多线程同步下载

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 MultiThreadDownLoad {
    static int ThreadCount = 3;
    static int finish = 0;
    // 确定下载地址http://10.16.154.24:8080/Nox.exe
    static String path = "http://10.16.154.24:8080/Nox.exe";

    public static void main(String[] args) {

        String filename = path.substring(path.lastIndexOf("/") + 1);
        // 发送GET请求，请求这个地址的资源
        try {
            URL url = new URL(path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(3000);
            conn.setConnectTimeout(3000);
            conn.setRequestMethod("GET");

            if (conn.getResponseCode() == 200) {
                // 拿到所有请求资源文件的长度
                int length = conn.getContentLength();

                File file = new File(filename);
                // 随机存储文件对象，生成临时文件
                RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                // 设置临时文件的大小
                raf.setLength(length);
                raf.close();
                // 计算每个线程应该下载多少字节
                int size = length / ThreadCount;

                for (int i = 0; i < ThreadCount; i++) {
                    // 计算线程下载的开始和结束位置
                    int startIndex = i * size;
                    int endIndex = (i + 1) * size - 1;
                    // 如果是最后一个线程，那么结束位置写死
                    if (i == ThreadCount - 1) {
                        endIndex = length - 1;
                    }
                    new DownLoadThread(startIndex, endIndex, i).start();
                }

            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

class DownLoadThread extends Thread {
    int startIndex;
    int endIndex;
    int threadId;

    public DownLoadThread(int startIndex, int endIndex, int threadId) {
        super();
        this.startIndex = startIndex;
        this.endIndex = endIndex;
        this.threadId = threadId;
    }

    public void run() {
        String filename = MultiThreadDownLoad.path
                .substring(MultiThreadDownLoad.path.lastIndexOf("/") + 1);
        // 生成一个专门用来记录下载进度的临时文件
        File progressFile = new File(threadId + ".txt");

        // 再次发送http请求，下载源文件
        try {
            // 判断进度临时未见是否存在
            if (progressFile.exists()) {
                FileInputStream fis = new FileInputStream(progressFile);
                BufferedReader br = new BufferedReader(new InputStreamReader(
                        fis));
                // 从进度临时文件中读取上一次下载的总进度，然后与原本的开始位置相加，得到新的开始位置
                startIndex += Integer.parseInt(br.readLine());
                fis.close();
            }
            URL url = new URL(MultiThreadDownLoad.path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(3000);
            conn.setConnectTimeout(3000);
            conn.setRequestMethod("GET");
            // 设置本次http请求的数据的区间
            conn.setRequestProperty("Range", "byte=" + startIndex + "-"
                    + endIndex);

            // 请求部分数据，相应码是206
            if (conn.getResponseCode() == 206) {
                // 流里此时只有1/3源文件的数据
                InputStream is = conn.getInputStream();
                byte[] buffer = new byte[1024];
                int len = 0, total = 0;
                File file = new File(filename);
                // 随机存储文件对象，生成临时文件
                RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                // 把文件的写入位置移动到startIndex
                raf.seek(startIndex);
                while ((len = is.read(buffer)) != -1) {
                    // 每次读取流里数据之后，同步把数据写入临时文件
                    raf.write(buffer, 0, len);
                    total += len;
                    System.out.println("线程" + threadId + "下载了" + total);

                    RandomAccessFile progressRaf = new RandomAccessFile(
                            progressFile, "rwd");
                    // 每次读取流里数据之后，同步把当前线程下载的总进度写入进度临时文件中
                    progressRaf.write((total + "").getBytes());
                    progressRaf.close();

                }
                raf.close();
                MultiThreadDownLoad.finish++;
                synchronized (MultiThreadDownLoad.path) {
                    if (MultiThreadDownLoad.finish == MultiThreadDownLoad.ThreadCount) {
                        for (int i = 0; i < MultiThreadDownLoad.ThreadCount; i++) {
                            File f = new File(i + ".txt");
                            f.delete();
                        }
                    }
                    MultiThreadDownLoad.finish = 0;
                }

            }
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}