LibGDX && Sensors

I need an analog sensor Box2D, in bullet physics.
Tried to do so but can not find nothing

init

   btGhostPairCallback ghostCall = new btGhostPairCallback();
        collisionWorld.getBroadphase().getOverlappingPairCache().setInternalGhostPairCallback(ghostCall);

        btGhostObject ghostObj = new btGhostObject();
        btCollisionShape shape = new btBoxShape(new Vector3(2, 2, 2));
        ghostObj.setCollisionShape(shape);
        Matrix4 trans = new Matrix4();
        trans.idt();
        trans.setTranslation(0,5,0);
        ghostObj.setWorldTransform(trans);
        ghostObj.userData = "LOL";
        ghostObj.setCollisionFlags( btCollisionObject.CollisionFlags.CF_NO_CONTACT_RESPONSE | ghostObj.getCollisionFlags());
        collisionWorld.addCollisionObject(ghostObj, (short)btBroadphaseProxy.CollisionFilterGroups.SensorTrigger,(short)(btBroadphaseProxy.CollisionFilterGroups.AllFilter & btBroadphaseProxy.CollisionFilterGroups.SensorTrigger));

update()

 int count = collisionWorld.getNumCollisionObjects();
        btCollisionObjectArray array =  collisionWorld.getCollisionObjectArray();
        for(int i = 0;i < array.size() ; i++) {
            btCollisionObject object = array.at(i);
            {
                if (object instanceof btGhostObject) {
                    btCollisionObjectArray array1 = ((btGhostObject) object).getOverlappingPairs();
                    for (int i1 = 0; i1 < array1.size(); i++) {
                        System.out.println("Objects : " + array1.at(i1).userData);
                    }
                }
             }
        }