Replacing repetitive get statement with Java 8 Optional

Question

I have a use case, where I have nested classes and an object of the top class. I want to get a value which is at the Nth level. I'm using getters repetitively to achieve this to avoid NPE. Sample code (assuming getters are there)

class A {
    String a1;
    String getA1() {
        return a1;
    }
}

class B {
    A a;
    A getA() {
        return a;
    }
}

class C {
    B b;
    B getB() {
        return b;
    }
}

class D {
    C c;
    C getC() {
        return c;
    }
}

If I have an object d of class D, and want to get the String a1 of A, what I'm doing is following:

String getAValue(D d) {
    String aValue = null;
    if(d != null && d.getC() != null && d.getC().getB() != null && d.getC().getB().getA() != null) {
        aValue = d.getC().getB().getA().getA1();
    }
    return aValue;
}

This repetitive a is looking really ugly. How do I avoid it by using java8 Optional?

EDIT: I can't modify the above classes. Assume this d object is returned to me as a service call. I'm exposed to these getters only.

Answer 1

Use Optional with a series of map() calls for a nice one-liner:

String getAValue(D d) {
   return Optional.ofNullable(d)
       .map(D::getC).map(C::getB).map(B::getA).map(A::getA1).orElse(null);
}

If anything is null along the chain, including d itself, the orElse() will execute.

Answer 2

Wrap each nested class in an Optional:

Class A {
    String a1;
}
Class B {
    Optional<A> a;
}
Class C {
    Optional<B> b;
}
Class D {
    Optional<C> c;
}

Then use flatMap and map to operate on these optional values:

String a1 = d.flatMap(D::getC) // flatMap operates on Optional
             .flatMap(C::getB) // flatMap also returns an Optional
             .flatMap(B::getA) // that's why you can keep calling .flatMap()
             .map(A::getA1)    // unwrap the value of a1, if any
             .orElse("Something went wrong.") // in case anything fails

You might want to check out the concept of Monads. And if you're feeling adventurous, Scala is too distant from Java.