandLink id="cmdbtn">
    <f:ajax event="click" execute="@form"
            listener="#{screenShotBean.takeScreenshot}" />
</h:commandLink>

它工作正常,但当我像这样取消它,

<!--        <h:commandLink id="cmdbtn"> -->
<!--            <f:ajax event="click" execute="@form" -->
<!--                    listener="#{screenShotBean.takeScreenshot}" /> -->
<!--        </h:commandLink> -->

然后它抛出以下异常:

javax.el.PropertyNotFoundException: Property 'takeScreenshot' not found on type monstage.test.com.ScreenShotBean
    at javax.el.BeanELResolver$BeanProperties.get(BeanELResolver.java:237)
    at javax.el.BeanELResolver$BeanProperties.access$400(BeanELResolver.java:214)
    at javax.el.BeanELResolver.property(BeanELResolver.java:325)
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:85)
    at com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176)
    at com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:169)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
    at com.sun.faces.facelets.el.ELText$ELTextVariable.toString(ELText.java:217)
    at com.sun.faces.facelets.el.ELText$ELTextComposite.toString(ELText.java:157)
    at com.sun.faces.facelets.compiler.CommentInstruction.write(CommentInstruction.java:77)
    at com.sun.faces.facelets.compiler.UIInstructions.encodeBegin(UIInstructions.java:82)
    at com.sun.faces.facelets.compiler.UILeaf.encodeAll(UILeaf.java:183)
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:168)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1779)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:424)
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:125)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121)
    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:594)

当我用括号更改方法表达式时,如下所示,

<!--        <h:commandLink id="cmdbtn"> -->
<!--            <f:ajax event="click" execute="@form" -->
<!--                    listener="#{screenShotBean.takeScreenshot()}" /> -->
<!--        </h:commandLink> -->

然后不抛出异常,但它仍然被调用.

这是怎么造成的,我该如何解决？

Answer 1

仔细观察堆栈跟踪.这是相关部分:

...
org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
com.sun.faces.facelets.el.ELText$ELTextVariable.toString(ELText.java:217)
com.sun.faces.facelets.el.ELText$ELTextComposite.toString(ELText.java:157)
com.sun.faces.facelets.compiler.CommentInstruction.write(CommentInstruction.java:77)
...

因此,它在评论块中评估EL(可识别CommentInstruction).注释块被视为模板文本.Facelets默认情况下还会#{}在模板文本中评估EL .这就像你在<p>#{screenShotBean.takeScreenshot}</p>没有任何JSF标签的情况下写作一样.

你有几个选择:

1. 完全删除评论块.

2. 用前缀逃避它在评论EL表达式\作为

   \#{screenShotBean.takeScreenshot}
   

   这样他们就不会被评估.

3. 将整个注释块包装起来<ui:remove>,使其不出现在组件树中(也不会出现在生成的HTML输出中).

4. 通过将以下上下文参数添加到Facelets,禁用Facelets 对所有注释的解析web.xml:

   <context-param>
       <param-name>javax.faces.FACELETS_SKIP_COMMENTS</param-name>
       <param-value>true</param-value>
   </context-param>
   

   请注意,没有任何评论会以这种方式生成HTML输出.