Y-CRDT JNI

Java bindings for y-crdt (yrs), providing CRDTs for collaborative editing on the JVM.

Installation

Releases are published to Maven Central under the net.carcdr namespace. In-development -SNAPSHOT versions are published to GitHub Packages.

Released versions (Maven Central)

Pull a single module:

// Core interfaces (required)
implementation 'net.carcdr:ycrdt-core:<version>'

// JNI implementation (recommended) - Java 21+
implementation 'net.carcdr:ycrdt-jni:<version>'

Or import the BOM and omit individual version numbers to keep all modules aligned:

dependencies {
    implementation platform('net.carcdr:ycrdt-bom:<version>')

    implementation 'net.carcdr:ycrdt-core'
    implementation 'net.carcdr:ycrdt-jni'
    implementation 'net.carcdr:yhocuspocus'
    // etc.
}

Snapshot versions (GitHub Packages)

Snapshots are published to GitHub Packages on every push to main. To consume them, add the GitHub Packages Maven repository and credentials (a GitHub personal access token with read:packages scope):

repositories {
    mavenCentral()
    maven {
        name = 'GitHubPackages'
        url = uri('https://maven.pkg.github.com/edpaget/y-crdt-jni')
        credentials {
            username = System.getenv('GITHUB_ACTOR') ?: findProperty('gpr.user')
            password = System.getenv('GITHUB_TOKEN') ?: findProperty('gpr.key')
        }
    }
}

dependencies {
    // See each module's `version.properties` for the current -SNAPSHOT version,
    // or resolve via Gradle's `+` qualifier: 'net.carcdr:ycrdt-core:0.+-SNAPSHOT'
    implementation 'net.carcdr:ycrdt-core:<snapshot-version>'
    implementation 'net.carcdr:ycrdt-jni:<snapshot-version>'
}

Usage

import net.carcdr.ycrdt.*;

YBinding binding = YBindingFactory.auto();
try (YDoc doc = binding.createDoc()) {
    try (YText text = doc.getText("myText")) {
        text.push("Hello, ");
        text.push("World!");
        System.out.println(text.toString()); // "Hello, World!"
    }

    // Sync state to another document
    byte[] update = doc.encodeStateAsUpdate();
    try (YDoc doc2 = binding.createDoc()) {
        doc2.applyUpdate(update);
    }
}

See ycrdt-jni/README.md for more examples.

Modules

Module	Description
ycrdt-core	Interfaces: YDoc, YText, YArray, YMap. No native deps.
ycrdt-jni	JNI implementation (Rust). Java 21+.
ycrdt-panama	Panama FFM implementation. Java 22+. Experimental.
yprosemirror	ProseMirror <-> Y-CRDT sync
yhocuspocus	Collaborative editing server (transport-agnostic)
yhocuspocus-websocket	WebSocket transport (Jetty 12)
yhocuspocus-spring-websocket	WebSocket transport (Spring)
yhocuspocus-redis	Redis extension for yhocuspocus
examples	Full-stack example apps (React + Tiptap + Java)

JNI vs Panama

	ycrdt-jni	ycrdt-panama
Java	21+	22+
Native access	JNI (Rust)	Panama FFM (yffi)
JVM args	None	--enable-native-access=ALL-UNNAMED
XML types	Yes	Not yet
Maturity	More mature	Experimental

YBinding jni    = YBindingFactory.jni();    // explicit JNI
YBinding panama = YBindingFactory.panama(); // explicit Panama
YBinding auto   = YBindingFactory.auto();   // first available

Documentation

• API Reference (Javadoc)
• Example apps

Development

Requires Java 21+ and Rust 1.70+ (for building from source). Gradle wrapper included.

./gradlew build          # build all modules
./gradlew test           # run all tests
./gradlew check          # tests + checkstyle

See .claude/CLAUDE.md for development guidelines and per-module PLAN.md files for roadmaps.

License

Apache License v2.0 -- see LICENSE.

Acknowledgments

• y-crdt -- Rust CRDT implementation
• jni-rs -- Rust JNI bindings
• Hocuspocus -- inspiration for yhocuspocus