关于struts2的checkboxlist、select等标签发生could not be resolved as a collection/array/ma

解决办法 ：

//解决办法是把初始化list的工作放到prepare拦截器中，因为prepare是在validate拦截器之前执行，即实现prepareble接口：
public class RoleAction extends ActionSupport implements Preparable{
    @Override
    public void prepare() throws Exception {
        //初始化list
    }
}

org.apache.jasper.JasperException: tag 'checkboxlist', field 'list', name 'selectRoleId': The requested list key 'roles' could not be resolved as a collection/array/map/enumeration/iterator type. Example: people or people.{name} - [unknown location]
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:541)

//http://www.blogjava.net/landor2004/archive/2009/04/11/265016.html