Welcome to the final lesson of this course! In this lesson, we will integrate context retrieval with a chat model using LangChain4j. This builds on the skills you've developed in previous lessons, where you learned about document embeddings and similarity search. Today, we'll focus on using Java's string manipulation techniques to format messages with extra context, enabling you to ask questions and receive answers based on the retrieved document content. This lesson will bring together all the skills you've learned so far, culminating in a comprehensive understanding of document processing and retrieval with Java.

Let's quickly recap what we've learned in previous lessons about preparing documents and creating a vector store. We'll load and prepare our document, "The Adventure of the Blue Carbuncle," and generate embeddings to create a vector store. This process is essential for effective context retrieval.

In this code, we load a document using LangChain4j's document loaders, split it into chunks with a paragraph splitter, generate embeddings using an OpenAI model, and create an in-memory vector store. This sets the stage for efficient context retrieval in our question-answering tasks.

Now that we have our vector store, we can integrate context retrieval with a chat model. First, we'll define a query and perform a similarity search to retrieve relevant documents based on the query. This will allow us to combine the retrieved document content to form a context for our question.

In this example, we define a query about the main mystery in the story, generate an embedding for it, and retrieve the top three most relevant document chunks. The content of these chunks is combined to form a context that will be used in the next step.

To effectively communicate with the chat model, we need to format our messages using Java's string manipulation techniques. Think of a template as a fill-in-the-blank form where you can insert specific pieces of information. In our case, we want to insert the context we retrieved from the similarity search and the question we want to ask.

In this code, we create a prompt template that includes placeholders for the context and the question. Java's String.format method helps us define this structure.

Now, let's print the formatted template to see how the context and question are structured in the message.

This will output something like:

By printing the formatted template, we can verify that the context and question are correctly inserted into the template. This ensures that the chat model receives a well-structured message, allowing it to generate a relevant and accurate response.

With our prompt ready, we can now move on to interacting with the chat model. We'll instantiate the chat model and use our formatted template to get a response.

In this section, we initialize a chat model using OpenAI's API and invoke it with our formatted prompt. The model processes the input and generates an answer based on the context and question provided. By printing both the question and the AI's answer, we can see how effectively the integration of context retrieval and templates enhances the interaction.

You've successfully completed this lesson, where you learned how to integrate context retrieval with a chat model using LangChain4j. We explored the use of Java's string manipulation techniques to format messages with extra context, allowing you to ask questions and receive answers based on the retrieved document content. This lesson consolidated all the skills you've acquired so far, equipping you with a solid understanding of document processing and retrieval with Java. As you continue your learning journey, consider experimenting with different queries and document types to deepen your understanding. Stay tuned for the next course, where we'll build on these concepts and explore even more advanced techniques.