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BAEL-3759: Guava's Futures and ListenableFuture
 * Added new module guava-modules/guava-concurrency * Added implementation code for simple usages of ListenableFuture * Added implementation code for complex usages of ListenableFuture
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‎guava-modules/guava-concurrency/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>guava-modules</artifactId>
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<groupId>com.baeldung</groupId>
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<version>0.0.1-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>guava-concurrency</artifactId>
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</project>

‎guava-modules/guava-concurrency/src/main/java/com/baeldung/guava/future/ListenableFutureService.java‎

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package com.baeldung.guava.future;
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import java.util.Arrays;
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import java.util.List;
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import java.util.Random;
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import java.util.concurrent.Executors;
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import java.util.concurrent.FutureTask;
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import java.util.concurrent.TimeUnit;
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import java.util.stream.Collectors;
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import com.baeldung.guava.future.exception.ListenableFutureException;
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import com.google.common.util.concurrent.Futures;
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import com.google.common.util.concurrent.ListenableFuture;
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import com.google.common.util.concurrent.ListenableFutureTask;
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import com.google.common.util.concurrent.ListeningExecutorService;
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import com.google.common.util.concurrent.MoreExecutors;
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public class ListenableFutureService {
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private final ListeningExecutorService lExecService;
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public ListenableFutureService() {
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this.lExecService = MoreExecutors.listeningDecorator(Executors.newSingleThreadExecutor());
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}
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public ListenableFutureService(ListeningExecutorService lExecService) {
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this.lExecService = lExecService;
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}
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public ListenableFuture<String> fetchConfig(String configKey) {
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return lExecService.submit(() -> {
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TimeUnit.MILLISECONDS.sleep(500);
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return String.format("%s.%d", configKey, new Random().nextInt(Integer.MAX_VALUE));
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});
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}
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public FutureTask<String> fetchConfigTask(String configKey) {
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return new FutureTask<>(() -> {
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TimeUnit.MILLISECONDS.sleep(500);
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return String.format("%s.%d", configKey, new Random().nextInt(Integer.MAX_VALUE));
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});
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}
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public ListenableFutureTask<String> fetchConfigListenableTask(String configKey) {
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return ListenableFutureTask.create(() -> {
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TimeUnit.MILLISECONDS.sleep(500);
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return String.format("%s.%d", configKey, new Random().nextInt(Integer.MAX_VALUE));
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});
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}
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public ListenableFuture<Integer> succeedingTask() {
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return Futures.immediateFuture(new Random().nextInt(Integer.MAX_VALUE));
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}
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public <T> ListenableFuture<T> failingTask() {
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return Futures.immediateFailedFuture(new ListenableFutureException());
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}
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public ListenableFuture<Integer> getCartId() {
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return lExecService.submit(() -> {
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TimeUnit.MILLISECONDS.sleep(500);
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return new Random().nextInt(Integer.MAX_VALUE);
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});
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}
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public ListenableFuture<String> getCustomerName() {
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String[] names = new String[] { "Mark", "Jane", "June" };
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return lExecService.submit(() -> {
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TimeUnit.MILLISECONDS.sleep(500);
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return names[new Random().nextInt(names.length)];
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});
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}
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public ListenableFuture<List<String>> getCartItems() {
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String[] items = new String[] { "Apple", "Orange", "Mango", "Pineapple" };
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return lExecService.submit(() -> {
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TimeUnit.MILLISECONDS.sleep(500);
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int noOfItems = new Random().nextInt(items.length);
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if (noOfItems == 0) ++noOfItems;
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return Arrays.stream(items, 0, noOfItems).collect(Collectors.toList());
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});
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}
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public ListenableFuture<String> generateUsername(String firstName) {
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return lExecService.submit(() -> {
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TimeUnit.MILLISECONDS.sleep(500);
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return firstName.replaceAll("[^a-zA-Z]+","")
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.concat("@service.com");
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});
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}
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public ListenableFuture<String> generatePassword(String username) {
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return lExecService.submit(() -> {
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TimeUnit.MILLISECONDS.sleep(500);
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if (username.contains("@")) {
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String[] parts = username.split("@");
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return parts[0] + "123@" + parts[1];
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} else {
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return username + "123";
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}
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});
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}
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}

‎guava-modules/guava-concurrency/src/main/java/com/baeldung/guava/future/exception/ListenableFutureException.java‎

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package com.baeldung.guava.future.exception;
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public class ListenableFutureException extends Exception {
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}

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