Simple RotateGestureDetector can be used in the same way as GestureDetector and ScaleGestureDetector.

RotateGestureDetector.java

import android.content.Context;
import android.view.MotionEvent;

public class RotateGestureDetector {
	public static interface OnRotateListener {
		boolean onRotate(float degrees, float focusX, float focusY);
	}

	public static class SimpleOnRotateGestureDetector implements OnRotateListener {
		@Override
		public boolean onRotate(float degrees, float focusX, float focusY) {
			return false;
		}
	}

	private static float RADIAN_TO_DEGREES = (float) (180.0 / Math.PI);
	private OnRotateListener listener;
	private float prevX = 0.0f;
	private float prevY = 0.0f;
	private float prevTan;

	public RotateGestureDetector(OnRotateListener listener) {
		this.listener = listener;
	}

	public boolean onTouchEvent(MotionEvent event) {
		if (event.getPointerCount() == 2 && event.getActionMasked() == MotionEvent.ACTION_MOVE) {
			boolean result = true;
			float x = event.getX(1) - event.getX(0);
			float y = event.getY(1) - event.getY(0);
			float focusX = (event.getX(1) + event.getX(0)) * 0.5f;
			float focusY = (event.getY(1) + event.getY(0)) * 0.5f;
			float tan = (float) Math.atan2(y, x);

			if (prevX != 0.0f && prevY != 0.0f) {
				result = listener.onRotate((tan - prevTan) * RADIAN_TO_DEGREES, focusX, focusY);
			}

			prevX = x;
			prevY = y;
			prevTan = tan;
			return result;
		} else {
			prevX = prevY = prevTan = 0.0f;
			return true;
		}
	}
}

UserActivity.java

public class UserActivity extends Activity {
	private RotateGestureDetector rotateGestureDetector;
	
	protected void onCreate(Bundle savedInstanceState) {
		rotateGestureDetector = new RotateGestureDetector(new RotateGestureDetector.SimpleOnRotateGestureDetector() {
			@Override
			public boolean onRotate(float degrees, float focusX, float focusY) {
				// something with rotate
				return true;
			}
		});
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		rotateGestureDetector.onTouchEvent(event);
		return true;
	}
}