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。

个人博客：

http://hoojo.cnblogs.com

http://blog.csdn.net/IBM_hoojo

email: hoojo_@126.com

 

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 hoojo_@126.com
 * @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 hoojo_@126.com
 * @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 hoojo_@126.com
 * @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 hoojo_@126.com
 * @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 hoojo_@126.com
 * @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 hoojo_@126.com
 * @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 hoojo_@126.com
 * @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);
    }
}

多线程下载主要在第三部和第四部，其他的地方还是很好理解。源码中提供相应的注释了，便于理解。