Servlet教程
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使用Servlet下载文件

要从服务器下载文件，请参见下面的简单示例。假设您要下载的D盘一个文件，需要创建一个程序来下载该文件。

1 准备下载的文件

文件所在目录和名称根据您的情况来定。

2 编写index.jsp

index.jsp用于点击下载链接：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>一点教程网-使用Servlet下载文件</title>
</head>
<body>
<h1>使用Servlet下载文件</h1>
<a href="Download">点击下载</a>
</body>
</html>

3 编写DownloadServlet

DownloadServlet用于完成核心下载逻辑：

import com.oreilly.servlet.MultipartRequest;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * 一点教程网 - http://www.yiidian.com
 */
public class DownloadServlet extends HttpServlet {

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

        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        String filename = "20200113_103731444.zip";
        String filepath = "d:\\upload\\";
        response.setContentType("APPLICATION/OCTET-STREAM");
        response.setHeader("Content-Disposition","attachment; filename=\"" + filename + "\"");

        FileInputStream fileInputStream = new FileInputStream(filepath + filename);

        int i;
        while ((i=fileInputStream.read()) != -1) {
            out.write(i);
        }
        fileInputStream.close();
        out.close();
    }

}

4 配置web.xml

web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">

    <servlet>
        <servlet-name>DownloadServlet</servlet-name>
        <servlet-class>DownloadServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>DownloadServlet</servlet-name>
        <url-pattern>/Download</url-pattern>
    </servlet-mapping>

</web-app>

5 运行测试 

 使用Servlet上传文件 使用Servlet发送邮件 

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