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Question

Is there a Null and NullPointer safe way to evaluate boolean expressions.

Here's an example from our codebase -

private boolean serviceReturnedSuccess(Response response) {
    boolean isSuccess = true;
    if (response.hasMetadata()) {
        Metadata responseMetadata = response.getMetadata();
        if (responseMetadata.hasReturnCode()) {
            if (responseMetadata.getReturnCode() != 0) {
                isSuccess = false;
            }
        }
    }
    return isSuccess;
}

What I would like to write is -

private boolean serviceReturnedSuccess(Response response) {
    return NullSafeBooleanEvaluator.valueOf(response.getMetadata().getReturnCode() != 0);
}

I couldn't find something that does this out of the box when I looked at BooleanUtils in apache commons or in Guava's common object utils .

I am ideally looking for an implementation in one of the standard libraries, otherwise I'm looking for a generic way to implement this.

Answer 1

There can't be a NullSafeBooleanEvaluator.valueOf(response.getMetadata().getReturnCode() != 0) since the argument expression must be evaluated before it is passed to NullSafeBooleanEvaluator.valueOf() . The closest solution would be

private boolean serviceReturnedSuccess(Response response) {
    try {
        return response.getMetadata().getReturnCode() != 0;
    }
    catch (NullPointerException e) {
        return false;
    }
}

which of course has some code smell.

As Egor already commented Java 8 introduced the new Optional class for such problems (see also this informative article ):

But I am not convinced that it leads to readable code:

if (response.flatMap(Response::getMetadata).map(MetaData::getReturnCode).orElse(0) != 0)

(probably lot of errors in this code, but you get the idea).

The above article also mentions Groovy's safe navigation operator ? which allows for a very elegant expression:

 if (response.getMetaData()?.getResponseCode()? != 0)

(again not tested). But Java is not Groovy, so I think your current code is probably the optimum if you don't want/can't use Optionals.