android实现多线程下载

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import java.io.File;import java.io.IOException;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.ProtocolException;import java.net.URL;import java.util.concurrent.Executor;import java.util.concurrent.Executors;import android.os.Environment;import android.os.Handler;import android.os.Message;/** * 多线程下载 * @author raid * */public class Download {    /**     * 创建一个线程池     */    private Executor threadPool = Executors.newFixedThreadPool(3);    /**     * 接收一个Handler对象，用于获取下载进度     */    private Handler handler;    /**     * 默认的下载线程个数为3     */    public static final int THREAD_COUNT = 3;        public Download(Handler handler) {        super();        this.handler = handler;    }    /**     * 下载线程，这里定义成静态类     * @author raid     *     */    static class DownLoadRunnable implements Runnable {        private String url;        private String fileName;        private long start;        private long end;        private Handler handler;                /**         * 构造方法         * @param url 需要下载的网站url         * @param fileName 下载回本地的文件名         * @param start 开始位置         * @param end 终止位置         * @param handler 用于更新UI显示下载进度         */        public DownLoadRunnable(String url, String fileName, long start,                long end, Handler handler) {            super();            this.url = url;            this.fileName = fileName;            this.start = start;            this.end = end;            this.handler = handler;        }        @Override        public void run() {            // TODO Auto-generated method stub            RandomAccessFile access = null;            InputStream in = null;            try {                HttpURLConnection conn = getConnection(url);                //设置请求读取文件的开始字节数和结束字节数                conn.setRequestProperty("Range", "bytes=" + start + "-" + end);                access = new RandomAccessFile(fileName, "rwd");                access.seek(start);                in = conn.getInputStream();                byte[] b = new byte[4*1024];                int len = 0;                while((len=in.read(b)) != -1) {                    access.write(b, 0, len);                }                                Message msg = Message.obtain();                msg.what = 1;                handler.sendMessage(msg);                            } catch (MalformedURLException e) {                // TODO Auto-generated catch block                e.printStackTrace();            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            } finally {                if (access != null) {                    try {                        access.close();                    } catch (IOException e) {                        // TODO Auto-generated catch block                        e.printStackTrace();                    }                }                if (in != null) {                    try {                        in.close();                    } catch (IOException e) {                        // TODO Auto-generated catch block                        e.printStackTrace();                    }                }            }        }            }        /**     * 调用多线程下载的方法     * @param url 下载的资源的地址     */    public void downloadFile(String url) {        HttpURLConnection conn = getConnection(url);        int count = conn.getContentLength();        int block = count / THREAD_COUNT;                String fileName = getFileName(url);        File parent = Environment.getExternalStorageDirectory();        File fileDownload = new File(parent, fileName);        for(int i = 0; i < THREAD_COUNT; i++) {            long start = i*block;            long end = (i+1) * block - 1;            if (i == THREAD_COUNT-1) {                end = count;            }            DownLoadRunnable runnable =                    new DownLoadRunnable(url,                            fileDownload.getAbsolutePath(),                            start, end, handler);            threadPool.execute(runnable);        }    }        private String getFileName(String url) {        return url.substring(url.lastIndexOf("/")+1);    }        private static HttpURLConnection getConnection(String url) {        URL httpUrl;        try {            httpUrl = new URL(url);            HttpURLConnection conn = (HttpURLConnection) httpUrl.openConnection();            conn.setReadTimeout(5000);            conn.setRequestMethod("GET");                        return conn;        } catch (MalformedURLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (ProtocolException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }                return null;    }}
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