c:forEach inside primefaces(e.g. p:panelgrid) inside ui:repeat

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The transition from the XHTML source code to the generated HTML output is a two-step process.

  1. First, during view build time, the XHTML source code is parsed and turned in a tree of Java UIComponent instances representing the JSF UI component tree, as available by FacesContext#getViewRoot().

  2. Then, during view render time, the JSF UI component tree produces HTML output and writes it to the HTTP resopnse, starting with UIViewRoot#encodeAll() method.

Taghandlers like all JSTL <c:xxx> tags, several JSF <f:xxx> tags and only a few Facelets <ui:xxx> tags run during view build time. UI components like all JSF <h:xxx> tags, several Facelets <ui:xxx> tags and only a few JSF <f:xxx> tags run during view render time.

The <c:forEach> is a taghandler and the <ui:repeat> is an UI component.

In other words, the UI components which are declared inside <c:forEach> are recreated multiple times in the JSF component tree based on <c:forEach items> during view build time which in turn individually produce each their own HTML output during view render time. The UI components which are declared inside <ui:repeat> are created only once in the JSF component tree during view build time which in turn are reused multiple times based on <ui:repeat value> to produce HTML output during view render time.

Your concrete problem is caused by the fact that <ui:repeat var="table"> is only available during view render time, not during view build time. The <c:forEach> is basically retrieving a #{null} as value when it’s about to run during view build time.

You can solve this by replacing the outer <ui:repeat> by <c:forEach>. Although I wonder if you couldn’t better use <ui:repeat><p:dataTable><p:columns> instead.

See also:

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