下载

把一个文件转换成字节数组，使用response.getOutputStream()传递给浏览器
2个响应头
Content-Type：文件的MIME类型
-调用ServletContext的getMimeType(文件名称),得到MIME类型
Content-Disposition：默认为inline（在浏览器中打开）attachment;filename=xxx
-在filename=后面跟随的显示在下载框中的文件名称
1个响应体（下载流）
=================
注意
====
显示在下载框中的文件名如果为中文，会出现乱码
浏览器使用的编码
*FirFox：Base64编码
*其他：URL编码

解决方案：

package com.web.servlet;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLEncoder;

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

import org.apache.commons.io.IOUtils;

import sun.misc.BASE64Encoder;

public class DonwloadServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String filename = "D:/CloudMusic/岸部真明 - 流れ行く云.mp3";
        
		//解决显示乱码问题
		String framename = filenameEncoding("岸部真明 - 流れ行く云.mp3", request);	
		//获取文件MIME类型
		String contentType = this.getServletContext().getMimeType(filename);
		String contentDisposition = "attacment;filename="+framename;
		//输入流
		FileInputStream input= new FileInputStream(filename);
		//设置头
		response.setHeader("Content-Type", contentType);
		response.setHeader("Content-Disposition", contentDisposition);
		
		//绑定流
		ServletOutputStream output = response.getOutputStream();
		
		IOUtils.copy(input, output);
		
	}

	public static String filenameEncoding(String filename,
			HttpServletRequest request) throws IOException {
		String agent = request.getHeader("User-Agent"); // 获取浏览器
		if (agent.contains("Firefox")) {
			BASE64Encoder base64Encoder = new BASE64Encoder();
			filename = "=?utf-8?B?"
					+ base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
		} else if (agent.contains("MSIE")) {
			filename = URLEncoder.encode(filename, "utf-8");
		} else {
			filename = URLEncoder.encode(filename, "utf-8");
		}
		return filename;
	}
}