多线程下载

这个是下载的工具类，改编自网上找到的annegu兄的代码，这位仁兄是多线程断点，但是我这里不需要断点，所以做了简化。

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 *
 *
 */
public class DownloadUtil {

    private static final Log log = LogFactory.getLog(DownloadUtil.class);
    private int threadNum = 5;
    private String urlStr;
    private File file = null;
    private AtomicBoolean statusError = new AtomicBoolean(false);
    private long sleepSeconds = 5;

    public DownloadUtil(String url, File file, int threadNum) {
        this(url, file, threadNum, 5);
    }

    public DownloadUtil(String url, File file, int threadNum, long sleepSec) {
        this.urlStr = url;
        this.file = file;
        if (threadNum > 0) {
            this.threadNum = threadNum;
        }
        if (sleepSec > 0) {
            this.sleepSeconds = sleepSec;
        }
    }

    public boolean download() {
        log.info("download the file " + file.getName() + " from " + urlStr);
        CountDownLatch latch = new CountDownLatch(threadNum);//这个是亮点
        try {
            file.createNewFile();
            HttpURLConnection con = (HttpURLConnection) new URL(urlStr).openConnection();
            setHeader(con);//这里是伪造头信息
            long contentLength = con.getContentLength();
            long threadLength = contentLength / threadNum;
            ExecutorService exec = Executors.newCachedThreadPool();
            for (int i = 0; i < threadNum; i++) {
                long end = threadLength * (i + 1) - 1;
                if (i == threadNum - 1) {
                    end = contentLength;
                }
                ChildThread thread = new ChildThread(this, latch, i,
                        threadLength * i, end);
                exec.execute(thread);
            }
            try {
                latch.await();
                exec.shutdown();
                if (file.length() != contentLength) {
                    log.warn("file download failed,because the size is not correct");
                    return false;
                }
                return true;
            } catch (InterruptedException e) {
                log.error(e.getMessage(), e);
            }
        } catch (IOException e) {
            log.error(e.getMessage(), e);
        }
        return false;
    }

    private class ChildThread implements Runnable {

        private DownloadUtil task;
        private int id;
        private long startPosition;
        private long endPosition;
        private final CountDownLatch latch;
        private RandomAccessFile file = null;

        public ChildThread(DownloadUtil task, CountDownLatch latch, int id,
                long startPos, long endPos) {
            super();
            this.task = task;
            this.id = id;
            this.startPosition = startPos;
            this.endPosition = endPos;
            this.latch = latch;
            try {
                file = new RandomAccessFile(task.file, "rw");
            } catch (IOException e) {
                log.error(e.getMessage(), e);
            }
        }

        public void run() {
            log.info("Thread " + id + " run ...");
            HttpURLConnection con = null;
            InputStream inputStream = null;
            for (;;) {
                try {
                    con = (HttpURLConnection) new URL(task.urlStr).openConnection();
                    setHeader(con);
                    // 设置连接超时时间为10000ms
                    con.setConnectTimeout(10000);
                    // 设置读取数据超时时间为10000ms
                    con.setReadTimeout(10000);

                    if (startPosition < endPosition) {
                        // 设置下载数据的起止区间
                        con.setRequestProperty("Range", "bytes=" + startPosition + "-" + endPosition);
                        log.debug("Thread " + id + " startPosition is " + startPosition + ", and endPosition is " + endPosition);

                        file.seek(startPosition);

                        // 判断http status是否为HTTP/1.1 206 Partial Content或者200 OK
                        // 如果不是以上两种状态，把status改为STATUS_HTTPSTATUS_ERROR
                        if (con.getResponseCode() != HttpURLConnection.HTTP_OK && con.getResponseCode() != HttpURLConnection.HTTP_PARTIAL) {
                            log.info("Thread " + id + ": code = " + con.getResponseCode() + ", status = " + con.getResponseMessage());
                            task.statusError.set(true);
                            file.close();
                            con.disconnect();
                            log.info("Thread " + id + " finished.");
                            latch.countDown();
                            break;
                        }

                        inputStream = con.getInputStream();
                        int len = 0;
                        byte[] b = new byte[1024];
                        while (!task.statusError.get() && (len = inputStream.read(b)) != -1) {
                            file.write(b, 0, len);
                            startPosition += len;
                        }

                        file.close();
                        inputStream.close();
                        con.disconnect();
                    }

                    log.info("Thread " + id + " finished.");
                    latch.countDown();
                    break;
                } catch (IOException ex) {
//                    log.error(ex.getMessage(), ex);
                    try {
                        TimeUnit.SECONDS.sleep(task.sleepSeconds);
                    } catch (InterruptedException e) {
                        log.error(e.getMessage(), e);
                    }
                    continue;
                }
            }
        }
    }

    private void setHeader(URLConnection con) {
        con.setRequestProperty(
                "User-Agent",
                "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008092510 Ubuntu/8.04 (hardy) Firefox/3.0.3");
        con.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3");
//        con.setRequestProperty("Accept-Encoding", "aa");
        con.setRequestProperty("Accept-Charset",
                "ISO-8859-1,utf-8;q=0.7,*;q=0.7");
        con.setRequestProperty("Keep-Alive", "300");
        con.setRequestProperty("Connection", "keep-alive");
        con.setRequestProperty("If-Modified-Since",
                "Fri, 02 Jan 2009 17:00:05 GMT");
        con.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\"");
        con.setRequestProperty("Cache-Control", "max-age=0");
//        con.setRequestProperty("Referer",
//                "http://www.skycn.com/soft/14857.html");
    }
}