多线程下载

    private void multiThreadDownload(String sourcePath, String targetPathDir, String targetFileName, int threadCount) {
        fileSize = getFileSize(sourcePath);
        int blockSize = fileSize / threadCount;
        System.out.println(blockSize);
        RandomAccessFile raf = null;
        try {
            raf = new RandomAccessFile(new File(targetPathDir, targetFileName), "rwd");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        for (int threadId = 1; threadId <= threadCount; threadId++) {
            int beginIndex = (threadId - 1) * blockSize;
            int endIndex = threadId * blockSize - 1;
            if (threadId == threadCount) {
                endIndex = fileSize - 1;
            }
            System.out.println(beginIndex + "  " + endIndex);
            new DownloadThread(sourcePath, beginIndex, endIndex, targetPathDir, targetFileName).start();
        }
    }

    public class DownloadThread extends Thread {
        private String sourcePath;
        private int beginIndex;
        private int endIndex;
        private String targetPathDir;
        private String targetFileName;

        public DownloadThread(String sourcePath, int beginIndex, int endIndex, String targetPathDir, String targetFileName) {
            this.sourcePath = sourcePath;
            this.beginIndex = beginIndex;
            this.endIndex = endIndex;
            this.targetFileName = targetFileName;
            this.targetPathDir = targetPathDir;
        }

        @Override
        public void run() {
            HttpURLConnection conn = null;
            RandomAccessFile raf = null;

            try {
                raf = new RandomAccessFile(new File(targetPathDir, targetFileName), "rwd");
                URL url = new URL(sourcePath);
                conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5000);
                conn.setRequestProperty("Range", "bytes=" + beginIndex + "-" + endIndex);
                int code = conn.getResponseCode();
                if (code == 206) {
                    InputStream is = conn.getInputStream();
                    raf.seek(beginIndex);
                    int len = 0;
                    byte[] buff = new byte[1024];
                    while ((len = is.read(buff)) != -1) {
                        raf.write(buff, 0, len);
                    }
                }
                runningThread--;
            } catch (IOException e) {
                e.printStackTrace();
            }finally {
                if (runningThread == 0) {
                    long endtime = System.currentTimeMillis();
                    long time = (endtime - beginTime) / 1000;
                    float speed = (float)fileSize/1024/1024/time;
                    System.out.println("over " +time + " " +speed);
                }else {
                    System.out.println(runningThread);
                }
            }
        }
    }

    private static int getFileSize(String sourcePath) {
        int fileSize = 0;
        HttpURLConnection conn = null;
        try {
            URL url = new URL(sourcePath);
            conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");
            conn.setConnectTimeout(5000);
            int code = conn.getResponseCode();
            if (code == 200) {
                fileSize = conn.getContentLength();
                System.out.println(fileSize);
            }
        } catch (java.io.IOException e) {
            e.printStackTrace();
        } finally {
            conn.disconnect();
        }
        return fileSize;
    }