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feat: add example on how to expose agent via A2A protocol
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‎a2a/pom.xml‎

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<version>${truth.version}</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.mockito</groupId>
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<artifactId>mockito-core</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<plugins>

‎contrib/samples/a2a_server/README.md‎

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# Google ADK A2A Agent Server Sample
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This sample demonstrates how to expose a Google ADK (Agent Development Kit)
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agent via the A2A (Agent-to-Agent) protocol using A2A SDK and Quarkus service.
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## Overview
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The application implements a simple conversational agent that checks whether
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given numbers are prime numbers. It uses the `LlmAgent` from the Google ADK and
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exposes it via an A2A server.
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### Key Components
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* **`Agent.java`**: Defines the `LlmAgent` instance (`check_prime_agent`) and
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the `checkPrime` tool function it uses to verify numbers.
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* **`AgentCardProducer.java`**: Loads and provides the `AgentCard` metadata
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(from `agent.json`) which defines the agent's identity and capabilities in
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the A2A network.
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* **`AgentExecutorProducer.java`**: Configures and provides the A2A
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`AgentExecutor`, implemented by the ADK library to wire ADK-owned agents
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automatically.
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* **`StartupConfig.java`**: Contains initialization logic, such as registering
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JSON modules for the Vert.x/Quarkus runtime.
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* **`application.properties`**: Contains a configuration for the Quarkus
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service and A2A, such as port where application will be exposed, application
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name and event processing timeouts.
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## Building the Project
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You can build the project using Maven:
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```shell
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mvn clean install
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```
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The Java server can be started using `mvn` as follow (don't forget to set your
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GOOGLE_API_KEY before running the service):
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```bash
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export GOOGLE_API_KEY=<YOUR_API_KEY>
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cd contrib/samples/a2a_server
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mvn quarkus:dev
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```
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## Sample request
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```bash
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curl -X POST http://localhost:9090 \
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-H 'Content-Type: application/json' \
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-d '{
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"jsonrpc": "2.0",
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"id": "cli-check-2",
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"method": "message/stream",
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"params": {
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"message": {
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"kind": "message",
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"contextId": "cli-demo-context",
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"messageId": "cli-check-2",
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"role": "user",
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"parts": [
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{
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"kind": "text",
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"text": "Is 2 prime?"
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}
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]
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}
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}
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}'
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```

‎contrib/samples/a2a_server/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.google.adk</groupId>
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<artifactId>google-adk-samples</artifactId>
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<version>0.7.1-SNAPSHOT</version><!-- {x-version-update:google-adk:current} -->
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<relativePath>..</relativePath>
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</parent>
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<artifactId>google-adk-sample-a2a-agent</artifactId>
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<packaging>jar</packaging>
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<name>Google ADK - Sample - A2A Agent Server</name>
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<description>Demonstrates exposing ADK agent via A2A.</description>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<java.version>17</java.version>
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<google-adk.version>${project.version}</google-adk.version>
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<google-adk-a2a.version>${project.version}</google-adk-a2a.version>
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<a2a.sdk.version>0.3.0.Beta1</a2a.sdk.version>
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<quarkus.platform.version>3.30.6</quarkus.platform.version>
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<flogger.version>0.8</flogger.version>
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</properties>
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<dependencyManagement>
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<dependencies>
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<dependency>
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<groupId>io.quarkus</groupId>
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<artifactId>quarkus-bom</artifactId>
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<version>${quarkus.platform.version}</version>
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<type>pom</type>
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<scope>import</scope>
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</dependency>
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</dependencies>
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</dependencyManagement>
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<dependencies>
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<dependency>
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<groupId>io.github.a2asdk</groupId>
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<artifactId>a2a-java-sdk-reference-jsonrpc</artifactId>
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<version>${a2a.sdk.version}</version>
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</dependency>
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<dependency>
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<groupId>io.quarkus</groupId>
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<artifactId>quarkus-resteasy-jackson</artifactId>
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</dependency>
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<dependency>
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<groupId>com.fasterxml.jackson.datatype</groupId>
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<artifactId>jackson-datatype-jsr310</artifactId>
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</dependency>
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<dependency>
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<groupId>com.google.adk</groupId>
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<artifactId>google-adk</artifactId>
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<version>${google-adk.version}</version>
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</dependency>
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<dependency>
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<groupId>com.google.adk</groupId>
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<artifactId>google-adk-a2a</artifactId>
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<version>${google-adk-a2a.version}</version>
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</dependency>
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<dependency>
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<groupId>io.github.a2asdk</groupId>
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<artifactId>a2a-java-sdk-spec</artifactId>
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<version>${a2a.sdk.version}</version>
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</dependency>
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<dependency>
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<groupId>io.quarkus</groupId>
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<artifactId>quarkus-arc</artifactId>
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</dependency>
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<dependency>
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<groupId>io.quarkus</groupId>
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<artifactId>quarkus-reactive-routes</artifactId>
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</dependency>
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<dependency>
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<groupId>io.quarkus</groupId>
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<artifactId>quarkus-jackson</artifactId>
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</dependency>
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<dependency>
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<groupId>io.github.a2asdk</groupId>
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<artifactId>a2a-java-sdk-client</artifactId>
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<version>${a2a.sdk.version}</version>
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</dependency>
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<dependency>
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<groupId>com.google.flogger</groupId>
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<artifactId>flogger</artifactId>
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<version>${flogger.version}</version>
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</dependency>
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<dependency>
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<groupId>com.google.flogger</groupId>
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<artifactId>google-extensions</artifactId>
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<version>${flogger.version}</version>
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</dependency>
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<dependency>
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<groupId>com.google.flogger</groupId>
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<artifactId>flogger-system-backend</artifactId>
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<version>${flogger.version}</version>
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</dependency>
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</dependencies>
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<build>
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<resources>
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<resource>
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<directory>src/main/java</directory>
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<includes>
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<include>**/*.json</include>
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</includes>
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</resource>
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<resource>
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<directory>src/main/resources</directory>
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</resource>
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</resources>
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<plugins>
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<plugin>
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<groupId>io.quarkus</groupId>
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<artifactId>quarkus-maven-plugin</artifactId>
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<version>${quarkus.platform.version}</version>
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<extensions>true</extensions>
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<executions>
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<execution>
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<goals>
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<goal>build</goal>
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<goal>generate-code</goal>
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<goal>generate-code-tests</goal>
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</goals>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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</project>

‎contrib/samples/a2a_server/src/main/java/com/google/adk/samples/a2aagent/AgentCardProducer.java‎

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package com.google.adk.samples.a2aagent;
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import io.a2a.server.PublicAgentCard;
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import io.a2a.spec.AgentCard;
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import io.a2a.util.Utils;
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import jakarta.enterprise.context.ApplicationScoped;
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import jakarta.enterprise.inject.Produces;
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import java.io.InputStream;
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import java.nio.charset.StandardCharsets;
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/** Produces the {@link AgentCard} from the bundled JSON resources. */
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@ApplicationScoped
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public class AgentCardProducer {
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@Produces
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@PublicAgentCard
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public AgentCard agentCard() {
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try (InputStream is = getClass().getResourceAsStream("/agent/agent.json")) {
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if (is == null) {
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throw new RuntimeException("agent.json not found in resources");
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}
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// Read the JSON file content
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String json = new String(is.readAllBytes(), StandardCharsets.UTF_8);
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// Use the SDK's built-in mapper to convert JSON string to AgentCard record
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return Utils.OBJECT_MAPPER.readValue(json, AgentCard.class);
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} catch (Exception e) {
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throw new RuntimeException("Failed to load AgentCard from JSON", e);
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}
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}
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}

‎contrib/samples/a2a_server/src/main/java/com/google/adk/samples/a2aagent/AgentExecutorProducer.java‎

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package com.google.adk.samples.a2aagent;
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import com.google.adk.a2a.executor.AgentExecutorConfig;
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import com.google.adk.samples.a2aagent.agent.Agent;
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import com.google.adk.sessions.InMemorySessionService;
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import io.a2a.server.agentexecution.AgentExecutor;
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import jakarta.enterprise.context.ApplicationScoped;
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import jakarta.enterprise.inject.Produces;
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import org.eclipse.microprofile.config.inject.ConfigProperty;
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/** Produces the {@link AgentExecutor} instance that handles agent interactions. */
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@ApplicationScoped
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public class AgentExecutorProducer {
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@ConfigProperty(name = "my.adk.app.name", defaultValue = "default-app")
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String appName;
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@Produces
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public AgentExecutor agentExecutor() {
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InMemorySessionService sessionService = new InMemorySessionService();
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return new com.google.adk.a2a.executor.AgentExecutor.Builder()
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.agent(Agent.ROOT_AGENT)
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.appName(appName)
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.sessionService(sessionService)
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.agentExecutorConfig(AgentExecutorConfig.builder().build())
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.build();
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}
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}

‎contrib/samples/a2a_server/src/main/java/com/google/adk/samples/a2aagent/StartupConfig.java‎

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package com.google.adk.samples.a2aagent;
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import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
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import io.quarkus.runtime.StartupEvent;
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import io.vertx.core.json.jackson.DatabindCodec;
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import jakarta.enterprise.context.ApplicationScoped;
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import jakarta.enterprise.event.Observes;
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/** Configuration applied on startup, such as Jackson module registrations. */
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@ApplicationScoped
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public class StartupConfig {
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void onStart(@Observes StartupEvent ev) {
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// Register globally for Vert.x's internal JSON handling
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DatabindCodec.mapper().registerModule(new JavaTimeModule());
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}
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}

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