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">

</head>

<body>
    
    <%
//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("/")+1);
    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="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<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>

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实现文件下载的java代码

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