动手学servlet(四) cookie和session

Cookie

  cookie是保存在客户端的一个“键值对”，用来存储用户的一些信息

   cookie的应用：

       -在电子商务会话中标识用户

       -对网站进行定制，比如你经常浏览哪些内容，就展示哪些页面给你

       -网站广告，比如百度联盟，你搜索了什么关键字，在各个网站就可以看到那个关键字的广告

  创建cookie

package servletdemo;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class TestCookie
 */
@WebServlet("/TestCookie")
public class TestCookie extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public TestCookie() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
                //构造函数第一个参数是key，第二个是value
        Cookie c=new Cookie("name", "henry");        
           //设置时间，最低级是秒，此处就是60秒乘以60，也就是一个小时
        c.setMaxAge(60*60);
              //将创建的cookie添加到客户端
        response.addCookie(c);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

  获取cookie

package servletdemo;

import java.io.IOException;
import java.util.Iterator;

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

/**
 * Servlet implementation class TestGetCookie
 */
@WebServlet("/TestGetCookie")
public class TestGetCookie extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public TestGetCookie() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        Cookie [] cookies=request.getCookies();
        if(cookies!=null)
        {
            for(Cookie c:cookies)
            {
                String name=c.getName();
                String value=c.getValue();
                System.out.println(name+":"+value);
            }
        }
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

  运行结果

Session

  HTTP协议是无状态的，那么我们如何将对象数据持久化的保存呢，java有两个解决办法，一个是cookie，一个就是session，它是用来跟踪用户状态的一种机制，是针对浏览器和服务器的一对一关系

  Session接口HttpSession，通常我们会使用它，接口的实现由WEB容器来完成

  -可以从HttpServletRequest中获取HttpSession，request.getSession();返回一个HttpSession接口

  -将信息保存在HttpSession中，session.setAttribute("usersession",obj);

  -从HttpSession中获得信息，session.getAttribute("usersession");

  -使session失效，session.invalidate();

  创建session

package servletdemo;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class SetSession
 */
@WebServlet("/SetSession")
public class SetSession extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SetSession() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        HttpSession session=request.getSession();
        session.setAttribute("session_name", "session_value");
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

  获得session

package servletdemo;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class GetSession
 */
@WebServlet("/GetSession")
public class GetSession extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public GetSession() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        HttpSession session=request.getSession();
        String value=(String)session.getAttribute("session_name");
        System.out.println("value:"+value);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}