Deezpatch

A simple dispatch library.

The library aims to help build applications which apply the Command Query Responsibility Segregation (CQRS) pattern.

🛠️ Get Deezpatch

Gradle

implementation "io.github.joel-jeremy.deezpatch:deezpatch-core:${version}"

Maven

<dependency>
    <groupId>io.github.joel-jeremy.deezpatch</groupId>
    <artifactId>deezpatch-core</artifactId>
    <version>${version}</version>
</dependency>

🧩 Java 9 Module Names

Deezpatch jars are published with Automatic-Module-Name manifest attribute:

Core - io.github.joeljeremy.deezpatch.core

Module authors can use above module names in their module-info.java:

module foo.bar {
    requires io.github.joeljeremy.deezpatch.core;
}

🚀 Performance

What differentiates Deezpatch from other messaging/dispatch libraries? The library takes advantage of the benefits provided by java.lang.invoke.LambdaMetafactory to avoid the cost of invoking methods reflectively. This results in performance close to directly invoking the request handler and event handler methods!

Java 11 Benchmarks

Java 17 Benchmarks

✉️ Requests

Requests are messages that either:

Initiate a state change/mutation
- Commands in CQRS
Retrieve/query data
- Queries in CQRS

public class GreetCommand implements Request<Void> {
    private final String name;
    
    public GreetRequest(String name) {
        this.name = name;
    }
    
    public String name() {
        return name;
    }
}

public class PingQuery implements Request<Pong> {}

📨 Request Handlers

Requests are handled by request handlers. Request handlers can be registered through the use of the @RequestHandler annotation.

A request must only have a single request handler.

(@RequestHandlers fully support methods with void return types! No need to set method return type to Void and return null for no reason.)

public class GreetCommandHandler {
    @RequestHandler
    public void handle(GreetCommand command) {
        sayHi(command.name());
    }
}

public class PingQueryHandler {
    @RequestHandler
    public Pong handle(PingQuery query) {
        return new Pong("Here's your pong!");
    }
}

🏤 Request Dispatcher

Requests are dispatched to a single request handler and this can be done through a dispatcher.

public static void main(String[] args) {
    // Use Spring's application context as InstanceProvider in this example
    // but any other DI framework can be used e.g. Guice, Dagger, etc.
    ApplicationContext applicationContext = springApplicationContext();

    // Deezpatch implements the Dispatcher interface.
    Dispatcher dispatcher = Deezpatch.builder()
        .instanceProvider(applicationContext::getBean)
        .requests(config -> config.handlers(
            GreetCommandHandler.java,
            PingQueryHandler.java
        ))
        .build();

    // Send command!
    dispatcher.send(new GreetCommand("Deez"));

    // Send query!
    Optional<Pong> pong = dispatcher.send(new PingQuery());
}

✉️ Events

Events are messages that indicate that something has occurred in the system.

public class GreetedEvent implements Event {
    private final String greeting;

    public GreetedEvent(String greeting) {
        this.greeting = greeting;
    }

    public String greeting() {
        return greeting;
    }
}

📨 Event Handlers

Events are handled by event handlers. Event handlers can be registered through the use of the @EventHandler annotation.

An event can have zero or more event handlers.

public class GreetedEventHandler {
    @EventHandler
    public void sayHello(GreetedEvent event) {
        // Well, hello!
    }

    @EventHandler
    public void sayKumusta(GreetedEvent event) {
        // Well, kumusta?
    }

    @EventHandler
    public void sayGotEm(GreetedEvent event) {
        // Got 'em! 
    }
}

📣 Event Publisher

Events are dispatched to zero or more event handlers and this can be done through a publisher.

public static void main(String[] args) {
    // Use Spring's application context as InstanceProvider in this example
    // but any other DI framework can be used e.g. Guice, Dagger, etc.
    ApplicationContext applicationContext = springApplicationContext();

    // Deezpatch implements the Publisher interface.
    Publisher publisher = Deezpatch.builder()
        .instanceProvider(applicationContext::getBean)
        .events(config -> config.handlers(
            GreetedEventHandler.java
        ))
        .build();

    // Publish event!
    publisher.publish(new GreetedEvent("Hi from Deez!"));
}

🔩 Easy Integration with Dependency Injection (DI) Frameworks

The library provides an InstanceProvider interface as an extension point to let users customize how request/event handler instances should be instantiated. This can be as simple as new-ing up request/event handlers or getting instances from a DI framework such as Spring's ApplicationContext, Guice's Injector, etc.

Example with No DI framework

// Application.java

public static void main(String[] args) {
  Deezpatch deezpatch = Deezpatch.builder()
      .instanceProvider(Application::getInstance)
      .requests(...)
      .events(...)
      .build();
}

private static Object getInstance(Class<?> handlerType) {
  if (MyRequestHandler.class.equals(handlerType)) {
    return new MyRequestHandler();
  } else if (MyEventHandler.class.equals(handlerType)) {
    return new MyEventHandler();
  }

  throw new IllegalStateException("Failed to get instance for " + handlerType.getName() + ".");
}

Example with Spring's ApplicationContext

public static void main(String[] args) {
  ApplicationContext applicationContext = springApplicationContext();
  Deezpatch deezpatch = Deezpatch.builder()
      .instanceProvider(applicationContext::getBean)
      .requests(...)
      .events(...)
      .build();
}

Example with Guice's Injector

public static void main(String[] args) {
  Injector injector = guiceInjector();
  Deezpatch deezpatch = Deezpatch.builder()
      .instanceProvider(injector::getInstance)
      .requests(...)
      .events(...)
      .build();
}

🎛️ Custom Request/Event Handler Annotations

In cases where a project is built in such a way that bringing in external dependencies is considered a bad practice (e.g. domain layer/package in a Hexagonal (Ports and Adapters) architecture), Deezpatch provides a way to use custom request/event handler annotations (in addition to the built-in RequestHandler and EventHandler annotations) to annotate request/event handlers.

This way, Deezpatch can still be used without adding the core Deezpatch library as a dependency of a project's domain layer/package. Instead, it may be used in the outer layers/packages to wire things up.

// Let's say below classes are declared in a project's core/domain package:

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface AwesomeRequestHandler {}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface AwesomeEventHandler {}

public class MyRequestHandler {
  @AwesomeRequestHandler
  public void handle(TestRequest request) {
    // Handle.
  }
}

public class MyEventHandler {
  @AwesomeEventHandler
  public void handle(TestEvent event) {
    // Handle.
  }
}

// To wire things up:

public static void main(String[] args) {
  // Use Spring's application context as InstanceProvider in this example
  // but any other DI framework can be used e.g. Guice, Dagger, etc.
  ApplicationContext applicationContext = springApplicationContext();

  // Register handlers and custom annotations.
  Deezpatch deezpatch = Deezpatch.builder()
      .instanceProvider(applicationContext::getBean)
      .requests(config -> 
          config.handlerAnnotations(AwesomeRequestHandler.class)
              .handlers(MyRequestHandler.class))
      .events(config -> 
          config.handlerAnnotations(AwesomeEventHandler.java)
              .handlers(MyEventHandler.class))
      .build();
}

tedyoung / deezpatch