Struts2 validation.xml 正则表达式不起作用

<validators>
<field name="username">
<field-validator type="requiredstring">
<param name="trim">true</param>
<message>用户名不能为空</message>
</field-validator>
<field-validator type="regex">
<param name="regexExpression"><![CDATA[(\w{4,20})]]></param>
<message>长度为4-25</message>
</field-validator>
</field>

<field name="password">
<field-validator type="requiredstring">
<param name="trim">true</param>
<message>密码不能为空</message>
</field-validator>
<field-validator type="regex">
<param name="regexExpression"><![CDATA[(\w{4,20})]]></param>
<message>密码4-25</message>
</field-validator>
</field>
</validators>

修改：

<param name="expression"><![CDATA[(\w{4,25})]]></param>参数名字改为regexExpression了<param name="regexExpression"><![CDATA[(\w{4,25})]]></param>