事件监听器，监听同一个用户重复登陆

事件监听器

一；监听同一个用户重复登陆

   下面以一个用户登陆列；来讲解sessiong监听器的原理和用法

1，  创建一个容器来封装登陆用户的信息，代码如下：

package org.luojs.lister; import java.util.ArrayList; import java.util.List; import com.luojs.struts.form.UserForm; public class ListLister {        private static List list = new ArrayList();        public ListLister(){                 super();     }       public List getList(){         return list;     }     public void addList(UserForm user){         this.list.add(user);     }     public void remove(int n){         list.remove(n);     }     /**      * 判断新来的用户是否也存在，如果存在，返回ture      * @param user      * @return true;      */     public boolean isExec(UserForm user){               boolean flag = false;         for (int i = 0; i < list.size(); i++) {             UserForm userForm = (UserForm)list.get(i);             if(userForm.getUsername().equals(user.getUsername())){                 flag = true;                 break;             }         }               return flag;     } }

 

 

 

2，  监听器需要实现一个接口（implements HttpSessionAttributeListener），

package org.luojs.lister;   import javax.servlet.http.HttpSessionAttributeListener; import javax.servlet.http.HttpSessionBindingEvent;   import com.luojs.struts.form.UserForm;   public class SessionLister implements HttpSessionAttributeListener{             /* 创建一个 ListLister 来封装登陆的用户对象 */         private static ListLister list = new ListLister();         /**          *  实现attributeAdded 方法，当用户向session 中添加用户对象时，触法次方法          *  这个方法将把该用户的信息保存到 ListLister 中          */        public void attributeAdded(HttpSessionBindingEvent arg0) {            System.out.println("wcome you ! add ");            if(arg0.getName().equals("username")){               System.out.println("wcome you ! add sssssssssssssss");               UserForm answer = (UserForm)arg0.getValue();               list.addList(answer);            }                 }         /**          * 当有用户登陆来时，判断他是否已存在，如果存在，让他出去          */        public void attributeRemoved(HttpSessionBindingEvent arg0) {            System.out.println("wcome come your removed ");              int n=0;              UserForm p1 = (UserForm)arg0.getValue();               for(int i=0;i<list.getList().size();i++){               UserForm p2 = (UserForm)list.getList().get(i);               if(p1.getUsername().equals(p2.getUsername())){                    n=i;                    break;               }               }               list.getList().remove(n);        }        public void attributeReplaced(HttpSessionBindingEvent arg0) {        }      }

 

3, 处理用户提交时的代码：（这是在Struts 中的验证）

public ActionForward longin(ActionMapping mapping, ActionForm form,            HttpServletRequest request, HttpServletResponse response) {        UserForm userForm = (UserForm) form;// TODO Auto-generated method stub        boolean flag = false;        ListLister listuser = new ListLister();        HttpSession session = request.getSession();        String user = userForm.getUsername();        String pass = userForm.getPassword();        flag = userbiz.selectByName(user, pass);        if (flag) {            if (!listuser.isExec(userForm)) {               session.setAttribute("username", userForm);               return mapping.findForward("indexto");// 如果登陆成功，把权限转交给JobsAction            } else  {               error = "<h3><li>Sorry! 此用户也存在，不能重复登陆 ！</h3>";            }        } else {            error = "<h3><li> sorry ! this is your userName or passwrod error !</h3>";        }        request.setAttribute("error", error);        return mapping.findForward("backToIndex");// 回到登陆页     }

3，  在web.xml中注册监听器；

<listener>   <listener-class>org.luojs.lister.SessionLister</listener-class>     </listener>