Java 8 CompletableFuture Example
December 03, 2014
CompletableFuture.supplyAsync
supplyAsync accepts a Supplier as an argument and complete its job asynchronously. The result of supplier is run by a task from ForkJoinPool.commonPool() as default. We can also pass our Executor. Finally supplyAsync method returns CompletableFuture on which we can apply other methods.CompletableFuture.thenApply
thenApply method accepts a function as an argument. Once the calling CompletableFuture completes , then on the result of this stage, that function is applied by thenApply method and returns a CompletableFuture.CompletableFuture.join
join method returns the result after completion or throws CompletionException. This method waits for the completion of calling completion stage.CompletableFutureOneExample.java
package com.concretepage.util.concurrent;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CompletableFuture;
public class CompletableFutureOneExample {
public static void main(String[] args) throws InterruptedException {
List<Integer> list = Arrays.asList(10,20,30,40);
list.stream().map(data->CompletableFuture.supplyAsync(()->getNumber(data))).
map(compFuture->compFuture.thenApply(n->n*n)).map(t->t.join())
.forEach(s->System.out.println(s));
}
private static int getNumber(int a){
return a*a;
}
}
10000 160000 810000 2560000
CompletableFuture.thenAccept
thenAccept method accepts Consumer as an argument. On the completion of any completion stage, thenAccept method applies Consumer on the result and returns CompletableFuture.CompletableFutureTwoExample.java
package com.concretepage.util.concurrent;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CompletableFuture;
public class CompletableFutureTwoExample {
public static void main(String[] args) throws InterruptedException {
List<String> list = Arrays.asList("A","B","C","D");
list.stream().map(data->CompletableFuture.supplyAsync(()->"Processing:"+data)).
map(compFuture->compFuture.thenAccept(s->System.out.println(s))).map(t->t.join())
.count();
}
}
Processing:A Processing:B Processing:C Processing:D
CompletableFuture.whenComplete
whenComplete method uses BiConsumer as an argument. Once the calling completion stage completes, whenComplete method applies completion stage result on BiConsumer. BiConsumer takes first argument as result and second argument as error if any.CompletableFutureThreeExample.java
package com.concretepage.util.concurrent;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CompletableFuture;
public class CompletableFutureThreeExample {
public static void main(String[] args) {
List<String> list = Arrays.asList("A","B","C","D");
list.stream().map(s->CompletableFuture.supplyAsync(()->s+s))
.map(f->f.whenComplete((result,error)->System.out.println(result+" Error:"+error))).count();
}
}
AA Error:null BB Error:null CC Error:null DD Error:null
CompletableFuture.getNow
getNow is a method that if calling completion stage is not completed then the value passed to getNow will be set to result.CompletableFutureFourExample.java
package com.concretepage.util.concurrent;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CompletableFuture;
public class CompletableFutureFourExample {
public static void main(String[] args) {
List<String> list = Arrays.asList("A","B","C","D");
list.stream().map(s->CompletableFuture.supplyAsync(()->s+s))
.map(f->f.getNow("Not Done")).forEach(s->System.out.println(s));
}
}
Not Done Not Done CC Not Done
