Android camera2判断设备是否有相机功能，获取摄像头数量

通过CameraManager 获取相机摄像头信息

        	CameraManager cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
            String[] cameraIdList = cameraManager.getCameraIdList();
            if (cameraIdList.length>0) {    
            	//cameraIdList.length 是否有摄像头和摄像头个数
            }