原始图片下载 图片加水印

 private final String PATH = "http://pic33.nipic.com/20131007/13639685_123501617185_2.jpg";
 /**
     * todo 不使用RxJava去下载图片
     * @param view
     */
    public void r03(View view) {

        progressDialog = new ProgressDialog(this);
        progressDialog.setMessage("正在下载中...");
        progressDialog.show();

        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(2000);

                    URL url = new URL(PATH);
                    URLConnection urlConnection = url.openConnection();
                    HttpURLConnection httpURLConnection = (HttpURLConnection) urlConnection;
                    httpURLConnection.setConnectTimeout(5000);
                    int responseCode = httpURLConnection.getResponseCode();
                    if (HttpURLConnection.HTTP_OK == responseCode) {
                       Bitmap bitmap = BitmapFactory.decodeStream(httpURLConnection.getInputStream());
                       Message message = handler.obtainMessage();
                       message.obj = bitmap;
                       handler.sendMessage(message);
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }

    private Handler handler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            Bitmap bitmap = (Bitmap) msg.obj;
            imageView.setImageBitmap(bitmap);

            // 隐藏加载框
            if (progressDialog != null)
                progressDialog.dismiss();
            return false;
        }
    });

 /**
     * todo 使用RxJava去下载图片
     * @param view
     */
    public void r04(View view) {

        // 起点

        // 上游 被观察者 Observable
        Observable.just(PATH)  // 内部发射

        // String Path  变换  Bitmap
        .map(new Function() {
            @Override
            public Bitmap apply(String s) throws Exception {

                try {
                    Thread.sleep(2000);

                    URL url = new URL(PATH);
                    URLConnection urlConnection = url.openConnection();
                    HttpURLConnection httpURLConnection = (HttpURLConnection) urlConnection;
                    httpURLConnection.setConnectTimeout(5000);
                    int responseCode = httpURLConnection.getResponseCode();
                    if (HttpURLConnection.HTTP_OK == responseCode) {
                        Bitmap bitmap = BitmapFactory.decodeStream(httpURLConnection.getInputStream());
                        return bitmap;
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }

                return null;
            }
        })

        .map(new Function() {
            @Override
            public Bitmap apply(Bitmap bitmap) throws Exception {
                // 给图片加水印
                Paint paint = new Paint();
                paint.setColor(Color.RED);
                paint.setTextSize(30);
                Bitmap bitmapSuccess = drawTextToBitmap(bitmap, "同学们大家好", paint, 60, 60);
                return bitmapSuccess;
            }
        })

        // 比如：增加一个 日志纪录功能，只需要添加要给 变换操作符
        .map(new Function() {
            @Override
            public Bitmap apply(Bitmap bitmap) throws Exception {
                Log.d(TAG, "apply: 下载的Bitmap 是这个样子的" + bitmap);
                return bitmap;
            }
        })

        .subscribeOn(Schedulers.io()) // todo  给上游分配 异步线程
        .observeOn(AndroidSchedulers.mainThread()) // todo  给下游分配 主线程

        .subscribe(new Observer() { // 下游
            @Override
            public void onSubscribe(Disposable d) {
                progressDialog = new ProgressDialog(MainActivity8.this);
                progressDialog.setMessage("RxJava下载图片中..");
                progressDialog.show();
            }

            @Override
            public void onNext(Bitmap bitmap) {
                if (imageView != null)
                    imageView.setImageBitmap(bitmap);
            }

            @Override
            public void onError(Throwable e) { // 发生异常
               //  if (imageView != null)
                   //  imageView.setImageResource(R.mipmap.ic_launcher); // 下载错误的图片
            }

            @Override
            public void onComplete() { // 终点
                if (progressDialog != null)
                    progressDialog.dismiss();
            }
        });
    }


    //图片上绘制文字
    private Bitmap drawTextToBitmap(Bitmap bitmap, String text, Paint paint, int paddingLeft, int paddingTop) {
        Bitmap.Config bitmapConfig = bitmap.getConfig();

        paint.setDither(true); // 获取跟清晰的图像采样
        paint.setFilterBitmap(true);// 过滤一些
        if (bitmapConfig == null) {
            bitmapConfig = Bitmap.Config.ARGB_8888;
        }
        bitmap = bitmap.copy(bitmapConfig, true);
        Canvas canvas = new Canvas(bitmap);

        canvas.drawText(text, paddingLeft, paddingTop, paint);
        return bitmap;
    }