使用&& EL中的错误会导致错误:实体名称必须紧跟在'&'之后在实体参考中 [英] Using && in EL results in error: The entity name must immediately follow the '&' in the entity reference
问题描述
我正在尝试在jsf中使用的el表达式中使用条件表达式，但是它不起作用.
I'm trying to use a conditional expression in an el expression used in jsf, but it does not work.
<h:outputText value="#{(sel.description !=null) && (sel.description !='') ? sel.description : 'Empty description'} - "/>
但是它不起作用，编译器说:
but it does not work, the compiler says:
已跟踪错误[行:118]实体名称必须紧跟在 '&'在实体参考中.
Error Traced[line: 118] The entity name must immediately follow the '&' in the entity reference.
您有什么建议吗? 谢谢！
Do you have any suggestions? Thank you!
推荐答案
您似乎正在使用Facelets(这很好).但是，它是一种基于XML的视图技术.您在Facelets中编写的所有内容都必须是语法上有效的XML. &在XML中是一个特殊字符，表示实体的开头，例如&，<，>， 等
You seem to be using Facelets (which is perfectly fine). It's however a XML based view technology. Everything which you write in Facelets has to be syntactically valid XML. The & is in XML a special character denoting the start of an entity like &, <, >,  , etc.
如果您想按XML形式表示&，则必须将其替换为&.
If you would like to represent the & as-is in XML, then you'd have to replace it by &.
<h:outputText value="#{(sel.description !=null) && (sel.description !='') ? sel.description : 'Empty description'} - "/>
但是，这不太容易理解，您希望为此使用替代EL运算符and(另请参见EL中的运算符以了解EL中所有可用运算符的概述):
However, that's not pretty readable, you would rather like to use the alternative EL operator and for this (see also operators in EL for an overview of all available operators in EL):
<h:outputText value="#{(sel.description !=null) and (sel.description !='') ? sel.description : 'Empty description'} - "/>
总而言之，这反过来很笨拙，因为有一个更简单的empty关键字用于测试空和空.在您的特定情况下，可以将其用作:
All with all, this is in turn pretty clumsy as there's a simpler empty keyword for the purpose of testing both nullness and emptiness. This can in your particular case be used as:
<h:outputText value="#{not empty sel.description ? sel.description : 'Empty description'} - "/>
或
<h:outputText value="#{!empty sel.description ? sel.description : 'Empty description'} - "/>
或
<h:outputText value="#{empty sel.description ? 'Empty description' sel.description} - "/>
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