java多线程下载服务器端支持

转自http://m.oschina.net/blog/167665

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）
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： 
[html] view plaincopyprint? 
<!-- 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： 
[java] view plaincopyprint? 
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; 
} 


}