如何编写通用 java 方法以通过 null 检查返回值？

Question

I have some code which copies values from one object to another.

When I have to null check values my code becomes very lengthy and harder to read, so I want a method that gets the instance of the object and returnd the value I need with a null check.

Is there a way to make such a method?

My usages are similar to the following:

    objectInstance.setName(methodNullCheck(object.getName()));
    
    objectInstance.setAddress(methodNullCheck(object.getAddress().getFullAddress));

My intention is to have a function that could have a NullPointerException check on the input parameter and return the value if it exists.

How do I write such a method?

Answer 1

Here is example code:

   public <T> T methodNullCheck(T value) {
        if (value != null) {
            return value;
        } else {
            throw new IllegalArgumentException("null value");
        }
    }

I would suggest to use Lombok and @NonNull annotation on input parameters of setName() , setAddress() , etc.

Answer 2

you can create a null safe Function

interface NullSafeFunction<T, R> extends Function<T, R> {

    default <V> NullSafeFunction<T, V> andThen(Function<? super R, ? extends V> after) {
        return (T t) -> Optional.ofNullable(t).map(this::apply).map(after).orElse(null);
    }

    static <T> NullSafeFunction<T, T> identity() {
        return t -> t;
    }
}

and then use it as follows

A a1 = new A();

String result1 = NullSafeFunction.<A>identity()
        .andThen(A::getB)
        .andThen(B::getC)
        .andThen(C::getD)
        .apply(a1);

System.out.println(result1); //null

A a2 = new A(new B(new C("yes")));

String result2 = NullSafeFunction.<A>identity()
        .andThen(A::getB)
        .andThen(B::getC)
        .andThen(C::getD)
        .apply(a2);

System.out.println(result2); //yes