下載

把一個文件轉換成字節數組，使用response.getOutputStream()傳遞給瀏覽器
2個響應頭
Content-Type：文件的MIME類型
-調用ServletContext的getMimeType(文件名稱),得到MIME類型
Content-Disposition：默認爲inline（在瀏覽器中打開）attachment;filename=xxx
-在filename=後面跟隨的顯示在下載框中的文件名稱
1個響應體（下載流）
=================
注意
====
顯示在下載框中的文件名如果爲中文，會出現亂碼
瀏覽器使用的編碼
*FirFox：Base64編碼
*其他：URL編碼

解決方案：

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/岸部眞明 - 流れ行く雲.mp3";
        
		//解決顯示亂碼問題
		String framename = filenameEncoding("岸部眞明 - 流れ行く雲.mp3", request);	
		//獲取文件MIME類型
		String contentType = this.getServletContext().getMimeType(filename);
		String contentDisposition = "attacment;filename="+framename;
		//輸入流
		FileInputStream input= new FileInputStream(filename);
		//設置頭
		response.setHeader("Content-Type", contentType);
		response.setHeader("Content-Disposition", contentDisposition);
		
		//綁定流
		ServletOutputStream output = response.getOutputStream();
		
		IOUtils.copy(input, output);
		
	}

	public static String filenameEncoding(String filename,
			HttpServletRequest request) throws IOException {
		String agent = request.getHeader("User-Agent"); // 獲取瀏覽器
		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;
	}
}