Topic subscription with gazebo and ROSJava

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Hi would like to be notified when the position of an object in gazebo changes. I have found the following options:

1. Subscribe to gazebo/ModelStates and check for the object attributes
2. Use the service call Get_model_state provided by Gazebo to retrieve state and property information about the object

I am trying the first one since I haven't found any documentation about calling a gazebo service from ROSJava. Check here

I started with the basic Subscriber from the official RosJava documentation. Now I need to define a new subscriber

Subscriber<gazebo_msgs.ModelStates> subscriber = connectedNode.newSubscriber("chatter", gazebo_msgs.ModelStates._TYPE);
    subscriber.addMessageListener(new MessageListener<gazebo_msgs.ModelStates>() {
      @Override
      public void onNewMessage(gazebo_msgs.ModelStates message) {
        log.info("I heard: \"" + message.getName() + "\"");
      }
    });

I would like to subscribe to a topic which exchanges gazebo_msgs/ModelStates messages.

string[] name                 # model names
geometry_msgs/Pose[] pose     # desired pose in world frame
geometry_msgs/Twist[] twist   # desired twist in world frame

Catkin_make returns the error:

gazebo_msgs does not exist
Subscriber<gazebo_msgs.modelstates> subscriber = connectedNode.newSubscriber("chatter", gazebo_msgs.ModelStates._TYPE);

Question How do I include this type of message in ROSJava?