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A2A Hello World Example

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

Prerequisites

  • Java 11 or higher
  • JBang (see INSTALL_JBANG.md for quick installation instructions)
  • Python 3.8 or higher
  • uv (recommended) or pip
  • Git

Setup and Run the Python A2A Server

The Python A2A server 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 server with uv (recommended):

    uv run .

The server will start running on http://localhost:9999.

Run the Java A2A Client with JBang

The Java client can be run using JBang, which allows you to run Java source files directly without any manual compilation.

Build the A2A Java SDK

First, ensure you have built the a2a-java project:

cd /path/to/a2a-java
mvn clean install

Using the JBang script

A JBang script is provided in the example directory to make running the client easy:

  1. Make sure you have JBang installed. If not, follow the JBang installation guide.

  2. Navigate to the example directory:

    cd examples/helloworld/client/src/main/java/io/a2a/examples/helloworld/

  3. Run the client using the JBang script:

    jbang HelloWorldRunner.java

This script automatically handles the dependencies and sources for you.

What the Example Does

The Java client (HelloWorldClient.java) performs the following actions:

  1. Fetches the server's public agent card
  2. Fetches the server's extended agent card
  3. Creates a 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.

Notes

  • Make sure the Python server is running before starting the Java client.
  • The client will wait for 10 seconds to collect streaming responses before exiting.
  • You can modify the message text or server URL in the HelloWorldClient.java file if needed.