java web文件下載功能實現（轉）

時間 2019-11-17

標籤 java web 文件下載功能實現欄目 Java 简体版

原文原文鏈接

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

需求：實現一個具備文件下載功能的網頁，主要下載壓縮包和圖片java

兩種實現方法：瀏覽器

一：經過超連接實現下載

在HTML網頁中，經過超連接連接到要下載的文件的地址

[html] view plain copy

print ?

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>經過連接下載文件</h1>
<a href="/day06/download/cors.zip">壓縮包</a>
<a href="/day06/download/1.png">圖片</a>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>經過連接下載文件</h1>
<a href="/day06/download/cors.zip">壓縮包</a>
<a href="/day06/download/1.png">圖片</a>
</body>
</html>

其中day06/download是文檔路徑，本實例的程序結構以下：

程序運行後，能夠經過單擊須要下載文檔實現下載

可是這裏會出現一個問題，就是單擊下載壓縮包的時候會彈出下載頁面，可是下載圖片的時候瀏覽器就直接打開了圖片，沒有下載。

這是由於經過超連接下載文件時，若是瀏覽器能夠識別該文件格式，瀏覽器就會直接打開。只有瀏覽器不能識別該文件格式的時候，纔會實現下載。所以利用第二種方法實現下載功能。

二：經過Servlet程序實現下載

經過Servlet下載文件的原理是經過servlet讀取目標程序，將資源返回客戶端。

[html] view plain copy

print ?

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>經過連接下載文件</h1>
<a href="/day06/download/cors.zip">壓縮包</a>
<a href="/day06/download/1.png">圖片</a>
<h1>經過servlet程序下載文件</h1>
<a href="/day06/ServletDownload?filename=cors.zip">壓縮包</a>
<a href="/day06/ServletDownload?filename=1.png">圖片</a>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>經過連接下載文件</h1>
<a href="/day06/download/cors.zip">壓縮包</a>
<a href="/day06/download/1.png">圖片</a>
<h1>經過servlet程序下載文件</h1>
<a href="/day06/ServletDownload?filename=cors.zip">壓縮包</a>
<a href="/day06/ServletDownload?filename=1.png">圖片</a>
</body>
</html>

其中，/day06/ServletDownload 是servlet程序的映射路徑

而後新建一個servlet，名稱爲ServletDownload,URL映射爲/ServletDownload

添加代碼以下：

[java] view plain copy

print ?

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
//得到請求文件名
String filename = request.getParameter("filename");
System.out.println(filename);
//設置文件MIME類型
response.setContentType(getServletContext().getMimeType(filename));
//設置Content-Disposition
response.setHeader("Content-Disposition", "attachment;filename="+filename);
//讀取目標文件，經過response將目標文件寫到客戶端
//獲取目標文件的絕對路徑
String fullFileName = getServletContext().getRealPath("/download/" + filename);
//System.out.println(fullFileName);
//讀取文件
InputStream in = new FileInputStream(fullFileName);
OutputStream out = response.getOutputStream();
//寫文件
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
		
		//得到請求文件名
		String filename = request.getParameter("filename");
		System.out.println(filename);
		
		//設置文件MIME類型
		response.setContentType(getServletContext().getMimeType(filename));
		//設置Content-Disposition
		response.setHeader("Content-Disposition", "attachment;filename="+filename);
		//讀取目標文件，經過response將目標文件寫到客戶端
		//獲取目標文件的絕對路徑
		String fullFileName = getServletContext().getRealPath("/download/" + filename);
		//System.out.println(fullFileName);
		//讀取文件
		InputStream in = new FileInputStream(fullFileName);
		OutputStream out = response.getOutputStream();
		
		//寫文件
		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
	}

}

重啓tomcat服務器，便可實現對壓縮包和對圖片的下載。