/**
 * FileName: DownloadUtil
 * Author:   梁庆昌
 * Date:     2018/3/21 10:52
 * Description:多线程下载文件
 */


import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;


public class DownloadUtil {
    // 定义成员变量
    private String path; // 远程资源路径
    private String targetPath; // 本地存储路径
    private DownFileThread[] threads; // 线程list
    private int threadNum; // 线程数量
    private long length; // 下载的文件大小

    // 构造初始化
    public DownloadUtil(String path, String targetPath, int threadNum) {
        super();
        this.path = path;
        this.targetPath = targetPath;
        this.threads = new DownFileThread[threadNum];
        this.threadNum = threadNum;
    }

    // 多线程下载文件资源
    public void download() {
        URL url;
        try {
            url = new URL(path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(5 * 1000); // 设置超时时间为5秒
            conn.setRequestMethod("GET");
            conn.setRequestProperty("connection", "keep-alive");
            conn.setRequestProperty("accept", "*/*");

            // 获取远程文件的大小
            length = conn.getContentLength();
            conn.disconnect();

            // 设置本地文件大小
            RandomAccessFile targetFile = new RandomAccessFile(targetPath, "rw");
            targetFile.setLength(length);

            // 每个线程下载大小
            long avgPart = length / threadNum + 1;
            // 下载文件
            for (int i = 0; i < threadNum; i++) {
                long startPos = avgPart * i;
                RandomAccessFile targetTmp = new RandomAccessFile(targetPath,
                        "rw");
                targetTmp.seek(startPos); // 分段下载
                threads[i] = new DownFileThread(startPos, targetTmp, avgPart);
                threads[i].start();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 监控下载进度
    public double getDownRate() {
        int currentSize = 0;
        for (int i = 0; i < threadNum; i++) {
            currentSize += threads[i].length;
        }
        return currentSize * 1.0 / length ;
    }

    // 定义线程类
    class DownFileThread extends Thread {
        private long startPos;
        private RandomAccessFile raf;
        private long size;
        private long length;

        public DownFileThread(long startPos, RandomAccessFile raf, long size) {
            super();
            this.startPos = startPos;
            this.raf = raf;
            this.size = size;
        }
        @Override
        public void run() {
            URL url;
            try {
                url = new URL(path);
                HttpURLConnection conn = (HttpURLConnection) url
                        .openConnection();
                conn.setReadTimeout(5 * 1000); // 设置超时时间为5秒
                conn.setRequestMethod("GET");
                conn.setRequestProperty("connection", "keep-alive");
                conn.setRequestProperty("accept", "*/*");

                InputStream in = conn.getInputStream();
                in.skip(this.startPos);
                byte[] buf = new byte[1024];
                int hasRead = 0;
                while (length < size && (hasRead = in.read(buf)) != -1) {
                    raf.write(buf, 0, hasRead);
                    length += hasRead;
                }
                raf.close();
                in.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    // 测试
    public static void main(String[] args) {
        String path = "http://ftp-idc.pconline.com.cn/956b950ead9d83001388407babb2f47c/pub/download/201010/65.0.3325.162_chrome_installer.exe";
        String targetPath = "D:/1.exe";
        final DownloadUtil download = new DownloadUtil(path, targetPath, 4);
        download.download();
        // 主线程负责下载文件，在启动一个线程负责监控下载的进度
        new Thread(new Runnable() {

            @Override
            public void run() {
                while (download.getDownRate() < 1) {
                    System.out.println(String.format("%.1f",download.getDownRate()*100)+"%");
                    try {
                        Thread.sleep(1000); // 200毫秒扫描一次
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }

        }).start();
    }
}