Java 多线程断点下载文件

基本原理：利用URLConnection获取要下载文件的长度、头部等相关信息，并设置响应的头部信息。并且通过URLConnection获取输入流，将文件分成指定的块，每一块单独开辟一个线程完成数据的读取、写入。通过输入流读取下载文件的信息，然后将读取的信息用RandomAccessFile随机写入到本地文件中。同时，每个线程写入的数据都文件指针也就是写入数据的长度，需要保存在一个临时文件中。这样当本次下载没有完成的时候，下次下载的时候就从这个文件中读取上一次下载的文件长度，然后继续接着上一次的位置开始下载。并且将本次下载的长度写入到这个文件中。
一、下载文件信息类、实体
封装即将下载资源的信息

package com.hoo.entity;/** * <b>function:</b> 下载文件信息类 * @author hoojo * @createDate 2011-9-21 下午05:14:58 * @file DownloadInfo.java * @package com.hoo.entity * @project MultiThreadDownLoad * @blog http://blog.csdn.net/IBM_hoojo * @email [e-mail] * @version 1.0 */public class DownloadInfo {    //下载文件url    private String url;    //下载文件名称    private String fileName;    //下载文件路径    private String filePath;    //分成多少段下载， 每一段用一个线程完成下载    private int splitter;    //下载文件默认保存路径    private final static String FILE_PATH = "C:/temp";    //默认分块数、线程数    private final static int SPLITTER_NUM = 5;    public DownloadInfo() {        super();    }    /**     * @param url 下载地址     */    public DownloadInfo(String url) {        this(url, null, null, SPLITTER_NUM);    }    /**     * @param url 下载地址url     * @param splitter 分成多少段或是多少个线程下载     */    public DownloadInfo(String url, int splitter) {        this(url, null, null, splitter);    }    /***     * @param url 下载地址     * @param fileName 文件名称     * @param filePath 文件保存路径     * @param splitter 分成多少段或是多少个线程下载     */    public DownloadInfo(String url, String fileName, String filePath, int splitter) {        super();        if (url == null || "".equals(url)) {            throw new RuntimeException("url is not null!");        }        this.url =  url;        this.fileName = (fileName == null || "".equals(fileName)) ? getFileName(url) : fileName;        this.filePath = (filePath == null || "".equals(filePath)) ? FILE_PATH : filePath;        this.splitter = (splitter < 1) ? SPLITTER_NUM : splitter;    }    /**     * <b>function:</b> 通过url获得文件名称     * @author hoojo     * @createDate 2011-9-30 下午05:00:00     * @param url     * @return     */    private String getFileName(String url) {        return url.substring(url.lastIndexOf("/") + 1, url.length());    }    public String getUrl() {        return url;    }    public void setUrl(String url) {        if (url == null || "".equals(url)) {            throw new RuntimeException("url is not null!");        }        this.url = url;    }    public String getFileName() {        return fileName;    }    public void setFileName(String fileName) {        this.fileName = (fileName == null || "".equals(fileName)) ? getFileName(url) : fileName;    }    public String getFilePath() {        return filePath;    }    public void setFilePath(String filePath) {        this.filePath = (filePath == null || "".equals(filePath)) ? FILE_PATH : filePath;    }    public int getSplitter() {        return splitter;    }    public void setSplitter(int splitter) {        this.splitter = (splitter < 1) ? SPLITTER_NUM : splitter;    }    @Override    public String toString() {        return this.url + "#" + this.fileName + "#" + this.filePath + "#" + this.splitter;    }}

二、随机写入一段文件

package com.hoo.download;import java.io.IOException;import java.io.RandomAccessFile;/** * <b>function:</b> 写入文件、保存文件 * @author hoojo * @createDate 2011-9-21 下午05:44:02 * @file SaveItemFile.java * @package com.hoo.download * @project MultiThreadDownLoad * @blog http://blog.csdn.net/IBM_hoojo * @email [e-mail] * @version 1.0 */public class SaveItemFile {    //存储文件    private RandomAccessFile itemFile;    public SaveItemFile() throws IOException {        this("", 0);    }    /**     * @param name 文件路径、名称     * @param pos 写入点位置 position     * @throws IOException     */    public SaveItemFile(String name, long pos) throws IOException {        itemFile = new RandomAccessFile(name, "rw");        //在指定的pos位置开始写入数据        itemFile.seek(pos);    }    /**     * <b>function:</b> 同步方法写入文件     * @author hoojo     * @createDate 2011-9-26 下午12:21:22     * @param buff 缓冲数组     * @param start 起始位置     * @param length 长度     * @return     */    public synchronized int write(byte[] buff, int start, int length) {        int i = -1;        try {            itemFile.write(buff, start, length);            i = length;        } catch (IOException e) {            e.printStackTrace();        }        return i;    }    public void close() throws IOException {        if (itemFile != null) {            itemFile.close();        }    }}

这个类主要是完成向本地的指定文件指针出开始写入文件，并返回当前写入文件的长度（文件指针）。这个类将被线程调用，文件被分成对应的块后，将被线程调用。每个线程都将会调用这个类完成文件的随机写入。

三、单个线程下载文件

package com.hoo.download;  import java.io.IOException;  import java.io.InputStream;  import java.net.HttpURLConnection;  import java.net.MalformedURLException;  import java.net.URL;  import java.net.URLConnection;  import com.hoo.util.LogUtils;  /**  * <b>function:</b> 单线程下载文件  * @author hoojo  * @createDate 2011-9-22 下午02:55:10  * @file DownloadFile.java  * @package com.hoo.download  * @project MultiThreadDownLoad  * @blog http://blog.csdn.net/IBM_hoojo  * @email [e-mail]  * @version 1.0  */  public class DownloadFile extends Thread {      //下载文件url      private String url;      //下载文件起始位置        private long startPos;      //下载文件结束位置      private long endPos;      //线程id      private int threadId;      //下载是否完成      private boolean isDownloadOver = false;      private SaveItemFile itemFile;      private static final int BUFF_LENGTH = 1024 * 8;      /**      * @param url 下载文件url      * @param name 文件名称      * @param startPos 下载文件起点      * @param endPos 下载文件结束点      * @param threadId 线程id      * @throws IOException      */      public DownloadFile(String url, String name, long startPos, long endPos, int threadId) throws IOException {          super();          this.url = url;          this.startPos = startPos;          this.endPos = endPos;          this.threadId = threadId;          //分块下载写入文件内容          this.itemFile = new SaveItemFile(name, startPos);      }      @Override      public void run() {          while (endPos > startPos && !isDownloadOver) {              try {                  URL url = new URL(this.url);                  HttpURLConnection conn = (HttpURLConnection) url.openConnection();                  // 设置连接超时时间为10000ms                  conn.setConnectTimeout(10000);                  // 设置读取数据超时时间为10000ms                  conn.setReadTimeout(10000);                  setHeader(conn);                  String property = "bytes=" + startPos + "-";                  conn.setRequestProperty("RANGE", property);                  //输出log信息                  LogUtils.log("开始 " + threadId + "：" + property + endPos);                  //printHeader(conn);                  //获取文件输入流，读取文件内容                  InputStream is = conn.getInputStream();                  byte[] buff = new byte[BUFF_LENGTH];                  int length = -1;                  LogUtils.log("#start#Thread: " + threadId + ", startPos: " + startPos + ", endPos: " + endPos);                  while ((length = is.read(buff)) > 0 && startPos < endPos && !isDownloadOver) {                      //写入文件内容，返回最后写入的长度                      startPos += itemFile.write(buff, 0, length);                  }                  LogUtils.log("#over#Thread: " + threadId + ", startPos: " + startPos + ", endPos: " + endPos);                  LogUtils.log("Thread " + threadId + " is execute over!");                  this.isDownloadOver = true;              } catch (MalformedURLException e) {                  e.printStackTrace();              } catch (IOException e) {                  e.printStackTrace();              } finally {                  try {                      if (itemFile != null) {                          itemFile.close();                      }                  } catch (IOException e) {                      e.printStackTrace();                  }              }          }          if (endPos < startPos && !isDownloadOver) {              LogUtils.log("Thread " + threadId  + " startPos > endPos, not need download file !");              this.isDownloadOver = true;          }          if (endPos == startPos && !isDownloadOver) {              LogUtils.log("Thread " + threadId  + " startPos = endPos, not need download file !");              this.isDownloadOver = true;          }      }      /**      * <b>function:</b> 打印下载文件头部信息      * @author hoojo      * @createDate 2011-9-22 下午05:44:35      * @param conn HttpURLConnection      */      public static void printHeader(URLConnection conn) {          int i = 1;          while (true) {              String header = conn.getHeaderFieldKey(i);              i++;              if (header != null) {                  LogUtils.info(header + ":" + conn.getHeaderField(i));              } else {                  break;              }          }      }      /**      * <b>function:</b> 设置URLConnection的头部信息，伪装请求信息      * @author hoojo      * @createDate 2011-9-28 下午05:29:43      * @param con      */      public static void setHeader(URLConnection conn) {          conn.setRequestProperty("User-Agent", "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008092510 Ubuntu/8.04 (hardy) Firefox/3.0.3");          conn.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3");          conn.setRequestProperty("Accept-Encoding", "utf-8");          conn.setRequestProperty("Accept-Charset", "ISO-8859-1,utf-8;q=0.7,*;q=0.7");          conn.setRequestProperty("Keep-Alive", "300");          conn.setRequestProperty("connnection", "keep-alive");          conn.setRequestProperty("If-Modified-Since", "Fri, 02 Jan 2009 17:00:05 GMT");          conn.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\"");          conn.setRequestProperty("Cache-conntrol", "max-age=0");          conn.setRequestProperty("Referer", "http://www.baidu.com");      }      public boolean isDownloadOver() {          return isDownloadOver;      }      public long getStartPos() {          return startPos;      }      public long getEndPos() {          return endPos;      }  }  

这个类主要是完成单个线程的文件下载，将通过URLConnection读取指定url的资源信息。然后用InputStream读取文件内容，然后调用调用SaveItemFile类，向本地写入当前要读取的块的内容。

四、分段多线程写入文件内容

package com.hoo.download;import java.io.DataInputStream;import java.io.DataOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;import com.hoo.entity.DownloadInfo;import com.hoo.util.LogUtils;/** * <b>function:</b> 分批量下载文件 * @author hoojo * @createDate 2011-9-22 下午05:51:54 * @file BatchDownloadFile.java * @package com.hoo.download * @project MultiThreadDownLoad * @blog http://blog.csdn.net/IBM_hoojo * @email [e-mail] * @version 1.0 */public class BatchDownloadFile implements Runnable {    //下载文件信息     private DownloadInfo downloadInfo;    //一组开始下载位置    private long[] startPos;    //一组结束下载位置    private long[] endPos;    //休眠时间    private static final int SLEEP_SECONDS = 500;    //子线程下载    private DownloadFile[] fileItem;    //文件长度    private int length;    //是否第一个文件    private boolean first = true;    //是否停止下载    private boolean stop = false;    //临时文件信息    private File tempFile;    public BatchDownloadFile(DownloadInfo downloadInfo) {        this.downloadInfo = downloadInfo;        String tempPath = this.downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName() + ".position";        tempFile = new File(tempPath);        //如果存在读入点位置的文件        if (tempFile.exists()) {            first = false;            //就直接读取内容            try {                readPosInfo();            } catch (IOException e) {                e.printStackTrace();            }        } else {            //数组的长度就要分成多少段的数量            startPos = new long[downloadInfo.getSplitter()];            endPos = new long[downloadInfo.getSplitter()];        }    }    @Override    public void run() {        //首次下载，获取下载文件长度        if (first) {            length = this.getFileSize();//获取文件长度            if (length == -1) {                LogUtils.log("file length is know!");                stop = true;            } else if (length == -2) {                LogUtils.log("read file length is error!");                stop = true;            } else if (length > 0) {                /**                 * eg                  * start: 1, 3, 5, 7, 9                 * end: 3, 5, 7, 9, length                 */                for (int i = 0, len = startPos.length; i < len; i++) {                    int size = i * (length / len);                    startPos[i] = size;                    //设置最后一个结束点的位置                    if (i == len - 1) {                        endPos[i] = length;                    } else {                        size = (i + 1) * (length / len);                        endPos[i] = size;                    }                    LogUtils.log("start-end Position[" + i + "]: " + startPos[i] + "-" + endPos[i]);                }            } else {                LogUtils.log("get file length is error, download is stop!");                stop = true;            }        }        //子线程开始下载        if (!stop) {            //创建单线程下载对象数组            fileItem = new DownloadFile[startPos.length];//startPos.length = downloadInfo.getSplitter()            for (int i = 0; i < startPos.length; i++) {                try {                    //创建指定个数单线程下载对象，每个线程独立完成指定块内容的下载                    fileItem[i] = new DownloadFile(                        downloadInfo.getUrl(),                         this.downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName(),                         startPos[i], endPos[i], i                    );                    fileItem[i].start();//启动线程，开始下载                    LogUtils.log("Thread: " + i + ", startPos: " + startPos[i] + ", endPos: " + endPos[i]);                } catch (IOException e) {                    e.printStackTrace();                }            }            //循环写入下载文件长度信息            while (!stop) {                try {                    writePosInfo();                    LogUtils.log("downloading……");                    Thread.sleep(SLEEP_SECONDS);                    stop = true;                } catch (IOException e) {                    e.printStackTrace();                } catch (InterruptedException e) {                    e.printStackTrace();                }                for (int i = 0; i < startPos.length; i++) {                    if (!fileItem[i].isDownloadOver()) {                        stop = false;                        break;                    }                }            }            LogUtils.info("Download task is finished!");        }    }    /**     * 将写入点数据保存在临时文件中     * @author hoojo     * @createDate 2011-9-23 下午05:25:37     * @throws IOException     */    private void writePosInfo() throws IOException {        DataOutputStream dos = new DataOutputStream(new FileOutputStream(tempFile));        dos.writeInt(startPos.length);        for (int i = 0; i < startPos.length; i++) {            dos.writeLong(fileItem[i].getStartPos());            dos.writeLong(fileItem[i].getEndPos());            //LogUtils.info("[" + fileItem[i].getStartPos() + "#" + fileItem[i].getEndPos() + "]");        }        dos.close();    }    /**     * <b>function:</b>读取写入点的位置信息     * @author hoojo     * @createDate 2011-9-23 下午05:30:29     * @throws IOException     */    private void readPosInfo() throws IOException {        DataInputStream dis = new DataInputStream(new FileInputStream(tempFile));        int startPosLength = dis.readInt();        startPos = new long[startPosLength];        endPos = new long[startPosLength];        for (int i = 0; i < startPosLength; i++) {            startPos[i] = dis.readLong();            endPos[i] = dis.readLong();        }        dis.close();    }    /**     * <b>function:</b> 获取下载文件的长度     * @author hoojo     * @createDate 2011-9-26 下午12:15:08     * @return     */    private int getFileSize() {        int fileLength = -1;        try {            URL url = new URL(this.downloadInfo.getUrl());            HttpURLConnection conn = (HttpURLConnection) url.openConnection();            DownloadFile.setHeader(conn);            int stateCode = conn.getResponseCode();            //判断http status是否为HTTP/1.1 206 Partial Content或者200 OK            if (stateCode != HttpURLConnection.HTTP_OK && stateCode != HttpURLConnection.HTTP_PARTIAL) {                LogUtils.log("Error Code: " + stateCode);                return -2;            } else if (stateCode >= 400) {                LogUtils.log("Error Code: " + stateCode);                return -2;            } else {                //获取长度                fileLength = conn.getContentLength();                LogUtils.log("FileLength: " + fileLength);            }            //读取文件长度            /*for (int i = 1; ; i++) {                String header = conn.getHeaderFieldKey(i);                if (header != null) {                    if ("Content-Length".equals(header)) {                        fileLength = Integer.parseInt(conn.getHeaderField(i));                        break;                    }                } else {                    break;                }            }            */            DownloadFile.printHeader(conn);        } catch (MalformedURLException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }        return fileLength;    }}

这个类主要是完成读取指定url资源的内容，获取该资源的长度。然后将该资源分成指定的块数，将每块的起始下载位置、结束下载位置，分别保存在一个数组中。每块都单独开辟一个独立线程开始下载。在开始下载之前，需要创建一个临时文件，写入当前下载线程的开始下载指针位置和结束下载指针位置。

五、工具类、测试类
日志工具类

package com.hoo.util;/** * <b>function:</b> 日志工具类 * @author hoojo * @createDate 2011-9-21 下午05:21:27 * @file LogUtils.java * @package com.hoo.util * @project MultiThreadDownLoad * @blog http://blog.csdn.net/IBM_hoojo * @email [e-mail] * @version 1.0 */public abstract class LogUtils {    public static void log(Object message) {        System.err.println(message);    }    public static void log(String message) {        System.err.println(message);    }    public static void log(int message) {        System.err.println(message);    }    public static void info(Object message) {        System.out.println(message);    }    public static void info(String message) {        System.out.println(message);    }    public static void info(int message) {        System.out.println(message);    }}

下载工具类

package com.hoo.util;import com.hoo.download.BatchDownloadFile;import com.hoo.entity.DownloadInfo;/** * <b>function:</b> 分块多线程下载工具类 * @author hoojo * @createDate 2011-9-28 下午05:22:18 * @file DownloadUtils.java * @package com.hoo.util * @project MultiThreadDownLoad * @blog http://blog.csdn.net/IBM_hoojo * @email [e-mail] * @version 1.0 */public abstract class DownloadUtils {    public static void download(String url) {        DownloadInfo bean = new DownloadInfo(url);        LogUtils.info(bean);        BatchDownloadFile down = new BatchDownloadFile(bean);        new Thread(down).start();    }    public static void download(String url, int threadNum) {        DownloadInfo bean = new DownloadInfo(url, threadNum);        LogUtils.info(bean);        BatchDownloadFile down = new BatchDownloadFile(bean);        new Thread(down).start();    }    public static void download(String url, String fileName, String filePath, int threadNum) {        DownloadInfo bean = new DownloadInfo(url, fileName, filePath, threadNum);        LogUtils.info(bean);        BatchDownloadFile down = new BatchDownloadFile(bean);        new Thread(down).start();    }}

下载测试类

package com.hoo.test;import com.hoo.util.DownloadUtils;/** * <b>function:</b> 下载测试 * @author hoojo * @createDate 2011-9-23 下午05:49:46 * @file TestDownloadMain.java * @package com.hoo.download * @project MultiThreadDownLoad * @blog http://blog.csdn.net/IBM_hoojo * @email [e-mail] * @version 1.0 */public class TestDownloadMain {    public static void main(String[] args) {        /*DownloadInfo bean = new DownloadInfo("http://i7.meishichina.com/Health/UploadFiles/201109/2011092116224363.jpg");        System.out.println(bean);        BatchDownloadFile down = new BatchDownloadFile(bean);        new Thread(down).start();*/        //DownloadUtils.download("http://i7.meishichina.com/Health/UploadFiles/201109/2011092116224363.jpg");        DownloadUtils.download("http://mp3.baidu.com/j?j=2&url=http%3A%2F%2Fzhangmenshiting2.baidu.com%2Fdata%2Fmusic%2F1669425%2F%25E9%2599%25B7%25E5%2585%25A5%25E7%2588%25B1%25E9%2587%258C%25E9%259D%25A2.mp3%3Fxcode%3D2ff36fb70737c816553396c56deab3f1", "aa.mp3", "c:/temp", 5);    }}

转自：http://blog.csdn.net/ibm_hoojo/article/details/6838222