有条件地显示 JSF 组件 [英] Conditionally displaying JSF components
问题描述
首先，我是 Java EE 的新手，具有强大的 ASP .NET 开发背景.我已经浏览了网络，我可能会错过这个，但似乎没有关于如何将支持 bean 类连接到 JSF 组件的简单直接的教程.
First, I am new to Java EE, came from a strong ASP .NET development background. I have gone through the net, and I might miss this but it seems like there is no simple and straight-to-the-point tutorials on how I could connect backing bean class to a JSF components.
一个很好的例子是这样的，目前我正在尝试创建一个 JSF 页面，其中有一组链接作为菜单栏和一组表单.我打算做的是，当单击链接时，将呈现特定的表单.
A good example is like this, currently I am trying to create a JSF page where there is a set of links as menu bar and a set of forms. What I am planning to do is, when clicking a link, a particular form will be rendered.
在 ASP.NET 中，我可以轻松地检索元素，然后将属性设置为可显示.我想知道在 JSF 中是否有简单的方法(见鬼，甚至任何方法)来做到这一点.
In ASP.NET, I could easily retrieve the element and then set the attribute to be displayable. I am wondering if there is easy way (heck, even any way) to do this in JSF.
表单已在页面中，只需在单击特定链接时将render"属性设置为 true.
The forms is already in the page, it is just a matter of setting the "render" attribute to true when I click a particular link.
推荐答案
是的，使用 rendered 属性.
<h:form rendered="#{some boolean condition}">
您通常将其绑定到模型上，而不是让模型抓取组件并对其进行操作.
You usually tie it to the model rather than letting the model grab the component and manipulate it.
例如
<h:form rendered="#{bean.booleanValue}" />
<h:form rendered="#{bean.intValue gt 10}" />
<h:form rendered="#{bean.objectValue eq null}" />
<h:form rendered="#{bean.stringValue ne 'someValue'}" />
<h:form rendered="#{not empty bean.collectionValue}" />
<h:form rendered="#{not bean.booleanValue and bean.intValue ne 0}" />
<h:form rendered="#{bean.enumValue eq 'ONE' or bean.enumValue eq 'TWO'}" />
注意基于关键字的EL运算符的重要性，例如gt、ge、le 和 lt 代替 >、>=、<= 和 < 作为尖括号 < 和 > 被保留XML 中的字符.另请参阅此相关问答:解析 XHTML 时出错:元素的内容必须由格式正确的字符数据或标记组成.
Note the importance of keyword based EL operators such as gt, ge, le and lt instead of >, >=, <= and < as angle brackets < and > are reserved characters in XML. See also this related Q&A: Error parsing XHTML: The content of elements must consist of well-formed character data or markup.
至于您的具体用例，让我们假设链接正在传递如下参数:
As to your specific use case, let's assume that the link is passing a parameter like below:
<a href="page.xhtml?form=1">link</a>
然后您可以显示如下表格:
You can then show the form as below:
<h:form rendered="#{param.form eq '1'}">
(#{param} 是一个隐式 EL 对象，引用一个表示请求参数的 Map)
(the #{param} is an implicit EL object referring to a Map representing the request parameters)
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