java 多线程下载

  import java.io.ByteArrayOutputStream;
import java.io.InputStream;

public class StreamTool {
    /**
     * 把一个inputstream里面的内容转化成一个byte[]
     */
    public static byte[] getBytes(InputStream is) throws Exception {
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int len = 0;
        while ((len = is.read(buffer)) != -1) {
            bos.write(buffer, 0, len);
        }
        is.close();
        bos.flush();
        byte[] result = bos.toByteArray();
        System.out.println(new String(result));
        return result;
    }
}

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

public class TestDownload {
    public static final String path = "http://192.168.1.100:8080/aaa.exe";

    public static void main(String[] args) throws Exception {
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setConnectTimeout(5000);
        conn.setRequestProperty("User-Agent",
           "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
        int code = conn.getResponseCode();
        if (code == 200) {
            int len = conn.getContentLength();
            RandomAccessFile file = new RandomAccessFile(
               "C:/Users/DELL/Desktop/" + getFilenName(path), "rwd");
            // 1.设置本地文件大小跟服务器的文件大小一致
            file.setLength(len);

            // 2 .假设开启3 个线程
            int threadnumber = 3;
            int blocksize = len / threadnumber;
            /**
             * 线程1 0~ blocksize 线程2 1*bolocksize ~ 2*blocksize 线程3 2                   *blocksize ~
             * 文件末尾
             */
            for (int i = 0; i < threadnumber; i++) {
                int startposition = i * blocksize;
                int endpositon = (i + 1) * blocksize;
                if (i == (threadnumber - 1)) {
                    // 最后一个线程
                    endpositon = len;
                }
                DownLoadTask task = new DownLoadTask(
                       i, path, startposition,endpositon);
                task.start();
            }
        }
    }

    public static String getFilenName(String path) {
        int start = path.lastIndexOf("/") + 1;
        return path.substring(start, path.length());
    }

}

class DownLoadTask extends Thread {
    public static final String path = "http://192.168.1.100:8080/aaa.exe";
    int threadid;
    String filepath;
    int startposition;
    int endpositon;

    public DownLoadTask(int threadid, String filepath, 
                int startposition, int endpositon) {
        this.threadid = threadid;
        this.filepath = filepath;
        this.startposition = startposition;
        this.endpositon = endpositon;
    }

    @Override
    public void run() {
        try {
            File postionfile = new File(threadid + ".txt");
            URL url = new URL(filepath);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            System.out.println("线程" + threadid + "正在下载 " + "开始位置 : "
                    + startposition + "结束位置 " + endpositon);

            // 断点操作
            if (postionfile.exists()) { 
                FileInputStream fis = new FileInputStream(postionfile);
                byte[] result = StreamTool.getBytes(fis);
                int newstartposition = Integer.parseInt(new String(result));
                if (newstartposition > startposition) { // 如果新的位置 > 开始位置。
                    startposition = newstartposition;
                }
            }

            // "Range", "bytes=2097152-4194303")
            conn.setRequestProperty("Range", "bytes=" + startposition + "-"
                    + endpositon);
            conn.setRequestMethod("GET");
            conn.setConnectTimeout(5000);
            conn.setRequestProperty("User-Agent",
                    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
            InputStream is = conn.getInputStream();
            RandomAccessFile file = new RandomAccessFile(
                    "C:/Users/DELL/Desktop/" + getFilenName(path), "rwd");
            // 设置 数据从文件哪个位置开始写
            file.seek(startposition);
            byte[] buffer = new byte[1024];
            int len = 0;
            
            // 代表当前读到的服务器数据的位置 ,同时这个值已经存储的文件的位置
            int currentPostion = startposition;
            
            // 创建一个文件对象 ,记录当前某个文件的下载位置
            while ((len = is.read(buffer)) != -1) {
                file.write(buffer, 0, len);

                currentPostion += len;
                // 需要把currentPostion 信息给持久化到存储设备
                String position = currentPostion + "";
                System.out.println("线程 .." + threadid + "....开始位置..."
                        + startposition + "..当前位置..." + currentPostion
                        + "...结束位置...." + endpositon);
                FileOutputStream fos = new FileOutputStream(postionfile);
                fos.write(position.getBytes());
                fos.flush();
                fos.close();
            }
            file.close();
            System.out.println("线程" + threadid + "下载完毕");
            // 当线程下载完毕后 把文件删除掉
            if (postionfile.exists()) {
                postionfile.delete();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        super.run();
    }

    public static String getFilenName(String path) {
        int start = path.lastIndexOf("/") + 1;
        return path.substring(start, path.length());
    }

}

public class test1 {
    public static void main(String[] args) throws Exception {
        RandomAccessFile file = new RandomAccessFile("haha.txt", "rwd");
        file.setLength(1024 * 1024);
    }
}