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;  
    }  
      
      
}