JavaEE
文章目录
CookieAPI的使用
- 下面代码展示通过设置cookie存活时间来保存用户名
package servlet;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 java.io.IOException;
import java.io.PrintWriter;public class LoginServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();String userName ="";String checked = "";//得到客户端保存的Cookie数据Cookie[] cookies = request.getCookies();for (int i = 0;cookies!=null && i < cookies.length; i++) {if("userName".equals(cookies[i].getName())){userName = cookies[i].getValue();//如果有cookie则自动填充checked = "checked='checked'";//如果有cookie则自动勾选}}out.write("<form action='"+request.getContextPath()+"/doLogin' method='post'>");out.write("用户名：<input type='text' name='userName' value='"+userName+"'/><br/>");out.write("密码：<input type='password' name='pwd'/><br/>");out.write("<input type='checkbox' name='remember' "+checked+" />记住用户名<br/>");out.write("<input type='submit' value='登录'/><br/>");out.write("</form>");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}
- 上面Servlet实现了登录界面，下面Servlet用来实现获取表单数据、处理业务逻辑、分发转向的功能
package servlet;import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class DoLoginServlet 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();//获取表单数据String userName = request.getParameter("userName");String pwd = request.getParameter("pwd");String remember = request.getParameter("remember");Cookie ck = new Cookie("userName", userName);//创建Cookieck.setPath("/");//设置Cookie的路径为项目路径//处理业务逻辑//分发转向if("tom".equals(userName)&&"123".equals(pwd)){if(remember!=null){ck.setMaxAge(Integer.MAX_VALUE);//设置Cookie的有效保存时间}else{ck.setMaxAge(0);//设置时间为0表示立即删除Cookie}response.addCookie(ck);//将Cookie写回到客户端，当时间设置为0时，执行删除操作out.write("登录成功！");}else{out.write("登录失败！");//设置2秒跳到重新登录response.setHeader("refresh", "2;url="+request.getContextPath()+"/login");}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}
}
- 下面代码利用cookie实现保存用户最近三条浏览记录的功能。
- 需要用到的类包括两个Servlet、一个商品（书）类和一个工具类（用来模拟对数据库的读取操作）。
- 两个Servlet分别用来展示所有书和每个书的详细信息。其中用来展示所有书的页面包括了最近浏览的三条记录。
- 经过分析发现添加cookie的功能应该在详细信息的Servlet中写，因为只有点了某本书，才会将这本书添加到cookie中。而读取cookie的功能则应该写在展示所有书信息的Servlet中。
package servlet;import java.io.IOException;
import java.io.PrintWriter;
import java.util.Map;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 entity.Book;
import util.DBUtil;//该Servlet是用来展示所有书信息和历史浏览记录的
public class ShowAllBooksServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();out.write("本网站有以下好书：<br/>");Map<String, Book> books = DBUtil.findAllBooks();for (Map.Entry<String, Book> book : books.entrySet()) {//每一本书都连接到详细信息页面，不过需要在跳转链接中加上书的idout.write("<a href='"+request.getContextPath()+"/showBookDetail?id="+book.getKey()+"' target='_blank'>"+book.getValue().getName()+"</a><br/>");}out.write("<hr/>您最近浏览过的书有：<br/>");Cookie[] cookies = request.getCookies();//获取cookie数组for (int i = 0;cookies!=null && i < cookies.length; i++) {if("historyBookId".equals(cookies[i].getName())){//判断是否有historyBookId的cookie//获取名为historyBookId的cookie值，也就是历史浏览书本的id拼接的字符串String value = cookies[i].getValue(); String[] ids = value.split("-");for (int j = 0; j < ids.length; j++) {Book book = DBUtil.findBookById(ids[j]);//根据ID得到指定的书out.print(book.getName()+"<br/>");}}}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}
- 上面是用来展示全部商品信息的Servlet，下面是用来展示商品详细信息的Servlet
package servlet;import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;import javax.naming.LinkLoopException;
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 entity.Book;
import util.DBUtil;public class ShowBookDetail extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();//显示图书的详细信息//获得id。无论是post还是get方式提交都可以通过该方法来获取值String id = request.getParameter("id");Book book = DBUtil.findBookById(id);//out.write(book.toString());out.print(book);//把当前浏览过的书的id写回到客户端cookie//organizeId方法能够读取原本cookie中有关历史记录的cookie值，然后将其修改后返回回来String historyBookId = organizeId(id,request);Cookie ck = new Cookie("historyBookId",historyBookId);ck.setPath("/");ck.setMaxAge(Integer.MAX_VALUE);//设置cookie的保存时间response.addCookie(ck);//写回到客户端cookie}/*** 客户端 点击的书ID 修改后的cookie值* 没有Cookie 1 historyBookId=1* 有Cookie，但没有historyBookId 1 historyBookId=1* historyBookId=1 2 historyBookId=2-1* historyBookId=1-2 2 historyBookId=2-1* historyBookId=1-2-3 2 historyBookId=2-1-3* historyBookId=1-2-3 4 historyBookId=4-1-2*/private String organizeId(String id, HttpServletRequest request) {//得到客户端的CookieCookie[] cookies = request.getCookies();if(cookies==null){return id;}//查找有没有name叫做historyBookId的cookieCookie historyBook = null;for (int i = 0; i < cookies.length; i++) {if("historyBookId".equals(cookies[i].getName())){historyBook = cookies[i];}}//如果没有historyBookId的cookie，则还返回idif(historyBook==null){return id;}//获取名为historyBookId的cookie值，也就是历史浏览书本的id拼接的字符串String value = historyBook.getValue();String[] values = value.split("-");LinkedList<String> list = new LinkedList<String>(Arrays.asList(values));//历史记录中最多只保存3条记录if(list.size()<3){ // 1 2if(list.contains(id)){list.remove(id);//如果包含当前id的值，则删除这个id}}else{if(list.contains(id)){list.remove(id);}else{//说明有3本书的id了list.removeLast();//把最后一个id删除 }}list.addFirst(id);//最新书的id添加到最前面StringBuffer sb = new StringBuffer();for (int i=0; i< list.size();i++) {if(i>0){sb.append("-");}sb.append(list.get(i));}return sb.toString();//将StringBuffer类型转为String类型}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}
package servlet;import java.util.HashMap;
import java.util.Map;import entity.Book;public class DBUtil {private static Map<String, Book> books = new HashMap<String, Book>();static{books.put("1", new Book("1", "金瓶梅", 20, "王瑞鑫"));books.put("2", new Book("2", "葵花宝典", 20, "杨成毅"));books.put("3", new Book("3", "九阴真经", 30, "陈光"));books.put("4", new Book("4", "玉女心经", 10, "陈志家"));}//得到所有书public static Map<String, Book> findAllBooks(){return books;}/*** 根据id查找指定的书* @param id* @return*/public static Book findBookById(String id){return books.get(id);}
}
HttpSession
- HttpSession也是一个域对象，它是介于ServletContext和ServletRequest中间的域对象。ServletRequest的范围只限于同一个request，ServletContext的范围是整个项目资源都可以进行设置和获取对象。而HttpSession则是同一会话中的所有资源通向同一个HttpSession对象，可以设置和获取对象。不同的会话对应着不同的HttpSession。
- HttpSession与Cookie的区别在于：
- Cookie是客户端技术，只能存取字符串
- HttpSession是服务器端技术，可以存取对象
- 下面展示一个例子，通过HttpSession实现购物车功能，能够区别不同用户（购物车存在HttpSession当中）
- 包括三个Servlet（用于展示所有商品信息，用于添加一本选中的书到购物车中，用于展示购物车中的内容）、两个类（Book和DBUtil用来模拟数据库，跟上面一个例子相同）
package servlet;import java.io.IOException;
import java.io.PrintWriter;
import java.util.Map;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import entity.Book;
import util.DBUtil;//
public class ShowAllBooksServlet 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("本网站有以下好书：<br/>");Map<String, Book> books = DBUtil.findAllBooks();for (Map.Entry<String, Book> book : books.entrySet()) {//点击链接添加商品到购物车，关联一个Servletout.print("<a href='"+request.getContextPath()+"/addCart?id="+book.getKey()+"' >"+book.getValue().getName()+"</a><br/>");}//点击链接查看购物车，关联一个Servletout.print("<a href='"+request.getContextPath()+"/showCart"+"'>查看购物车</a>");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}
}
- 下面是添加商品的Servlet，在这个Servlet中，需要获取HttpSession，往里面存放的代表购物车的List中添加商品，然后再将List放回HttpSession中。
package 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.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;import entity.Book;
import util.DBUtil;public class AddCart extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();//根据id得到书String id = request.getParameter("id");Book book = DBUtil.findBookById(id);//得到session对象HttpSession session = request.getSession();//从session中取出list（购物车）List<Book> list = (List<Book>)session.getAttribute("cart");if(list==null){list = new ArrayList<Book>();}list.add(book);session.setAttribute("cart", list);//把list放回到session域中out.print("购买成功！");response.setHeader("refresh", "2;url="+request.getContextPath()+"/showAllBooksServlet");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}
}
- 下面是展示购物车内容的Servlet，在这个Servlet中也需要获取到HttpSession，获取里面的List购物车。
package 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 entity.Book;public class ShowCart 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("购物车有以下商品：<br/>");HttpSession session = request.getSession();//得到session对象List<Book> books = (List<Book>)session.getAttribute("cart");if(books==null){out.print("你还什么都没买呢");response.setHeader("refresh", "2;url="+request.getContextPath()+"/showAllBooksServlet");return;}for (Book book : books) {out.write(book.getName()+"<br/>");}//可以设置session的处于非激活状态的存活时长，当时间一到，session销毁，里面存放的东西也都会销毁//session.setMaxInactiveInterval(10);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}
- getSession():内部执行原理
- 获取名称为JSESSIONID的cookie的值。
- 没有这样的cookie，创建一个新的HttpSession对象，分配一个唯一的SessionID，并且向客户端写了一个名字为JSESSIONID=sessionID的cookie
- 有这样的Cookie，获取cookie的值（即HttpSession对象的值），从服务器的内存中根据ID找那个HttpSession对象。如果找不到（由于过期等原因），重新创建一个新的HttpSession对象。
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