Dmitry

String number = new String(jsonObject.get("KEY").toString().getBytes(), "UTF-8");
String strr = new String("CHECK_MESSAGE".getBytes(), "UTF-8");

//has object
Class<? extends Object> clazz = object.getClass();
Field[] fields = clazz.getDeclaredFields();
for(Field field: fields){
    String fieldName = field.getName();
    if(!field.isAccessible()){
        field.setAccessible(true);
    }
    Object value = field.get(object);
}

public class User {
        .......
        @ManyToOne
        @JoinColumn(name="group_id")
        Group group;
        .......
       @Basic
       @Column(name= "group_id")
        long groupId;
    }