Build a RAG-Powered Knowledge Base with Spring Boot, Milvus, and Ollama

1. Introduction

1.1 What is RAG?

Retrieval‑Augmented Generation (RAG) combines a large language model (LLM) with an external knowledge base to improve the accuracy and relevance of generated text.

RAG enables the model to retrieve relevant documents from a set of files and incorporate that information into its responses, rather than relying solely on its pre‑trained knowledge.

1.2 What is a vector database?

A vector database stores embeddings (numeric vectors) and performs similarity search instead of exact matching. It allows you to find items with similar semantic meaning, such as images or sentences.

Example: the text "I love Spring full‑stack case source code" is converted by an embedding model into a vector like [0.24, -0.56, 0.89].

1.3 Milvus Overview

Milvus is a popular open‑source vector database. For this tutorial we only need to know how to use it; detailed documentation is available at https://milvus.io/docs/zh .

2. Practical Example

2.1 Environment Preparation

Install Milvus (standalone) using the provided script.

Install the bge‑m3 embedding model with ollama pull bge-m3:latest .

<code># Download script
$ curl -sfL https://raw.githubusercontent.com/milvus-io/milvus/master/scripts/standalone_embed.sh -o standalone_embed.sh
# Start container
$ bash standalone_embed.sh start
</code>

2.2 Project Configuration

Add the following Maven dependencies:

<code>&lt;dependency&gt;
  &lt;groupId&gt;org.springframework.ai&lt;/groupId&gt;
  &lt;artifactId&gt;spring-ai-milvus-store-spring-boot-starter&lt;/artifactId&gt;
&lt;/dependency&gt;
&lt;dependency&gt;
  &lt;groupId&gt;org.springframework.ai&lt;/groupId&gt;
  &lt;artifactId&gt;spring-ai-ollama-spring-boot-starter&lt;/artifactId&gt;
&lt;/dependency&gt;
&lt;dependency&gt;
  &lt;groupId&gt;com.alibaba.cloud.ai&lt;/groupId&gt;
  &lt;artifactId&gt;spring-ai-alibaba-starter&lt;/artifactId&gt;
  &lt;version&gt;1.0.0-M6.1&lt;/version&gt;
&lt;/dependency&gt;
</code>

Key configuration (YAML style):

<code>spring:
  ai:
    dashscope:
      api-key: sk-xxxooo
      base-url: https://dashscope.aliyuncs.com/compatible-mode/v1
      chat:
        options:
          model: qwen-turbo
      embedding:
        enabled: false
---
spring:
  ai:
    ollama:
      chat:
        enabled: false
      base-url: http://localhost:11111
      embedding:
        enabled: true
        model: bge-m3:latest
---
spring:
  ai:
    vectorstore:
      milvus:
        client:
          host: localhost
          port: 19530
          username: root
          password: root
        initialize-schema: true
        embeddingDimension: 1024
</code>

2.3 Vector Store Operations

Service to save documents and perform similarity search:

<code>@Service
public class DocumentService {
  private final VectorStore vectorStore;
  public DocumentService(VectorStore vectorStore) {
    this.vectorStore = vectorStore;
  }
  // Save sample texts
  public void save() {
    List<Document> documents = List.of(
        new Document("banana"),
        new Document("apple"),
        new Document("orange"),
        new Document("strawberry"),
        new Document("Java"),
        new Document("python"),
        new Document("C#"),
        new Document("tiger"));
    this.vectorStore.add(documents);
  }
  // Similarity search
  public List<Document> query(String prompt, int topK) {
    SearchRequest request = SearchRequest.builder()
        .query(prompt)
        .topK(topK)
        .build();
    return this.vectorStore.similaritySearch(request);
  }
}
</code>

Controller exposing endpoints:

<code>@RestController
@RequestMapping("/rag")
public class RagController {
  private final DocumentService documentService;
  public RagController(DocumentService documentService) {
    this.documentService = documentService;
  }
  @GetMapping("/save")
  public ResponseEntity<String> save() {
    this.documentService.save();
    return ResponseEntity.ok("success");
  }
  @GetMapping("/{topK}")
  public ResponseEntity<List<Document>> query(@PathVariable Integer topK, String prompt) {
    return ResponseEntity.ok(this.documentService.query(prompt, topK));
  }
}
</code>

2.4 Combine with LLM

Configure a ChatClient bean:

<code>@Configuration
public class ChatConfig {
  @Bean
  ChatClient chatClient(ChatClient.Builder builder) {
    return builder.defaultAdvisors(List.of(new SimpleLoggerAdvisor()))
                  .build();
  }
}
</code>

Endpoint that retrieves relevant documents, builds a prompt, and calls the LLM:

<code>@GetMapping("/query/{topK}")
public ResponseEntity<String> queryLLM(@PathVariable Integer topK,
                                        @RequestParam String prompt) {
  SearchRequest request = SearchRequest.builder()
      .query(prompt)
      .topK(topK)
      .build();
  List<Document> docs = this.vectorStore.similaritySearch(request);
  PromptTemplate template = new PromptTemplate("{userMessage}\n\n Use the following information to answer the question:\n {contents}");
  Prompt finalPrompt = template.create(Map.of("userMessage", prompt, "contents", docs));
  String result = this.chatClient.prompt(finalPrompt).call().content();
  return ResponseEntity.ok(result);
}
</code>

Running /rag/save stores the sample texts in Milvus; /rag/{topK}?prompt=... performs similarity search; the final LLM step filters and formats the answer.