什么是Session
使用Cookie和附加URL参数都可以将上一次请求的状态信息传递到下一次请求中，但是如果传递的状态信息较多，将极大降低网络传输效率和增大服务器端程序处理的难度。
Session技术是一种将会话状态保存在服务器端的技术 ，它可以比喻成是医院发放给病人的病历卡和医院为每个病人保留的病历档案的结合方式 。
客户端需要接收、记忆和回送 Session的会话标识号，Session可以且通常是借助Cookie来传递会话标识号。
同一用户的不同页面共享数据（Session）
如何理解Session
Session的跟踪机制
1.Servlet API规范中定义了一个HttpSession接口，HttpSession接口定义了各种管理和操作会话状态的方法。
2.HttpSession对象是保持会话状态信息的存储结构，一个客户端在WEB服务器端对应一个各自的HttpSession对象。
3.WEB服务器并不会在客户端开始访问它时就创建HttpSession对象，只有客户端访问某个能与客户端开启会话的Servlet程序时，WEB应用程序才会创建一个与该客户端对应的HttpSession对象。
4.WEB服务器为HttpSession对象分配一个独一无二的会话标识号，然后在响应消息中将这个会话标识号传递给客户端。客户端需要记住会话标识号，并在后续的每次访问请求中都把这个会话标识号传送给WEB服务器，WEB服务器端程序依据回传的会话标识号就知道这次请求是哪个客户端发出的，从而选择与之对应的HttpSession对象
如何使用Session
Session的超时管理
WEB服务器无法判断当前的客户端浏览器是否还会继续访问，也无法检测客户端浏览器是否关闭，所以，即使客户已经离开或关闭了浏览器，WEB服务器还要保留与之对应的HttpSession对象。
随着时间的推移而不断增加新的访问客户端，WEB服务器内存中将会因此积累起大量的不再被使用的HttpSession对象，并将最终导致服务器内存耗尽。
WEB服务器采用“超时限制”的办法来判断客户端是否还在继续访问，如果某个客户端在一定的时间之内没有发出后续请求，WEB服务器则认为客户端已经停止了活动，结束与该客户端的会话并将与之对应的HttpSession对象变成垃圾。
如果客户端浏览器超时后再次发出访问请求，WEB服务器则认为这是一个新的会话的开始，将为之创建新的HttpSession对象和分配新的会话标识号。
会话的超时间隔可以在web.xml文件中设置，其默认值由Servlet容器定义。
<session-config>
<session-timeout>30</session-timeout>
</session-config>
session实现原理
IE禁用Cookie后的session处理
解决方案：URL重写
response. encodeRedirectURL(java.lang.String url)
用于对sendRedirect方法后的url地址进行重写。
response. encodeURL(java.lang.String url)
用于对表单action和超链接的url地址进行重写
Session案例
1.实现简单的购物车 （将点击了购买链接的书籍放到购物车页面显示出来即可）
IndexServletShopping.java
package com.hbsi.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.hbsi.dao.BookDao;
import com.hbsi.domain.Book;
public class IndexServletShopping extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out=response.getWriter();
out.print("本网站有如下商品：
");
BookDao db=new BookDao();
List list=db.getAll();
for(Book book:list){
String url=response.encodeRedirectURL("BookHistory/servlet/BuyServlet?id="+book.getId());
out.print(book.getName()+"购买
");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
CartDisplayServlet.java
package com.hbsi.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.hbsi.domain.Book;
public class CartDisplayServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
List list = (List) request.getSession().getAttribute("cart");
for(Book book:list){
out.print(book.getName()+"
");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
BuyServlet.java
package com.hbsi.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import com.hbsi.dao.BookDao;
import com.hbsi.domain.Book;
public class BuyServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out=response.getWriter();
String bookid=request.getParameter("id");
BookDao bd=new BookDao();
Book book=bd.getBook(bookid);
HttpSession session=request.getSession();
Cookie cookie=new Cookie("JSESSIONID",session.getId());
cookie.setMaxAge(30*60);
cookie.setPath("/BookHistory");
response.addCookie(cookie);
List list=(List) session.getAttribute("cart");
if(list==null){
list=new ArrayList();
session.setAttribute("cart", list);
}
list.add(book);
String url=response.encodeRedirectURL("/BookHistory/servlet/CartDisplayServlet");
response.sendRedirect(url);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
2.使用Session完成用户登陆 利用Session实现验证码校验
IndexServletShopping.java
package com.hbsi.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import com.hbsi.dao.BookDao;
import com.hbsi.domain.Book;
import com.hbsi.domain.User;
public class IndexServletShopping extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
HttpSession session= request.getSession();
User user = (User) session.getAttribute("user");
if(user!=null){
out.print("欢迎您："+user.getUsername()+" ");
}
out.print("<a href='/BookHistory/Login.html'>登陆</a> ");
out.print("<a href='/BookHistory/servlet/LogoutServlet'>注销</a><br><br> ");
out.print("本网站有如下商品：<br>");
BookDao db = new BookDao();
List<Book> list = db.getAll();
for(Book book:list){
String url = response.encodeURL("/BookHistory/servlet/BuyServlet?id="+book.getId());
out.print(book.getName()+"<a href='"+url+"'>购买</a><br>");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
CartDisplayServlet.java
package com.hbsi.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.hbsi.domain.Book;
public class CartDisplayServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
List<Book> list = (List<Book>) request.getSession().getAttribute("cart");
for(Book book:list){
out.print(book.getName()+"<br>");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
BuyServlet.java
package com.hbsi.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import com.hbsi.dao.BookDao;
import com.hbsi.domain.Book;
public class BuyServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
String bookid = request.getParameter("id");
BookDao bd = new BookDao();
Book book = bd.getBook(bookid);
HttpSession session = request.getSession();
Cookie cookie = new Cookie("JSESSIONID",session.getId());
cookie.setMaxAge(30*60);
cookie.setPath("/BookHistory");
response.addCookie(cookie);
List list = (List) session.getAttribute("cart");
if(list==null){
list = new ArrayList();
session.setAttribute("cart",list);
}
list.add(book);
String url = response.encodeRedirectURL("/BookHistory/servlet/CartDisplayServlet");
response.sendRedirect(url);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
LoginServlet.java
package com.hbsi.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.hbsi.dao.UserDao;
import com.hbsi.domain.User;
public class LoginServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
String username = request.getParameter("username");
String password = request.getParameter("password");
String checkcode = request.getParameter("checkcode");
System.out.println(checkcode);
String imgcode = (String) request.getSession().getAttribute("imgcode");
System.out.println(imgcode);
if(checkcode!=null && imgcode!=null && checkcode.equals(imgcode)){
//处理登陆请求
UserDao udao = new UserDao();
User user = udao.find(username, password);
if(user!=null){
request.getSession().setAttribute("user",user);
response.sendRedirect("/BookHistory/servlet/IndexServletShopping");
}
out.print("用户名密码错");
}else{
out.print("验证码错误！！！");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
LogoutServlet.java
package com.hbsi.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class LogoutServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
HttpSession session = request.getSession(false);
if(session==null){
response.sendRedirect("/BookHistory/servlet/IndexServletShopping");
return;
}
session.removeAttribute("user");
// session.invalidate();
response.sendRedirect("/BookHistory/servlet/IndexServletShopping");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
package com.hbsi.servlet;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Response3 extends HttpServlet {
private static final int WIDTH=130;
private static final int HEIGHT=30;
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//1.创建图片
BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);
//2.得到图片
Graphics g = image.getGraphics();
//3 对图片进行绘制
//a.设置图片的背景色
setBackGround(g);
//b.设置矩形边框
setBorder(g);
//c.添加干扰线
setRandomLine(g);
//g.向图形中写数据
String checkcode = setRandomNum(g);
request.getSession().setAttribute("imgcode",checkcode);
//4.把图片写给浏览器
//response.setHeader("content-type","image/jpeg");
response.setContentType("image/jpeg");
//告诉浏览器不要缓存
response.setHeader("Pragma", "no-cache");
response.setHeader("Cache-Control", "no-cache");
response.setIntHeader("Expires",-1);
ImageIO.write(image,"JPEG",response.getOutputStream());
}
private String setRandomNum(Graphics g) {
//g.setColor(Color.BLACK);
g.setFont(new Font("宋体",Font.BOLD,20));
Random random = new Random();
String base = "\u7684\u4e00\u4e86\u662f\u6211\u4e0d\u5728\u4eba\u4eec\u6709\u6765\u4ed6\u8fd9\u4e0a\u7740\u4e2a\u5730\u5230\u5927\u91cc\u8bf4\u5c31\u53bb\u5b50\u5f97\u4e5f\u548c\u90a3\u8981\u4e0b\u770b\u5929\u65f6\u8fc7\u51fa\u5c0f\u4e48\u8d77\u4f60\u90fd\u628a\u597d\u8fd8\u591a\u6ca1\u4e3a\u53c8\u53ef\u5bb6\u5b66\u53ea\u4ee5\u4e3b\u4f1a\u6837\u5e74\u60f3\u751f\u540c\u8001\u4e2d\u5341\u4ece\u81ea\u9762\u524d\u5934\u9053\u5b83\u540e\u7136\u8d70\u5f88\u50cf\u89c1\u4e24\u7528\u5979\u56fd\u52a8\u8fdb\u6210\u56de\u4ec0\u8fb9\u4f5c\u5bf9\u5f00\u800c\u5df1\u4e9b\u73b0\u5c71\u6c11\u5019\u7ecf\u53d1\u5de5\u5411\u4e8b\u547d\u7ed9\u957f\u6c34\u51e0\u4e49\u4e09\u58f0\u4e8e\u9ad8\u624b\u77e5\u7406\u773c\u5fd7\u70b9\u5fc3\u6218\u4e8c\u95ee\u4f46\u8eab\u65b9\u5b9e\u5403\u505a\u53eb\u5f53\u4f4f\u542c\u9769\u6253\u5462\u771f\u5168\u624d\u56db\u5df2\u6240\u654c\u4e4b\u6700\u5149\u4ea7\u60c5\u8def\u5206\u603b\u6761\u767d\u8bdd\u4e1c\u5e2d\u6b21\u4eb2\u5982\u88ab\u82b1\u53e3\u653e\u513f\u5e38\u6c14\u4e94\u7b2c\u4f7f\u5199\u519b\u5427\u6587\u8fd0\u518d\u679c\u600e\u5b9a\u8bb8\u5feb\u660e\u884c\u56e0\u522b\u98de\u5916\u6811\u7269\u6d3b\u90e8\u95e8\u65e0\u5f80\u8239\u671b\u65b0\u5e26\u961f\u5148\u529b\u5b8c\u5374\u7ad9\u4ee3\u5458\u673a\u66f4\u4e5d\u60a8\u6bcf\u98ce\u7ea7\u8ddf\u7b11\u554a\u5b69\u4e07\u5c11\u76f4\u610f\u591c\u6bd4\u9636\u8fde\u8f66\u91cd\u4fbf\u6597\u9a6c\u54ea\u5316\u592a\u6307\u53d8\u793e\u4f3c\u58eb\u8005\u5e72\u77f3\u6ee1\u65e5\u51b3\u767e\u539f\u62ff\u7fa4\u7a76\u5404\u516d\u672c\u601d\u89e3\u7acb\u6cb3\u6751\u516b\u96be\u65e9\u8bba\u5417\u6839\u5171\u8ba9\u76f8\u7814\u4eca\u5176\u4e66\u5750\u63a5\u5e94\u5173\u4fe1\u89c9\u6b65\u53cd\u5904\u8bb0\u5c06\u5343\u627e\u4e89\u9886\u6216\u5e08\u7ed3\u5757\u8dd1\u8c01\u8349\u8d8a\u5b57\u52a0\u811a\u7d27\u7231\u7b49\u4e60\u9635\u6015\u6708\u9752\u534a\u706b\u6cd5\u9898\u5efa\u8d76\u4f4d\u5531\u6d77\u4e03\u5973\u4efb\u4ef6\u611f\u51c6\u5f20\u56e2\u5c4b\u79bb\u8272\u8138\u7247\u79d1\u5012\u775b\u5229\u4e16\u521a\u4e14\u7531\u9001\u5207\u661f\u5bfc\u665a\u8868\u591f\u6574\u8ba4\u54cd\u96ea\u6d41\u672a\u573a\u8be5\u5e76\u5e95\u6df1\u523b\u5e73\u4f1f\u5fd9\u63d0\u786e\u8fd1\u4eae\u8f7b\u8bb2\u519c\u53e4\u9ed1\u544a\u754c\u62c9\u540d\u5440\u571f\u6e05\u9633\u7167\u529e\u53f2\u6539\u5386\u8f6c\u753b\u9020\u5634\u6b64\u6cbb\u5317\u5fc5\u670d\u96e8\u7a7f\u5185\u8bc6\u9a8c\u4f20\u4e1a\u83dc\u722c\u7761\u5174\u5f62\u91cf\u54b1\u89c2\u82e6\u4f53\u4f17\u901a\u51b2\u5408\u7834\u53cb\u5ea6\u672f\u996d\u516c\u65c1\u623f\u6781\u5357\u67aa\u8bfb\u6c99\u5c81\u7ebf\u91ce\u575a\u7a7a\u6536\u7b97\u81f3\u653f\u57ce\u52b3\u843d\u94b1\u7279\u56f4\u5f1f\u80dc\u6559\u70ed\u5c55\u5305\u6b4c\u7c7b\u6e10\u5f3a\u6570\u4e61\u547c\u6027\u97f3\u7b54\u54e5\u9645\u65e7\u795e\u5ea7\u7ae0\u5e2e\u5566\u53d7\u7cfb\u4ee4\u8df3\u975e\u4f55\u725b\u53d6\u5165\u5cb8\u6562\u6389\u5ffd\u79cd\u88c5\u9876\u6025\u6797\u505c\u606f\u53e5\u533a\u8863\u822c\u62a5\u53f6\u538b\u6162\u53d4\u80cc\u7ec6";
StringBuffer sb = new StringBuffer();
int x=10;
for(int i=0;i<4;i++){
int rand = random.nextInt(base.length()-1);
String str = base.charAt(rand)+"";
sb.append(str);
g.setColor(new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255)));
int degree = random.nextInt()%30;
((Graphics2D)g).rotate(degree*Math.PI/180, x, 20);
g.drawString(str, x, 20);
((Graphics2D)g).rotate(-degree*Math.PI/180, x, 20);
x +=30;
}
return sb.toString();
}
private void setRandomNum1(Graphics g) {
//g.setColor(Color.BLACK);
g.setFont(new Font("宋体",Font.BOLD,20));
Random random = new Random();
int x=10;
for(int i=0;i<4;i++){
//产生随机数
String str = String.valueOf(random.nextInt(10));
g.setColor(new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255)));
int degree = random.nextInt()%30;
((Graphics2D)g).rotate(degree*Math.PI/180, x, 20);
g.drawString(str, x, 20);
((Graphics2D)g).rotate(-degree*Math.PI/180, x, 20);
x +=30;
}
}
private void setRandomLine(Graphics g) {
g.setColor(Color.green);
Random random = new Random();
for(int i=0;i<5;i++){
int x1 = random.nextInt(WIDTH);
int y1 = random.nextInt(HEIGHT);
int x2 = random.nextInt(WIDTH);
int y2 = random.nextInt(HEIGHT);
g.drawLine(x1, y1, x2, y2);
}
}
private void setBorder(Graphics g) {
g.setColor(Color.BLUE);
g.drawRect(1, 1, WIDTH-2, HEIGHT-2);
}
private void setBackGround(Graphics g) {
g.setColor(Color.WHITE);
g.fillRect(0,0, WIDTH, HEIGHT);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}