BAEL-7932: CompletableFuture vs Mono (eugenp#16574)

pom.xml

@@ -784,6 +784,7 @@
                 <module>quarkus-modules</module>
                 <module>reactive-systems</module>
                 <module>reactor-core</module>
+                <module>reactor-core-2</module>
                 <module>rsocket</module>
                 <module>rule-engines-modules</module>
                 <module>rxjava-modules</module>
@@ -1033,6 +1034,7 @@
                 <module>quarkus-modules</module>
                 <module>reactive-systems</module>
                 <module>reactor-core</module>
+                <module>reactor-core-2</module>
                 <module>rsocket</module>
                 <module>rule-engines-modules</module>
                 <module>rxjava-modules</module>

reactor-core-2/README.md

@@ -0,0 +1,3 @@
+## Reactor Core (2)
+
+### Relevant articles

reactor-core-2/pom.xml

@@ -0,0 +1,47 @@
+<?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">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>org.baeldung</groupId>
+    <artifactId>reactor-core-2</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>reactor-core-2</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.projectreactor</groupId>
+            <artifactId>reactor-core</artifactId>
+            <version>${reactor.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>io.projectreactor</groupId>
+            <artifactId>reactor-test</artifactId>
+            <version>${reactor.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>io.projectreactor.addons</groupId>
+            <artifactId>reactor-extra</artifactId>
+            <version>${reactor-extra.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <reactor.version>3.6.0</reactor.version>
+        <reactor-extra.version>3.5.1</reactor-extra.version>
+    </properties>
+
+</project>

reactor-core-2/src/main/java/com/baeldung/reactor/completablefuturevsmono/AsyncApiCall.java

@@ -0,0 +1,41 @@
+package com.baeldung.reactor.completablefuturevsmono;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.function.BiConsumer;
+
+public class AsyncApiCall {
+
+    public static void main(String[] args) {
+        AsyncApiCall apiCall = new AsyncApiCall();
+        CompletableFuture<String> completableFuture = apiCall.nonBlockingApiCall("test parameter");
+
+        completableFuture.thenAccept(result -> System.out.println("Future completed successfully: " + result))
+            .exceptionally(error -> {
+                System.out.println("Future completed exceptionally: " + error.getMessage());
+                return null;
+            });
+    }
+
+    public void myAsyncCall(String param, BiConsumer<String, Throwable> callback) {
+        new Thread(() -> {
+            try {
+                Thread.sleep(1000);
+                callback.accept("Response from API with param: " + param, null);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
+        }).start();
+    }
+
+    public CompletableFuture<String> nonBlockingApiCall(String param) {
+        CompletableFuture<String> completableFuture = new CompletableFuture<>();
+        myAsyncCall(param, (result, error) -> {
+            if (error != null) {
+                completableFuture.completeExceptionally(error);
+            } else {
+                completableFuture.complete(result);
+            }
+        });
+        return completableFuture;
+    }
+}

reactor-core-2/src/main/java/com/baeldung/reactor/completablefuturevsmono/CompletableFutureDemo.java

@@ -0,0 +1,26 @@
+package com.baeldung.reactor.completablefuturevsmono;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+
+public class CompletableFutureDemo {
+
+    public static void main(String[] args) {
+
+        CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> {
+            try {
+                Thread.sleep(1000);
+            } catch (InterruptedException e) {
+                Thread.currentThread()
+                    .interrupt();
+            }
+            return "Finished completableFuture";
+        });
+
+        try {
+            completableFuture.get(); // This blocks the main thread
+        } catch (InterruptedException | ExecutionException e) {
+            Thread.currentThread().interrupt();
+        }
+    }
+}

reactor-core-2/src/main/java/com/baeldung/reactor/completablefuturevsmono/MonoDemo.java

@@ -0,0 +1,17 @@
+package com.baeldung.reactor.completablefuturevsmono;
+
+import reactor.core.publisher.Mono;
+import reactor.core.scheduler.Schedulers;
+
+public class MonoDemo {
+
+    public static void main(String[] args) {
+        Mono<String> reactiveMono = Mono.fromCallable(() -> {
+                Thread.sleep(1000);
+                return "Reactive Data";
+            })
+            .subscribeOn(Schedulers.boundedElastic());
+
+        reactiveMono.subscribe(System.out::println);
+    }
+}

reactor-core-2/src/main/resources/logback.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

reactor-core-2/src/test/java/com/baeldung/reactor/completablefuturevsmono/CompletableFutureUnitTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.reactor.completablefuturevsmono;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+import org.junit.jupiter.api.Test;
+
+class CompletableFutureUnitTest {
+
+    @Test
+    void whenGetMethodOnCompletableFutureItBlocksMainThread() {
+        CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
+            try {
+                Thread.sleep(5000);
+                return "Delayed result";
+            } catch (InterruptedException e) {
+                Thread.currentThread()
+                    .interrupt();
+                return null;
+            }
+        });
+
+        assertThrows(TimeoutException.class, () -> future.get(2, TimeUnit.SECONDS));
+    }
+}

reactor-core-2/src/test/java/com/baeldung/reactor/completablefuturevsmono/MonoUnitTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.reactor.completablefuturevsmono;
+
+import org.junit.jupiter.api.Test;
+
+import reactor.core.publisher.Mono;
+import reactor.core.scheduler.Schedulers;
+import reactor.test.StepVerifier;
+
+class MonoUnitTest {
+
+    @Test
+    void givenMonoAssureItRunsCorrectly() {
+        Mono<String> reactiveMono = Mono.fromCallable(() -> {
+                Thread.sleep(1000);
+                return "Reactive Data";
+            })
+            .subscribeOn(Schedulers.boundedElastic());
+
+        StepVerifier.create(reactiveMono)
+            .expectNext("Reactive Data")
+            .verifyComplete();
+    }
+}