Session对象的灵活使用

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

实例:
package chap03;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class GetSession extends HttpServlet
{
public 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”);
}
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException,IOException
{
doGet(request,response);
}
}

package chap03;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class SaveInfo extends HttpServlet
{
public 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>”);
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException,IOException
{
doGet(request,response);
}
}

Session对象的灵活使用

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