【java多線程】Java內存映射文件實現多線程下載

package com.thread.download;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel.MapMode;

class Worker implements Runnable {
    //多線程下載的數量
    private static int THREADS = 4;
    //每一個線程下載開始的位置
    private int startIndex;
    //每一個線程下載內容的長度
    private int length;
    //文件保存位置
    private String localFile;
    //遠程文件的流
    InputStream in;
    private Worker(String urlFile, String localFile, int startIndex, int length) throws IOException {
        this.startIndex = startIndex;
        this.length = length;
        this.localFile = localFile;
        init(urlFile);
    }
    /**
    *    主線程打開網絡文件,先分割爲指定的大小，而後開啓多線程下載
    */
    public Worker(String urlFile, String localFile) throws IOException {
        this.localFile = localFile;
        int contentLength = init(urlFile);
        int step = contentLength / THREADS;
        int index = 0;
        for (int i = 0; i < THREADS; i++) {
            if (i == 0) {
                this.startIndex = 0;
                this.length = step;
                new Thread(this).start();
            } else if (i == THREADS - 1) {
                Worker worker = new Worker(urlFile, localFile, index, contentLength - index);
                new Thread(worker).start();
            } else {
                Worker worker = new Worker(urlFile, localFile, index, step);
                new Thread(worker).start();
            }
            index = index + step;
        }
    }
    private int init(String urlFile) throws IOException {
        URL url;
        url = new URL(urlFile);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setConnectTimeout(5 * 1000);
        connection.setRequestMethod("GET");
        connection.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, " + "application/x-shockwave-flash, application/xaml+xml, "
                + "application/vnd.ms-xpsdocument, application/x-ms-xbap, " + "application/x-ms-application, application/vnd.ms-excel, " + "application/vnd.ms-powerpoint, application/msword, */*");

        connection.setRequestProperty("Accept-Language", "zh-CN");
        connection.setRequestProperty("Charset", "UTF-8");
        connection.setRequestProperty("Connection", "Keep-Alive");
        InputStream in = connection.getInputStream();
        this.in = in;
        return connection.getContentLength();
    }

 

    @Override

    public void run() {
        System.out.println(this);
        try {
            RandomAccessFile localRandomFile = new RandomAccessFile(localFile, "rw");
            MappedByteBuffer buffer = localRandomFile.getChannel().map(MapMode.READ_WRITE, startIndex, length);
            int i = 0;
            in.skip(startIndex);
            while (i < length) {
                buffer.put((byte) in.read());
                i++;
            }
            buffer.force();
            in.close();
            localRandomFile.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override

    public String toString() {
        return "Worker [localFile=" + localFile + ", startIndex=" + startIndex + ", length=" + length + "]";
    }
    public static void main(String[] args) throws IOException {
        new Worker("http://mirrors.cnnic.cn/apache/tomcat/tomcat-7/v7.0.56/bin/apache-tomcat-7.0.56.zip", "tomcat.zip");
    }
}