需求:实现一个具有文件下载功能的网页,主要下载压缩包和图片
两种实现方法:
一:通过超链接实现下载
在HTML网页中,通过超链接链接到要下载的文件的地址
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="UTF-8">
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<title>Insert title here</title>
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</head>
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<body>
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<h1>通过链接下载文件</h1>
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<a href="/day06/download/cors.zip">压缩包</a>
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<a href="/day06/download/1.png">图片</a>
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</body>
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</html>
其中day06/download是文档路径,本实例的程序结构如下:
程序运行后,可以通过单击需要下载文档实现下载
但是这里会出现一个问题,就是单击下载压缩包的时候会弹出下载页面,但是下载图片的时候浏览器就直接打开了图片,没有下载。
这是因为通过超链接下载文件时,如果浏览器可以识别该文件格式,浏览器就会直接打开。只有浏览器不能识别该文件格式的时候,才会实现下载。因此利用第二种方法实现下载功能。
二:通过Servlet程序实现下载
通过Servlet下载文件的原理是通过servlet读取目标程序,将资源返回客户端。
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="UTF-8">
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<title>Insert title here</title>
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</head>
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<body>
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<h1>通过链接下载文件</h1>
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<a href="/day06/download/cors.zip">压缩包</a>
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<a href="/day06/download/1.png">图片</a>
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<h1>通过servlet程序下载文件</h1>
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<a href="/day06/ServletDownload?filename=cors.zip">压缩包</a>
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<a href="/day06/ServletDownload?filename=1.png">图片</a>
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</body>
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</html>
其中,/day06/ServletDownload 是servlet程序的映射路径
然后新建一个servlet,名称为ServletDownload,URL映射为/ServletDownload
添加代码如下:
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package com.lsgjzhuwei.servlet.response;
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import java.io.FileInputStream;
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import java.io.FileOutputStream;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.OutputStream;
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import javax.servlet.ServletException;
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import javax.servlet.annotation.WebServlet;
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import javax.servlet.http.HttpServlet;
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import javax.servlet.http.HttpServletRequest;
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import javax.servlet.http.HttpServletResponse;
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/**
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* Servlet implementation class ServletDownload
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*/
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@WebServlet(asyncSupported = true, urlPatterns = { "/ServletDownload" })
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public class ServletDownload extends HttpServlet {
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private static final long serialVersionUID = 1L;
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/**
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* @see HttpServlet#HttpServlet()
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*/
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public ServletDownload() {
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super();
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// TODO Auto-generated constructor stub
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}
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/**
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* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
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*/
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protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
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// TODO Auto-generated method stub
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//获得请求文件名
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String filename = request.getParameter("filename");
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System.out.println(filename);
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//设置文件MIME类型
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response.setContentType(getServletContext().getMimeType(filename));
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//设置Content-Disposition
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response.setHeader("Content-Disposition", "attachment;filename="+filename);
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//读取目标文件,通过response将目标文件写到客户端
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//获取目标文件的绝对路径
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String fullFileName = getServletContext().getRealPath("/download/" + filename);
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//System.out.println(fullFileName);
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//读取文件
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InputStream in = new FileInputStream(fullFileName);
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OutputStream out = response.getOutputStream();
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//写文件
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int b;
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while((b=in.read())!= -1)
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{
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out.write(b);
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}
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in.close();
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out.close();
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}
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/**
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* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
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*/
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protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
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// TODO Auto-generated method stub
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}
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}
重启tomcat服务器,即可实现对压缩包和对图片的下载。
1 /**
2 * TODO 下载文件到本地
3 * @author nadim
4 * @date Sep 11, 2015 11:45:31 AM
5 * @param fileUrl 远程地址
6 * @param fileLocal 本地路径
7 * @throws Exception
8 */
9 public void downloadFile(String fileUrl,String fileLocal) throws Exception {
10 URL url = new URL(fileUrl);
11 HttpURLConnection urlCon = (HttpURLConnection) url.openConnection();
12 urlCon.setConnectTimeout(6000);
13 urlCon.setReadTimeout(6000);
14 int code = urlCon.getResponseCode();
15 if (code != HttpURLConnection.HTTP_OK) {
16 throw new Exception("文件读取失败");
17 }
18
19 //读文件流
20 DataInputStream in = new DataInputStream(urlCon.getInputStream());
21 DataOutputStream out = new DataOutputStream(new FileOutputStream(fileLocal));
22 byte[] buffer = new byte[2048];
23 int count = 0;
24 while ((count = in.read(buffer)) > 0) {
25 out.write(buffer, 0, count);
26 }
27 out.close();
28 in.close();
29 }