<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>