1public class MainActivity extends AppCompatActivity {
2
3    private ImageView mImageView;
4    @Override
5    protected void onCreate(Bundle savedInstanceState) {
6        super.onCreate(savedInstanceState);
7        setContentView(R.layout.activity_main);
8        mImageView = (ImageView) findViewById(R.id.image);
9    }
10
11 // 给图片加水印的方法
12    private Bitmap createWatermark(Bitmap bitmap, String mark) {
13        int w = bitmap.getWidth();
14        int h = bitmap.getHeight();
15        Bitmap bmp = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
16        Canvas canvas = new Canvas(bmp);
17        Paint p = new Paint();
18        // 水印颜色
19        p.setColor(Color.parseColor("#C5FF0000"));
20        // 水印字体大小
21        p.setTextSize(150);
22        //抗锯齿
23        p.setAntiAlias(true);
24        //绘制图像
25        canvas.drawBitmap(bitmap, 0, 0, p);
26        //绘制文字
27        canvas.drawText(mark, 0, h / 2, p);
28        canvas.save(Canvas.ALL_SAVE_FLAG);
29        canvas.restore();
30        return bmp;
31    }
32}

1new Thread(new Runnable() {
2    @Override
3    public void run() {
4        try {
5            URL url = new URL("https://www.baidu.com/img/bd_logo1.png?where=super");
6            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
7            InputStream inputStream = urlConnection.getInputStream();
8            Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
9            // 加一个水印
10            bitmap = createWatermark(bitmap,"RxJava2.0");
11            // 显示到图片
12            Message message = Message.obtain();
13            message.obj = bitmap;
14            mHandler.sendMessage(message);
15        } catch (IOException e) {
16            e.printStackTrace();
17        }
18    }
19}).start();
20
21private Handler mHandler = new Handler(){
22    @Override
23    public void handleMessage(Message msg) {
24        Bitmap bitmap = (Bitmap) msg.obj;
25        mImageView.setImageBitmap(bitmap);
26    }
27}

1Observable.just("https://www.baidu.com/img/bd_logo1.png?where=super")
2  .map(new Function<String, Bitmap>() { // 事件变换
3
4      @Override
5      public Bitmap apply(@NonNull String urlPath) throws Exception {
6          URL url = new URL(urlPath);
7          HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
8          InputStream inputStream = urlConnection.getInputStream();
9          Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
10          return bitmap;
11      }
12  })
13  .map(new Function<Bitmap, Bitmap>() {
14
15      @Override
16      public Bitmap apply(@NonNull Bitmap bitmap) throws Exception {
17          bitmap = createWatermark(bitmap, "RxJava2.0");
18          return bitmap;
19      }
20  })
21  .subscribeOn(Schedulers.io())
22  .observeOn(AndroidSchedulers.mainThread())
23  .subscribe(new Consumer<Bitmap>() {
24
25      @Override
26      public void accept(Bitmap bitmap) throws Exception {
27          mImageView.setImageBitmap(bitmap);
28      }
29  });