I have a sequence of methods that I need to run sequentially, using the result of each method as a parameter in the next. However, I also check that the result of each method is "good" before calling the next method (if it's "bad" then I exit the method early. The methods return an empty Optional if they were not successful.
Is there a refactoring that I can perform to improve the code? Chain of Responsibility feels a little overboard.
private boolean isSequenceSuccessful() {
Optional<byte[]> result1 = doSomething();
if (!result1.isPresent()) {
return false;
}
Optional<byte[]> result2 = doAnotherThing(result1.get());
if (!result2.isPresent()) {
return false;
}
Optional<byte[]> result3 = doSomethingElse(result2.get());
if (!result3.isPresent()) {
return false;
}
return doMoreStuff(result3.get());
}
I don't want to use Exceptions to control the flow of the method because that's a code smell (I expect to sometimes get "bad" results).
You can write it shorter using Optional and mapping:
private boolean isSequenceSuccessful() {
return Optional.of(doSomething())
.flatMap(result1 -> doAnotherThing(result1))
.flatMap(result2 -> doSomethingElse(result2))
.map(result3 -> doMoreStuff(result3))
.orElse(false);
}
Or using method references even shorter:
private boolean isSequenceSuccessful2() {
return Optional.of(doSomething())
.flatMap(this::doAnotherThing)
.flatMap(this::doSomethingElse)
.map(this::doMoreStuff)
.orElse(false);
}
It depends what you prefer. If you want to keep the intermediate result variables use the lambda version.
Since the methods doAnotherThing and doSomethingElse do return an Optional<byte[]>, Optional.flatMap is needed to continue the mapping. Otherwise you could change the return type of these methods to return byte[] solely. Then you would use Optinal.map only, which would be more consistent.
The mapping will only be performed as long as a value is present in the Optional. If all mappings could be applied the value of the last is returned as result. Otherwise the processing will fail fast and bypass all remainig mappings to the last statement orElse and return it's value. This is false according to your code.
You could use the map method:
private boolean isSequenceSuccessful() {
Optional<byte[]> result = doSomething().map(this::doAnotherThing)
.map(this::doSomethingElse);
if (result.isPresent()) return doMoreStuff(result.get());
else return false;
}
Look at the template pattern which I sometimes refer to as the pizza pattern because it is analogous to making a pizza. (eg. createDough(), putIngredients(), bake(), package(), deliver()). This might apply to your case. There are several examples and implementations out there but pick and choose which applies best to you. In your example above, I would create an abstract class and create concrete classes/implementations. Example to give you an idea:
public abstract class SequenceChecker {
// ...
public boolean isSequenceSuccessful() {
Optional<byte[]> result1 = doSomething();
Optional<byte[]> result2 = doAnotherThing(result1);
Optional<byte[]> result3 = doSomethingElse(result2);
return doMoreStuff(result3);
}
protected abstract boolean doMoreStuff(Optional<byte[]> result);
protected abstract Optional<byte[]> doSomethingElse(Optional<byte[]> result);
protected abstract Optional<byte[]> doAnotherThing(Optional<byte[]> result);
protected abstract Optional<byte[]> doSomething();
// ...
}
Use Optional::flatMap.
private boolean isSequenceSuccessful() {
Optional<Boolean> result = doSomething()
.flatMap(this::doAnotherThing)
.flatMap(this::doSomethingElse)
.map(this::doMoreStuff);
return result.isPresent() ? result.get() : false;
}
Related
I am using the Single RxJava object and I want to run a void method in the critical path of the async workflow but return the previous result.
For example, I have something like:
Single<Integer> method() {
Single<Integer> value = Single.just(10);
return value.<RxJava Method>(Consumer<Integer> or Runnable<Integer>);
}
method().blockingGet();
returns
> 10
The stuff I do in Consumer<Integer> or Runnable<Integer>, I want to make sure happens before I return the value 10. Is there a built in method in Single for this?
ie: I am just wondering if there is a cleaner way to portray:
Single<Integer> method() {
Single<Integer> value = Single.just(10);
return value.map(result -> {
// call void method
return result;
});
}
method().blockingGet();
I have these two methods which call an async API and return a Mono<Boolean> if a value exists. I am returning a random boolean value for the sake of this example,
private Mono<Boolean> checkFirstExists() {
// Replacing actual API call here
return Mono.just(Boolean.FALSE);
}
private Mono<Boolean> checkSecondExists() {
// Replacing actual API call here
return Mono.just(Boolean.TRUE);
}
Now, I have another method that should combine the results of these two methods and simply return a boolean if either checkFirstExists or checkSecondExists is true.
private boolean checkIfExists() {
// Should return true if any of the underlying method returns true
final Flux<Boolean> exists = Flux.concat(checkFirstExists(), checkSecondExists());
return exists.blockFirst();
}
What's the best way of doing this? Mono.zip maybe? Any help would be great.
Mono.zip is the correct approach for awaiting completion of multiple async operations before continuing. Something like this should work:
return Mono.zip(checkFirstExists(), checkSecondExists(), (first, second) -> first && second);
Or if a list is provided instead:
private boolean checkIfExists()
{
return allTrue(Arrays.asList(checkFirstExists(), checkSecondExists())).blockOptional().orElseThrow(() -> new IllegalStateException("Invalid State"));
}
private Mono<Boolean> allTrue(List<Mono<Boolean>> toAggregate)
{
return mergeMonos(toAggregate).map(list -> list.stream().allMatch(val -> val));
}
#SuppressWarnings("unchecked")
private <T> Mono<List<T>> mergeMonos(List<Mono<T>> toAggregate)
{
return Mono.zip(toAggregate, array -> Stream.of(array).map(o -> (T) o).collect(Collectors.toList()));
}
Unrelated Note:
In general, it is worth keeping the operation async as long as possible when constructing reactive flows. It may be worth having the 'checkIfExists' function return a Mono instead of blocking.
I understand you can't return from a ifPresent() so this example does not work:
public boolean checkSomethingIfPresent() {
mightReturnAString().ifPresent((item) -> {
if (item.equals("something")) {
// Do some other stuff like use "something" in API calls
return true; // Does not compile
}
});
return false;
}
Where mightReturnAString() could return a valid string or an empty optional. What I have done that works is:
public boolean checkSomethingIsPresent() {
Optional<String> result = mightReturnAString();
if (result.isPresent()) {
String item = result.get();
if (item.equals("something") {
// Do some other stuff like use "something" in API calls
return true;
}
}
return false;
}
which is longer and does not feel much different to just checking for nulls in the first place. I feel like there must be a more succinct way using Optional.
I think all you're looking for is simply filter and check for the presence then:
return result.filter(a -> a.equals("something")).isPresent();
How about mapping to a boolean?
public boolean checkSomethingIfPresent() {
return mightReturnAString().map(item -> {
if (item.equals("something")) {
// Do some other stuff like use "something" in API calls
return true; // Does not compile
}
return false; // or null
}).orElse(false);
}
While #nullpointer and #Ravindra showed how to merge the Optional with another condition, you'll have to do a bit more to be able to call APIs and do other stuff as you asked in the question. The following looks quite readable and concise in my opinion:
private static boolean checkSomethingIfPresent() {
Optional<String> str = mightReturnAString();
if (str.filter(s -> s.equals("something")).isPresent()) {
//call APIs here using str.get()
return true;
}
return false;
}
A better design would be to chain methods:
private static void checkSomethingIfPresent() {
mightReturnFilteredString().ifPresent(s -> {
//call APIs here
});
}
private static Optional<String> mightReturnFilteredString() {
return mightReturnAString().filter(s -> s.equals("something"));
}
private static Optional<String> mightReturnAString() {
return Optional.of("something");
}
The ideal solution is “command-query separation”: Make one method (command) for doing something with the string if it is present. And another method (query) to tell you whether it was there.
However, we don’t live an ideal world, and perfect solutions are never possible. If in your situation you cannot separate command and query, my taste is for the idea already presented by shmosel: map to a boolean. As a detail I would use filter rather than the inner if statement:
public boolean checkSomethingIfPresent() {
return mightReturnAString().filter(item -> item.equals("something"))
.map(item -> {
// Do some other stuff like use "something" in API calls
return true; // (compiles)
})
.orElse(false);
}
What I don’t like about it is that the call chain has a side effect, which is not normally expected except from ifPresent and ifPresentOrElse (and orElseThrow, of course).
If we insist on using ifPresent to make the side effect clearer, that is possible:
AtomicBoolean result = new AtomicBoolean(false);
mightReturnAString().filter(item -> item.equals("something"))
.ifPresent(item -> {
// Do some other stuff like use "something" in API calls
result.set(true);
});
return result.get();
I use AtomicBoolean as a container for the result since we would not be allowed to assign to a primitive boolean from within the lambda. We don’t need its atomicity, but it doesn’t harm either.
Link: Command–query separation on Wikipedia
By the way if you really want to get value from Optional, use:
Optional<User> user = service.getCurrentUset();
return user.map(User::getId);
I just wanted to return a boolean from an Optional object by doing a check on the getProductType() on the ProductDetails object as shown below:
public boolean isElectronicProduct(String productName) {
Optional<ProductDetails> optProductDetails = findProductDetails(productName);
if(optProductDetails.isPresent()) {
return optProductDetails.get().getProductType() == ProductType.ELECTRONICS;
}
return false;
}
Intellij complains stating that the above code can be replaced in functional style, is there really any way to simplify the above Optional object and return a boolean?
This is what you need:
return findProductDetails(productName)
.map(ProductDetails::getProductType)
.map(ProductType.ELECTRONICS::equals)
.orElse(false);
I prefer to split things out with the extra map call, rather than calling productDetails.getProductType() directly before the comparison. I think it's just slightly easier to read.
Change this:
if(optProductDetails.isPresent()) {
return optProductDetails.get().getProductType() == ProductType.ELECTRONICS;
}
return false;
To:
return optProductDetails
.filter(prodDet -> prodDet.getProductType() == ProductType.ELECTRONICS) // Optional<ProductDetails> which match the criteria
.isPresent(); // boolean
You can read more about functional-style operations on Optional values at: https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html
optProductDetails.map(d -> d.getProductType() == ProductType.ELECTRONICS) //Optional<Boolean>
.orElse(false); //Boolean
I am a little confused on "how to do this properly":
// return true: if present and number of lines != 0
boolean isValid(Optional<File> optFile) {
return optFile.ifPresentOrElse(f -> return !isZeroLine(f), return false);
}
private boolean isZeroLine(File f) {
return MyFileUtils.getNbLinesByFile(f) == 0;
}
I know the syntax is not correct and not compiling, but it's just for you to get the idea.
How can I turn this into 'clean code'?
i.e. avoid doing:
if (optFile.isPresent()) {//} else {//}
Dealing with boolean return type(easily inferred Predicates), one way to do that could be to use Optional.filter :
boolean isValid(Optional<File> optFile) {
return optFile.filter(this::isZeroLine).isPresent();
}
But, then using Optionals arguments seems to be a poor practice. As suggested in comments by Carlos as well, another way of implementing it could possibly be:
boolean isValid(File optFile) {
return Optional.ofNullable(optFile).map(this::isZeroLine).orElse(false);
}
On another note, ifPresentOrElse is a construct to be used while performing some actions corresponding to the presence of the Optional value something like :
optFile.ifPresentOrElse(this::doWork, this::doNothing)
where the corresponding actions could be -
private void doWork(File f){
// do some work with the file
}
private void doNothing() {
// do some other actions
}