How to use && in EL boolean expressions in Facelets?

问题

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}" />

But I keep getting:

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

回答1:

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}"

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

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

See also:

• Java EE 6 tutorial - Operators in EL

---

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}"

回答2:

In addition to the answer of BalusC, use the following Java RegExp to replace && with and:

Search:  (#\{[^\}]*)(&&)([^\}]*\})
Replace: $1and$3

You have run this regular expression replacement multiple times to find all occurences in case you are using >2 literals in your EL expressions. Mind to replace the leading # by $ if your EL expression syntax differs.

来源：https://stackoverflow.com/questions/8552901/how-to-use-in-el-boolean-expressions-in-facelets