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

Author: jason-m-s

guava-modules/guava-concurrency/pom.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>guava-modules</artifactId>
+        <groupId>com.baeldung</groupId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>guava-concurrency</artifactId>
+
+</project>

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

@@ -0,0 +1,105 @@
+package com.baeldung.guava.future;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Random;
+import java.util.concurrent.Executors;
+import java.util.concurrent.FutureTask;
+import java.util.concurrent.TimeUnit;
+import java.util.stream.Collectors;
+
+import com.baeldung.guava.future.exception.ListenableFutureException;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.common.util.concurrent.ListenableFutureTask;
+import com.google.common.util.concurrent.ListeningExecutorService;
+import com.google.common.util.concurrent.MoreExecutors;
+
+public class ListenableFutureService {
+
+    private final ListeningExecutorService lExecService;
+
+    public ListenableFutureService() {
+        this.lExecService = MoreExecutors.listeningDecorator(Executors.newSingleThreadExecutor());
+    }
+
+    public ListenableFutureService(ListeningExecutorService lExecService) {
+        this.lExecService = lExecService;
+    }
+
+    public ListenableFuture<String> fetchConfig(String configKey) {
+        return lExecService.submit(() -> {
+            TimeUnit.MILLISECONDS.sleep(500);
+            return String.format("%s.%d", configKey, new Random().nextInt(Integer.MAX_VALUE));
+        });
+    }
+
+    public FutureTask<String> fetchConfigTask(String configKey) {
+        return new FutureTask<>(() -> {
+            TimeUnit.MILLISECONDS.sleep(500);
+            return String.format("%s.%d", configKey, new Random().nextInt(Integer.MAX_VALUE));
+        });
+    }
+
+    public ListenableFutureTask<String> fetchConfigListenableTask(String configKey) {
+        return ListenableFutureTask.create(() -> {
+            TimeUnit.MILLISECONDS.sleep(500);
+            return String.format("%s.%d", configKey, new Random().nextInt(Integer.MAX_VALUE));
+        });
+    }
+
+    public ListenableFuture<Integer> succeedingTask() {
+        return Futures.immediateFuture(new Random().nextInt(Integer.MAX_VALUE));
+    }
+
+    public <T> ListenableFuture<T> failingTask() {
+        return Futures.immediateFailedFuture(new ListenableFutureException());
+    }
+
+    public ListenableFuture<Integer> getCartId() {
+        return lExecService.submit(() -> {
+            TimeUnit.MILLISECONDS.sleep(500);
+            return new Random().nextInt(Integer.MAX_VALUE);
+        });
+    }
+
+    public ListenableFuture<String> getCustomerName() {
+        String[] names = new String[] { "Mark", "Jane", "June" };
+        return lExecService.submit(() -> {
+            TimeUnit.MILLISECONDS.sleep(500);
+            return names[new Random().nextInt(names.length)];
+        });
+    }
+
+    public ListenableFuture<List<String>> getCartItems() {
+        String[] items = new String[] { "Apple", "Orange", "Mango", "Pineapple" };
+        return lExecService.submit(() -> {
+            TimeUnit.MILLISECONDS.sleep(500);
+
+            int noOfItems = new Random().nextInt(items.length);
+            if (noOfItems == 0) ++noOfItems;
+
+            return Arrays.stream(items, 0, noOfItems).collect(Collectors.toList());
+        });
+    }
+
+    public ListenableFuture<String> generateUsername(String firstName) {
+        return lExecService.submit(() -> {
+            TimeUnit.MILLISECONDS.sleep(500);
+            return firstName.replaceAll("[^a-zA-Z]+","")
+                    .concat("@service.com");
+        });
+    }
+
+    public ListenableFuture<String> generatePassword(String username) {
+        return lExecService.submit(() -> {
+            TimeUnit.MILLISECONDS.sleep(500);
+            if (username.contains("@")) {
+                String[] parts = username.split("@");
+                return parts[0] + "123@" + parts[1];
+            } else {
+                return username + "123";
+            }
+        });
+    }
+}

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

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