Properly handle null value from SQL query?

Question

I use this code to get Merchant name by ID.

@GetMapping("pages")
public Page<WpfPaymentsDTO> pages(@RequestParam(value = "page") int page, @RequestParam(value = "size") int size) {
    return wpfPaymentsService.findAll(page, size)
                             .map(g -> WpfPaymentsDTO.builder()
                             .id(g.getId())
                             .status(g.getStatus())
                             .merchant_id(getMerchantName(g.getMerchant_id()))
                             .build());  
}

private String getMerchantName(int id) {      
    Optional<Merchants> obj = merchantService.findById(id);       
    return obj.get().getName();
}

But when name is not found I get java.lang.NullPointerException: null at this line: .merchant_id(getMerchantName(g.getMerchant_id()))

Is there some way to set empty string and not to break the code when Object is not found?

Just add obj.ifPresent() check in getMerchantName method. If it is true use your code. Else return empty string. — Prasath, Apr 01 '19 at 09:38
You can try including the code nested inside a "try, catch" expression, capturing the NullPointerException to prevent it from stopping the code — Pablo Alvarez, Apr 01 '19 at 09:38
@PabloAlvarez No. https://stackoverflow.com/questions/18265940/when-is-it-ok-to-catch-nullpointerexception — m0skit0, Apr 01 '19 at 09:39

Kamil Rafałko · Accepted Answer · 2019-04-01T11:01:28.543

2

Instead of calling obj.get().getName() use more optional-way solution like:

obj.map(Merchants::getName).orElse("");

which will return empty string when Merchants is not found. You can change "" in code above to any other default value which is more appropriate to your case.

If g.getMerchant_id() can be null code below will also handle this situation:

private String getMerchantName(Integer id) {      
    return Optional.ofNullable(id)
        .flatMap(i -> merchantService.findById(i))
        .map(Merchants::getName)
        .orElse(<default value>);
}

It will turn id into optional so when it will be null this code will just return <default value> otherwise it will use id to find Merchants and then get its name. flatMap is here to remove nested optionals.

edited Apr 01 '19 at 11:01

answered Apr 01 '19 at 09:50

Kamil Rafałko

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2
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g.getMerchant_id() is empty in some cases. How I can handle this case? – Peter Penzov Apr 01 '19 at 10:01
Change `getMerchantName` method signature to: `private String getMerchantName(Integer id)` and then inside it's body `return Optional.ofNullable(id).flatMap(i -> merchantService.findById(i)).map().orElse()` – Kamil Rafałko Apr 01 '19 at 10:42
bad news. I get at this line `.contract_id(getContractName(g.getContract_id()))` java.lang.NullPointerException: null this is because probably `g.getMerchant_id()` is empty. Is there some solution for this? – Peter Penzov Apr 01 '19 at 11:11
I don't see line that you mentions in your question. – Kamil Rafałko Apr 01 '19 at 13:48
I cut it in order to save space but the code is the same. – Peter Penzov Apr 01 '19 at 13:49

Prasath · Answer 2 · 2019-04-01T10:15:43.643

1

private String getMerchantName(int id) {      
    Optional<Merchants> obj = merchantService.findById(id);    

    return obj.isPresent() ?  obj.get().getName() : "";
}

edited Apr 01 '19 at 10:15

answered Apr 01 '19 at 09:42

Prasath

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`ifPresent` takes a consumer, it is not an expression. – RealSkeptic Apr 01 '19 at 09:59
That one is not `ifPresent`, it's `isPresent`. In any case, this is an antipattern, and using `map` and `orElse` should be preferred. – RealSkeptic Apr 01 '19 at 10:13
Oh yes it is isPresent – Prasath Apr 01 '19 at 10:15
I changed my answer – Prasath Apr 01 '19 at 10:31

Andrianekena Moise · Answer 3 · 2019-04-01T09:48:55.737

1

You can return an empty string to avoid the NPE if the name is null :

private String getMerchantName(int id) {      
    Optional<Merchants> obj = merchantService.findById(id);       
    return obj.isPresent() ?  obj.get().getName() : "";
}

Then the method merchant_id should handle an empty string and perhaps throws an exception (IllegalArgumentException for example).

edited Apr 01 '19 at 09:48

answered Apr 01 '19 at 09:44

Andrianekena Moise

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I get The method ifPresent(Consumer super Merchants>) in the type Optional is not applicable for the arguments () – Peter Penzov Apr 01 '19 at 09:47
Sorry, the method is `Optional.isPresent()`. – Andrianekena Moise Apr 01 '19 at 09:49
1

`isPresent` followed by `get` is an anti-pattern. This is what `orElse` was invented for. – RealSkeptic Apr 01 '19 at 09:57
Looks like I'm facing one more issue. g.getMerchant_id() is empty in some cases. So I need to add here case also to handle null value. – Peter Penzov Apr 01 '19 at 10:00

score 0 · Answer 4 · answered Apr 01 '19 at 09:59

0

I think we can determine if this object is empty before we return it

answered Apr 01 '19 at 09:59

Capiudor Blus

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Properly handle null value from SQL query?

4 Answers4