public class MainActivity extends AppCompatActivity {

 private ImageView mImgRectRound;
 private ImageView mImgRound;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  mImgRectRound = (ImageView) findViewById(R.id.img_rect_rounded);
  mImgRound = (ImageView) findViewById(R.id.img_rounded);
  rectRoundBitmap();
  roundBitmap();
 }

 private void rectRoundBitmap(){
  //得到资源文件的BitMap
  Bitmap image= BitmapFactory.decodeResource(getResources(),R.drawable.dog);
  //创建RoundedBitmapDrawable对象
  RoundedBitmapDrawable roundImg =RoundedBitmapDrawableFactory.create(getResources(),image);
  //抗锯齿
  roundImg.setAntiAlias(true);
  //设置圆角半径
  roundImg.setCornerRadius(30);
  //设置显示图片
  mImgRectRound.setImageDrawable(roundImg);
 }

 private void roundBitmap(){
  //如果是圆的时候，我们应该把bitmap图片进行剪切成正方形， 然后再设置圆角半径为正方形边长的一半即可
  Bitmap image = BitmapFactory.decodeResource(getResources(), R.drawable.dog);
  Bitmap bitmap = null;
  //将长方形图片裁剪成正方形图片
  if (image.getWidth() == image.getHeight()) {
   bitmap = Bitmap.createBitmap(image, image.getWidth() / 2 - image.getHeight() / 2, 0, image.getHeight(), image.getHeight());
  } else {
   bitmap = Bitmap.createBitmap(image, 0, image.getHeight() / 2 - image.getWidth() / 2, image.getWidth(), image.getWidth());
  }
  RoundedBitmapDrawable roundedBitmapDrawable = RoundedBitmapDrawableFactory.create(getResources(), bitmap);
  //圆角半径为正方形边长的一半
  roundedBitmapDrawable.setCornerRadius(bitmap.getWidth() / 2);
  //抗锯齿
  roundedBitmapDrawable.setAntiAlias(true);
  mImgRound.setImageDrawable(roundedBitmapDrawable);
 }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:id="@+id/activity_main"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical"
 tools:context="com.cjl.roundedbitmap.MainActivity">

 <ImageView
  android:id="@+id/img_rect_rounded"
  android:layout_width="200dp"
  android:layout_height="300dp"
  android:layout_marginTop="20dp"
  android:layout_gravity="center_horizontal"/>

 <ImageView
  android:id="@+id/img_rounded"
  android:layout_marginTop="20dp"
  android:layout_width="200dp"
  android:layout_height="200dp"
  android:layout_gravity="center_horizontal"/>
</LinearLayout>