Android--完整版的下载示例

在AndroidManifest.xml添加权限和属性

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.servicebestpractice">

    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <application
        android:requestLegacyExternalStorage="true"//添加这个属性才能访问SD卡的Download目录
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.ServiceBestPractice">
        <service
            android:name=".DownloadService"
            android:enabled="true"
            android:exported="true">
        </service>

        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

下载状态回调接口

public interface DownloadListener {

    void onProgress(int progress);//通知当前下载进度

    void onSuccess();//通知下载成功事件

    void onFailed();//通知下载失败事件

    void onPause();//通知下载停止事件

    void onCanceled();//通知下载取消事件

}

新建DownloadTask继承自AsyncTask实现下载功能

public class DownloadTask extends AsyncTask<String, Integer, Integer> {

    //四种下载状态
    public static final int TYPE_SUCCESS = 0;
    public static final int TYPE_FAILED = 1;
    public static final int TYPE_PAUSED = 2;
    public static final int TYPE_CANCELED = 3;

    private DownloadListener listener;

    private boolean isCanceled = false;
    private boolean isPaused = false;

    private int lastProgress;//最新的下载进度

    public DownloadTask(DownloadListener listener) {
        this.listener = listener;
    }

    @Override
    protected Integer doInBackground(String... params) {
        InputStream is = null;//读数据
        RandomAccessFile saveFile = null;//写数据
        File file = null;
        try {
            //记录已下载的文件长度
            long downloadedLength = 0;
            //获取到要下载的URL地址
            String downloadUrl = params[0];
            //根据URL地址解析出要下载的文件名
            String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));
            //然后指定将文件下载到Environment.DIRECTORY_DOWNLOADS目录下，也就是SD卡的Download目录下
            String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getAbsolutePath();

            file = new File(directory + fileName);//目录+文件名
            //判断Download目录下是否存在要下载的文件
            if (file.exists()) {
                //如果存在该文件，则读取已下载的字节数
                downloadedLength = file.length();
            }
            //获取待下载文件的总长度
            long contentLength = getContentLength(downloadUrl);
            //如果待下载文件长度为0，说明文件有问题，直接返回TYPE_FAILED
            if (contentLength == 0) {
                return TYPE_FAILED;
            }//如果已下载字节数等于待下载文件总字数，说明下载完成了
            else if (contentLength == downloadedLength){
                return TYPE_SUCCESS;
            }

            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    //断点下载，告诉服务器我们想要从哪个字节开始下载，防止重复下载
                    .addHeader("RANGE", "bytes=" + downloadedLength + "-")
                    .url(downloadUrl)
                    .build();
            Response response = client.newCall(request).execute();
            if (response != null) {
                is = response.body().byteStream();
                saveFile = new RandomAccessFile(file, "rw");
                //跳过已下载的字节
                saveFile.seek(downloadedLength);

                byte[] b = new byte[1024];
                int total = 0;
                int len;
                while ((len = is.read(b)) != -1) {
                    //前两个if用于中断下载
                    if (isCanceled) {
                        return TYPE_CANCELED;
                    } else if (isPaused) {
                        return TYPE_PAUSED;
                    } else {
                        total += len;
                        saveFile.write(b, 0 ,len);
                        //计算已下载的百分比
                        int progress = (int) ((total + downloadedLength) * 100 / contentLength);
                        publishProgress(progress);//自动调用onProgressUpdate()方法
                    }
                }
            }
            response.body().close();
            return TYPE_SUCCESS;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (is != null) {
                    is.close();
                }
                if (saveFile != null) {
                    saveFile.close();
                }
                if (isCanceled && file != null) {
                    file.delete();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        //获取下载进度
        int progress = values[0];
        //和上一次的进度对比
        if (progress > lastProgress) {
            listener.onProgress(progress);
            lastProgress = progress;
        }
    }

    @Override
    protected void onPostExecute(Integer status) {//根据传入的下载进度进行回调
        switch (status) {
            case TYPE_SUCCESS:
                listener.onSuccess();
                break;
            case TYPE_FAILED:
                listener.onFailed();
                break;
            case TYPE_PAUSED:
                listener.onPause();
                break;
            case TYPE_CANCELED:
                listener.onCanceled();
                break;
            default:
                break;
        }
    }

    public void pauseDownload() {
        isPaused = true;
    }
    public void cancelDownload() {
        isCanceled = true;
    }

    private long getContentLength(String downloadUrl) throws IOException {
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(downloadUrl)
                .build();
        Response response = client.newCall(request).execute();
        if (response != null && response.isSuccessful()) {
            long contentLength = response.body().contentLength();
            response.body().close();
            return contentLength;
        }
        return 0;
    }

}

创建一个下载的服务保证DownloadTask一直在后台运行

@RequiresApi(api = Build.VERSION_CODES.O)
public class DownloadService extends Service {

    private DownloadTask downloadTask;

    private String downloadUrl;

    private String channelId = "download";

    private DownloadListener listener = new DownloadListener() {
        @Override
        public void onProgress(int progress) {
            //构建一个用于显示下载进度的通知
            getNotificationManager().notify(1, getNotification("Downloading...", progress));
        }

        @Override
        public void onSuccess() {
            downloadTask = null;
            //下载完成后将前台服务关闭
            stopForeground(true);
            //并创建一个下载成功的通知
            getNotificationManager().notify(1, getNotification("Download Success", -1));
            Toast.makeText(DownloadService.this, "Download Success", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onFailed() {
            downloadTask = null;
            //下载失败时将前台服务关闭，并创建一个下载失败的通知
            stopForeground(true);
            getNotificationManager().notify(1, getNotification("Download Failed", -1));
            Toast.makeText(DownloadService.this, "Download Failed", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onPause() {
            downloadTask = null;
            Toast.makeText(DownloadService.this, "Paused", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onCanceled() {
            downloadTask = null;
            //取消下载后关闭前台服务
            stopForeground(true);
            Toast.makeText(DownloadService.this, "Canceled", Toast.LENGTH_SHORT).show();
        }
    };

    private DownloadBinder mBinder = new DownloadBinder();

    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    class DownloadBinder extends Binder {

        public void startDownload(String url) {
            if (downloadTask == null) {
                downloadUrl = url;
                downloadTask = new DownloadTask(listener);
                //开启后台下载
                downloadTask.execute(downloadUrl);
                //同时让这个下载任务成为一个前台服务
                startForeground(1, getNotification("Download...", 0));
                Toast.makeText(DownloadService.this, "Downloading...", Toast.LENGTH_SHORT).show();
            }
        }

        public void pauseDownload() {
            if (downloadTask == null) {
                downloadTask.pauseDownload();
            }
        }

        public void cancelDownload() {
            if (downloadTask != null) {
                downloadTask.cancelDownload();
            }
            if (downloadUrl != null) {
                //取消下载时需将文件删除，并将通知关闭
                String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));
                String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getAbsolutePath();
                File file = new File(directory + fileName);
                if (file.exists()) {
                    file.delete();
                }
                getNotificationManager().cancel(1);
                stopForeground(true);
                Toast.makeText(DownloadService.this, "Canceled", Toast.LENGTH_SHORT).show();
            }
        }
    }

    public DownloadService() {
    }

    private NotificationManager getNotificationManager() {
        NotificationManager manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        return manager;
    }

    private Notification getNotification(String title, int progress) {
        Intent intent = new Intent(this, DownloadActivity.class);
        PendingIntent pending = PendingIntent.getActivity(this, 0, intent, 0);
        NotificationManager manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        NotificationChannel channel = new NotificationChannel(channelId, "task", NotificationManager.IMPORTANCE_HIGH);
        manager.createNotificationChannel(channel);
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this, channelId);
        builder.setContentTitle(title);
        builder.setSmallIcon(R.mipmap.ic_launcher);
        builder.setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher));
        builder.setContentIntent(pending);
        //只有progress大于0时才显示进度
        if (progress > 0) {
            builder.setContentText(progress + "%");
            builder.setProgress(100, progress, false);
        }
        return builder.build();
    }
}

在活动中申请权限、开启绑定服务等

public class DownloadActivity extends AppCompatActivity implements View.OnClickListener{

    private DownloadService.DownloadBinder downloadBinder;

    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
            downloadBinder = (DownloadService.DownloadBinder) iBinder;
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {

        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_download);
        Button startDownload = (Button) findViewById(R.id.start_download);
        Button pauseDownload = (Button) findViewById(R.id.pause_download);
        Button cancelDownload = (Button) findViewById(R.id.cancel_download);
        startDownload.setOnClickListener(this);
        pauseDownload.setOnClickListener(this);
        cancelDownload.setOnClickListener(this);
        //启动服务
        Intent intent = new Intent(this, DownloadService.class);
        startService(intent);
        //绑定服务
        bindService(intent, connection, BIND_AUTO_CREATE);
        if (ContextCompat.checkSelfPermission(DownloadActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(DownloadActivity.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},1);
        }

    }

    @Override
    public void onClick(View view) {
        if (downloadBinder == null) {
            return;
        }
        switch (view.getId()) {
            case R.id.start_download:
                String url = "https://raw.githubusercontent.com/guolindev/eclipse/master/eclipse-inst-win64.exe";
                downloadBinder.startDownload(url);
                break;
            case R.id.pause_download:
                downloadBinder.pauseDownload();
                break;
            case R.id.cancel_download:
                downloadBinder.cancelDownload();
                break;
            default:
                break;
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode) {
            case 1:
                if (grantResults.length > 0 && grantResults[0] != PackageManager.PERMISSION_GRANTED) {
                    Toast.makeText(this, "拒绝权限将无法使用程序", Toast.LENGTH_SHORT).show();
                    finish();
                }
                break;
            default:
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        //解绑服务
        unbindService(connection);
    }

}

Android--完整版的下载示例

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