<form action ="<%=request.getContextPath()%>/UserWXPServlet" method = "post"> 
  用户名š<input type = "text" name = "username"/><br/> 
  密码š<input type = "text" name = "password"/><br/> 
  <input type = "submit" value ="提交"/> 
</form> 

private String username; 
private String password; 
public User() { 
} 
public User(String user, String password) { 
  super(); 
  this.username = user; 
  this.password = password; 
} 
public String getUsername() { 
  return username; 
} 
public void setUsername(String username) { 
  this.username = username; 
} 
public String getPassword() { 
  return password; 
} 
public void setPassword(String password) { 
  this.password = password; 
} 

public boolean dologin(User user){ 
    Properties pro = new Properties(); 
    InputStream is = UserWXPServlet.class.getClassLoader().getResourceAsStream("user_wxp.properties"); 
    String password = null; 
    System.out.println(is+"--------->"+pro); 
    if(user==null){ 
      return false;  
    } 
    try { 
      pro.load(is); 
      password = pro.getProperty(user.getUsername()); 
      if(user.getPassword()!=null&&user.getPassword().equals(password)){ 
        System.out.println("登陆成功"); 
        return true; 
      } 
    } catch (IOException e) { 
      e.printStackTrace(); 
    }finally{ 
      if(is!=null){ 
        try { 
          is.close(); 
        } catch (IOException e) { 
          e.printStackTrace(); 
        } 
      } 
    } 
    return false; 
  } 

/** 
   * 每一个用户存放一个session。便于各种操作！！！ 
   */ 
  public static Map<String, HttpSession> mapSession = new HashMap<String,HttpSession>(); 
用户退出的代码（必须飞废除session或是remove相应的用户对象）：
[java] view plain copy
public static void userLogout(String username){ 
  if(mapSession.get(username)!=null){ 
    //得到需要退出的用户的session 
    HttpSession session = mapSession.get(username); 
    //在map<username,session>中移除该用户，记住想要退出该用户，必须将该session废除或是remove掉user 
    mapSession.remove(username); 
    //得到session的所属性合集 
    Enumeration e = session.getAttributeNames(); 
    //删除所有属性 
    while(e.hasMoreElements()){ 
      String sessionName = (String) e.nextElement(); 
      session.removeAttribute(sessionName); 
    } 
    //废除该session 
    session.invalidate(); 
  } 
} 

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
  String username = request.getParameter("username"); 
  String password = request.getParameter("password"); 
  User user = new User(username, password); 
  UserService userService = new UserService(); 
  HttpSession session = request.getSession(); 
  if(userService.dologin(user)){ 
    //登录成功之后将用户插入到session中 
    session.setAttribute("user", user); 
    if(cheackSession(username)){ 
      //如果该session在此之前已经存在，则将该用户进行退出操作 
      DbUtil.userLogout(username); 
    } 
    //将新的session存放到map<username,session>中 
    DbUtil.mapSession.put(username, session); 
    //操作成功，跳转，此处最好为重定向，让别人知道登录成功了 
    request.getRequestDispatcher("login").forward(request, response); 
    return ; 
  } 
  //此处跳转到失败页面，如果读者有兴趣，可以自行添加 
} 

/** 
 * 检查是否已经含有此session 
 * @param username 
 * @return true:已经存在，该删！ false：未存在 
 */ 
private boolean cheackSession(String username){ 
  HttpSession session = DbUtil.mapSession.get(username); 
  if(session!=null){ 
    return true; 
  } 
  return false; 
} 

<servlet> 
  <description> 
  用于测试 ，用户不可重复登录 
  </description> 
  <display-name>UserWXPServlet</display-name> 
  <servlet-name>UserWXPServlet</servlet-name> 
  <servlet-class>com.fingard.rabbit.wxp_test.Servlet.UserWXPServlet</servlet-class> 
</servlet> 
<servlet-mapping> 
  <servlet-name>UserWXPServlet</servlet-name> 
  <url-pattern>/UserWXPServlet</url-pattern> 
</servlet-mapping>