package com.xmyself.servlet;

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

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

public class DownloadServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	public void init(ServletConfig config) throws ServletException {
	}

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

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws IOException, ServletException {
		response.setContentType("text/plain");
		response.setHeader("Content-Disposition", "attachment; filename=test.jpg");
		OutputStream outputStream = response.getOutputStream();
		File file = new File("D:\\test.jpg");
		InputStream inputStream = null;
		try {
			inputStream = new FileInputStream(file);
			byte[] buffer = new byte[1024];
			int i = -1;
			while ((i = inputStream.read(buffer)) != -1) {
				outputStream.write(buffer, 0, i);
			}
			outputStream.flush();
			outputStream.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public void destroy() {
	}
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	version="2.5">
	<display-name>servlet</display-name>

	<servlet>
		<servlet-name>download</servlet-name>
		<servlet-class>com.xmyself.servlet.DownloadServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>download</servlet-name>
		<url-pattern>/download</url-pattern>
	</servlet-mapping>
</web-app>

http://localhost:8080/servlet/download