使用IntentService给自己的Android应用写一个文件下载器。

接着上一篇的http://www.cnblogs.com/zhengxt/p/3657833.html，当我们想给自己的APP写一个文件下载器时，可以用重写IntentService来实现。

使用IntentService有几个好处，IntentService继承于Service，适合拿来处理一些耗时又不需要去管它的任务。把要执行的任务用Intent加入到队列中，IntentService会有一个工作线程来取出队列中的Intent来处理。需要实现抽象方法onHandleIntent方法来执行这些任务。当所有任务都完成后，IntentService会自动停止。

同时使用Notification在通知栏让用户直观的知道下载进度，推荐使用Android3.0(API11)后提供的Notification.Builder来构建Notification。我这里为了让程序兼容Android2.1-2.3就没有使用Notification.Builder，用被废弃的Notification(int, CharSequence, long)来构建Notification。

还是按照上一篇一样，假设这是个版本更新文件的下载器，当更新文件下载完成后自动弹出安装界面。

IntentService代码：

public class DownloadFileService extends IntentService {
    private static final String TAG = DownloadFileService.class.getSimpleName();
    public DownloadFileService() {
        super("com.test.download");
    }
    
    private NotificationManager notificationManager;
    private Notification notification;
    private RemoteViews rViews;
    protected void onHandleIntent(Intent intent) {
        Bundle bundle = intent.getExtras();
        // 获得下载文件的url
        String downloadUrl = bundle.getString("url");
        // 设置文件下载后的保存路径，保存在SD卡根目录的Download文件夹
        File dirs = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/Download");
        // 检查文件夹是否存在，不存在则创建
        if (!dirs.exists()) {
            dirs.mkdir();
        }
        File file = new File(dirs, "file.apk");
        // 设置Notification
        notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        notification = new Notification(R.drawable.ic_launcher, "版本更新下载", System.currentTimeMillis());
        Intent intentNotifi = new Intent(this, Main.class);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intentNotifi, 0);
        notification.contentIntent = pendingIntent;
        // 加载Notification的布局文件
        rViews = new RemoteViews(getPackageName(), R.layout.downloadfile_layout);
        // 设置下载进度条
        rViews.setProgressBar(R.id.downloadFile_pb, 100, 0, false);
        notification.contentView = rViews;
        notificationManager.notify(0, notification);
        // 开始下载
        downloadFile(downloadUrl, file);
        // 移除通知栏
        notificationManager.cancel(0);
        // 广播出去，由广播接收器来处理下载完成的文件
        Intent sendIntent = new Intent("com.test.downloadComplete");
        // 把下载好的文件的保存地址加进Intent
        sendIntent.putExtra("downloadFile", file.getPath());
        sendBroadcast(sendIntent);
    }
    private int fileLength, downloadLength;
    private void downloadFile(String downloadUrl, File file){
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(file);
        } catch (FileNotFoundException e) {
            Log.e(TAG, "找不到保存下载文件的目录");
            e.printStackTrace();
        }
        InputStream ips = null;
        try {
            URL url = new URL(downloadUrl);
            HttpURLConnection huc = (HttpURLConnection) url.openConnection();
            huc.setRequestMethod("GET");
            huc.setReadTimeout(10000);
            huc.setConnectTimeout(3000);
            fileLength = Integer.valueOf(huc.getHeaderField("Content-Length"));
            ips = huc.getInputStream();
            // 拿到服务器返回的响应码
            int hand = huc.getResponseCode();
            if (hand == 200) {
                // 开始检查下载进度
                handler.post(run);
                // 建立一个byte数组作为缓冲区，等下把读取到的数据储存在这个数组
                byte[] buffer = new byte[8192];
                int len = 0;
                while ((len = ips.read(buffer)) != -1) {
                    fos.write(buffer, 0, len);
                    downloadLength = downloadLength + len;
                }
            } else {
                Log.e(TAG, "服务器返回码" + hand);
            }

        } catch (ProtocolException e) {
            e.printStackTrace();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (fos != null) {
                    fos.close();
                }
                if (ips != null) {
                    ips.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    
    
    
    public void onDestroy() {
        // 移除定時器
        handler.removeCallbacks(run);
        super.onDestroy();
    }

    // 定时器，每隔一段时间检查下载进度，然后更新Notification上的ProgressBar
    private Handler handler = new Handler();
    private Runnable run = new Runnable() {
        public void run() {
            rViews.setProgressBar(R.id.downloadFile_pb, 100, downloadLength*100 / fileLength, false);
            notification.contentView = rViews;
            notificationManager.notify(0, notification);
            handler.postDelayed(run, 1000);
        }
    };
    
}

还要记得要在AndroidManifest.xml的application节点里注册Service。例如这样：

<service android:name="com.saetest.DownloadFileService"></service>

我们下载个谷歌地图来试试看。

　　　public void onClick(View v) {
        // new CheckedUpdate().execute();
        String url = "http://www.appchina.com/market/d/1603385/cop.baidu_0/com.google.android.apps.maps.apk";
        Intent downloadIntent = new Intent(this, DownloadFileService.class);
        Bundle bundle = new Bundle();
        bundle.putString("url", url);
        downloadIntent.putExtras(bundle);
        startService(downloadIntent);
        // 设置广播接收器，当新版本的apk下载完成后自动弹出安装界面
        IntentFilter intentFilter = new IntentFilter("com.test.downloadComplete");
        receiver = new BroadcastReceiver() {

            public void onReceive(Context context, Intent intent) {
                Intent install = new Intent(Intent.ACTION_VIEW);
                String pathString = intent.getStringExtra("downloadFile");
                install.setDataAndType(Uri.fromFile(new File(pathString)), "application/vnd.android.package-archive");
                install.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                context.startActivity(install);
            }
        };
        registerReceiver(receiver, intentFilter);
    }

    protected void onDestroy() {
        // 移除广播接收器
        if (receiver != null) {
            unregisterReceiver(receiver);
        }
        super.onDestroy();
    }