Outcommented Facelets code still invokes EL expressions like #{bean.action()} and causes javax.el.PropertyNotFoundException on #{bean.action}

问题

I\'ve the following code snippet in my Facelet:

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

It works fine, but when I outcomment it like this,

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

then it throws the following exception:

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)

When I change the method expression with parentheses as below,

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

Then doesn\'t throw the exception, but it\'s still invoked.

How is this caused and how can I solve it?

回答1:

Look closer at the stack trace. Here's the relevant part:

...
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)
...

It's thus evaluating EL in a comment block (recognizable by CommentInstruction). A comment block is considered as template text. Facelets evaluates by default also EL #{} in template text. It's like as if you're writing <p>#{screenShotBean.takeScreenshot}</p> without any JSF tag.

You've several options:

1. Remove the comment block altogether.

2. Escape EL expressions in the comment by prefixing it with \ as in

   \#{screenShotBean.takeScreenshot}
   

   so that they won't be evaluated.

3. Wrap the entire comment block in <ui:remove> so that it doesn't appear in the component tree (nor in the generated HTML output).

4. Disable parsing of all comments by Facelets by adding the following context parameter to web.xml:

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

   Note that no one comment will end up in generated HTML output this way.

回答2:

In addition to the options BalusC already provided you could also add the attribute rendered="false" to your commandLink.

If you have several components you want to be able to toggle quickly, you might want to consider creating a debug property in a bean or use the project stage:

rendered="#{facesContext.application.projectStage == 'Development'}"

回答3:

You could also use the context parameter that skips comments in your web.xml.

This is the parâmeter:

javax.faces.FACELETS_SKIP_COMMENTS 

来源：https://stackoverflow.com/questions/14692560/outcommented-facelets-code-still-invokes-el-expressions-like-bean-action-an