如何使用&&在Facelets的EL布尔表达式中? [英] How to use && in EL boolean expressions in Facelets?

问题描述

我在弄清楚Facelets中EL表达式的处理方法和方法时遇到了一些麻烦. 所以基本上我有:

I am having a little trouble figuring out how to do and's on EL expressions in Facelets. So basically I have:

<h:outputText id="Prompt"
    value="Fobar" 
    rendered="#{beanA.prompt == true && beanB.currentBase !=null}" />

但我不断得到:

已跟踪错误[行:69]实体名称必须紧跟在'&'之后 在实体参考中.

Error Traced[line: 69] The entity name must immediately follow the '&' in the entity reference.

推荐答案

Facelets是一种基于XML的视图技术. &是XML中的特殊字符，表示像以;字符结尾.您需要逃避它，这很丑:

Facelets is a XML based view technology. The & is a special character in XML representing the start of an entity like & which ends with the ; character. You'd need to either escape it, which is ugly:

rendered="#{beanA.prompt == true && beanB.currentBase != null}"

或改用and关键字，这在可读性和可维护性方面是首选:

or to use the and keyword instead, which is preferred as to readability and maintainability:

rendered="#{beanA.prompt == true and beanB.currentBase != null}"

另请参见:

• Java EE 6教程-EL中的运算符

See also:

• Java EE 6 tutorial - Operators in EL

无关与具体问题无关，当表达式已经期望布尔结果时，将布尔值与布尔值进行比较就没有多大意义了.我会摆脱== true:

Unrelated to the concrete problem, comparing booleans with booleans makes little sense when the expression expects a boolean outcome already. I'd get rid of == true:

rendered="#{beanA.prompt and beanB.currentBase != null}"

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