实现文件下载的java代码
//这是实现下载类（servlet），详细思路代码例如以下：//也可连接数据库package com.message;import javax.servlet.*;
import javax.servlet.http.*;import java.io.*;import java.util.*;public class FileDownServlet extends HttpServlet {
private static final String CONTENT_TYPE = "text/html; charset=GBK";//Initialize global variables
public void init() throws ServletException { }//Process the HTTP Get request
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType(CONTENT_TYPE); //得到下载文件的名字 //String filename=request.getParameter("filename"); //解决中文乱码问题 String filename=new String(request.getParameter("filename").getBytes("iso-8859-1"),"gbk");//创建file对象
File file=new File("F://book//WebRoot//"+filename);//设置response的编码方式
response.setContentType("application/x-msdownload");//写明要下载的文件的大小
response.setContentLength((int)file.length());//设置附加文件名称
// response.setHeader("Content-Disposition","attachment;filename="+filename); //解决中文乱码 response.setHeader("Content-Disposition","attachment;filename="+new String(filename.getBytes("gbk"),"iso-8859-1"));
//读出文件到i/o流
FileInputStream fis=new FileInputStream(file); BufferedInputStream buff=new BufferedInputStream(fis);byte [] b=new byte[1024];//相当于我们的缓存
long k=0;//该值用于计算当前实际下载了多少字节
//从response对象中得到输出流,准备下载
OutputStream myout=response.getOutputStream();
//開始循环下载
while(k<file.length()){
int j=buff.read(b,0,1024);
k+=j;//将b中的数据写到client的内存
myout.write(b,0,j);}
//将写入到client的内存的数据,刷新到磁盘
myout.flush();}
//Process the HTTP Post request
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }//Clean up resources
public void destroy() { }}//这是javabean写法 ，主要是实现和数据库连接的，假设没有连接数据库，就可直接不要这
package com;public class MessageBean {
private String Message;public String getMessage() {
return Message; }public void setMessage(String message) {
Message = message; }} //HTML页面加载写发，也可连接数据库（案例代码也在）<%@ page language="java" import="java.util.*,com.message.*" pageEncoding="gbk"%><jsp:directive.page import="com.MessageBean;"/><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html> <head> <base href="<%=basePath%>"> <title>My JSP 'book.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --></head>
<body> <!-- <a href="java.rar">5.1下载书--java</a> <br>--> <% //Vector vv=(Vector)session.getAttribute("message"); //for(int i=0;i<vv.size();i++){ // MessagesBean mb=(MessagesBean)vv.get(i); // out.println("<tr>"); // out.println("<td>"+mb.getSender()+"</td>"); // out.println("<td>"+mb.getMess_time()+"</td>"); // out.println("<td>"+mb.getGeter()+"</td>"); // out.println("<td>"+mb.getMess_content()+"</td>");String filename=null;session.setAttribute("java.rar",filename); //取得文件名称 // filename=getFilepath().substring(mb.getFilepath().lastIndexOf("); out.println("<td><a href=FileDownServlet?filename=java.rar>5.1下载书--java</a></td>");//java.rar这个能够改成变量 out.println("<td><a href=FileDownServlet?filename=dos.rar>dos视频教程</a></td>"); out.println("<td><a href=FileDownServlet?filename=经常使用DOS命令.rar>经常使用DOS命令</a></td>"); out.println("</tr>"); // } %> </body></html> //这是web.xml配置文件，这非常重要，不然，非常难实现哦<?xml version="1.0" encoding="UTF-8"?><web-app version="2.4" xmlns="" xmlns:xsi="" xsi:schemaLocation=" "> <servlet> <description>This is the description of my J2EE component</description> <display-name>This is the display name of my J2EE component</display-name> <servlet-name>FileDownServlet</servlet-name> <servlet-class>com.message.FileDownServlet</servlet-class> </servlet><servlet-mapping>
<servlet-name>FileDownServlet</servlet-name> <url-pattern>/FileDownServlet</url-pattern> </servlet-mapping></web-app>