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Java 服务器端支持断点续传的源代码【支持快车、迅雷】(仅支持 HTTP 协议)

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  网上关于 Java 支持 HTTP 断点续传的文章不少,但关于 Java 服务器端支持 HTTP 断点续传的却比较少。
        本文是 Java 服务器端支持 HTTP 断点续传的源代码,支持快车、迅雷。
        本文使用一个简单的 Servlet 来作为支持断点续传的下载示例,在 Java Web 项目下部署好后,可以使用诸如 http://localhost/cds/http 的链接来调用 Servlet,进而被快车/迅雷监听进行下载。

        ArcSyncHttpDownloadServlet 源代码:

package com.defonds.cds.common;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.io.RandomAccessFile;

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

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.defonds.cds.common.util.CommonUtil;

//HTTP 断点续传 demo(客户端测试工具:快车、迅雷)
public class ArcSyncHttpDownloadServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	final static Log log = LogFactory.getLog(ArcSyncHttpDownloadServlet.class);
	
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		this.doPost(req, resp);
	}
	
	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response) {
		File downloadFile = new File("D:/defonds/book/pattern/SteveJobsZH.pdf");//要下载的文件
    	long fileLength = downloadFile.length();//记录文件大小
		long pastLength = 0;//记录已下载文件大小
		int rangeSwitch = 0;//0:从头开始的全文下载;1:从某字节开始的下载(bytes=27000-);2:从某字节开始到某字节结束的下载(bytes=27000-39000)
		long toLength = 0;//记录客户端需要下载的字节段的最后一个字节偏移量(比如bytes=27000-39000,则这个值是为39000)
		long contentLength = 0;//客户端请求的字节总量
		String rangeBytes = "";//记录客户端传来的形如“bytes=27000-”或者“bytes=27000-39000”的内容 
		RandomAccessFile raf = null;//负责读取数据
		OutputStream os = null;//写出数据
		OutputStream out = null;//缓冲
		byte b[] = new byte[1024];//暂存容器
		
		if (request.getHeader("Range") != null) {// 客户端请求的下载的文件块的开始字节
			response.setStatus(javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT);
			log.info("request.getHeader(\"Range\")=" + request.getHeader("Range"));
			rangeBytes = request.getHeader("Range").replaceAll("bytes=", "");
			if (rangeBytes.indexOf('-') == rangeBytes.length() - 1) {//bytes=969998336-
				rangeSwitch = 1;
				rangeBytes = rangeBytes.substring(0, rangeBytes.indexOf('-'));
				pastLength = Long.parseLong(rangeBytes.trim());
				contentLength = fileLength - pastLength + 1;//客户端请求的是 969998336 之后的字节
			} else {//bytes=1275856879-1275877358
				rangeSwitch = 2;
				String temp0 = rangeBytes.substring(0,rangeBytes.indexOf('-'));
				String temp2 = rangeBytes.substring(rangeBytes.indexOf('-') + 1, rangeBytes.length());
				pastLength = Long.parseLong(temp0.trim());//bytes=1275856879-1275877358,从第 1275856879 个字节开始下载
				toLength = Long.parseLong(temp2);//bytes=1275856879-1275877358,到第 1275877358 个字节结束
				contentLength = toLength - pastLength + 1;//客户端请求的是 1275856879-1275877358  之间的字节
			}
		} else {//从开始进行下载
			contentLength = fileLength;//客户端要求全文下载
		}
		
		/**
		 * 如果设设置了Content-Length,则客户端会自动进行多线程下载。如果不希望支持多线程,则不要设置这个参数。
		 * 响应的格式是:
		 * Content-Length: [文件的总大小] - [客户端请求的下载的文件块的开始字节]
		 * ServletActionContext.getResponse().setHeader("Content-Length",
		 * new Long(file.length() - p).toString());
		 */
		response.reset();//告诉客户端允许断点续传多线程连接下载,响应的格式是:Accept-Ranges: bytes
		response.setHeader("Accept-Ranges", "bytes");//如果是第一次下,还没有断点续传,状态是默认的 200,无需显式设置;响应的格式是:HTTP/1.1 200 OK
		if (pastLength != 0) {
			//不是从最开始下载,
			//响应的格式是:
			//Content-Range: bytes [文件块的开始字节]-[文件的总大小 - 1]/[文件的总大小]
			log.info("----------------------------不是从开始进行下载!服务器即将开始断点续传...");
			switch (rangeSwitch) {
				case 1 : {//针对 bytes=27000- 的请求
					String contentRange = new StringBuffer("bytes ").append(new Long(pastLength).toString()).append("-").append(new Long(fileLength - 1).toString()).append("/").append(new Long(fileLength).toString()).toString();
					response.setHeader("Content-Range", contentRange);
					break;
				}
				case 2 : {//针对 bytes=27000-39000 的请求
					String contentRange = rangeBytes + "/" + new Long(fileLength).toString();
					response.setHeader("Content-Range", contentRange);
					break;
				}
				default : {
					break;
				}
			}
		} else {
			//是从开始下载
			log.info("----------------------------是从开始进行下载!");
		}
		
		try {
	    	response.addHeader("Content-Disposition", "attachment; filename=\"" + downloadFile.getName() + "\"");
	    	response.setContentType( CommonUtil.setContentType(downloadFile.getName()));// set the MIME type.
	        response.addHeader("Content-Length", String.valueOf(contentLength));
			os = response.getOutputStream();
	    	out = new BufferedOutputStream(os);
	    	raf = new RandomAccessFile(downloadFile, "r");
	    	try {
	    		switch (rangeSwitch) {
		    		case 0 : {//普通下载,或者从头开始的下载
		    			//同1
		    		}
		    		case 1 : {//针对 bytes=27000- 的请求
		    			raf.seek(pastLength);//形如 bytes=969998336- 的客户端请求,跳过 969998336  个字节
				        int n = 0;
				        while ((n = raf.read(b, 0, 1024)) != -1) {
				        	out.write(b, 0, n);
				        }
		    			break;
		    		}
		    		case 2 : {//针对 bytes=27000-39000 的请求
		    			raf.seek(pastLength - 1);//形如 bytes=1275856879-1275877358 的客户端请求,找到第 1275856879 个字节
		    			int n = 0;
		    			long readLength = 0;//记录已读字节数
		    			while (readLength <= contentLength - 1024) {//大部分字节在这里读取
		    				n = raf.read(b, 0, 1024);
		    				readLength += 1024;
		    				out.write(b, 0, n);
		    			}
		    			if (readLength <= contentLength) {//余下的不足 1024 个字节在这里读取
		    				n = raf.read(b, 0, (int)(contentLength - readLength));
		    				out.write(b, 0, n);
		    			}
//		    			
//		    			raf.seek(pastLength);//形如 bytes=1275856879-1275877358 的客户端请求,找到第 1275856879 个字节
//			        	while (raf.getFilePointer() < toLength) {
//			        		out.write(raf.read());
//			        	}
		    			break;
		    		}
		    		default : {
		    			break;
		    		}
	    		}
		        out.flush();
	    	} catch(IOException ie) {
	    		/**
				 * 在写数据的时候,
				 * 对于 ClientAbortException 之类的异常,
				 * 是因为客户端取消了下载,而服务器端继续向浏览器写入数据时,
				 * 抛出这个异常,这个是正常的。
				 * 尤其是对于迅雷这种吸血的客户端软件,
				 * 明明已经有一个线程在读取 bytes=1275856879-1275877358,
				 * 如果短时间内没有读取完毕,迅雷会再启第二个、第三个。。。线程来读取相同的字节段,
				 * 直到有一个线程读取完毕,迅雷会 KILL 掉其他正在下载同一字节段的线程,
				 * 强行中止字节读出,造成服务器抛 ClientAbortException。
				 * 所以,我们忽略这种异常
				 */
				//ignore
	    	}
		} catch (Exception e) {
			log.error(e.getMessage(), e);
		} finally {
			if (out != null) {
				try {
					out.close();
				} catch (IOException e) {
					log.error(e.getMessage(), e);
				}
			}
			if (raf != null) {
				try {
					raf.close();
				} catch (IOException e) {
					log.error(e.getMessage(), e);
				}
			}
		}
	}
}

 

 ArcSyncHttpDownloadServlet 的 web.xml 配置清单:

		<!-- HTTP 断点续传 demo:127.0.0.1/cds/http -->
	<servlet>
		<servlet-name>httpServlet</servlet-name>
		<servlet-class>com.defonds.cds.common.ArcSyncHttpDownloadServlet</servlet-class>
	</servlet>	
	<servlet-mapping>
		<servlet-name>httpServlet</servlet-name>
		<url-pattern>/http</url-pattern>
	</servlet-mapping>	

  ArcSyncHttpDownloadServlet 调用到的工具类 com.defonds.cds.common.util.CommonUtil 源代码:

 

 

 

package com.defonds.cds.common.util;

public class CommonUtil {

	public static String setContentType(String returnFileName){
		String contentType = "application/octet-stream";
		if (returnFileName.lastIndexOf(".") < 0)
			return contentType;
		returnFileName = returnFileName.toLowerCase();
		returnFileName = returnFileName.substring(returnFileName.lastIndexOf(".")+1);
		
		if (returnFileName.equals("html") || returnFileName.equals("htm") || returnFileName.equals("shtml")){
			contentType = "text/html";
		} else if (returnFileName.equals("css")){
			contentType = "text/css";
		} else if (returnFileName.equals("xml")){
			contentType = "text/xml";
		} else if (returnFileName.equals("gif")){
			contentType = "image/gif";
		} else if (returnFileName.equals("jpeg") || returnFileName.equals("jpg")){
			contentType = "image/jpeg";
		} else if (returnFileName.equals("js")){
			contentType = "application/x-javascript";
		} else if (returnFileName.equals("atom")){
			contentType = "application/atom+xml";
		} else if (returnFileName.equals("rss")){
			contentType = "application/rss+xml";
		} else if (returnFileName.equals("mml")){
			contentType = "text/mathml"; 
		} else if (returnFileName.equals("txt")){
			contentType = "text/plain";
		} else if (returnFileName.equals("jad")){
			contentType = "text/vnd.sun.j2me.app-descriptor";
		} else if (returnFileName.equals("wml")){
			contentType = "text/vnd.wap.wml";
		} else if (returnFileName.equals("htc")){
			contentType = "text/x-component";
		} else if (returnFileName.equals("png")){
			contentType = "image/png";
		} else if (returnFileName.equals("tif") || returnFileName.equals("tiff")){
			contentType = "image/tiff";
		} else if (returnFileName.equals("wbmp")){
			contentType = "image/vnd.wap.wbmp";
		} else if (returnFileName.equals("ico")){
			contentType = "image/x-icon";
		} else if (returnFileName.equals("jng")){
			contentType = "image/x-jng";
		} else if (returnFileName.equals("bmp")){
			contentType = "image/x-ms-bmp";
		} else if (returnFileName.equals("svg")){
			contentType = "image/svg+xml";
		} else if (returnFileName.equals("jar") || returnFileName.equals("var") || returnFileName.equals("ear")){
			contentType = "application/java-archive";
		} else if (returnFileName.equals("doc")){
			contentType = "application/msword";
		} else if (returnFileName.equals("pdf")){
			contentType = "application/pdf";
		} else if (returnFileName.equals("rtf")){
			contentType = "application/rtf";
		} else if (returnFileName.equals("xls")){
			contentType = "application/vnd.ms-excel"; 
		} else if (returnFileName.equals("ppt")){
			contentType = "application/vnd.ms-powerpoint";
		} else if (returnFileName.equals("7z")){
			contentType = "application/x-7z-compressed";
		} else if (returnFileName.equals("rar")){
			contentType = "application/x-rar-compressed";
		} else if (returnFileName.equals("swf")){
			contentType = "application/x-shockwave-flash";
		} else if (returnFileName.equals("rpm")){
			contentType = "application/x-redhat-package-manager";
		} else if (returnFileName.equals("der") || returnFileName.equals("pem") || returnFileName.equals("crt")){
			contentType = "application/x-x509-ca-cert";
		} else if (returnFileName.equals("xhtml")){
			contentType = "application/xhtml+xml";
		} else if (returnFileName.equals("zip")){
			contentType = "application/zip";
		} else if (returnFileName.equals("mid") || returnFileName.equals("midi") || returnFileName.equals("kar")){
			contentType = "audio/midi";
		} else if (returnFileName.equals("mp3")){
			contentType = "audio/mpeg";
		} else if (returnFileName.equals("ogg")){
			contentType = "audio/ogg";
		} else if (returnFileName.equals("m4a")){
			contentType = "audio/x-m4a";
		} else if (returnFileName.equals("ra")){
			contentType = "audio/x-realaudio";
		} else if (returnFileName.equals("3gpp") || returnFileName.equals("3gp")){
			contentType = "video/3gpp";
		} else if (returnFileName.equals("mp4") ){
			contentType = "video/mp4";
		} else if (returnFileName.equals("mpeg") || returnFileName.equals("mpg") ){
			contentType = "video/mpeg";
		} else if (returnFileName.equals("mov")){
			contentType = "video/quicktime";
		} else if (returnFileName.equals("flv")){
			contentType = "video/x-flv";
		} else if (returnFileName.equals("m4v")){
			contentType = "video/x-m4v";
		} else if (returnFileName.equals("mng")){
			contentType = "video/x-mng";
		} else if (returnFileName.equals("asx") || returnFileName.equals("asf")){
			contentType = "video/x-ms-asf";
		} else if (returnFileName.equals("wmv")){
			contentType = "video/x-ms-wmv";
		} else if (returnFileName.equals("avi")){
			contentType = "video/x-msvideo";
		}
		
		return contentType;
	}
	
	
}

 

本文示例代码在客户端使用快车(FlashGet)3、迅雷7 进行断点续传的环境下测试 OK。

        本文仅为用来技术交流的演示 Demo,技术水平及知识面所限,其中错误和不当之处在所难免,敬请谅解。欢迎联系作者进行批评指正,技术交流 MSN:defonds(at)hotmail(dot)com,也可以给我发邮件,email:defonds(at)163(dot)com。

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