多线程下载 断点续传

package wml.dl;
import java.io.BufferedInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.util.Properties;
 import wml.dl.io.BufferedRandomOutputStream;
 * 下载线程，负责下载DLBlock
 * @author wml
public class DLThread implements Runnable {
    private static final int INPUT_BUFFER_SIZE = 1024;
    private static final int OUTPUT_BUFFER_SIZE = 8192;  
    private DLTask task;
    private DLBlock block;
    private boolean isDone;
    private boolean isStop;
    public DLBlock getBlock() {
        return block;
    public DLThread(DLTask task, DLBlock block) {
        this.task = task;
        this.block = block;
    @Override
    public void run() { 
        block.setStatus(DLBlock.STATUS_RUNNING);
        BufferedRandomOutputStream randomOutputStream = null;
        try {  http://www.huiyi8.com/gundongdaima/ 滚动代码
            randomOutputStream = new BufferedRandomOutputStream(task.openRandomAccessFile(), OUTPUT_BUFFER_SIZE);   
        } catch (FileNotFoundException e) {
            block.setThrowable(e);
            e.printStackTrace();
            isDone = true;
            return;
        HttpURLConnection conn = null;
        long downloadPosition = 0;
        try { 
            if(task.isSupportedContentRange()) {//断点续传
                block.setDownloaded(Math.max(block.getDownloaded() - OUTPUT_BUFFER_SIZE, 0));// -8kb保证下载结果(有可能之前写入失败)           
                downloadPosition = block.getBegin() + block.getDownloaded();     
                randomOutputStream.seek(downloadPosition);
            Properties reqProps = new Properties();
            if(task.isSupportedContentRange()) {//设置下载范围
                reqProps.setProperty("Range", "bytes=" + downloadPosition + "-" + block.getEnd());
            conn = DLUtils.getChromeURLConnection(task.getUri(), false, reqProps);
            InputStream in = new BufferedInputStream(DLUtils.getInputStream(conn.getInputStream(), conn.getContentEncoding()), INPUT_BUFFER_SIZE);
            byte[] buf = new byte[INPUT_BUFFER_SIZE];
            int len;     
            while((len = in.read(buf)) != -1) {
     randomOutputStream.write(buf, 0, len);
                block.updateDownloaded(len);
                 
                downloadPosition += len;
                 
                if(task.isSupportedContentRange() && downloadPosition >= block.getEnd()
                        || isStop
                        || !task.isRunning()) {
                    //也许将任务部分分配给了其他线程（增加了线程），在后面做详细处理
                    break;
        } catch (IOException e) {
             
            block.setThrowable(e);
            e.printStackTrace();
             
        } finally {
 
            DLUtils.close(conn);
            DLUtils.close(randomOutputStream);
             
            isDone = true;
             
            if(downloadPosition >= block.getEnd()) {
     
                //块下载完成
                block.setStatus(DLBlock.STATUS_DONE);
                 
            } else {
                 
                //停止下载
                block.setStatus(DLBlock.STATUS_PAUSE);
            try {//检查并设置任务状态
                task.checkDone();
            } catch (FileNotFoundException e) {
                 
                block.setThrowable(e);
                e.printStackTrace();
    public boolean isDone() {
        return isDone;
    }
 
    public void stop() {
        isStop = true;
    }