feat: add exchange rates currency sample #434

cmtoan · 2026-01-11T21:51:44Z

Description

Add sample agent to provide currency conversion. This agent demonstrates multi-turn dialogue (input-required) and streaming responses.

gemini-code-assist · 2026-01-11T21:52:09Z

Summary of Changes

Hello @cmtoan, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a comprehensive new sample agent written in Java, designed to handle currency exchange rate queries. The agent exemplifies advanced features of the A2A protocol, such as managing multi-turn conversations where it can request additional user input, and providing real-time updates through streaming responses. It integrates with an external API for live data and uses an LLM for intelligent processing, offering a robust example for developing interactive and data-driven agents.

Highlights

New Sample Agent: Added a new sample agent for currency conversion, demonstrating multi-turn dialogue and streaming responses.
Technology Stack: Implemented the agent using Quarkus LangChain4j, integrating with the Frankfurter API for real-time exchange rates and leveraging Ollama LLM.
Client Implementation: Included a client application to showcase interaction with the currency agent, supporting both JSON-RPC and gRPC transports and handling conversational flows.

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Code Review

This pull request introduces a new sample agent for currency conversion, which is a great addition to demonstrate multi-turn dialogue and streaming responses. The implementation using Quarkus and LangChain4j is well-structured. My review focuses on improving code clarity, robustness, and adherence to best practices. I've included suggestions for making configurations more flexible, enhancing logging, improving error handling in the API client, and refactoring for better readability.

gemini-code-assist · 2026-01-11T21:54:16Z

...a/agents/currency_exchange_rates/client/src/main/java/com/samples/a2a/client/TestClient.java

+    public static void main(String[] args) {
+        String serverUrl = DEFAULT_SERVER_URL;
+
+        try {
+            System.out.println("Connecting to currency agent at: " + serverUrl);
+
+            // Fetch the public agent card
+            AgentCard publicAgentCard =
+                new A2ACardResolver(serverUrl).getAgentCard();
+            System.out.printf("""
+                Successfully fetched public agent card:
+                %s
+                Using public agent card for client initialization.%n
+                """, objectMapper.writeValueAsString(publicAgentCard));
+
+            ClientConfig clientConfig = new ClientConfig.Builder()
+                .setAcceptedOutputModes(List.of("text"))
+                .build();
+
+            // Create and send the message without INPUT_REQUIRED
+            StreamingClient streamingClient = getStreamingClient(publicAgentCard, clientConfig);
+            sendMessage(streamingClient.client(), "how much is 10 USD in INR?", null, null, streamingClient.messageResponse());
+
+            // Create and send the message with INPUT_REQUIRED
+            StreamingClient streamingClient1 = getStreamingClient(publicAgentCard, clientConfig);
+            StreamingClient streamingClient2 = getStreamingClient(publicAgentCard, clientConfig);
+
+            MessageResponse message1 = sendMessage(streamingClient1.client(), "How much is the exchange rate for 1 USD?", null, null, streamingClient1.messageResponse());
+
+            // Resubscribe to a task to send additional information for this task
+            streamingClient2.client().resubscribe(new TaskIdParams(message1.taskId()),
+                streamingClient2.consumers(), streamingClient2.streamingErrorHandler());
+            sendMessage(streamingClient2.client(), "CAD", message1.contextId(), message1.taskId(), streamingClient2.messageResponse());
+        } catch (Exception e) {
+            System.err.println("An error occurred: " + e.getMessage());
+            e.printStackTrace();
+        }
+    }


The main method is quite long and handles multiple scenarios (single-turn and multi-turn conversations). To improve readability and maintainability, consider refactoring it by extracting the logic for each scenario into separate private methods, for example runSingleTurnDemo() and runMultiTurnDemo().

gemini-code-assist · 2026-01-11T21:54:16Z

...nts/currency_exchange_rates/server/src/main/java/com/samples/a2a/server/CurrencyService.java

+            if (!data.containsKey("rates")) {
+                Log.error("Invalid API response format");
+            }


This validation only logs an error but still returns the potentially invalid data map. This could confuse the LLM, as the tool output would not match its expectations. It's better to throw a RuntimeException here to signal that the tool execution has failed. LangChain4j will catch this and can potentially retry or inform the LLM about the failure.

Suggested change

if (!data.containsKey("rates")) {

Log.error("Invalid API response format");

}

if (data == null || !data.containsKey("rates")) {

throw new RuntimeException("Invalid API response format from Frankfurter API");

}

gemini-code-assist · 2026-01-11T21:54:16Z

...nts/currency_exchange_rates/server/src/main/java/com/samples/a2a/server/CurrencyService.java

+                throw new RuntimeException("Request exchange rate failed with status " + response.statusCode());
+            }
+
+            Map<String, Object> data = mapper.readValue(response.body(), Map.class);


Deserializing the API response to a generic Map<String, Object> is not type-safe and can lead to runtime errors if the API response structure changes. It's a better practice to create a dedicated DTO (Data Transfer Object) class that models the expected JSON response. This improves code readability and robustness.

For example:

public record FrankfurterResponse(java.math.BigDecimal amount, String base, String date, java.util.Map<String, java.math.BigDecimal> rates) {}

Then you can deserialize to this record: FrankfurterResponse data = mapper.readValue(response.body(), FrankfurterResponse.class);

gemini-code-assist · 2026-01-11T21:54:16Z

...a/agents/currency_exchange_rates/client/src/main/java/com/samples/a2a/client/TestClient.java

+        String serverUrl = DEFAULT_SERVER_URL;
+
+        try {
+            System.out.println("Connecting to currency agent at: " + serverUrl);


Using System.out.println for logging is common in simple examples, but it's a good practice to use a proper logging framework like SLF4J even in samples. This makes logging more configurable and consistent.

gemini-code-assist · 2026-01-11T21:54:16Z

samples/java/agents/currency_exchange_rates/README.md

+    ````
+   ollama pull qwen2.5:7b
+   ollama run qwen2.5:7b
+    ````


The code block uses four backticks (````), which is not standard Markdown and may not render correctly on all platforms. Please use three backticks and specify the language for syntax highlighting.

Suggested change

````

ollama pull qwen2.5:7b

ollama run qwen2.5:7b

````

```bash

ollama pull qwen2.5:7b

ollama run qwen2.5:7b

```

gemini-code-assist · 2026-01-11T21:54:16Z

...cy_exchange_rates/server/src/main/java/com/samples/a2a/server/CurrencyAgentCardProducer.java

+        return new AgentCard.Builder()
+            .name("Currency Agent")
+            .description("Assistant for currency conversions")
+            .url("http://localhost:" + getHttpPort())


The agent URL is constructed with a hardcoded "localhost". This is not ideal for environments where the service might be exposed on a different hostname or IP address (e.g., in a Docker container). Consider making the hostname configurable, for example, via an application property.

gemini-code-assist · 2026-01-11T21:54:16Z

...xchange_rates/server/src/main/java/com/samples/a2a/server/CurrencyAgentExecutorProducer.java

+
+            // call the currency agent with the message
+            ResponseFormat response = agent.handleRequest(message);
+            System.out.printf("Response: %s %n", response);


It's better to use a proper logging framework (like the one provided by Quarkus, io.quarkus.logging.Log) instead of System.out.printf. This provides more control over log levels and output formats. You would need to add import io.quarkus.logging.Log; to the file.

Suggested change

System.out.printf("Response: %s %n", response);

Log.infof("Response: %s", response);

gemini-code-assist · 2026-01-11T21:54:17Z

samples/java/agents/currency_exchange_rates/README.md

+
+## How It Works
+
+This agent uses Ollama LLM (for example qwen2.5:7b) to provide currency exchange information. 


A minor grammar fix would improve readability. It's more natural to say "an Ollama LLM" and add a comma after "for example".

Suggested change

This agent uses Ollama LLM (for example qwen2.5:7b) to provide currency exchange information.

This agent uses an Ollama LLM (for example, qwen2.5:7b) to provide currency exchange information.

gemini-code-assist · 2026-01-11T21:54:17Z

samples/java/agents/currency_exchange_rates/README.md

@@ -0,0 +1,144 @@
+# Currency Exchange Rates
+
+This sample demonstrates a currency conversion agent and exposed through the A2A protocol. 


There's a minor grammatical error here. It should be "...agent exposed through..." instead of "...agent and exposed through...".

Suggested change

This sample demonstrates a currency conversion agent and exposed through the A2A protocol.

This sample demonstrates a currency conversion agent exposed through the A2A protocol.

gemini-code-assist · 2026-01-11T21:54:17Z

...ents/currency_exchange_rates/server/src/main/java/com/samples/a2a/server/ResponseFormat.java

+    public ResponseFormat(String message) {
+        this(Status.INPUT_REQUIRED, message);
+    }


This convenience constructor is not used anywhere in the code. It also makes a potentially misleading assumption that any response created with just a message should have the status INPUT_REQUIRED. To avoid dead code and potential confusion, it's best to remove it.

cmtoan · 2026-01-11T23:45:01Z

@fjuma When you have time, could you review this PR?

…ulti-turn dialogue and streaming responses.

gemini-code-assist bot reviewed Jan 11, 2026

View reviewed changes

cmtoan force-pushed the feat/exchange_rates_currency branch from 967d256 to 9f768f9 Compare January 11, 2026 22:14

cmtoan changed the title ~~Feat/exchange rates currency~~ feat: add exchange rates currency sample Jan 11, 2026

cmtoan force-pushed the feat/exchange_rates_currency branch from 063b2cc to b669e42 Compare January 11, 2026 23:24

feat: add sample agent providing currency conversion to demonstrate m…

14b151a

…ulti-turn dialogue and streaming responses.

cmtoan force-pushed the feat/exchange_rates_currency branch from f8b1892 to 14b151a Compare January 13, 2026 22:55

cmtoan added 2 commits January 14, 2026 00:23

feat: add sample agent providing currency conversion to demonstrate m…

ba5077e

…ulti-turn dialogue and streaming responses.

feat: add sample agent providing currency conversion to demonstrate m…

077b9f0

…ulti-turn dialogue and streaming responses.

cmtoan mentioned this pull request Jan 14, 2026

Implement the currency conversion agent with A2A Protocol a2aproject/a2a-java#588

Open

	System.out.printf("Response: %s %n", response);
	Log.infof("Response: %s", response);


		## How It Works

		This agent uses Ollama LLM (for example qwen2.5:7b) to provide currency exchange information.

	This agent uses Ollama LLM (for example qwen2.5:7b) to provide currency exchange information.
	This agent uses an Ollama LLM (for example, qwen2.5:7b) to provide currency exchange information.

		@@ -0,0 +1,144 @@
		# Currency Exchange Rates

		This sample demonstrates a currency conversion agent and exposed through the A2A protocol.

feat: add exchange rates currency sample #434

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cmtoan commented Jan 11, 2026

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