如何在JSF页面中通过EL将数据放入视图范围

Question

在我的JSF页面中,这有效:

${requestScope.put('test', 'data')}
${requestScope.get('test')}

这会导致异常:

${viewScope.put('test', 'data')}
${viewScope.get('test')}

例外:

java.lang.NullPointerException
    javax.el.BeanELResolver.invoke(BeanELResolver.java:159)
    javax.el.CompositeELResolver.invoke(CompositeELResolver.java:84)
    org.apache.el.parser.AstValue.getValue(AstValue.java:157)
    org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:184)
    com.sun.faces.facelets.el.ELText$ELTextVariable.writeText(ELText.java:238)
    com.sun.faces.facelets.el.ELText$ELTextComposite.writeText(ELText.java:154)
    com.sun.faces.facelets.compiler.TextInstruction.write(TextInstruction.java:85)
    com.sun.faces.facelets.compiler.UIInstructions.encodeBegin(UIInstructions.java:82)
    com.sun.faces.facelets.compiler.UILeaf.encodeAll(UILeaf.java:183)
    javax.faces.render.Renderer.encodeChildren(Renderer.java:176)
    javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:889)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
    com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:456)
    com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
    com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
    com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

如何requestScope在JSF页面以外使用？我当然可以有一个视图范围的bean,但我认为我可以直接使用范围变量.我有Mojarra 2.2.10的Tomcat 8.0.21.

Answer 1

这不是从Facelets模板中将数据放入特定范围的正确方法.

你应该用<c:set>它.

将数据放入请求范围:

<c:set var="test" value="data" scope="request" />
..
#{test}

将数据放入视图范围:

<c:set var="test" value="data" scope="view" />
..
#{test}

该scope属性还支持session和application.

将数据放入Flash作用域的方式略有不同:

<c:set target="#{flash}" property="test" value="data" />
...
#{flash.test}