Overview

A2A Java Bridge (A2AJava) turns annotated Java methods into a running Model Context Protocol (MCP) server and registers them as A2A-discoverable actions. Instead of writing server boilerplate or manual service registration, you annotate methods, start the bridge, and the library automatically exposes those methods over MCP so agents and other MCP-capable clients can discover and invoke them.

This pattern is useful when you already have business logic implemented as plain Java methods and want to make those methods available to AI agents or other automated “app-to-app” workflows. The bridge handles scanning, wiring, and lightweight HTTP/JSON transport so you can focus on implementing action logic rather than integration plumbing.

Features

Automatic scanning of annotated Java methods and classes
Exposes methods as MCP server actions without manual registration
Simple annotation-driven API to describe action name, inputs, and outputs
Lightweight runtime with minimal dependencies—works in existing JVM apps
Discoverable actions for A2A/MCP-capable clients and agents
Example project and quick-start usage for local development

Installation / Configuration

There are two common ways to get the bridge into your project: use the published JAR (if available) or build from source. Replace group/artifact coordinates with the actual coordinates from the repo if a published package exists.

Add a dependency with Maven (example placeholder coordinates):

<dependency>
  <groupId>com.vishalmysore</groupId>
  <artifactId>a2ajava</artifactId>
  <version>0.1.0</version>
</dependency>

Or with Gradle:

implementation 'com.vishalmysore:a2ajava:0.1.0'

Build from source:

git clone https://github.com/vishalmysore/a2ajava.git
cd a2ajava
./mvnw package
# use the produced jar from target/ to include in your app

Basic configuration when starting the bridge typically includes which package(s) to scan and the port to listen on. Example programmatically starting a server:

import com.example.a2a.A2ABridge;

public class App {
  public static void main(String[] args) {
    A2ABridge bridge = A2ABridge.builder()
      .scanPackage("com.myapp.actions")
      .port(8080)
      .start();
    // bridge runs until shutdown; add shutdown hook if needed
  }
}

Check the repository README or javadoc for the exact builder/constructor API names.

Quick Annotated Example

Annotate a method to expose it as an action:

import com.vishalmysore.a2ajava.annotations.A2AAction;

public class MathActions {

  @A2AAction(name = "add", description = "Adds two integers")
  public static Map<String, Object> add(Map<String, Object> input) {
    int a = (int) input.getOrDefault("a", 0);
    int b = (int) input.getOrDefault("b", 0);
    return Map.of("result", a + b);
  }
}

When the bridge scans the package containing MathActions, the “add” action will be discoverable over MCP.

Available Resources

GitHub repository (source, examples, issues): https://github.com/vishalmysore/a2ajava
Example projects and sample actions inside the repo to reference runtime patterns
Issues and pull requests on GitHub for community support and bug reports
Inline Javadoc or generated docs (check the repo for /docs or javadoc artifacts)

Use Cases

AI agent integrations: Expose application-level utilities (data lookups, business operations) as discoverable actions the agent can call during reasoning or planning.
Rapid prototyping: Turn existing Java utilities into network-accessible actions without creating REST controllers or additional services.
Internal automation: Allow orchestration systems or chatops bots to invoke tasks (e.g., deploy, build, query) implemented as plain Java methods.
Testing and simulation: Mock MCP endpoints by exposing simple annotated methods locally for integration tests.
Microservices bootstrap: Provide a low-friction way to expose functionality before committing to a full HTTP API or RPC contract.

Notes and Best Practices

Keep annotated methods focused and idempotent when possible; consider input/output JSON structure consistency.
Validate incoming payloads inside your annotated method to avoid runtime errors.
Use a dedicated package (for example com.myapp.actions) so the bridge can efficiently scan only relevant classes.
Remember to secure the MCP endpoint in production (authentication, network controls) if the bridge runs in an exposed environment.

For detailed API usage, configuration options, and operational tips, consult the repository README and example code bundled with the project.

A2A Java Bridge for MCP Server Integration