如何在EL JSF中使用方括号 [英] How to use square bracket in EL JSF

问题描述

我见过人们在JSF中使用方括号，但不确定我是否正确理解其用法.所以也许JSF专家可以帮助我理解它

I have seen people using square bracket in JSF, and I am not sure if I understand its use correctly. So maybe an JSF guru can help me understand it

1.可以说我有这个

#{bean.x}

并且x是二维数组(x [] [])，如何使用EL显示x[0]?我想在这种情况下我需要使用方括号.我想我使用#{bean.x[0]}，但是出现异常.

and x is a two dimensional array (x[][]), how do I display x[0] using EL? I would imagine that I need to use square bracket in this case. I think I use #{bean.x[0]}, but I got exception.

2.第二种情况来自BalusC代码将参数传递给复合组件动作属性

2.The second scenario is from BalusC code Pass Argument to a composite-component action attribute

<composite:interface>
   <composite:attribute name="bean" type="java.lang.Object" />
   <composite:attribute name="action" type="java.lang.String" />
   <composite:attribute name="property" type="java.lang.String" />
</composite:interface>
<composite:implementation>
   <h:commandButton value="Remove" action="#{cc.attrs.bean[cc.attrs.action]}">
      <f:setPropertyActionListener target="#{cc.attrs.bean[cc.attrs.property]}" value="Somestring" />
   </h:commandButton>
</composite:implementation>

我了解代码在做什么，并且效果很好，但是如果有人可以解释这种情况下方括号的用途，我将不胜感激.非常感谢

I understand what the code is doing and it works beautifully, but I would appreciate if someone can explain what is the use of the square bracket in this case. Thank you very much

推荐答案

我想我使用#{bean.x[0]}，但出现异常.

I think I use #{bean.x[0]}, but I got exception.

很遗憾，您没有共享例外详细信息.但是，只要有一个getX()方法返回给定索引确实存在的非null数组，这应该就可以了.

It's unfortunate that you didn't share the exception details. But this should just work, provided that there's a getX() method which returns a non-null array of which the given index really exists.

第二种情况是从BalusC代码传递参数到复合组件操作属性

在这种特殊情况下，大括号符号[]使您可以使用动态属性名称或操作方法名称.以下内容当然不起作用

In this particular case, the brace notation [] enables you to use a dynamic property name or action method name. The following of course don't work

#{cc.attrs.bean.cc.attrs.action}

它只会尝试调用bean.getCc().getAttrs().action().

在Map<K, V>上也使用大括号符号.它允许您指定包含点的键(这些键又不应被EL评估为属性)

The brace notation is also used on Map<K, V>. It allows you to specify keys which contain dots (which in turn shouldn't be EL-evaluated as properties)

#{bean.map['key.with.dots']}

当然，它还允许您指定动态地图键:

It of course also allows you to specify a dynamic map key:

#{bean.map[otherBean.mapKey]}

另请参见:

• 我们的EL Wiki页面

See also:

• Our EL wiki page

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