一、session介绍
Session用于保存服务端与客户端“会话”的信息。例如你逛淘宝时添加到购物车中的商品的信息就是保存到Session中。与Cookies不同的是，Session保存在服务端。每个客户端会有一个与之关联的Session，服务器会将Session的ID写到客户端的Cookies或者URL。如果客户端禁止Cookies了，服务器会将ID写到URL中。
二、Session实例
public class ShowSession extends HttpServlet { /** * */ private static final long serialVersionUID = 1L; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); String title = "Session Tracking Example"; //得到客户端对应的session对象，true表示如果在服务器端找不到对应的session对象则创建一个 //得到的是一个session引用，实现HttpSession的具体类 HttpSession session = request.getSession(true); String heading; // Use getAttribute instead of getValue in version 2.2. //得到Session内,与accessCount名字所对应的值Integer accessCount = (Integer) session.getAttribute("accessCount"); if (accessCount == null) { accessCount = new Integer(0); heading = "Welcome, Newcomer"; } else { heading = "Welcome Back"; accessCount = new Integer(accessCount.intValue() + 1); } // Use setAttribute instead of putValue in version 2.2. //像Session内放入对象，第一个参数作为key或者称之为名字，与Map差不多 session.setAttribute("accessCount", accessCount);out.println("<html><head><title>Session追踪</title></head>" + "<BODY BGCOLOR="#FDF5E6"> " + "<H1 ALIGN="CENTER">" + heading + "</H1> " + "<H2>Information on Your Session:</H2> " + "<TABLE BORDER=1 ALIGN="CENTER"> " + "<TR BGCOLOR="#FFAD00"> " + " <TH>Info Type<TH>Value " + "<TR> " + " <TD>ID " + " <TD>" + session.getId() + " " + "<TR> " + " <TD>Creation Time " + " <TD>" //表示Session对象的创建时间 + new Date(session.getCreationTime()) + " " + "<TR> " + " <TD>Time of Last Access " + " <TD>" //最后一次访问时间 + new Date(session.getLastAccessedTime()) + " " + "<TR> " + " <TD>Number of Previous Accesses " + " <TD>" + accessCount + " " + "</TABLE> " + "</BODY></HTML>"); }
三、第二个Seesion实例
public class SessionInfoServlet extends HttpServlet{ /** * */ private static final long serialVersionUID = 1L; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{ HttpSession mySession = request.getSession(true); response.setContentType("text/html"); //response表示服务端的回应 PrintWriter out = response.getWriter(); out.println("<HTML>"); out.println("<HEAD>"); out.println("<TITLE>Session Info Servlet</TITLE>"); out.println("</HEAD>"); out.println("<BODY>"); out.println("<H3>Session Information</H3>"); //判断Session是否创建 out.println("New Session: " + mySession.isNew()); //得到Session的ID out.println("<BR>Session ID: " + mySession.getId()); out.println("<BR>Session Creation Time: " + new java.util.Date(mySession.getCreationTime())); out.println("<BR>Session Last Accessed Time: " + new java.util.Date(mySession.getLastAccessedTime())); out.println("<H3>Request Information</H3>"); out.println("Session ID from Request: " + //request代表客户端的请求，获得从客户端带来的ID request.getRequestedSessionId()); out.println("<BR>Session ID via Cookie: " + //判断ID号是否从Cookie内取出来的 request.isRequestedSessionIdFromCookie()); out.println("<BR>Session ID via rewritten URL: " + //判断ID号是否从URL内取出来的 request.isRequestedSessionIdFromURL()); out.println("<BR>Valid Session ID: " + //判断从客户端取出的ID是否合法 request.isRequestedSessionIdValid()); out.println("</BODY></HTML>"); out.close(); //close output stream }
四、Session URL重写
public class URLSession extends HttpServlet { /** * */ private static final long serialVersionUID = 1L; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); HttpSession session = request.getSession(true); out.println("<html><head><title>Session追踪</title></head>" + "<BODY> " + "session id:" + session.getId() + "</br>" + "from url:" + request.isRequestedSessionIdFromURL() + "</br>" + "from cookie:" + request.isRequestedSessionIdFromCookie() + "</br>" //URL重写 + "<a href=" + response.encodeURL(request.getRequestURL().toString())
+ ">test</a> </br>"
//得到当前访问的Session地址
+ "<a href=" + request.getRequestURI().toString() + ">test</a>"
+ "</BODY></HTML>");
}
五、Session总结
Session是服务器端的一块内存
Session与客户端窗口对应，只要客户端窗口不关就可以访问到，默认失效时间30m，在Tomacat的conf文件夹下的web.xml文件中配置。
<!-- ==================== Default Session Configuration ================= --> <!-- You can set the default session timeout (in minutes) for all newly --> <!-- created sessions by modifying the value below. --> <session-config> <session-timeout>30</session-timeout> </session-config>
客户端与服务器有对应的SessionID
客户端向服务器端发送SessionID的时候有两种方式：
1、Cookie
2、重写URL