关于struts中bean的使用？

[flylyke]

代码如下：
<%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean" %>
<%@ taglib uri="/WEB-INF/struts-html.tld" prefix="html" %>
<%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic" %>
<%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>
<jsp:useBean id="departmentBean" class="struts.DepartmentBean" scope="session"/>
<c:set var="departments" value="${departmentBean.departments}"/>
<html:select property="employee.department" name="employeeForm">
<html:options collection="departments" property="id"labelProperty="name"/>
</html:select>
departmentbBean.departments返回的是collection类型的值。
但运行时出现：javax.servlet.jsp.JspException: Cannot find bean under name departments
我调了好久，不知道什么原因。快没脾气了。上来问问各位大侠