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Session:由同一个IE窗口向同一个WEBAPP发的所有请求的总称，一个会话
同一个会话的多个额请求可以从前到后多个请求。？？祖给孙，孙不给祖
浏览器：搜集sessionID信息，并发到服务器。没有就不发送。
查找sessionID，若找到，看servlet是否需要session，需要就从服务器内存提取旧的session对象。否则维持旧的Session不动，修改session的使用时间。
如果没找到，看是否需要session，再创建session对象，并且保持session对象在服务器中，把sessionID写到IE中。
sessionID放到IE浏览器，浏览器通过request把id带到服务器端
HttpSession session = request.getSession(false);// 这里false只能用就得Session
True有旧的找旧的，否则建新的
Session.setMaxInactiveInterval两次请求之间的最长的时间间隔单位：s。相当于Session最大存活时间，超过之后服务器销毁这个session。比如登陆之后有一定时间，超出就销毁。0表示立即过期，-1表示永不过期
设置最大时间的原因：
(1)Session是容器，要长时间占用内存。所以限定最大时间间隔
(2)安全考虑
Session.isNew（）是不是新的
自杀，用于安全退出或者清空购物车
以下参考：http://copperfield.iteye.com/blog/890018
二、session使用 以登录为例
业务逻辑：login.jsp提交表单，loginServlet判断用户名密码是不是对，如果不对转到login.jsp，如果对转到DealServlet（这个类判断是否登录还有效，无效就返回login，比如163邮箱），也可以通过该容器logout，可以logout返回login页面或者主页
UserLoginServlet
public class UserLoginServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String logid = request.getParameter("logid");
String logpwd = request.getParameter("logpwd");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>logincontent</TITLE></HEAD>");
out.println(" <BODY>");
int flag=0;
HttpSession session = request.getSession();
if("Admin".equals(logid) && "123".equals(logpwd)){
session.setAttribute("userid", logid);
session.setMaxInactiveInterval(20);
//System.out.println("here");
//response.sendRedirect("http://localhost:8888/TestmyJSP/logout.servlet");
response.sendRedirect("deal.servlet"); // 不是类名而是url
}else{
out.write("<script>alert('login error'); history.go(-1);</script>");
}
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
}
public class DealLoginServlet extends HttpServlet {
/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
HttpSession session = request.getSession(false);
if(session == null){
response.sendRedirect("login.jsp");
}else{
Object o = session.getAttribute("userid");
if(null == o){
response.sendRedirect("login.jsp");
}else{
out.write(o.toString());
}
}
out.println("<a href='logout.servlet'>登出</a> ");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
}
public class LogoutServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
HttpSession session = request.getSession();
session.setMaxInactiveInterval(0);
session.invalidate();
response.sendRedirect("login.jsp");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
}
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原文地址：http://blog.csdn.net/u011026968/article/details/47091107
