reflection - Merging two objects in Java

Question

I have two objects of same type.

Class A {
  String a;
  List b;
  int c;
}

A obj1 = new A();
A obj2 = new A();

obj1 => {a = "hello"; b = null; c = 10}
obj2 => {a = null; b = new ArrayList(); c = default value}

Can you please let me know what is the best way to combine this objects into single object?

obj3 = {a = "hello"; b = (same arraylist from obj2); c = 10}

Answer 1

This works as long as you have POJOs with their own getters and setters. The method updates obj with non-null values from update. It calls setParameter() on obj with the return value of getParameter() on update:

public void merge(Object obj, Object update){
    if(!obj.getClass().isAssignableFrom(update.getClass())){
        return;
    }

    Method[] methods = obj.getClass().getMethods();

    for(Method fromMethod: methods){
        if(fromMethod.getDeclaringClass().equals(obj.getClass())
                && fromMethod.getName().startsWith("get")){

            String fromName = fromMethod.getName();
            String toName = fromName.replace("get", "set");

            try {
                Method toMetod = obj.getClass().getMethod(toName, fromMethod.getReturnType());
                Object value = fromMethod.invoke(update, (Object[])null);
                if(value != null){
                    toMetod.invoke(obj, value);
                }
            } catch (Exception e) {
                e.printStackTrace();
            } 
        }
    }
}