使用id =“#{...}"导致java.lang.IllegalArgumentException:不允许使用空的id属性 [英] Using id="#{...}" causes java.lang.IllegalArgumentException: Empty id attribute is not allowed

问题描述

我需要通过为JSF中的某些组件生成动态ID来解决我的问题.

I need to solve my problem with generating dynamic ID for some components in JSF.

看看这个例子:

<h:outputText id="#{bean.id}" value="#{bean.value}" />

我的问题是出现此错误:

My problem is that I am getting this error:

java.lang.IllegalArgumentException: Empty id attribute is not allowed

当我查看生成的HTML输出时，组件的ID为空.这是怎么引起的，我该如何解决?

The ID of the component is empty when I look at generated HTML output. How is this caused and how can I solve it?

推荐答案

您是正确的.我在数据表中使用它.

然后，如果#{bean}表示var属性中声明的当前迭代对象，则可能发生这种情况，

Then this can happen if the #{bean} represents the currently iterated object as declared in var attribute like so:

<h:dataTable value="#{someBean.beans}" var="bean">
    <h:column>
        <h:outputText id="#{bean.id}" value="#{bean.value}" />

JSF组件的id(和binding)属性在视图构建期间(即需要组成JSF组件树的那一刻)进行评估.但是，#{bean}仅在视图渲染期间可用，此时<h:dataTable>需要遍历所有对象并为每个对象生成HTML表行.因此，#{bean}在视图构建期间不可用，并评估为null，最终将EL强制为空字符串.因此是例外java.lang.IllegalArgumentException: Empty id attribute is not allowed.

The id (and binding) attribute of a JSF component is evaluated during view build time, that moment when the JSF component tree needs to be composed. However, the #{bean} is only available during view render time, that moment when <h:dataTable> needs to iterate over all objects and generate HTML table rows for each of them. The #{bean} is thus not available during view build time and evaluates to null which ultimately gets EL-coerced to an empty string. And hence the exception java.lang.IllegalArgumentException: Empty id attribute is not allowed.

您基本上有3个选择:

1. 使用视图构建时间标签来遍历集合.您只需要自己编写所有HTML样板即可:

1. Use a view build time tag instead to iterate over a collection. You'd only need to write all HTML boilerplate yourself:

<table>
    <c:forEach items="#{someBean.beans}" var="bean">
        <tr>
            <td>
                <h:outputText id="#{bean.id}" value="#{bean.value}" />

使用纯HTML元素:

Use a plain HTML element:

<h:dataTable value="#{someBean.beans}" var="bean">
    <h:column>
        <span id="#{bean.id}">#{bean.value}</span>

不设置动态ID，而是固定ID. JSF将通过在表的行索引前添加HTML输出来确保其唯一性:

Don't set a dynamic ID, but a fixed ID. JSF will ensure of uniqueness in HTML output by prepending it with row index of the table:

<h:dataTable value="#{someBean.beans}" var="bean">
    <h:column>
        <h:outputText id="id" value="#{bean.value}" />

另请参见:

• JSF2 Facelets中的JSTL ...有意义吗?(您可以用动态ID"替换"JSTL")

See also:

• JSTL in JSF2 Facelets... makes sense? (you can substitute "JSTL" with "dynamic ID")

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