Java实现多线程断点下载

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 MutileThreadDownload {   /**    * 线程的数量    */   private static int threadCount = 3;    /**    * 每个下载区块的大小    */   private static long blocksize;    /**    * 正在运行的线程的数量    */   private static int runningThreadCount;    /**    * @param args    * @throws Exception    */   public static void main(String[] args) throws Exception {     // 服务器文件的路径     String path = "http://192.168.1.100:8080/ff.exe";     URL url = new URL(path);     HttpURLConnection conn = (HttpURLConnection) url.openConnection();     conn.setRequestMethod("GET");     conn.setConnectTimeout(5000);     int code = conn.getResponseCode();     if (code == 200) {       long size = conn.getContentLength();// 得到服务端返回的文件的大小       System.out.println("服务器文件的大小：" + size);       blocksize = size / threadCount;       // 1.首先在本地创建一个大小跟服务器一模一样的空白文件。       File file = new File("temp.exe");       RandomAccessFile raf = new RandomAccessFile(file, "rw");       raf.setLength(size);       // 2.开启若干个子线程分别去下载对应的资源。       runningThreadCount = threadCount;       for (int i = 1; i <= threadCount; i++) {         long startIndex = (i - 1) * blocksize;         long endIndex = i * blocksize - 1;         if (i == threadCount) {           // 最后一个线程           endIndex = size - 1;         }         System.out.println("开启线程：" + i + "下载的位置：" + startIndex + "~"             + endIndex);         new DownloadThread(path, i, startIndex, endIndex).start();       }     }     conn.disconnect();   }    private static class DownloadThread extends Thread {     private int threadId;     private long startIndex;     private long endIndex;     private String path;      public DownloadThread(String path, int threadId, long startIndex,         long endIndex) {       this.path = path;       this.threadId = threadId;       this.startIndex = startIndex;       this.endIndex = endIndex;     }      @Override     public void run() {       try {         // 当前线程下载的总大小         int total = 0;         File positionFile = new File(threadId + ".txt");         URL url = new URL(path);         HttpURLConnection conn = (HttpURLConnection) url             .openConnection();         conn.setRequestMethod("GET");         // 接着从上一次的位置继续下载数据         if (positionFile.exists() && positionFile.length() > 0) {// 判断是否有记录           FileInputStream fis = new FileInputStream(positionFile);           BufferedReader br = new BufferedReader(               new InputStreamReader(fis));           // 获取当前线程上次下载的总大小是多少           String lasttotalstr = br.readLine();           int lastTotal = Integer.valueOf(lasttotalstr);           System.out.println("上次线程" + threadId + "下载的总大小："               + lastTotal);           startIndex += lastTotal;           total += lastTotal;// 加上上次下载的总大小。           fis.close();         }          conn.setRequestProperty("Range", "bytes=" + startIndex + "-"             + endIndex);         conn.setConnectTimeout(5000);         int code = conn.getResponseCode();         System.out.println("code=" + code);         InputStream is = conn.getInputStream();         File file = new File("temp.exe");         RandomAccessFile raf = new RandomAccessFile(file, "rw");         // 指定文件开始写的位置。         raf.seek(startIndex);         System.out.println("第" + threadId + "个线程：写文件的开始位置："             + String.valueOf(startIndex));         int len = 0;         byte[] buffer = new byte[512];         while ((len = is.read(buffer)) != -1) {           RandomAccessFile rf = new RandomAccessFile(positionFile,               "rwd");           raf.write(buffer, 0, len);           total += len;           rf.write(String.valueOf(total).getBytes());           rf.close();         }         is.close();         raf.close();        } catch (Exception e) {         e.printStackTrace();       } finally {         // 只有所有的线程都下载完毕后 才可以删除记录文件。         synchronized (MutileThreadDownload.class) {           System.out.println("线程" + threadId + "下载完毕了");           runningThreadCount--;           if (runningThreadCount < 1) {             System.out.println("所有的线程都工作完毕了。删除临时记录的文件");             for (int i = 1; i <= threadCount; i++) {               File f = new File(i + ".txt");               System.out.println(f.delete());             }           }         }        }     }   } }