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feat: Implement Actor Model pattern
* feat: Implement Actor Model pattern #3232 * feat: Implement Actor Model pattern #3232 * feat: update Actor Model implementation with multi-actor logic #3251 * feat: update Actor Model implementation with multi-actor logic and loose coupling #3251 * test: add unit test for actor model #3251 * test: add test for App.java to increase coverage * docs: add complete README for Actor Model pattern also implemented changes #3251
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‎actor-model/README.md

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

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‎actor-model/etc/actor-model.urm.puml

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

‎actor-model/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<!--
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This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
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The MIT License
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Copyright © 2014-2022 Ilkka Seppälä
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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THE SOFTWARE.
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-->
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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
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http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>java-design-patterns</artifactId>
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<version>1.26.0-SNAPSHOT</version>
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</parent>
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<artifactId>actor-model</artifactId>
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<name>Actor Model</name>
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<!-- Force unified JUnit version to avoid classpath mismatches -->
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<dependencyManagement>
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<dependencies>
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<dependency>
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<groupId>org.junit</groupId>
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<artifactId>junit-bom</artifactId>
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<version>5.11.0</version>
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<type>pom</type>
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<scope>import</scope>
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</dependency>
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</dependencies>
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</dependencyManagement>
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<dependencies>
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<dependency>
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<groupId>org.junit.jupiter</groupId>
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<artifactId>junit-jupiter-api</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.junit.jupiter</groupId>
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<artifactId>junit-jupiter-engine</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.junit.platform</groupId>
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<artifactId>junit-platform-launcher</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.slf4j</groupId>
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<artifactId>slf4j-api</artifactId>
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</dependency>
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<dependency>
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<groupId>ch.qos.logback</groupId>
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<artifactId>logback-classic</artifactId>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<!-- Assembly plugin for creating fat JARs -->
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-assembly-plugin</artifactId>
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<version>3.3.0</version>
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<configuration>
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<descriptorRefs>
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<descriptorRef>jar-with-dependencies</descriptorRef>
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</descriptorRefs>
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<archive>
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<manifest>
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<mainClass>com.iluwatar.actormodel.App</mainClass>
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</manifest>
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</archive>
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</configuration>
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<executions>
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<execution>
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<id>make-assembly</id>
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<phase>package</phase>
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<goals>
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<goal>single</goal>
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</goals>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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</project>

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