How to search for null values inside a java object?

Question

I'm writing a JUnit test to assert that my algorithm's output object does not present any null value or empty strings.

For simplicity imagine 3 classes : Parent, Child, Car, where Parent is the object that I have to validate.

@Data
@AllArgsConstructor
@FieldDefaults(level = AccessLevel.PRIVATE)
@Builder
public class Child {
    String name;
    int age;
}

@Data
@AllArgsConstructor
@FieldDefaults(level = AccessLevel.PRIVATE)
@Builder
public class Car {
    String brand;
    String model;
}

@Data
@AllArgsConstructor
@FieldDefaults(level = AccessLevel.PRIVATE)
@Builder
public class Parent {
    String name;
    int age;
    List<Child> children;
    Car car;
}

what is the best and easy way to search for null values or empty strings?

I'm currently using the following method as a validator, checking field by field for null values and empty strings.

private boolean isValid(Parent parent) {
    if(parent == null) return false;

    boolean isObjectNull = Stream.of(parent.getName(), parent.getChildren(), parent.getCar()).anyMatch(Objects::isNull);

    if(isObjectNull) return false;

    isObjectNull = Stream.of(parent.getCar().getBrand(), parent.getCar().getModel()).anyMatch(Objects::isNull);

    if(isObjectNull) return false;
    
    for(Child child : parent.getChildren()){
        isObjectNull = Stream.of(child.getName()).anyMatch(Objects::isNull);
        
        if(isObjectNull) return false;

        if(!isValidString(child.getName())) return false;
    }
    
    return isValidString(parent.getName(), parent.getCar().getBrand(), parent.getCar().getModel());
}

private boolean isValidString(String... values){
    for(String s : values){
        if(s.isEmpty())
    }
}

But I would love something I can also use for other objects I will create in the future.

It would be better not to permit construction of invalid objects in the first place. How are this objects created, and why can't you validate the data used to create them? — erickson, Jun 28 '22 at 14:34
I need this for the JUnit test, to test the output. @erickson — Paul Marcelin Bejan, Jun 28 '22 at 14:48

tquadrat · Accepted Answer · 2022-06-28T14:39:31.017

You can use reflection to obtain all the getters from your objects that do return a reference (instead of a primitive). Then iterate over that list (or array, your choice) and execute them; when the return value for any of these is null, return false or throw an appropriate exception.

A little bit like this:

public final void validateNonNull( final Object candidate ) throws ValidationException
{
  if( isNull( candidate ) throw new ValidationException( "candidate is null" );

  final var candidateClass = candidate.getClass();
  final List<Method> getters = Arrays.stream( candidateClass.getMethods() ) // getters are always public!
    .filter( m -> !m.getName().equals( "getClass" ) )
    .filter( m -> m.getName().startsWith( "get" ) )
    .filter( m -> m.getParameterCount() == 0 )
    .filter( m -> !m.getReturnType().isPrimitive() )
    .collect( Collectors.toList() );

  for( var method : methods )
  {
    if( isNull( method.invoke( candidate ) ) throw new ValidationException( "candidate.%s() returned null".formatted( method.getName() ) );
  }
}

ValidationException is a custom exception, and you need to declare the checked exceptions that are declared for Method::invoke.

To check for empty Strings, too, change the for loop like this:

…
for( var method : methods )
{
  var retValue = method.invoke( candidate );
  if( retValue instanceof String aString && aString.isEmpty() ) throw new ValidationException( "candidate.%s() returned the empty String".formatted( method.getName() ) ); 
  if( isNull( retValue ) throw new ValidationException( "candidate.%s() returned null".formatted( method.getName() ) );
}

Good idea! The answer of https://stackoverflow.com/questions/2466038/how-do-i-iterate-over-class-members can be helpful to start coding iteration over object Fields. — Arthur Araújo, Jun 28 '22 at 14:21

How to search for null values inside a java object?

1 Answers1