Cookie案例：简单登录界面中的应用

ServletDemo1.java

package ztq.servlet.study;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletDemo1 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //设置服务器端以UTF-8编码进行输出
        response.setCharacterEncoding("UTF-8");
        //设置浏览器以UTF-8编码进行接收，解决中文乱码问题
        response.setContentType("text/html;charset = UTF-8");
        PrintWriter out = response.getWriter();
        
        //获取cookie
        String username = "";
        String check = "";
        Cookie[] cookies = request.getCookies();
        for(int i = 0; cookies != null && i < cookies.length; i++){
            Cookie c = cookies[i];
            if("username".equals(c.getName())){
                username = c.getValue();
                check = "checked = 'checked'";
                break;
            }
        }
        
        //登录页面
        out.write("<form action = '" + request.getContextPath() + "/servlet/ServletDemo2' method = 'post'>");
        out.write("用户名：<input type = 'text' name = 'username' value = '" + username + "'><br />");
        out.write("密码：<input type = 'password' name = 'password' value = ''><br />");
        out.write("记住用户名：<input type = 'checkbox' name = 'remember'" + check + "'><br />");
        out.write("<input type = 'submit' name = 'submit' value = '登录'><br />");
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

ServletDemo2.java

package ztq.servlet.study;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletDemo2 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String username = request.getParameter("username");
        String remember = request.getParameter("remember");
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset = UTF-8");
        PrintWriter out = response.getWriter();
        
        //创建一个新的Cookie
        Cookie cookie = new Cookie("username", username);
        cookie.setPath(request.getContextPath());
        if(remember != null){
            //如果选择了记住用户名，则设置Cookie的有效期为一个不为0的整数
            cookie.setMaxAge(Integer.MAX_VALUE);
        }else{
            //否则则把有效期设置为0，即命令浏览器删除该cookie
            cookie.setMaxAge(0);
        }
        //将cookie对象添加到response对象中，这样服务器在输出response对象中的内容时就会把cookie也输出到客户端服务器
        response.addCookie(cookie);
        out.write("登录成功！");
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

结果：

输入用户名和密码，选择记住用户名，然后点击登录。

页面显示登录成功！

重新打开浏览器，再次访问登录界面，会显示如图。