Java实现的断点续传功能

import java.io.File;import java.io.FileNotFoundException;import java.io.IOException;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/* * Encode:UTF-8 *  * Author:zhiming.xu *  * 多线程的断点下载程序，根据输入的url和指定线程数，来完成断点续传功能。 *  * 每个线程支负责某一小段的数据下载；再通过RandomAccessFile完成数据的整合。 */public class MultiTheradDownLoad {    private String filepath = null;    private String filename = null;    private String tmpfilename = null;    private int threadNum = 0;    private CountDownLatch latch = null;//设置一个计数器，代码内主要用来完成对缓存文件的删除    private long fileLength = 0l;    private long threadLength = 0l;    private long[] startPos;//保留每个线程下载数据的起始位置。    private long[] endPos;//保留每个线程下载数据的截止位置。    private boolean bool = false;    private URL url = null;    //有参构造函数，先构造需要的数据    public MultiTheradDownLoad(String filepath, int threadNum) {        this.filepath = filepath;        this.threadNum = threadNum;        startPos = new long[this.threadNum];        endPos = new long[this.threadNum];        latch = new CountDownLatch(this.threadNum);    }    /*     * 组织断点续传功能的方法     */    public void downloadPart() {        File file = null;        File tmpfile = null;        HttpURLConnection httpcon = null;        //在请求url内获取文件资源的名称；此处没考虑文件名为空的情况，此种情况可能需使用UUID来生成一个唯一数来代表文件名。        filename = filepath.substring(filepath.lastIndexOf('/') + 1, filepath                .contains("?") ? filepath.lastIndexOf('?') : filepath.length());        tmpfilename = filename + "_tmp";        try {            url = new URL(filepath);            httpcon = (HttpURLConnection) url.openConnection();            setHeader(httpcon);            fileLength = httpcon.getContentLengthLong();//获取请求资源的总长度。            file = new File(filename);            tmpfile = new File(tmpfilename);            threadLength = fileLength / threadNum;//每个线程需下载的资源大小。            System.out.println("fileName: " + filename + " ," + "fileLength= "                    + fileLength + " the threadLength= " + threadLength);            if (file.exists() && file.length() == fileLength) {                System.out                        .println("the file you want to download has exited!!");                return;            } else {                setBreakPoint(startPos, endPos, tmpfile);                ExecutorService exec = Executors.newCachedThreadPool();                for (int i = 0; i < threadNum; i++) {                    exec.execute(new DownLoadThread(startPos[i], endPos[i],                            this, i, tmpfile, latch));                }                latch.await();//当你的计数器减为0之前，会在此处一直阻塞。                exec.shutdown();            }        } catch (MalformedURLException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        } catch (InterruptedException e) {            e.printStackTrace();        }        if (file.length() == fileLength) {            if (tmpfile.exists()) {                System.out.println("delect the temp file!!");                tmpfile.delete();            }        }    }    /*     * 断点设置方法，当有临时文件时，直接在临时文件中读取上次下载中断时的断点位置。没有临时文件，即第一次下载时，重新设置断点。     *      * rantmpfile.seek()跳转到一个位置的目的是为了让各个断点存储的位置尽量分开。     *      * 这是实现断点续传的重要基础。     */    private void setBreakPoint(long[] startPos, long[] endPos, File tmpfile) {        RandomAccessFile rantmpfile = null;        try {            if (tmpfile.exists()) {                System.out.println("the download has continued!!");                rantmpfile = new RandomAccessFile(tmpfile, "rw");                for (int i = 0; i < threadNum; i++) {                    rantmpfile.seek(8 * i + 8);                    startPos[i] = rantmpfile.readLong();                    rantmpfile.seek(8 * (i + 1000) + 16);                    endPos[i] = rantmpfile.readLong();                    System.out.println("the Array content in the exit file: ");                    System.out.println("thre thread" + (i + 1) + " startPos:"                            + startPos[i] + ", endPos: " + endPos[i]);                }            } else {                System.out.println("the tmpfile is not available!!");                rantmpfile = new RandomAccessFile(tmpfile, "rw");                                //最后一个线程的截止位置大小为请求资源的大小                for (int i = 0; i < threadNum; i++) {                    startPos[i] = threadLength * i;                    if (i == threadNum - 1) {                        endPos[i] = fileLength;                    } else {                        endPos[i] = threadLength * (i + 1) - 1;                    }                    rantmpfile.seek(8 * i + 8);                    rantmpfile.writeLong(startPos[i]);                    rantmpfile.seek(8 * (i + 1000) + 16);                    rantmpfile.writeLong(endPos[i]);                    System.out.println("the Array content: ");                    System.out.println("thre thread" + (i + 1) + " startPos:"                            + startPos[i] + ", endPos: " + endPos[i]);                }            }        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        } finally {            try {                if (rantmpfile != null) {                    rantmpfile.close();                }            } catch (IOException e) {                e.printStackTrace();            }        }    }        /*     * 实现下载功能的内部类，通过读取断点来设置向服务器请求的数据区间。     */    class DownLoadThread implements Runnable {        private long startPos;        private long endPos;        private MultiTheradDownLoad task = null;        private RandomAccessFile downloadfile = null;        private int id;        private File tmpfile = null;        private RandomAccessFile rantmpfile = null;        private CountDownLatch latch = null;        public DownLoadThread(long startPos, long endPos,                MultiTheradDownLoad task, int id, File tmpfile,                CountDownLatch latch) {            this.startPos = startPos;            this.endPos = endPos;            this.task = task;            this.tmpfile = tmpfile;            try {                this.downloadfile = new RandomAccessFile(this.task.filename,                        "rw");                this.rantmpfile = new RandomAccessFile(this.tmpfile, "rw");            } catch (FileNotFoundException e) {                e.printStackTrace();            }            this.id = id;            this.latch = latch;        }        @Override        public void run() {            HttpURLConnection httpcon = null;            InputStream is = null;            int length = 0;            System.out.println("the thread " + id + " has started!!");            while (true) {                try {                    httpcon = (HttpURLConnection) task.url.openConnection();                    setHeader(httpcon);                                        //防止网络阻塞，设置指定的超时时间；单位都是ms。超过指定时间，就会抛出异常                    httpcon.setReadTimeout(20000);//读取数据的超时设置                    httpcon.setConnectTimeout(20000);//连接的超时设置                    if (startPos < endPos) {                                                //向服务器请求指定区间段的数据，这是实现断点续传的根本。                        httpcon.setRequestProperty("Range", "bytes=" + startPos                                + "-" + endPos);                        System.out                                .println("Thread " + id                                        + " the total size:---- "                                        + (endPos - startPos));                        downloadfile.seek(startPos);                        if (httpcon.getResponseCode() != HttpURLConnection.HTTP_OK                                && httpcon.getResponseCode() != HttpURLConnection.HTTP_PARTIAL) {                            this.task.bool = true;                            httpcon.disconnect();                            downloadfile.close();                            System.out.println("the thread ---" + id                                    + " has done!!");                            latch.countDown();//计数器自减                            break;                        }                        is = httpcon.getInputStream();//获取服务器返回的资源流                        long count = 0l;                        byte[] buf = new byte[1024];                        while (!this.task.bool && (length = is.read(buf)) != -1) {                            count += length;                            downloadfile.write(buf, 0, length);                                                        //不断更新每个线程下载资源的起始位置，并写入临时文件；为断点续传做准备                            startPos += length;                            rantmpfile.seek(8 * id + 8);                            rantmpfile.writeLong(startPos);                        }                        System.out.println("the thread " + id                                + " total load count: " + count);                                                //关闭流                        is.close();                        httpcon.disconnect();                        downloadfile.close();                        rantmpfile.close();                    }                    latch.countDown();//计数器自减                    System.out.println("the thread " + id + " has done!!");                    break;                } catch (IOException e) {                    e.printStackTrace();                } finally {                    try {                        if (is != null) {                            is.close();                        }                    } catch (IOException e) {                        e.printStackTrace();                    }                }            }        }    }    /*     * 为一个HttpURLConnection模拟请求头，伪装成一个浏览器发出的请求     */    private void setHeader(HttpURLConnection con) {        con.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");        con.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3");        con.setRequestProperty("Accept-Encoding", "aa");        con.setRequestProperty("Accept-Charset",                "ISO-8859-1,utf-8;q=0.7,*;q=0.7");        con.setRequestProperty("Keep-Alive", "300");        con.setRequestProperty("Connection", "keep-alive");        con.setRequestProperty("If-Modified-Since",                "Fri, 02 Jan 2009 17:00:05 GMT");        con.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\"");        con.setRequestProperty("Cache-Control", "max-age=0");        con.setRequestProperty("Referer",                "http://www.skycn.com/soft/14857.html");    }}

 

 下面是测试代码：

public class DownLoadTest {    /**     * @param args     */    public static void main(String[] args) {                String filepath = "http://127.0.0.1:8080/file/loadfile.mkv";        MultiTheradDownLoad load = new MultiTheradDownLoad(filepath ,4);            load.downloadPart();        }}