GenAI LangChain4j

First steps with LangChain4j

I found myself with some free time this week when train problems forced me to travel from Manchester to Sheffield via Leeds. I used that delay to set up a basic ‘Hello World’ example using Langchain4J. This proved a touch harder than expected.

The example on used a generate method on ChatLanguageModel that didn’t work for the latest versions of the libraries (0.26.1 at the time of writing).

Not a helpful example…

I soon cobbled together some working code using the latest version of the langchain4j-core and langchain4j libraries as well as a langchain4j-open-ai dependency. I originally used a couple of hello world queries, which produced boring responses, so I decided to ask OpenAI to tell me a joke.

package com.orbific;

import dev.langchain4j.model.openai.OpenAiChatModel;
import dev.langchain4j.model.output.Response;

public class App
    public static void main( String[] args )

        ChatLanguageModel model = OpenAiChatModel.builder()

        String message = "Tell me a joke.";
        AiMessage mine = AiMessage.aiMessage(message);
        Response<AiMessage> answer = model.generate(mine);
        System.out.println("Reply\n" + answer.content().text());

The response made me smile:

Why don’t scientists trust atoms?

Because they make up everything!

What’s weird is that I kept getting the same joke, even when setting a higher temperature in the model or rephrasing the query. But requesting a joke about cats produced a pun about cheetahs. And asking repeatedly for jokes about underwater creatures brings back different responses. There’s obviously something here that I’m missing.

I set up a paid chatGPT account but that did not seem to grant me access to the API, and I also had to top up some credits as well. I’m not entirely sure whether I needed the paid account so will look into that before the subscription renews.

There’s an interesting question as to whether it would have been faster for me to read the documentation rather than flail around for a solution, but that’s the whole point of a quickstart, right? Although my flailing wasn’t helped much by tiredness and a dodgy mobile internet connection.

I have a genuine excitement about getting this working. It’s not much, but it opens up some exciting possibilities. Now to go and read some documentation.

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