public class Download implements Serializable {    private static final int START = 1;                 // 开始下载    private static final int PUBLISH = 2;               // 更新进度    private static final int PAUSE = 3;                 // 暂停下载    private static final int CANCEL = 4;                // 取消下载    private static final int ERROR = 5;                 // 下载错误    private static final int SUCCESS = 6;               // 下载成功    private static final int GOON = 7;                  // 继续下载         private static ExecutorService mThreadPool;         // 线程池         static {        mThreadPool = Executors.newFixedThreadPool(5);  // 默认5个     }             private int mDownloadId;                            // 下载id    private String mFileName;                           // 本地保存文件名    private String mUrl;                                // 下载地址    private String mLocalPath;                          // 本地存放目录     private boolean isPause = false;                    // 是否暂停    private boolean isCanceled = false;                 // 是否手动停止下载         private OnDownloadListener mListener;               // 监听器         /**     * 配置下载线程池的大小     * @param maxSize 同时下载的最大线程数     */    public static void configDownloadTheadPool(int maxSize) {        mThreadPool = Executors.newFixedThreadPool(maxSize);    }         /**     * 添加下载任务     * @param downloadId 下载任务的id     * @param url        下载地址     * @param localPath   本地存放地址     */    public Download(int downloadId, String url, String localPath) {        if (!new File(localPath).exists()) {            new File(localPath).mkdirs();        }                 Log.log("下载地址；" + url);                 mDownloadId = downloadId;        mUrl = url;        String[] tempArray = url.split("/");        mFileName = tempArray[tempArray.length-1];        mLocalPath = localPath;    }         /**     * 设置监听器     * @param listener 设置下载监听器     * @return this     */    public Download setOnDownloadListener(OnDownloadListener listener) {        mListener = listener;        return this;    }         /**     * 获取文件名     * @return 文件名     */    public String getFileName() {        return mFileName;    }     /**     * 开始下载     * params isGoon是否为继续下载     */    public void start(final boolean isGoon) {        // 处理消息        final Handler handler = new Handler() {            @Override            public void handleMessage(Message msg) {                switch (msg.what) {                case ERROR:                    mListener.onError(mDownloadId);                    break;                case CANCEL:                    mListener.onCancel(mDownloadId);                    break;                case PAUSE:                    mListener.onPause(mDownloadId);                    break;                case PUBLISH:                    mListener.onPublish(mDownloadId, Long.parseLong(msg.obj.toString()));                    break;                case SUCCESS:                    mListener.onSuccess(mDownloadId);                    break;                case START:                    mListener.onStart(mDownloadId, Long.parseLong(msg.obj.toString()));                    break;                case GOON:                    mListener.onGoon(mDownloadId, Long.parseLong(msg.obj.toString()));                    break;                }            }        };                 // 真正开始下载        mThreadPool.execute(new Runnable() {            @Override            public void run() {                download(isGoon,handler);            }        });    }         /**     * 下载方法     * @param handler 消息处理器     */    private void download(boolean isGoon, Handler handler) {        Message msg = null;        Log.log("开始下载。。。");        try {            RandomAccessFile localFile = new RandomAccessFile(new File(                    mLocalPath + File.separator + mFileName), "rwd");             DefaultHttpClient client = new DefaultHttpClient();            client.setParams(getHttpParams());            HttpGet get = new HttpGet(mUrl);             long localFileLength = getLocalFileLength();            final long remoteFileLength = getRemoteFileLength();            long downloadedLength = localFileLength;                         // 远程文件不存在            if (remoteFileLength == -1l) {                Log.log("下载文件不存在...");                localFile.close();                handler.sendEmptyMessage(ERROR);                return;            }             // 本地文件存在            if (localFileLength > -1l && localFileLength < remoteFileLength) {                Log.log("本地文件存在...");                localFile.seek(localFileLength);                get.addHeader("Range", "bytes=" + localFileLength + "-"                        + remoteFileLength);            }                         msg = Message.obtain();                         // 如果不是继续下载            if(!isGoon) {                // 发送开始下载的消息并获取文件大小的消息                msg.what = START;                msg.obj = remoteFileLength;            }else {                msg.what = GOON;                msg.obj = localFileLength;            }                         handler.sendMessage(msg);                         HttpResponse response = client.execute(get);            int httpCode = response.getStatusLine().getStatusCode();            if (httpCode >= 200 && httpCode <= 300) {                InputStream in = response.getEntity().getContent();                byte[] bytes = new byte[1024];                int len = -1;                while (-1 != (len = in.read(bytes))) {                    localFile.write(bytes, 0, len);                    downloadedLength += len;//                  Log.log((int)(downloadedLength/(float)remoteFileLength * 100));                    if ((int)(downloadedLength/(float)remoteFileLength * 100) % 10 == 0) {                        // 发送更新进度的消息                        msg = Message.obtain();                        msg.what = PUBLISH;                        msg.obj = downloadedLength;                        handler.sendMessage(msg);//                      Log.log(mDownloadId + "已下载" + downloadedLength);                    }                                         // 暂停下载， 退出方法                    if (isPause) {                        // 发送暂停的消息                        handler.sendEmptyMessage(PAUSE);                        Log.log("下载暂停...");                        break;                    }                                         // 取消下载， 删除文件并退出方法                    if (isCanceled) {                        Log.log("手动关闭下载。。");                        localFile.close();                        client.getConnectionManager().shutdown();                        new File(mLocalPath + File.separator + mFileName)                                .delete();                        // 发送取消下载的消息                        handler.sendEmptyMessage(CANCEL);                        return;                    }                }                 localFile.close();                client.getConnectionManager().shutdown();                // 发送下载完毕的消息                if(!isPause) handler.sendEmptyMessage(SUCCESS);            }         } catch (Exception e) {            // 发送下载错误的消息            handler.sendEmptyMessage(ERROR);        }    }     /**     * 暂停/继续下载     * param pause 是否暂停下载     * 暂停 return true     * 继续 return false     */    public synchronized boolean pause(boolean pause) {        if(!pause) {            Log.log("继续下载");            isPause = false;            start(true); // 开始下载        }else {            Log.log("暂停下载");            isPause = true;        }        return isPause;    }     /**     * 关闭下载， 会删除文件     */    public synchronized void cancel() {        isCanceled = true;        if(isPause) {            new File(mLocalPath + File.separator + mFileName)            .delete();        }    }     /**     * 获取本地文件大小     * @return 本地文件的大小 or 不存在返回-1     */    public synchronized long getLocalFileLength() {        long size = -1l;        File localFile = new File(mLocalPath + File.separator + mFileName);        if (localFile.exists()) {            size = localFile.length();        }        Log.log("本地文件大小" + size);        return size <= 0 ? -1l : size;    }     /**     * 获取远程文件打下 or 不存在返回-1     * @return     */    public synchronized long getRemoteFileLength() {        long size = -1l;        try {            DefaultHttpClient client = new DefaultHttpClient();            client.setParams(getHttpParams());            HttpGet get = new HttpGet(mUrl);             HttpResponse response = client.execute(get);            int httpCode = response.getStatusLine().getStatusCode();            if (httpCode >= 200 && httpCode <= 300) {                size = response.getEntity().getContentLength();            }             client.getConnectionManager().shutdown();        } catch (Exception e) {            e.printStackTrace();        }         Log.log("远程文件大小" + size);        return size;    }     /**     * 设置http参数 不能设置soTimeout     * @return HttpParams http参数     */    private static HttpParams getHttpParams() {        HttpParams params = new BasicHttpParams();         HttpProtocolParams.setContentCharset(params, HTTP.UTF_8);        HttpProtocolParams.setUseExpectContinue(params, true);        HttpProtocolParams                .setUserAgent(                        params,                        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2041.4 Safari/537.36");        ConnManagerParams.setTimeout(params, 4000);        HttpConnectionParams.setConnectionTimeout(params, 4000);                 return params;    }         /**     * 关闭下载线程池     */    public static void closeDownloadThread() {        if(null != mThreadPool) {            mThreadPool.shutdownNow();        }    }     public interface OnDownloadListener {        public void onStart(int downloadId, long fileSize);  // 回调开始下载        public void onPublish(int downloadId, long size);    // 回调更新进度        public void onSuccess(int downloadId);               // 回调下载成功        public void onPause(int downloadId);                 // 回调暂停        public void onError(int downloadId);                 // 回调下载出错        public void onCancel(int downloadId);                // 回调取消下载        public void onGoon(int downloadId, long localSize);  // 回调继续下载    }}

如何调用，如下：

            Download d = new Download(1, "http://baidu.com/test.zip","/sdcard/download/");            d.setOnDownloadListener(new Download.OnDownloadListener() {                @Override                public void onSuccess(int downloadId) {                    System.out.println(downloadId + "下载成功");                }                     @Override                public void onStart(int downloadId, long fileSize) {                    System.out.println(downloadId + "开始下载，文件大小：" + fileSize);                }                     @Override                public void onPublish(int downloadId, long size) {                    System.out.println("更新文件" + downloadId + "大小：" + size);                }                     @Override                public void onPause(int downloadId) {                    System.out.println("暂停下载" + downloadId);                }                     @Override                public void onGoon(int downloadId, long localSize) {                    System.out.println("继续下载" + downloadId);                }                     @Override                public void onError(int downloadId) {                    System.out.println("下载出错" + downloadId);                }                     @Override                public void onCancel(int downloadId) {                    System.out.println("取消下载" + downloadId);                }            });                 d.start(false);