java多线程下载

import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.URL;
import java.net.URLConnection;

public class DLRunnable implements Runnable {
    static final int BUF_SIZE = 1024;
    URL url = Task.url;
    File file = Task.file;
    long pStart, pEnd, pCur, readLen = 0;
    int id, isDone = 0, isResume = 0;

    public DLRunnable(int id, long start, long end) {
        this.pStart = start;
        this.pEnd = end;
        this.id = id;
        this.pCur = this.pStart;
    }

    public void run() {
        try {
            url = new URL("http://dl_dir.qq.com/qqfile/qq/QQ2011/QQ2011.exe");
            URLConnection conn =  url.openConnection();
            conn.setAllowUserInteraction(true);
            BufferedInputStream bins = new BufferedInputStream(
                    conn.getInputStream());
            RandomAccessFile fos = null;
            if (isResume == 0) {
                conn.setRequestProperty("Range", "bytes=" + pStart + "-" + pEnd);
                fos = new RandomAccessFile(file, "rw");
                fos.seek(pStart);
                System.out.println("线程" + id + "开始下载...");
                pCur = pStart;
            } else {
                conn.setRequestProperty("Range", "bytes=" + pCur + "-" + pEnd);
                fos = new RandomAccessFile(file, "rw");
                fos.seek(pCur);
                System.out.println("线程" + id + "继续开始下载...");
            }
            long startTime = System.currentTimeMillis();
            while (pCur < pEnd) {
                byte buf[] = new byte[BUF_SIZE];
                int len = bins.read(buf, 0, BUF_SIZE);
                if (len == -1)
                    break;
                fos.write(buf, 0, len);
                pCur += len;
                if (pCur > pEnd) {
                    readLen += (pEnd - (pCur - len) + 1);
                } else {
                    readLen += len;
                }
            }
            long totalTime = System.currentTimeMillis() - startTime;
            isDone = 1;
            System.out.println("线程" + id + "下载完毕!大小" + readLen + "字节"
                    + totalTime + "ms");
            bins.close();
            fos.close();
            Task.runnableArray.remove(this);
            Task.threadArray.remove(Task.threadArray.get(id-1));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

实现runnable接口

import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;

public class Task {
    static int THREAD_NUM = 3;
    static ArrayList<Thread> threadArray = new ArrayList<Thread>();
    static ArrayList<DLRunnable> runnableArray = new ArrayList<DLRunnable>();
    static URL url = null;
    static File file = null;
    static long blockLen, totalLen, startTime, totalTime;

    private void initTask() {
        try {
            url = new URL("http://dl_dir.qq.com/qqfile/qq/QQ2011/QQ2011.exe");
            file = new File("D:\\Users\\Meng\\Downloads\\QQ2011.exe");
            URLConnection conn = url.openConnection();
            long totalLen = conn.getContentLength();
            System.out.println("文件总大小：" + totalLen + "字节");
            if (totalLen == -1)
                return;
            blockLen = (long) Math.ceil((double) totalLen / THREAD_NUM);
            System.out.println("每块长度：" + blockLen + "字节");
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void startTask() {
        System.out.println("开始下载...");
        startTime = System.currentTimeMillis();
        for (int i = 0; i < THREAD_NUM; i++) {
            DLRunnable dlr = new DLRunnable(i + 1, blockLen * i, blockLen
                    * (i + 1));
            runnableArray.add(dlr);
            Thread dlt = new Thread(dlr);
            threadArray.add(dlt);
            dlt.start();
        }
    }

    private void stopTask(){ 
    System.out.println("下载中断...");
        for (Thread dlt : threadArray) {
            threadArray.remove(dlt);
            dlt = null;
        }
    }

    private void resumeTask() {
        System.out.println("继续下载...");
        for (DLRunnable dlr : runnableArray) {
            dlr.isResume=1;
            Thread dlt = new Thread(dlr);
            threadArray.add(dlt);
            dlt.start();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        Task task = new Task();
        task.initTask();
        task.startTask();
        new Thread() {
            public void run() {
                while (true) {
                    if (runnableArray.isEmpty()&&threadArray.isEmpty()) {
                        totalTime = System.currentTimeMillis() - startTime;
                        System.out.println("下载总用时：" + totalTime + "ms,平均速度："
                                + totalLen / totalTime + "kb/s");
                        break;
                    }
                }
            }
        }.start();
        Thread.sleep(10000);
        task.stopTask();
        Thread.sleep(5000);
        task.resumeTask();
    }
}

task类