feat: Implement Actor Model pattern with automatic actor ID and communication with loose coupling #3251Actor model

actor-model/README.md

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+---
+title: "Actor Model Pattern in Java: Building Concurrent Systems with Elegance"
+shortTitle: Actor Model
+description: "Explore the Actor Model pattern in Java with real-world examples and practical implementation. Learn how to build scalable, message-driven systems using actors, messages, and asynchronous communication."
+category: Concurrency
+language: en
+tag:
+    - Concurrency
+    - Messaging
+    - Isolation
+    - Asynchronous
+    - Distributed Systems
+    - Actor Model
+---
+
+## Also Known As
+
+- Message-passing concurrency
+- Actor-based concurrency
+
+---
+
+## Intent of Actor Model Pattern
+
+The Actor Model pattern enables the construction of highly concurrent, distributed, and fault-tolerant systems by using isolated components (actors) that interact exclusively through asynchronous message passing.
+
+---
+
+## Detailed Explanation of Actor Model Pattern with Real-World Examples
+
+### 📦 Real-world Example
+
+Imagine a customer service system:
+- Each **customer support agent** is an **actor**.
+- Customers **send questions (messages)** to agents.
+- Each agent handles one request at a time and can **respond asynchronously** without interfering with other agents.
+
+---
+
+### 🧠 In Plain Words
+
+> "Actors are like independent workers that never share memory and only communicate through messages."
+
+---
+
+### 📖 Wikipedia Says
+
+> [Actor model](https://en.wikipedia.org/wiki/Actor_model) is a mathematical model of concurrent computation that treats "actors" as the universal primitives of concurrent computation.
+
+---
+
+### 🧹 Architecture Diagram
+
+![UML Class Diagram](./etc/Actor_Model_UML_Class_Diagram.png)
+
+---
+
+## Programmatic Example of Actor Model Pattern in Java
+
+### Actor.java
+
+```java
+public abstract class Actor implements Runnable {
+
+    @Setter @Getter private String actorId;
+    private final BlockingQueue<Message> mailbox = new LinkedBlockingQueue<>();
+    private volatile boolean active = true; 
+
+
+    public void send(Message message) {
+        mailbox.add(message); 
+    }
+
+    public void stop() {
+        active = false; 
+    }
+
+    @Override
+    public void run() {
+
+    }
+
+    protected abstract void onReceive(Message message);
+}
+
+```
+
+### Message.java
+
+```java
+
+@AllArgsConstructor
+@Getter
+@Setter
+public class Message {
+    private final String content;
+    private final String senderId;
+}
+```
+
+### ActorSystem.java
+
+```java
+public class ActorSystem {
+    public void startActor(Actor actor) {
+        String actorId = "actor-" + idCounter.incrementAndGet(); // Generate a new and unique ID
+        actor.setActorId(actorId); // assign the actor it's ID
+        actorRegister.put(actorId, actor); // Register and save the actor with it's ID
+        executor.submit(actor); // Run the actor in a thread
+    }
+    public Actor getActorById(String actorId) {
+        return actorRegister.get(actorId); //  Find by Id
+    }
+
+    public void shutdown() {
+        executor.shutdownNow(); // Stop all threads
+    }
+}
+```
+
+### App.java
+
+```java
+public class App {
+  public static void main(String[] args) {
+    ActorSystem system = new ActorSystem();
+      Actor srijan = new ExampleActor(system);
+      Actor ansh = new ExampleActor2(system);
+
+      system.startActor(srijan);
+      system.startActor(ansh);
+      ansh.send(new Message("Hello ansh", srijan.getActorId()));
+      srijan.send(new Message("Hello srijan!", ansh.getActorId()));
+
+      Thread.sleep(1000); // Give time for messages to process
+
+      srijan.stop(); // Stop the actor gracefully
+      ansh.stop();
+      system.shutdown(); // Stop the actor system
+  }
+}
+```
+
+---
+
+## When to Use the Actor Model Pattern in Java
+
+- When building **concurrent or distributed systems**
+- When you want **no shared mutable state**
+- When you need **asynchronous, message-driven communication**
+- When components should be **isolated and loosely coupled**
+
+---
+
+## Actor Model Pattern Java Tutorials
+
+- [Baeldung – Akka with Java](https://www.baeldung.com/java-akka)
+- [Vaughn Vernon – Reactive Messaging Patterns](https://vaughnvernon.co/?p=1143)
+
+---
+
+## Real-World Applications of Actor Model Pattern in Java
+
+- [Akka Framework](https://akka.io/)
+- [Erlang and Elixir concurrency](https://www.erlang.org/)
+- [Microsoft Orleans](https://learn.microsoft.com/en-us/dotnet/orleans/)
+- JVM-based game engines and simulators
+
+---
+
+## Benefits and Trade-offs of Actor Model Pattern
+
+### ✅ Benefits
+- High concurrency support
+- Easy scaling across threads or machines
+- Fault isolation and recovery
+- Message ordering within actors
+
+### ⚠️ Trade-offs
+- Harder to debug due to asynchronous behavior
+- Slight performance overhead due to message queues
+- More complex to design than simple method calls
+
+---
+
+## Related Java Design Patterns
+
+- [Command Pattern](../command)
+- [Mediator Pattern](../mediator)
+- [Event-Driven Architecture](../event-driven-architecture)
+- [Observer Pattern](../observer)
+
+---
+
+## References and Credits
+
+- *Programming Erlang*, Joe Armstrong
+- *Reactive Design Patterns*, Roland Kuhn
+- *The Actor Model in 10 Minutes*, [InfoQ Article](https://www.infoq.com/articles/actor-model/)
+- [Akka Documentation](https://doc.akka.io/docs/akka/current/index.html)
+

actor-model/etc/actor-model.urm.puml

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+@startuml actor-model
+
+title Actor Model - UML Class Diagram
+
+class ActorSystem {
+  +actorOf(actor: Actor): Actor
+  +shutdown(): void
+}
+
+class Actor {
+  -mailbox: BlockingQueue<Message>
+  -active: boolean
+  +send(message: Message): void
+  +stop(): void
+  +run(): void
+  #onReceive(message: Message): void
+}
+
+class ExampleActor {
+  +onReceive(message: Message): void
+}
+
+class Message {
+  -content: String
+  -sender: Actor
+  +getContent(): String
+  +getSender(): Actor
+}
+
+ActorSystem --> Actor : creates
+Actor <|-- ExampleActor : extends
+Actor --> Message : processes
+ExampleActor --> Message : uses
+
+@enduml

actor-model/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+
+    The MIT License
+    Copyright © 2014-2022 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<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>
+
+    <parent>
+        <groupId>com.iluwatar</groupId>
+        <artifactId>java-design-patterns</artifactId>
+        <version>1.26.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>actor-model</artifactId>
+    <name>Actor Model</name>
+
+    <!-- Force unified JUnit version to avoid classpath mismatches -->
+    <dependencyManagement>
+        <dependencies>
+            <dependency>
+                <groupId>org.junit</groupId>
+                <artifactId>junit-bom</artifactId>
+                <version>5.11.0</version>
+                <type>pom</type>
+                <scope>import</scope>
+            </dependency>
+        </dependencies>
+    </dependencyManagement>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-launcher</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>ch.qos.logback</groupId>
+            <artifactId>logback-classic</artifactId>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <!-- Assembly plugin for creating fat JARs -->
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <version>3.3.0</version>
+                <configuration>
+                    <descriptorRefs>
+                        <descriptorRef>jar-with-dependencies</descriptorRef>
+                    </descriptorRefs>
+                    <archive>
+                        <manifest>
+                            <mainClass>com.iluwatar.actormodel.App</mainClass>
+                        </manifest>
+                    </archive>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>make-assembly</id>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>single</goal>
+                        </goals>
+                    </execution>
+                </executions>
+
+            </plugin>
+        </plugins>
+    </build>
+
+</project>