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What's the advantage of Optional.ofNullable(itemKey) over itemKey == null

I was just wondering when do we need to choose Optional over if else or nested null check. say for example is there any advantage of one another below or do you think the Optional could be an overkill
String.valueOf(Optional.ofNullable(itemKey).map(ItemKey::getId).orElse(null));
vs
String.valueOf(itemKey == null ? null : itemKey.getId());
I always keen to use the Optional.of or Optional.ofNullable when I had to pick nested item of a given object like below,
private String formatCurrency(String symbol, BigDecimal value) {
return Optional.ofNullable(value)
.map(BigDecimal::doubleValue)
.map(Object::toString)
.map(val -> symbol + val.replaceAll(REGEX_REMOVE_TRAILING_ZEROS, "$2"))
.orElse("");
}
Can I please know where in the code the Optional is absolutely unnecessary.

If you already have itemKey in your code, there is no meaning of transforming it to an Optional, it just makes the code more complex. However, if you want to use optionals, I think it'd be more appropriate to do something like this:
public Optional<ItemKey> getItemKey() {
if (...) {
return Optional.of(new ItemKey());
}
return Optional.empty()
}
public void mainCode() {
String id = getItemKey().map(ItemKey::getId).orElse(null);
}

Possibility of getOrElseReturn in Kotlin

I often have a problem with Optional and similar classes Option, Try, Either from VAVR for example.
Let's say I have some Optional, and if it's empty I want to immediately return from a method (without exception, since my method is returning Optional aswell, so getOrElseThrow is out of the picture) and if it's present I want to further process it.
public Optional<Integer> converter() {
Optional<String> opt = getSomething();
if(!opt.isPresent())
return Optional.empty();
String value = opt.get();
// some manipulations on value, such as map and flatMap would cause a huge mess
return Integer.parseInt(value);
}
I just need to return immediately in case value is empty, I can't do chain of map and flatMap. The whole pain is doing .get(). Something like getOrElseThrow, but with return instead of throw would be fantastic - getOrElseReturn. Obviously not possible in Java, so I thought about trying this in Kotlin.
fun safeOptional(): Optional<Int> {
val extracted = Optional.of("123")
.getOrElseReturn { return Optional.empty() }
val modified = extracted.toInt() * 2
return Optional.of(modified)
}
private inline fun <T> Optional<T>.getOrElseReturn(block: (Optional<T>) -> T): T {
return if (!this.isPresent)
block(this)
else
this.get()
}
Much to my surprise it actually does what I want. If I change the Optional.of("123") to Optional.empty() it immediately returns from a method. I don't understand how it compiles though.
My method needs a block: (Optional<T>) -> T, otherwise it wouldn't compile. So in my case I have Optional<String> and I need to pass a block: (Optional<String>) -> String, but hey - the block that I have is nowhere close to this and it still compiles, how?
When I extract the block to variable it becomes val block: (Optional<String>) -> Nothing (I guess return statement is Nothing) and it still compiles, surprising me even more.
btw I know this code is not strictly what I want - someone can pass another block without non-local return to the method, but I don't think there is another way

Extract the second part of your method into another private method and call getSomething().map(this::otherPrivateMethod)
It will not be invoked if no value is present in getSomething()
Basically,
public Optional<Integer> converter() {
return getSomething().map(this::privateConverter);
}
private Integer privateConverter(Integer integer) {
// some manipulations on value, such as map and flatMap would cause a huge mess
return Integer.parseInt(value);
}

Answering the Kotlin part:
fun safeOptional(): Optional<Int> {
val extracted = Optional.of("123")
.getOrElseReturn { return Optional.empty() }
.......
}
The return here is not return from a lambda, but rather a return from function safeOptional so therefore lambda doesn't return anything (it returns Nothing). Lambda returning Nothing can be passed as lambda returning anything.
To get a compile error, you should return from lambda instead:
val extracted = Optional.of("123")
.getOrElseReturn { return#getOrElseReturn Optional.empty() }
Generally, Optional are not needed in Kotlin. You should use nullable types instead. You would combine them with nullsafe operators (e.g. the Elvis operator -- ?::
fun nullsafe(x: String?): Optional<Int> {
val extracted = x ?: return Optional.empty()
val modified = extracted.toInt() * 2
return Optional.of(modified)
}
nullsafe("2") // => Optional[4]
nullsafe(null) // => Optional.empty

Rewriting an if statement which throws an exception in a cleaner way

Let's suppose we have an if statement like this:
public A save(A a) {
if (isValid.test(a)) {
return aRepository.save(a);
}
throw new ANotValidException("A is not valid");
}
isValid is a Predicate and it may look like:
private Predicate<A> isValid = (a) -> (a != null);
What do you think? Can I make it cleaner somehow?
I mean, for example using an Optional to reduce it in 1 line with an .orElseThrow();

A more precise version using Optional and throwing a custom Exception shall be :
public A save(A a) throws ANotValidException { // throws the custom exception
return Optional.ofNullable(a) // since your predicate is to check for not null
.map(aRepository::save)
.orElseThrow(() -> new ANotValidException(a + "A is not valid"));
}

An Optional can make the code more readable, particularly around the use of your predicate object:
public A save(A a) {
return Optional.ofNullable(a)
.filter(isValid)
.map(aRepository::save)
.orElseThrow(() -> new ANotValidException("A is not valid"));
}
You can also get rid of the predicate altogether as it's simple enough to use Objects::nonNull (unless your real predicate's test is more complex). And in that case, keeping your current condition checks would probably make more sense (in my opinion).

One could argue that it would be more natural to read it in the opposite order, that is first handle the validation and the result of it and then move on to saving the object.
public A save(A a) {
if (!isValid.test(a)) {
throw new ANotValidException("A is not valid");
}
return aRepository.save(a);
}

Helper method that returns a thing, or causes a return in the calling scope / context

I can't figure out how to factor out this code.
private CompletionStage<Response<String>> foo(RequestContext rc) {
final Optional<String> campaignIdOpt = rc.request().parameter("campaignId").filter(s -> !s.isEmpty());
final Optional<String> creativeIdOpt = rc.request().parameter("creativeId").filter(s -> !s.isEmpty());
Optional<Uuid> campaignIdOptOfUuid = Optional.empty();
if (campaignIdOpt.isPresent()) {
try {
campaignIdOptOfUuid = Optional.of(UuidUtils.fromString(campaignIdOpt.get()));
} catch (IllegalArgumentException e) {
LOG.error(String.format("Invalid campaignId: %s", campaignIdOpt.get()), e);
return CompletableFuture.completedFuture(
Response.forStatus(Status.BAD_REQUEST.withReasonPhrase("Invalid campaignId provided.")));
}
}
Optional<Uuid> creativeIdOptOfUuid = Optional.empty();
if (creativeIdOpt.isPresent()) {
try {
creativeIdOptOfUuid = Optional.of(UuidUtils.fromString(creativeIdOpt.get()));
} catch (IllegalArgumentException e) {
LOG.error(String.format("Invalid creativeId: %s", creativeIdOpt.get()), e);
return CompletableFuture.completedFuture(
Response.forStatus(Status.BAD_REQUEST.withReasonPhrase("Invalid creativeId provided.")));
}
}
// Simplified, do something with Uuids.
return bar(campaignIdOptOfUuid, creativeIdOptOfUuid);
}
Basically, we very frequently need to parse Google protobuf Uuids from a query string to pass on to another service that will find (or not find). We need to pass along an empty optional if a parameter was not set or an empty string, as both cases mean, "Don't filter by this parameter." Finally, if the string doesn't parse at all, then we want to immediately return an error 400 (Bad Request), rather than pass along a non-sense param to the service.
So, codewise, I want a utility method that
takes an Optional<String>, and
returns an Optional<Uuid> if present, Optional.empty() otherwise, and
if an exception is thrown, return an error from the original context.
But obviously, I can't "double-return." What pattern do I use to achieve this though? I tried to create an encapsulator for both an Optional<Uuid> and a CompletionStage<Response<String>> but it was awkward. Is there some idiomatic way of doing this?

You can use a loop. A loop allows you to handle all elements equally, thus removing the code duplication, while still allowing to return immediately:
private CompletionStage<Response<String>> foo(RequestContext rc) {
String[] parameters = {"campaignId", "creativeId" };
List<Optional<Uuid>> uuids = new ArrayList<>(parameters.length);
for(String param: parameters) {
Optional<String> o1 = rc.request().parameter(param).filter(s -> !s.isEmpty());
Optional<Uuid> o2;
try {
o2 = o1.map(UuidUtils::fromString);
} catch(IllegalArgumentException e) {
LOG.error(String.format("Invalid %s: %s", param, o1.get()), e);
return CompletableFuture.completedFuture(
Response.forStatus(Status.BAD_REQUEST
.withReasonPhrase("Invalid "+param+ " provided.")));
}
uuids.add(o2);
}
// Simplified, do something with Uuids.
return bar(uuids.get(0), uuids.get(1));
}
Otherwise, you would need to create a method returning an object holding two alternative results (like Either); the JDK does not provide such a type yet. A method could simply throw on an erroneous condition but that would bring you back to square one when the common code is mostly the exception handling.
Note that calling Optional.map on an empty optional will already return an empty optional, without evaluating the provided function, so you don’t need to check via ifPresent, etc.

How to flip an Option<Try<Foo>> to a Try<Option<Foo>>

I have an Try<Option<Foo>>. I want to flatMap Foo into a Bar, using it using an operation that can fail. It's not a failure if my Option<Foo> is an Option.none(), (and the Try was a success) and in this case there's nothing to do.
So I have code like this, which does work:
Try<Option<Bar>> myFlatMappingFunc(Option<Foo> fooOpt) {
return fooOpt.map(foo -> mappingFunc(foo).map(Option::of) /* ew */)
.getOrElse(Try.success(Option.none()); // double ew
}
Try<Bar> mappingFunc(Foo foo) throws IOException {
// do some mapping schtuff
// Note that I can never return null, and a failure here is a legitimate problem.
// FWIW it's Jackson's readValue(String, Class<?>)
}
I then call it like:
fooOptionTry.flatMap(this::myFlatMappingFunc);
This does work, but it looks really ugly.
Is there a better way to flip the Try and Option around?
Note 1: I actively do not want to call Option.get() and catch that within the Try as it's not semantically correct. I suppose I could recover the NoSuchElementException but that seems even worse, code-wise.
Note 2 (to explain the title): Naively, the obvious thing to do is:
Option<Try<Bar>> myFlatMappingFunc(Option<Foo> fooOpt) {
return fooOpt.map(foo -> mappingFunc(foo));
}
except this has the wrong signature and doesn't let me map with the previous operation that could have failed and also returned a successful lack of value.

When you are working with monads, each monad type combine only with monads of same type. This is usually a problem because the code will come very unreadable.
In the Scala world, there are some solutions, like the OptionT or EitherT transformers, but do this kind of abstractions in Java could be difficult.
The simple solution is to use only one monad type.
For this case, I can think in two alternatives:
transform fooOpt to Try<Foo> using .toTry()
transform both to Either using .toEither()
Functional programmers are usually more comfortable with Either because exceptions will have weird behaviors, instead Either usually not, and both works when you just want to know why and where something failed.
Your example using Either will look like this:
Either<String, Bar> myFlatMappingFunc(Option<Foo> fooOpt) {
Either<String, Foo> fooE = fooOpt.toEither("Foo not found.");
return fooE.flatMap(foo -> mappingFunc(foo));
}
// Look mom!, not "throws IOException" or any unexpected thing!
Either<String, Bar> mappingFunc(Foo foo) {
return Try.of(() -> /*do something dangerous with Foo and return Bar*/)
.toEither().mapLeft(Throwable::getLocalizedMessage);
}

I believe this is simply a sequence function (https://static.javadoc.io/io.vavr/vavr/0.9.2/io/vavr/control/Try.html#sequence-java.lang.Iterable-) that you are looking for:
Try.sequence(optionalTry)

You can combine Try.sequence and headOption functions and create a new transform function with a little better look, in my opinion, also you can use generic types to get a more reusable function :) :
private static <T> Try<Option<T>> transform(Option<Try<T>> optT) {
return Try.sequence(optT.toArray()).map(Traversable::headOption);
}

If I understand correctly, you want to :
keep the first failure if happens
swap the second when mapping to json for an empty option.
Isn t it simpler if you decompose your function in such a way:
public void keepOriginalFailureAndSwapSecondOneToEmpty() {
Try<Option<Foo>> tryOptFoo = null;
Try<Option<Bar>> tryOptBar = tryOptFoo
.flatMap(optFoo ->
tryOptionBar(optFoo)
);
}
private Try<Option<Bar>> tryOptionBar(Option<Foo> optFoo) {
return Try.of(() -> optFoo
.map(foo -> toBar(foo)))
.orElse(success(none())
);
}
Bar toBar(Foo foo) throws RuntimeException {
return null;
}
static class Bar {
}
static class Foo {
}

The solution of throughnothing and durron597 helped me there. This is my groovy test case:
def "checkSomeTry"() {
given:
def ex = new RuntimeException("failure")
Option<Try<String>> test1 = Option.none()
Option<Try<String>> test2 = Option.some(Try.success("success"))
Option<Try<String>> test3 = Option.some(Try.failure(ex))
when:
def actual1 = Try.sequence(test1).map({ t -> t.toOption() })
def actual2 = Try.sequence(test2).map({ t -> t.toOption() })
def actual3 = Try.sequence(test3).map({ t -> t.toOption() })
then:
actual1 == Try.success(Option.none())
actual2 == Try.success(Option.some("success"))
actual3 == Try.failure(ex)
}