Conditionally displaying JSF components

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.

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.

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.

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.

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最佳答案

Yes, use the rendered attribute.

<h:form rendered="#{some boolean condition}">

You usually tie it to the model rather than letting the model grab the component and manipulate it.

E.g.

<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'}" />

Note the importance of ge0 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: ge1.

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>

You can then show the form as below:

<h:form rendered="#{param.form eq '1'}">

(the #{param} is an implicit EL object referring to a Map representing the request parameters)

See also:

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In addition to previous post you can have

<h:form rendered="#{!bean.boolvalue}" />
<h:form rendered="#{bean.textvalue == 'value'}" />

Jsf 2.0

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we can render a component in the form, for that we will use 'rendered' attribute

This attribute takes true/false. If the expression evaluates to a true then the specified component will be rendered otherwise it wont render in the screen.

Ex: I want to render a button for some condition.

<p:commandButton id="addCommentsBtn"
value="Add Comments" title="Add Comments"
rendered="#{backingBean.booleanResultOrVariable}">
</p:commandButton>

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