试试这个...请考虑Session Management登录和注销操作
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
    <servlet>
        <servlet-name>ServletLogic</servlet-name>
        <servlet-class>model.ServletLogic</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>ServletLogout</servlet-name>
        <servlet-class>model.ServletLogout</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ServletLogic</servlet-name>
        <url-pattern>/ServletLogic</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>ServletLogout</servlet-name>
        <url-pattern>/ServletLogout</url-pattern>
    </servlet-mapping>
    <session-config>
        <session-timeout>
            30
        </session-timeout>
    </session-config>
</web-app>
索引.jsp
<%@page import="java.util.Map"%>
<%@page import="java.util.HashMap"%>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
        <form action="ServletLogic" method="post">
            USER:<input type="text" name="user" id="user"/><br>
            PASS:<input type="password" name="pass" id="pass"/><br>
            <input type="submit" value="Login"/>
        </form>
    </body>
</html>
登录.jsp
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
        <h1>My Page</h1>
        <form action="ServletLogout" method="post">
              <input type="submit" value="Logout"/>
        </form>
    </body>
</html>
ServletLogic.java   //servlet
package model;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletLogic extends HttpServlet {
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        String user=request.getParameter("user");
        String pass=request.getParameter("pass");
        String res;
        if(user.equals("admin")&&pass.equals("admin"))
         res="Success!!!";
        else
          res="Failure!!!";
        request.getRequestDispatcher("login.jsp").forward(request, response); 
        try {
        } finally {            
            out.close();
        }
    }
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }
    @Override
    public String getServletInfo() {
        return "Short description";
    }
}
ServletLogout.java // servlet
package model;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletLogout extends HttpServlet {
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {
        request.getRequestDispatcher("index.jsp").forward(request, response); 
        } finally {            
            out.close();
        }
    }
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }
    @Override
    public String getServletInfo() {
        return "Short description";
    }
}