Java Language Server Protocol (LSP) Library

dev.secondsun:languageserver is a lightweight, pure-Java implementation of the Language Server Protocol (LSP) data structures and JSON-RPC message pump.

Features

• Standard LSP Data Types: Clean Java POJOs for LSP protocol requests, responses, notifications, diagnostics, code actions, code lenses, completion, hover, and symbols.
• Fast JSON-RPC Transport: Built-in streaming message pump (LSP.connect(...)) over standard input/output streams with Content-Length header framing and cancellation routing.
• Ultra-lightweight: Minimal external dependencies (only Google Gson).
• Modern Java: Targeted for Java 26 with full Java Platform Module System (JPMS) support (dev.secondsun.lsp).

Prerequisites

• Java Development Kit (JDK): Java 26 or newer.
• Build Tool: Apache Maven (or the included ./mvnw wrapper).

Quick Start

Build and Test

# Run all tests
./mvnw clean test

# Run a specific test
./mvnw test -Dtest=LanguageServerTest

# Package JAR, sources, and Javadoc
./mvnw clean package

Maven Dependency

<dependency>
    <groupId>dev.secondsun</groupId>
    <artifactId>languageserver</artifactId>
    <version>0.10.0</version>
</dependency>

Module Descriptor (module-info.java)

module my.custom.lsp {
    requires dev.secondsun.lsp;
}

Basic Usage

Implement the LanguageServer interface and connect it to your process's input/output streams:

import dev.secondsun.lsp.*;
import java.io.InputStream;
import java.io.OutputStream;

public class MyServer extends LanguageServer {
    private final LanguageClient client;

    public MyServer(LanguageClient client) {
        this.client = client;
    }

    @Override
    public InitializeResult initialize(InitializeParams params) {
        var result = new InitializeResult();
        // configure capabilities
        return result;
    }

    public static void main(String[] args) {
        InputStream in = System.in;
        OutputStream out = System.out;
        
        LSP.connect(MyServer::new, in, out);
    }
}

Agentic Development

This repository includes AGENTS.md as the canonical operational guide for AI agents and human pair programmers. Refer to AGENTS.md for build workflows, architectural invariants, and verification steps.

License

This project is licensed under the MIT License.