HttpURLConnection 多线程断点下载

使用HttpURLConnection多线程断点下载，废话不多说直接上代码。

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());
                        }
                    }
                }

            }
        }
    }
}