java web response提供文件下载功能

分类: java学习笔记

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webapp项目的结构如下图：

download.html文件的内容如下：

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
        <h1>资源下载:</h1>
       <p> 单纯地使用a标签时，只有浏览器不能解析的文件才会是下载，否则将被浏览器直接解析。</p>
        <a href="/WEB/resource/a.mp3" >a.mp3</a><br>
        <a href="/WEB/resource/a.exe" >a.exe</a><br>
        <a href="/WEB/resource/a.txt" >a.txt</a><br>
        <a href="/WEB/resource/a.xlsx" >a.xlsx</a><br>
        <a href="/WEB/resource/a.png" >a.png</a><br>

        <p>因此，使用a标签结合servlet的response指示浏览器不解析这些待下载文件</p>
        <a href="/WEB/download?filename=a.mp3" >a.mp3</a><br>
        <a href="/WEB/download?filename=a.exe" >a.exe</a><br>
        <a href="/WEB/download?filename=a.txt" >a.txt</a><br>
        <a href="/WEB/download?filename=a.xlsx" >a.xlsx</a><br>
        <a href="/WEB/download?filename=a.png" >a.png</a><br>
</body>
</html>

负责处理下载的Servlet——download.java文件的内容如下：

package com.download.servlet;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Download
 */
public class Download extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.获取请求下载的文件名
        String filename = request.getParameter("filename");

        //2.获取文件的文件系统路径
        String filePath = request.getServletContext().getRealPath("resource/"+filename);

        //3.设置响应头，提示浏览器不要解析响应的文件数据，而是以附件(attachment)的形式解析，即下载功能
        response.setContentType(this.getServletContext().getMimeType(filename));
        response.setHeader("Content-Disposition", "attachment;filename="+filename);

        //4.读取文件的 输入流，以及响应的输出流，并将数据输出给客户端
        InputStream in = new FileInputStream(filePath);
        ServletOutputStream out = response.getOutputStream();
        int len = 0;
        byte[] buf = new byte[1024];
        while((len=in.read(buf))!=-1) {
            out.write(buf, 0, len);
        }

        in.close();
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}