Java CompletableFuture applyToEither()
May 29, 2019
CompletableFuture implements CompletionStage and Future interfaces. CompletableFuture.applyToEither is inherited from CompletionStage. The applyToEither method returns a new CompletionStage that, when either this or the other given stage complete normally, is executed with the corresponding result as argument to the supplied function.
Find the method declaration of
applyToEither method from Java doc.
<U> CompletionStage<U> applyToEither(CompletionStage<? extends T> other, Function<? super T,U> fn)
The parameter other is the other
CompletionStage.
The parameter fn is the function to use to compute the value of the returned
CompletionStage.
applyToEither returns new CompletionStage.Find the examples.
Example-1:
ApplyToEitherDemo1.java
package com.concretepage;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
public class ApplyToEitherDemo1 {
public static void main(String[] args) throws InterruptedException, ExecutionException {
CompletableFuture<Person> primaryFuture = CompletableFuture.completedFuture(new Person("Mohan", "Varanasi"));
CompletableFuture<Person> secondaryFuture = CompletableFuture.completedFuture(new Person("Shyam", "Prayagraj"));
CompletableFuture<String> future =
primaryFuture.applyToEither(secondaryFuture, person -> person.getName() + " - " +person.getCity());
System.out.println(future.get());
}
}
Mohan - Varanasi
applyToEither method applies the result of this completion stage or other completion stage whichever completes normally earlier, to the given function and returns a new completion stage. In the above example, sometimes we will get result for primaryFuture and sometimes for secondaryFuture.
Example-2:
ApplyToEitherDemo2.java
package com.concretepage;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
public class ApplyToEitherDemo2 {
public static void main(String[] args) throws InterruptedException, ExecutionException {
CompletableFuture<Person> mainFuture = CompletableFuture.supplyAsync(() -> getPerson());
CompletableFuture<Person> defaultFuture = CompletableFuture.supplyAsync(() -> getDefaultFuture());
CompletableFuture<String> future = mainFuture.applyToEither(defaultFuture,
person -> person.getName() + " - " + person.getCity());
System.out.println(future.join());
}
private static Person getPerson() {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
return new Person("Krishna", "Delhi");
}
private static Person getDefaultFuture() {
return new Person("Default name", "Default city");
}
}
Default name - Default city
defaultFuture will complete earlier than mainFuture. So applyToEither will apply the result of defaultFuture to the given function.
Example-3: Find the example of
applyToEither with acceptEither method.
package com.concretepage;
import java.util.concurrent.CompletableFuture;
public class ApplyToEitherDemo3 {
public static void main(String[] args) {
CompletableFuture<Person> mainFuture = CompletableFuture.supplyAsync(() -> getPerson());
CompletableFuture<Person> defaultFuture = CompletableFuture.supplyAsync(() -> getDefaultFuture());
CompletableFuture<String> cfuture = mainFuture.applyToEither(defaultFuture,
person -> person.getName() + " - " + person.getCity());
CompletableFuture<String> otherCFuture = CompletableFuture.supplyAsync(() -> getMsg());
CompletableFuture<Void> cf = cfuture.acceptEither(otherCFuture, s -> System.out.println(s));
cf.join();
}
private static String getMsg() {
try {
Thread.sleep(400);
// Thread.sleep(1000);
} catch (InterruptedException e) {
System.err.println(e);
}
return "Namo - Gujraat";
}
private static Person getPerson() {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
return new Person("Krishna", "Delhi");
}
private static Person getDefaultFuture() {
try {
Thread.sleep(600);
} catch (InterruptedException e) {
e.printStackTrace();
}
return new Person("Default name", "Default city");
}
}
Namo - Gujraat
References
Class CompletableFutureJava CompletableFuture acceptEither()
