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：
[java] view plaincopyprint?
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;
}

}