Using id=“#{…}” causes java.lang.IllegalArgumentEx

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

Have a look at this example:

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

My problem is that I am getting this error:

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

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

You are right. I am using it inside datatable.

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}" />

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.

You've basically 3 options:

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}" />

Use a plain HTML element:

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

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}" />
```