Java实现多线程断点下载实例代码（下载过程中可以暂停）

import java.io.BufferedReader;import java.io.File;import java.io.FileInputStream;import java.io.InputStream;import java.io.InputStreamReader;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;public class DownLoad {  // 声明下载路径“红色警戒2”  public static final String PATH = "http://soft3.xzstatic.com/2015/10/hsjj2ghgzh.rar";  public static int threadCount = 0;// 声明线程数量  public static void main(String[] args) {    try {      URL url = new URL(PATH);      // 获取连接      HttpURLConnection conn = (HttpURLConnection) url.openConnection();      // 通过获取连接定义文件名      String[] str = PATH.split("/");      String fileName = str[5];      // 获取下载文件大小      int fileLength = conn.getContentLength();      System.out.println(fileName);      // 在本地创建一个与服务器大小一致的可随机写入文件      RandomAccessFile raf = new RandomAccessFile(fileName, "rwd");      System.out.println(fileLength);// 测试用      raf.setLength(fileLength);      // 自定义线程数量      threadCount = 3;      // 计算每条线程下载数据的大小      int blockSize = fileLength / threadCount;      // 启动线程下载      for (int threadId = 1; threadId <= threadCount; threadId++) {        // 核心代码，定义每个线程开始以及结束的下载位置        int startPos = (threadId - 1) * blockSize;// 开始下载的位置        int endPos = (threadId * blockSize) - 1;// 结束下载的位置（不包含最后一块）        if (threadCount == threadId) {          endPos = fileLength;        }        new Thread(new DownLoadThread(threadId, startPos, endPos, PATH))            .start();      }    } catch (Exception e) {      e.printStackTrace();    }  }  // 实现下载线程  static class DownLoadThread implements Runnable {    private int threadId;    private int startPos;    private int endPos;    private String path;    public DownLoadThread(int threadId, int startPos, int endPos,        String path) {      super();      this.threadId = threadId;      this.startPos = startPos;      this.endPos = endPos;      this.path = path;    }    public void run() {      try {        URL url = new URL(path);        String[] str = PATH.split("/");        String fileName = str[5];        HttpURLConnection conn = (HttpURLConnection) url            .openConnection();        // 设置URL请求的方法（具体参考API）        conn.setRequestMethod("GET");        // 设置500毫秒为超时值        conn.setReadTimeout(5000);        File file = new File(threadId + ".txt");        if (file.exists() && file.length() > 0) {          BufferedReader br = new BufferedReader(              new InputStreamReader(new FileInputStream(file)));          String saveStartPos = br.readLine();          if (saveStartPos != null && saveStartPos.length() > 0) {            startPos = Integer.parseInt(saveStartPos);          }        }        // 注意双引号内的格式，不能包含空格（等其他字符），否则报416        conn.setRequestProperty("Range", "bytes=" + startPos + "-"            + endPos);        RandomAccessFile raf = new RandomAccessFile(fileName, "rwd");// 存储下载文件的随机写入文件        raf.seek(startPos);// 设置开始下载的位置        System.out.println("线程" + threadId + ":" + startPos + "~~"            + endPos);        InputStream is = conn.getInputStream();        byte[] b = new byte[1024 * 1024 * 10];        int len = -1;        int newPos = startPos;        while ((len = is.read(b)) != -1) {          RandomAccessFile rr = new RandomAccessFile(file, "rwd");// 存储下载标记的文件          raf.write(b, 0, len);          // 将下载标记存入指定文档          String savaPoint = String.valueOf(newPos += len);          rr.write(savaPoint.getBytes());          rr.close();        }        is.close();        raf.close();        System.out.println("下载完成");      } catch (Exception e) {        e.printStackTrace();      }    }  }}