Servlet中HashMap问题

天台的故事 2016-02-09 04:21:28



package yuan.yu;



import java.io.IOException;

import java.io.PrintWriter;

import java.util.HashMap;

import java.util.Iterator;



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 yuan.util.Encoded;



public class session extends HttpServlet {

	

	/**

	 * Constructor of the object.

	 */

	public session() {

		super();

	}



	/**

	 * Destruction of the servlet. <br>

	 */

	public void destroy() {

		super.destroy(); // Just puts "destroy" string in log

		// Put your code here

	}



	public void doGet(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {



		response.setCharacterEncoding("UTF-8"); // 先指定输出流的编码

	    PrintWriter out = response.getWriter(); // 再拿到输出对象

	    response.setContentType("text/html;charset=UTF-8");

		

	    

	    HttpSession session = request.getSession(); 

	    

	    

	    

	    //获取书名的ID

	    String id = request.getParameter("val");

	    //获取get提交的书名

	    String bookname = Encoded.changeSring(request.getParameter("name"));

	    

	    //获取session数据

	    HashMap<String,Book> hm=(HashMap<String,Book>)session.getAttribute("mybooks");

	    

	    //判读当前是否有session

	    if(hm == null)

	    {

	    	hm = new HashMap<String,Book>();

	    	//构建一个Book对象

	    	Book book = new Book();

	    	book.setId(id);

	    	book.setName(bookname);

	    	book.setNum(1);

	    	hm.put(id, book);

	    	//把hm放入到session

	    	session.setAttribute("mybooks", book);

	    	

	    }

	    else

	    {

	    	//判读hm是否有该书

	    	if(hm.containsKey(id))

	    	{

	    		//表示书购买过一次

	    		//取出

	    		Book book = hm.get(id);

	    		int bookNum = book.getNum();

	    		book.setNum(bookNum+1);

	    	}

	    	else

	    	{

	    		Book book = new Book();

	    		book.setId(id);

	    		book.setName(bookname);

	    		book.setNum(1);

	    		hm.put(id, book);

	    	}

	    	

	    	

	    	//更新

	    	session.setAttribute("mybooks", hm);

	    	

	    }

	    

	    //获取session名称为mybooks所有数据

	    HashMap<String,Book> myBooks = (HashMap<String,Book>)session.getAttribute("mybooks");

	    



	    out.println("<h3>你的购物车有以下书籍:</h3>");

	    

	    Iterator<String> iter = myBooks.keySet().iterator();

	    while(iter.hasNext()) 

	    {

		  String key = iter.next();

		  Book book = myBooks.get(key);

		  out.println(book.getName()+" "+book.getNum()+"</br>");

	    }

	    out.println("<a href='/Session/session.html'>返回购物厅</a>");

	    

	   



	}



	public void doPost(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {



		response.setContentType("text/html");

		PrintWriter out = response.getWriter();

		this.doGet(request, response);

	}



	/**

	 * Initialization of the servlet. <br>

	 *

	 * @throws ServletException if an error occurs

	 */

	public void init() throws ServletException {

		// Put your code here

	}



}

[/code

下面是HTML静态文件

[code=html]

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <title>session.html</title>

	

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="this is my page">

    <meta http-equiv="content-type" content="text/html; charset=UTF-8">

    

    <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->



  </head>

  

  <body>

   C语言入门 <a href="/Session/session?val=1&name=C语言入门">购买</a></br>

   JAVA语言入门<a href="/Session/session?val=2&name=JAVA语言入门">购买</a></br>

    计算机编译原理<a href="/Session/session?val=3&name=计算机编译原理">购买</a></br>

    操作系统的概述<a href="/Session/session?val=4&name=操作系统的概述">购买</a></br>

   数据结构 <a href="/Session/session?val=5&name=数据结构">购买</a></br>

  大话设计模式   <a href="/Session/session?val=6&name=大话设计模式">购买</a></br>

  </body>

</html>

访问的时候报错，报了如下这个错:

HTTP Status 500 - yuan.yu.Book cannot be cast to java.util.HashMap

type Exception report

message yuan.yu.Book cannot be cast to java.util.HashMap

description The server encountered an internal error that prevented it from fulfilling this request.

exception

java.lang.ClassCastException: yuan.yu.Book cannot be cast to java.util.HashMap
yuan.yu.session.doGet(session.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.44 logs.

Apache Tomcat/6.0.44

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