LangChain4j RAG Implementation Guide

Overview

RAG (Retrieval-Augmented Generation) extends LLM knowledge by finding and injecting relevant information from your data into prompts before sending to the LLM.

What is RAG?

RAG helps LLMs answer questions using domain-specific knowledge by retrieving relevant information to reduce hallucinations.

RAG Flavors in LangChain4j

1. Easy RAG

Simplest way to start with minimal setup. Handles document loading, splitting, and embedding automatically.

2. Core RAG APIs

Modular components including:

• Document
• TextSegment
• EmbeddingModel
• EmbeddingStore
• DocumentSplitter

3. Advanced RAG

Complex pipelines supporting:

• Query transformation
• Multi-source retrieval
• Re-ranking with components like QueryTransformer and ContentRetriever

RAG Stages

1. Indexing

Pre-process documents for efficient search

2. Retrieval

Find relevant content based on user queries

Core Components

Documents with metadata

Structured representation of your content with associated metadata for filtering and context.

Text segments (chunks)

Smaller, manageable pieces of documents that are embedded and stored in vector databases.

Embedding models

Convert text segments into numerical vectors for similarity search.

Embedding stores (vector databases)

Store and efficiently retrieve embedded text segments.

Content retrievers

Find relevant content based on user queries.

Query transformers

Transform and optimize user queries for better retrieval.

Content aggregators

Combine and rank retrieved content.

Advanced Features

• Query transformation and routing
• Multiple retrievers for different data sources
• Re-ranking models for improved relevance
• Metadata filtering for targeted retrieval
• Parallel processing for performance

Implementation Example (Easy RAG)

// Load documents
List<Document> documents = FileSystemDocumentLoader.loadDocuments("/path/to/docs");

// Create embedding store
InMemoryEmbeddingStore<TextSegment> embeddingStore = new InMemoryEmbeddingStore<>();

// Ingest documents
EmbeddingStoreIngestor.ingest(documents, embeddingStore);

// Create AI service
Assistant assistant = AiServices.builder(Assistant.class)
    .chatModel(chatModel)
    .chatMemory(MessageWindowChatMemory.withMaxMessages(10))
    .contentRetriever(EmbeddingStoreContentRetriever.from(embeddingStore))
    .build();

Best Practices

1. Document Preparation: Clean and structure documents before ingestion
2. Chunk Size: Balance between context preservation and retrieval precision
3. Metadata Strategy: Include relevant metadata for filtering and context
4. Embedding Model Selection: Choose models appropriate for your domain
5. Retrieval Strategy: Select appropriate k values and filtering criteria
6. Evaluation: Continuously evaluate retrieval quality and answer accuracy