This example demonstrates how to use the A2A Java SDK to communicate with an A2A client. The example includes a Java server that receives both regular and streaming messages from a Python A2A client.

• Java 11 or higher
• Python 3.8 or higher
• uv
• Git

The Java server can be started using mvn as follows:

cd examples/helloworld/server
mvn quarkus:dev

The server supports multiple transport protocols. You can select which protocol to use via the quarkus.agentcard.protocol property:

Using JSONRPC (default):

mvn quarkus:dev

Using GRPC:

mvn quarkus:dev -Dquarkus.agentcard.protocol=GRPC

Using HTTP+JSON:

mvn quarkus:dev -Dquarkus.agentcard.protocol=HTTP+JSON

You can also change the default protocol by editing src/main/resources/application.properties and setting:

quarkus.agentcard.protocol=HTTP+JSON

Available protocols:

• JSONRPC - Uses JSON-RPC for communication (default)
• GRPC - Uses gRPC for communication
• HTTP+JSON - Uses HTTP with JSON payloads

The Python A2A client is part of the a2a-samples project. To set it up and run it:

1. Clone the a2a-samples repository:

   git clone https://github.com/google-a2a/a2a-samples.git
   cd a2a-samples/samples/python/agents/helloworld

2. Recommended method: Install dependencies using uv (much faster Python package installer):

   # Install uv if you don't have it already
   # On macOS and Linux
   curl -LsSf https://astral.sh/uv/install.sh | sh
   # On Windows
   powershell -c "irm https://astral.sh/uv/install.ps1 | iex"
   
   # Install the package using uv
   uv venv
   source .venv/bin/activate  # On Windows: .venv\Scripts\activate
   uv pip install -e .

3. Run the client with uv (recommended):

   uv run test_client.py

The client will connect to the Java server running on http://localhost:9999.

The Python A2A client (test_client.py) performs the following actions:

1. Fetches the server's public agent card
2. Fetches the server's extended agent card if supported by the server (see a2aproject#81)
3. Creates an A2A client using the extended agent card that connects to the Python server at http://localhost:9999.
4. Sends a regular message asking "how much is 10 USD in INR?".
5. Prints the server's response.
6. Sends the same message as a streaming request.
7. Prints each chunk of the server's streaming response as it arrives.

The server includes support for distributed tracing with OpenTelemetry. To enable it:

1. Run with the OpenTelemetry profile:

   mvn quarkus:dev -Popentelemetry

2. Access Grafana dashboard:

   • Quarkus Dev Services will automatically start a Grafana observability stack
   • Open Grafana at http://localhost:3001 (default credentials: admin/admin)
   • View traces in the "Explore" section using the Tempo data source

3. What gets traced:

   • All A2A protocol operations (send message, get task, cancel task, etc.)
   • Streaming message responses
   • Task lifecycle events
   • Custom operations in your AgentExecutor implementation (using @Trace annotation)

4. Configuration:

   • OpenTelemetry settings are in application.properties
   • OTLP exporters run on ports 5317 (gRPC) and 5318 (HTTP)
   • To use a custom OTLP endpoint, uncomment and modify:

     quarkus.otel.exporter.otlp.endpoint=http://localhost:4317

For more information, see the OpenTelemetry extras module documentation.

• Make sure the Java server is running before starting the Python client.
• The client will wait for 10 seconds to collect streaming responses before exiting.
• You can modify the server's response in AgentExecutorProducer.java if needed.
• You can modify the server's agent card in AgentCardProducer.java if needed.
• You can modify the server's URL in application.properties and AgentCardProducer.java if needed.