A2A Server

The A2A Java SDK provides a Java server implementation of the Agent2Agent (A2A) Protocol. To run your agentic Java application as an A2A server, follow the steps below.

Supported Transports

• JSON-RPC 2.0
• gRPC
• HTTP+JSON/REST

1. Add a Server Dependency

JSON-RPC

<dependency>
    <groupId>org.a2aproject.sdk</groupId>
    <artifactId>a2a-java-sdk-reference-jsonrpc</artifactId>
    <!-- Use a released version from https://github.com/a2aproject/a2a-java/releases -->
    <version>${org.a2aproject.sdk.version}</version>
</dependency>

gRPC

<dependency>
    <groupId>org.a2aproject.sdk</groupId>
    <artifactId>a2a-java-sdk-reference-grpc</artifactId>
    <version>${org.a2aproject.sdk.version}</version>
</dependency>

HTTP+JSON/REST

<dependency>
    <groupId>org.a2aproject.sdk</groupId>
    <artifactId>a2a-java-sdk-reference-rest</artifactId>
    <version>${org.a2aproject.sdk.version}</version>
</dependency>

You can add more than one transport dependency to support multiple protocols simultaneously.

2. Define an Agent Card

@ApplicationScoped
public class WeatherAgentCardProducer {

    private static final String AGENT_URL = "http://localhost:10001";

    @Produces
    @PublicAgentCard
    public AgentCard agentCard() {
        return AgentCard.builder()
                .name("Weather Agent")
                .description("Helps with weather")
                .supportedInterfaces(List.of(
                        new AgentInterface(TransportProtocol.JSONRPC.asString(), AGENT_URL)))
                .version("1.0.0")
                .capabilities(AgentCapabilities.builder()
                        .streaming(true)
                        .pushNotifications(false)
                        .build())
                .defaultInputModes(Collections.singletonList("text"))
                .defaultOutputModes(Collections.singletonList("text"))
                .skills(Collections.singletonList(AgentSkill.builder()
                        .id("weather_search")
                        .name("Search weather")
                        .description("Helps with weather in cities or states")
                        .tags(Collections.singletonList("weather"))
                        .examples(List.of("weather in LA, CA"))
                        .build()))
                .build();
    }
}

3. Implement an Agent Executor

@ApplicationScoped
public class WeatherAgentExecutorProducer {

    @Inject
    WeatherAgent weatherAgent;

    @Produces
    public AgentExecutor agentExecutor() {
        return new WeatherAgentExecutor(weatherAgent);
    }

    private static class WeatherAgentExecutor implements AgentExecutor {

        private final WeatherAgent weatherAgent;

        public WeatherAgentExecutor(WeatherAgent weatherAgent) {
            this.weatherAgent = weatherAgent;
        }

        @Override
        public void execute(RequestContext context, AgentEmitter agentEmitter) throws JSONRPCError {
            if (context.getTask() == null) {
                agentEmitter.submit();
            }
            agentEmitter.startWork();

            String userMessage = extractTextFromMessage(context.getMessage());
            String response = weatherAgent.chat(userMessage);

            agentEmitter.addArtifact(List.of(new TextPart(response)));
            agentEmitter.complete();
        }

        @Override
        public void cancel(RequestContext context, AgentEmitter agentEmitter) throws JSONRPCError {
            Task task = context.getTask();
            if (task == null) {
                agentEmitter.cancel();
                return;
            }
            if (task.getStatus().state() == TaskState.CANCELED ||
                task.getStatus().state() == TaskState.COMPLETED) {
                throw new TaskNotCancelableError();
            }
            agentEmitter.cancel();
        }

        private String extractTextFromMessage(Message message) {
            if (message == null) {
                return "";
            }
            StringBuilder textBuilder = new StringBuilder();
            for (Part<?> part : message.parts()) {
                if (part instanceof TextPart textPart) {
                    textBuilder.append(textPart.text());
                }
            }
            return textBuilder.toString();
        }
    }
}

4. Configuration

See Configuration for all config properties and tuning.

5. Task Authorization (Optional)

See Task Authorization for per-user access control.

Backward Compatibility with v0.3

See Backward Compatibility for multi-version modules, version routing, and v0.3 client support.

Server Integrations

• Quarkus — Reference implementations are Quarkus-based (JSON-RPC, gRPC, REST)
• Jakarta EE — a2a-jakarta works with any Jakarta EE Web Profile runtime

See CONTRIBUTING_INTEGRATIONS.md to submit your own integration.