一、session方法
Session:由同一个IE窗体向同一个WEBAPP发的全部请求的总称，一个会话
同一个会话的多个额请求能够从前到后多个请求。？？祖给孙。孙不给祖
浏览器：搜集sessionID信息。并发到server。
没有就不发送。
查找sessionID。若找到，看servlet是否须要session，须要就从server内存提取旧的session对象。否则维持旧的Session不动。改动session的使用时间。
假设没找到。看是否须要session，再创建session对象，而且保持session对象在server中。把sessionID写到IE中。
sessionID放到IE浏览器。浏览器通过request把id带到server端
HttpSession session = request.getSession(false);// 这里false仅仅能用就得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server销毁这个session。比方登陆之后有一定时间，超出就销毁。
0表示马上过期，-1表示永只是期
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
下面參考：http://copperfield.iteye.com/blog/890018
session.invalidate()是销毁跟用户关联session,比如有的用户强制关闭浏览器,而跟踪用户的信息的session还存在,但是用户已经离开了。
尽管session 生命周期浏览默认时间30分,可是在30分钟内别的用户还能够訪问到前一个用户的页面,需销毁用户的session。
session.removeAttribute()移除session中的某项属性。
在spring样例中宠物商店的注销登录的代码：
request.getSession().removeAttribute("userSession");
// 注销用户，使session失效。
request.getSession().invalidate();
二、session使用 以登录为例
业务逻辑：login.jsp提交表单，loginServlet推断usernamepassword是不是对，假设不正确转到login.jsp，假设对转到DealServlet（这个类推断是否登录还有效。无效就返回login，比方163邮箱），也能够通过该容器logout，能够logout返回login页面或者主页
事实上两个Servlet也能够做登陆
AServlet推断usernamepassword，正确就到Bservlet。B能够跳出，B中加上推断 假设找不到logid。就返回login，能找到就正常显示，这样仅仅要login之后。开心的标签页，还能够正常打开B
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();
}
}
DealLoginServlet
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();
}
}
LogoutServlet
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();
}
}