仅当未渲染另一个组件时才如何渲染组件？

到目前为止，标题中所述的问题可以具体回答为：

<rich:panel binding="#{panel1}" ...>    ...</rich:panel><rich:panel binding="#{panel2}" ...>    ...</rich:panel><rich:panel binding="#{panel3}" ...>    ...</rich:panel><rich:panel ... rendered="#{not panel1.rendered and not panel2.rendered and not panel3.rendered}">    ...</rich:panel>

但是，在这种特殊情况下，最好将那些冗长的表达式用别名别名

<c:set>

<c:set var="android" value="#{fn:containsIgnoreCase(header['User-Agent'], 'Android')}" scope="request" /><c:set var="iPhone" value="#{fn:containsIgnoreCase(header['User-Agent'], 'iPhone')}" scope="request" /><c:set var="blackBerry" value="#{fn:containsIgnoreCase(header['User-Agent'], 'BlackBerry')}" scope="request" /><rich:panel ... rendered="#{android}">    ...</rich:panel><rich:panel ... rendered="#{iPhone}">    ...</rich:panel><rich:panel ... rendered="#{blackBerry}">    ...</rich:panel><rich:panel ... rendered="#{not android and not iPhone and not blackBerry}">    ...</rich:panel>

请注意，有一种通过隐式

#{header}