EventBus

A flexible, high-performance, thread-safe subscriber-publisher framework designed with modern Java in mind.

Overview

The core functionality of EventBus is to provide a simple and efficient way to handle events in a decoupled manner.

Each event may have one or more buses associated with it, which are responsible for managing listeners and dispatching instances of the event object to them. To maximise performance, the underlying implementation is tailored on the fly based on the event's type, characteristics, inheritance chain and the number and type of listeners registered to the bus.

Quickstart guide

First, add the Forge Maven repository and the EventBus dependency to your project:

repositories {
    maven {
        name = "Forge"
        url = "https://maven.minecraftforge.net"
    }
}

dependencies {
    implementation "net.minecraftforge:eventbus:<version>"
}

You can find the list of available versions here.

Now you can start using EventBus in your project. Simple usage example:

import net.minecraftforge.eventbus.api.event.RecordEvent;
import net.minecraftforge.eventbus.api.bus.EventBus;

// Define an event and a bus for it
record PlayerLoggedInEvent(String username) implements RecordEvent {
    public static final EventBus<PlayerLoggedInEvent> BUS = EventBus.create(PlayerLoggedInEvent.class);
}

// Register an event listener
PlayerLoggedInEvent.BUS.addListener(event -> System.out.println("Player logged in: " + event.username()));

// Post an event to the registered listeners
PlayerLoggedInEvent.BUS.post(new PlayerLoggedInEvent("Paint_Ninja"));

Browse the net.minecraftforge.eventbus.api package and read the Javadocs for more information. For real-world examples, check out Forge's extensive use of EventBus here.

Nullability

The entirety of EventBus' API is @NullMarked and compliant with the jSpecify specification - this means that everything is non-null by default unless otherwise specified.

Attempting to pass a null value to a method param that isn't explicitly marked as @Nullable is an unsupported operation and won't be considered a breaking change if a future version throws an exception in such cases when it didn't before.

Contributing

One of the main goals of EventBus is performance. As such, any changes should be benchmarked with the jmh Gradle task to help ensure that there are no unintended performance regressions. If you are unsure how to do this or would like to discuss your ideas before submitting a PR, feel free to reach out to us on the Forge Discord.