jsf - 已淘汰的Facelets代码仍会调用＃{bean.action()}之类的EL表达式，并在＃{bean.action}上导致javax.el.PropertyNotFoundException

Question

我的Facelet中有以下代码段:

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

它工作正常，但是当我这样评价它时，

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

然后会引发以下异常:

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)

当我如下更改带有括号的方法表达式时，

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

然后不引发异常，但仍会调用它。

这是怎么引起的，我该如何解决？

Answer 1

仔细查看堆栈跟踪。这是相关的部分:

...
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，它将在注释块(可通过 CommentInstruction识别)中评估EL。注释块被视为模板文本。默认情况下，Facelets还会评估模板文本中的EL #{}。就像您在编写没有任何JSF标签的 <p>#{screenShotBean.takeScreenshot}</p>一样。

您有几种选择:

完全删除注释块。

在注释中使用\前缀在注释中转义EL表达式

\#{screenShotBean.takeScreenshot}

这样就不会对其进行评估。

将整个注释块包装在 <ui:remove> 中，以便它不会出现在组件树中(也不出现在生成的HTML输出中)。

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

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

请注意，没有任何注释将以这种方式最终出现在生成的HTML输出中。