jsf - JSF-ViewParameter 的名称可以是 EL-Expression 吗？

Question

可以写这样的东西吗？

<f:metadata>
    <f:viewParam name="#{constantsBean.viewParameterNameForIds}" value="#{displayBean.technicalId}" />
</f:metadata>

我总是收到 myfaces 错误，我认为它来自 View 参数名称中的 el 表达式。

编辑:完整的堆栈跟踪是:

java.lang.NullpointerException
at org.apache.myfaces.util.AbstractAttributeMap.get(AbstractAttributeMap.java:94)
at javax.faces.component.UIViewParameter.decode(UIViewParameter.java:78)
at javax.faces.component.UIComponentBase.processDecodes(UIComponentBase.java:1176)
at javax.faces.component.UIInput.processDecodes(UIInput.java:178)
at javax.faces.component.UIComponentBase.processDecodes(UIComponentBase.java:1170)
at javax.faces.component.UIComponentBase.processDecodes(UIComponentBase.java:1170)
at javax.faces.component.UIViewRoot._processDecodesDefault(UIViewRoot.java:1316)
at javax.faces.component.UIViewRoot.access$400(UIViewRoot.java:75)
at javax.faces.component.UIViewRoot$ApplyRequestValuesPhaseProcessor.process(UIViewRoot.java:1379)
at javax.faces.component.UIViewRoot._process(UIViewRoot.java:1282)
at javax.faces.component.UIViewRoot.processDecodes(UIViewRoot.java:718)
at org.apache.myfaces.lifecycle.ApplyRequestValuesExecutor.execute(ApplyRequestValuesExecutor.java:34)
at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:171)
at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at org.apache.myfaces.extensions.cdi.jsf2.impl.listener.phase.CodiLifecycleWrapper.execute(CodiLifecycleWrapper.java:95)
at org.apache.myfaces.extensions.validator.core.startup.ExtValLifecycleWrapper.execute(ExtValLifecycleWrapper.java:61)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:189)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1147)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:722)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:449)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:178)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.invokeTarget(WebAppFilterChain.java:125)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:92)
at gid.common.technical.filter.InboundProcessingFilter.doFilter(InboundProcessingFilter.java:46)
at com.ibm.ws.webcontainer.filter.FilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:192)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:89)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:919)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:1016)
at com.ibm.ws.webcontainer.servlet.CacheServletWrapper.handleRequest(CacheServletWrapper.java:87)
at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:883)
at com.ibm.ws.webcontainer.WSWebContainer.handleRequest(WSWebContainer.java:1659)
at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:195)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:452)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewRequest(HttpInboundLink.java:511)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.processRequest(HttpInboundLink.java:305)
at com.ibm.ws.http.channel.inbound.impl.HttpICLReadCallback.complete(HttpICLReadCallback.java:83)
at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:165)
at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:138)
at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:204)
at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:775)
at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:905)
at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1648)

顺便说一句。我正在使用 WebSphere 8 附带的 MyFaces、Myfaces Codi 和 ExtVal。

Answer 1

<f:viewParam> documentation关于 name 说了以下内容属性:

Name | Required | Request-Time | Type
-----+----------+--------------+-------------------------------------------------
name | true     | false        | javax.el.ValueExpression 
     |          |              | (must evaluate to java.lang.String)    

上面写着javax.el.ValueExpression ，不是java.lang.String (就像您在 id 属性上看到的那样，它确实不接受值表达式)。所以，它确实支持 EL。

我不使用 MyFaces，但我刚刚在 Mojarra 上进行了测试，它对我有用。我不确定您到底遇到了什么错误，因为您似乎出于某种原因将其视为不相关的信息，因此在您的问题中没有提及。错误消息通常包含问题的答案。如果您发布完整的错误消息，那么我们也许能够用通俗易懂的语言解释该消息，以便您能够理解该错误，从而解决方案将变得显而易见。例如，它可能有完全不同的原因，甚至可能是 MyFaces 中的错误。