java web文件下载功能实现（转）

2023-01-04 13:35:58

http://blog.csdn.net/longshengguoji/article/details/39433307

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

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>通过链接下载文件</h1>
<a href="/day06/download/cors.zip">压缩包</a>
<a href="/day06/download/1.png">图片</a>
</body>
</html>

<!DOCTYPE html>

<html>

<head>

<meta charset="UTF-8">

<title>Insert title here</title>

</head>

<body>

<h1>通过链接下载文件</h1>

<a href="/day06/download/cors.zip">压缩包</a>

<a href="/day06/download/1.png">图片</a>

</body>

</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。

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>通过链接下载文件</h1>
<a href="/day06/download/cors.zip">压缩包</a>
<a href="/day06/download/1.png">图片</a>
<h1>通过servlet程序下载文件</h1>
<a href="/day06/ServletDownload?filename=cors.zip">压缩包</a>
<a href="/day06/ServletDownload?filename=1.png">图片</a>
</body>
</html>

<!DOCTYPE html>

<html>

<head>

<meta charset="UTF-8">

<title>Insert title here</title>

</head>

<body>

<h1>通过链接下载文件</h1>

<a href="/day06/download/cors.zip">压缩包</a>

<a href="/day06/download/1.png">图片</a>

<h1>通过servlet程序下载文件</h1>

<a href="/day06/ServletDownload?filename=cors.zip">压缩包</a>

<a href="/day06/ServletDownload?filename=1.png">图片</a>

</body>

</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：

package com.lsgjzhuwei.servlet.response;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class ServletDownload
*/
@WebServlet(asyncSupported = true, urlPatterns = { "/ServletDownload" })
public class ServletDownload extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public ServletDownload() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
//获得请求文件名
String filename = request.getParameter("filename");
System.out.println(filename);
//设置文件MIME类型
response.setContentType(getServletContext().getMimeType(filename));
//设置Content-Disposition
response.setHeader("Content-Disposition", "attachment;filename="+filename);
//读取目标文件，通过response将目标文件写到客户端
//获取目标文件的绝对路径
String fullFileName = getServletContext().getRealPath("/download/" + filename);
//System.out.println(fullFileName);
//读取文件
InputStream in = new FileInputStream(fullFileName);
OutputStream out = response.getOutputStream();
//写文件
int b;
while((b=in.read())!= -1)
{
out.write(b);
}
in.close();
out.close();
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
}

package com.lsgjzhuwei.servlet.response;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/**

 * Servlet implementation class ServletDownload

 */

@WebServlet(asyncSupported = true, urlPatterns = { "/ServletDownload" })

public class ServletDownload extends HttpServlet {

	private static final long serialVersionUID = 1L;

    /**

     * @see HttpServlet#HttpServlet()

     */

    public ServletDownload() {

        super();

        // TODO Auto-generated constructor stub

    }

	/**

	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

	 */

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

		// TODO Auto-generated method stub

		//获得请求文件名

		String filename = request.getParameter("filename");

		System.out.println(filename);

		//设置文件MIME类型

		response.setContentType(getServletContext().getMimeType(filename));

		//设置Content-Disposition

		response.setHeader("Content-Disposition", "attachment;filename="+filename);

		//读取目标文件，通过response将目标文件写到客户端

		//获取目标文件的绝对路径

		String fullFileName = getServletContext().getRealPath("/download/" + filename);

		//System.out.println(fullFileName);

		//读取文件

		InputStream in = new FileInputStream(fullFileName);

		OutputStream out = response.getOutputStream();

		//写文件

		int b;

		while((b=in.read())!= -1)

		{

			out.write(b);

		}

		in.close();

		out.close();

	}

	/**

	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

	 */

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

		// TODO Auto-generated method stub

	}

}

重启tomcat服务器，即可实现对压缩包和对图片的下载。

码农公寓

一：通过超链接实现下载

二：通过Servlet程序实现下载

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