java_web4.serverlet session管理

为了保证客户端用户唯一性 使用session 管理用户

Session基于Cookie技术,Session保存在服务器端(一般会设置有效期),SessionID保存在客户端.Session里面保存!!若干个!!!"键-值"对,可以通过 void setAttribute(java.lang.String name, java.lang.Object value) 来修改/添加
HttpSession session = request.getSession();
session.setAttribute("abc",new Integer(567));//新增属性 键:abc 值:new Integer(567)
session.setAttribute("jkl",new Person());//新增属性 键:jkl 值:new Person()
session.setAttribute("abc",new Double(5.67));//已经存在 键abc,将会修改该键对应的值
Session本质上也是一组"键-值"对 其中的"键"保存在客户端(钥匙)是字符串 其中的"值"保存在服务器端(保险箱)可以是Object类型
sessionID与session的关系:钥匙与银行保险箱 钥匙在客户端 保险箱在服务器端
URL重写:解决了关闭浏览器cookie产生的问题
!!!!!!!!!!!!!Session在关闭浏览器时会失效,在下次访问时不能获得同一个Session了 

package main.server;

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

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 {
        
                response.setContentType("text/html;charset=GBK");
                PrintWriter out = response.getWriter();

                String user = "";
                //此处不新建session，只是去取已经创建的session
                HttpSession session = request.getSession(false);
                //如果session能够取到，说明用户已经登录
                if(session!=null)
                {
                user = (String)session.getAttribute("abc");
                out.println("获得创建的Session");
                out.println("<BR>");
                out.println("登录名："+user);
                }
                //否则，说明用户没有登录，跳转到登录页面让用户登录
                else
                {
                response.sendRedirect("../SessionLogin.htm");
                } 
    
    }

    /**
     * @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);
    }

}

package main.server;

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

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 {
		//验证登录者身份，验证过程此处省略
		//如果合法用户就产生一个session来放置其登录名
		//如果用户输入了用户名，则将其放在session中
		if(request.getParameter("userName")!=null)
		{
		HttpSession session = request.getSession();//没有Session就新建一个
		session.setAttribute("abc",
		request.getParameter("userName"));//在服务器端存储"键-值对"
		}
		response.setContentType("text/html;charset=GBK");
		PrintWriter out = response.getWriter();
		out.println("Session已经创建");
		out.println("<BR>");
		out.println("转到其他<A HREF=\"chap03.GetSession\">页面</A>"); 
	}

	/**
	 * @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);
	}

}