Question

I know how to serialize java objects. but what if I have an objects and inside another object that is null?

e.g.

My 1st class:

public class Invoice {

  private Adresse adresse;
  private Double betrag;
  private Double ust;
  private String zweck;

}

My 2nd class:

public class Adresse {

  private String name;
  private Ort ort;

}

My 3rd class:

public class Ort {

  private String plz;
  private String name;

}

And maybe more generated sub-classes…

I want to get this json object:

{"adresse":{"name":null,"ort"{"plz":null,"name":null}},"betrag":null,"Ust":null,"zweck":null}

I am not allowed to change my POJO’s.
What kind of framework can do this for me? I tried gson but gson is not working with subclasses.

regards, dave

Answer 1

I got it working! With Java Reflection, json and it’s recursive!

Here the code:

1. userDefined() checks if a class is user defined or primitive, can be customized as you wish.

   public boolean isUserDefined(Class o) {
     if (o.isAssignableFrom(String.class)) {
       return false;
     }
     if (o.isAssignableFrom(Double.class)) {
       return false;
     }
     if (o.isAssignableFrom(Integer.class)) {
       return false;
     }
     if (o.isAssignableFrom(Boolean.class)) {
       return false;
     }
     if (o.isAssignableFrom(Short.class)) {
       return false;
     }
     if (o.isAssignableFrom(Float.class)) {
       return false;
     }
     if (o.isAssignableFrom(Long.class)) {
       return false;
     }
     return true;
   }
   

2. getSetterMethod() returns the setter Method of a field.

   private static Method getSetterMethod(Object o, Field f) {       
       for (Method method : o.getClass().getMethods()) {
           String fieldname = "set" + f.getName();
           String methodname = method.getName().toLowerCase();
           if (fieldname.equals(methodname)) {
               return method;
           }
       }
       return null;
   }
   

3. And finally, invokeSetters() invoke user defined object setter Methods and those of the subclasses! yea. So my Invoice object I would put here as a parameter:

   Invoice i = new Invoice();
   invokeSetters(i);
   

and here it is:

        private void invokeSetters(Object o) throws IllegalArgumentException, IllegalAccessException, ClassNotFoundException, InstantiationException, NoSuchMethodException, InvocationTargetException {
        System.out.println("INVOKING THE OBJECT " + o.getClass().toString());
          for (Field f : o.getClass().getDeclaredFields()) {
            System.out.println("NOW IN THE FIELD: " + f.getName());
            f.setAccessible(true);
            Object obj = null;
            if (isUserDefined(f.getType()) && f.get(o) == null) {
                System.out.println("FIELD is USER DEFINED AND NULL");
                Class c = Class.forName(f.getType().getName());
                System.out.println("CLASS IS " + c.getName());
                obj = c.getConstructor().newInstance();
                System.out.println("GOING INSIDE " + obj.toString() + " NOW.");
                invokeSetters(obj);
            }
            if (obj != null) {
                Method setter = getSetterMethod(o, f);
                System.out.println("IM IN PARENT OBJECT " + o + " AND INVOKING METHOD " + setter.getName() + " WITH PARAMETER " + obj.toString());
                setter.invoke(o, obj);
                System.out.println("METHOD WAS INVOKED");
            }
          }
        }