安卓学习之路 -- JAVA多线程下载

代码没有优化，暂时先实现结果

package download;

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

/**
 * @author Liu Yutao
 * @className Down
 * @email koal@vip.qq.com
 * @date 2016/4/7 21:11
 */

public class Down {

    //下载地址
    public static final String DOWNFILE = "http://219.150.176.188/files/WindowsXP_SP2.exe";
    //线程数
    public static final int THREADCOUNT = 5;


    //格式化文件，得到文件名称
    public static String formatFileName(String value) {
        //得到最后一个/位置
        int indexOf = value.lastIndexOf("/");
        //截取/WindowsXP_SP2.exe文件名
        String fileName = value.substring(indexOf + 1, value.length());
        return fileName;
    }

    //下载文件
    public static void httpDownload(String downfile) {
        try {
            URL url = new URL(DOWNFILE);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            //超时5秒
            connection.setReadTimeout(5000);
            connection.setRequestMethod("GET");
            int code = connection.getResponseCode();
            if (code == 200) {
                //得到文件长度
                long length = connection.getContentLength();
                InputStream stream = connection.getInputStream();
                File file = new File(formatFileName(DOWNFILE));
                //用于创建一个和目标文件大小一样的空文件，为了就是占坑（rw是可读可写模式read,write）
                RandomAccessFile accessFile = new RandomAccessFile(file, "rw");
                accessFile.setLength(length);
                //分10个线程，每个线程的区块长度（总长度 ÷ 个数）
                long blockSize = length / THREADCOUNT;
                for (int threadId = 0; threadId < THREADCOUNT; threadId++) {
                    //开始区块
                    // 当前循环线程编号 x 当前线程区块长度（0x1024，1x1024,2x1024）
                    long beginIndex = threadId * blockSize;
                    //结束区块
                    // 当前线程+1 x 每个区块大小 = 下次循环的开始区块，再 -1 就等于本次区块的最后位置
                    long endIndex = (threadId + 1) * blockSize - 1;
                    //是否最后一个线程
                    if (threadId == (THREADCOUNT - 1)) {
                        endIndex = length - 1;
                    }
                    System.err.println("当前线程：" + (threadId+1) + "，开始区块：" + beginIndex + "，结束区块：" + endIndex);
                    new ThreadDownloadRun(threadId, beginIndex, endIndex).start();
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static class ThreadDownloadRun extends Thread {

        private long threadId;
        private long beginIndex;
        private long endIndex;

        //构造
        public ThreadDownloadRun(long threadId, long beginIndex, long endIndex) {
            this.threadId = threadId;
            this.beginIndex = beginIndex;
            this.endIndex = endIndex;
        }

        @Override
        public void run() {
            try {
                System.err.println("当前线程：" + (threadId+1) + "，开始下载......");
                URL url = new URL(DOWNFILE);
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setRequestMethod("GET");
                //设置http文件头的range(区间)
                urlConnection.setRequestProperty("Range", "bytes=" + beginIndex + "-" + endIndex);
                int code = urlConnection.getResponseCode();
                //区间返回是206
                if (code == 206) {
                    //得到数据
                    InputStream stream = urlConnection.getInputStream();
                    File file = new File(formatFileName(DOWNFILE));
                    RandomAccessFile accessFile = new RandomAccessFile(file, "rw");
                    //设置RandomAccessFile写入文件的区块开始长度
                    accessFile.seek(beginIndex);
                    //下载开始
                    byte[] bytes = new byte[1024 * 1024];
                    int len = 0;
                    while ((len = stream.read(bytes)) > 0) {
                        accessFile.write(bytes, 0, len);
                    }
                    accessFile.close();
                    stream.close();
                    System.err.println("当前线程：" + (threadId+1) + "，下载结束！！！");
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        httpDownload(DOWNFILE);
    }
}