如何在EL表达式中串联字符串? [英] How to concatenate Strings in EL expression?

问题描述

我需要为<h:commandButton>创建一个回调，而作为参数，我需要传递一个由字符串连接且带有外部参数id的参数:

I need to create a callback for <h:commandButton> while as a parameter I need to pass an argument that is string-concatenated with an external parameter id:

我尝试嵌套类似这样的EL表达式:

I tried nesting an EL expression something like this:

<h:commandButton ... action="#{someController.doSomething('#{id}SomeTableId')}" />

但是，此操作因EL异常而失败.什么是正确的语法/方法来做到这一点?

However this failed with an EL exception. What is a right syntax/approach to do this?

推荐答案

如果您已经在使用EL 3.0(Java EE 7； WildFly，Tomcat 8，GlassFish 4等)，则可以使用新的+=运算符:

If you're already on EL 3.0 (Java EE 7; WildFly, Tomcat 8, GlassFish 4, etc), then you could use the new += operator for this:

<h:commandButton ... action="#{someController.doSomething(id += 'SomeTableId')}" />

但是，如果您尚未使用EL 3.0，并且左手是真正的java.lang.String实例(因此不是例如java.lang.Long)，请使用EL 2.2功能调用带参数的直接方法，然后应用于String#concat():

If you're however not on EL 3.0 yet, and the left hand is a genuine java.lang.String instance (and thus not e.g. java.lang.Long), then use EL 2.2 capability of invoking direct methods with arguments, which you then apply on String#concat():

<h:commandButton ... action="#{someController.doSomething(id.concat('SomeTableId'))}" />

或者，如果您尚未使用EL 2.2，请使用JSTL <c:set>创建一个新的EL变量，其串联值仅内嵌在value中:

Or if you're not on EL 2.2 yet, then use JSTL <c:set> to create a new EL variable with the concatenated values just inlined in value:

<c:set var="tableId" value="#{id}SomeTableId" />
<h:commandButton ... action="#{someController.doSomething(tableId)}" />

另请参见:

• EL中用于动态ResourceBundle键的字符串连接

See also:

• String concatenation in EL for dynamic ResourceBundle key

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