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A2A Java SDK - MicroProfile Config Integration

This optional integration module provides MicroProfile Config support for the A2A Java SDK configuration system.

Overview

The A2A Java SDK core uses the A2AConfigProvider interface for configuration, with default values loaded from META-INF/a2a-defaults.properties files on the classpath.

This module provides MicroProfileConfigProvider, which integrates with MicroProfile Config to allow configuration via:

  • application.properties
  • Environment variables
  • System properties (-D flags)
  • Custom ConfigSources

Quick Start

1. Add Dependency

<dependency>
    <groupId>org.a2aproject.sdk</groupId>
    <artifactId>a2a-java-sdk-microprofile-config</artifactId>
    <version>${io.a2a.sdk.version}</version>
</dependency>

2. Configure Properties

Once the dependency is added, you can override any A2A configuration property:

application.properties:

# Executor configuration
a2a.executor.core-pool-size=10
a2a.executor.max-pool-size=100

# Timeout configuration
a2a.blocking.agent.timeout.seconds=60
a2a.blocking.consumption.timeout.seconds=10

Environment variables:

export A2A_EXECUTOR_CORE_POOL_SIZE=10
export A2A_BLOCKING_AGENT_TIMEOUT_SECONDS=60

System properties:

java -Da2a.executor.core-pool-size=10 -jar your-app.jar

How It Works

The MicroProfileConfigProvider implementation:

  1. First tries MicroProfile Config - Checks application.properties, environment variables, system properties, and custom ConfigSources
  2. Falls back to defaults - If not found, uses values from META-INF/a2a-defaults.properties provided by core modules and extras
  3. Priority 50 - Can be overridden by custom providers with higher priority

Configuration Fallback Chain

MicroProfile Config Sources (application.properties, env vars, -D flags)
  ↓ (not found?)
DefaultValuesConfigProvider
  → Scans classpath for ALL META-INF/a2a-defaults.properties files
  → Merges all discovered properties together
  → Throws exception if duplicate keys found
  ↓ (property exists?)
Return merged default value
  ↓ (not found?)
IllegalArgumentException

Note: All META-INF/a2a-defaults.properties files (from server-common, extras modules, etc.) are loaded and merged together by DefaultValuesConfigProvider at startup. This is not a sequential fallback chain, but a single merged set of defaults.

Available Configuration Properties

See the main README for a complete list of configuration properties.

Framework Compatibility

This module works with any MicroProfile Config implementation:

  • Quarkus - Built-in MicroProfile Config support
  • Helidon - Built-in MicroProfile Config support
  • Open Liberty - Built-in MicroProfile Config support
  • WildFly/JBoss EAP - Add smallrye-config dependency
  • Other Jakarta EE servers - Add MicroProfile Config implementation

Custom Config Providers

If you're using a different framework (Spring, Micronaut, etc.), you can implement your own A2AConfigProvider:

import io.a2a.server.config.A2AConfigProvider;
import io.a2a.server.config.DefaultValuesConfigProvider;
import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.inject.Alternative;
import jakarta.annotation.Priority;
import jakarta.inject.Inject;

@ApplicationScoped
@Alternative
@Priority(100)  // Higher than MicroProfileConfigProvider's priority of 50
public class OtherEnvironmentConfigProvider implements A2AConfigProvider {

    @Inject
    Environment env;

    @Inject
    DefaultValuesConfigProvider defaultValues;

    @Override
    public String getValue(String name) {
        String value = env.getProperty(name);
        if (value != null) {
            return value;
        }
        // Fallback to defaults
        return defaultValues.getValue(name);
    }

    @Override
    public Optional<String> getOptionalValue(String name) {
        String value = env.getProperty(name);
        if (value != null) {
            return Optional.of(value);
        }
        return defaultValues.getOptionalValue(name);
    }
}

Implementation Details

  • Package: io.a2a.integrations.microprofile
  • Class: MicroProfileConfigProvider
  • Priority: 50 (can be overridden)
  • Scope: @ApplicationScoped
  • Dependencies: MicroProfile Config API, A2A SDK server-common

Reference Implementations

The A2A Java SDK reference implementations (Quarkus-based) automatically include this integration module, so MicroProfile Config properties work out of the box.

If you're building a custom server implementation, add this dependency to enable property-based configuration.