spring-ai-mcp-server-patterns

# Spring AI MCP Server Implementation Patterns

Implements MCP servers with Spring AI for AI function calling, tool handlers, and MCP transport configuration.

## Overview

Production-ready MCP server patterns: `@Tool` functions, `@PromptTemplate` resources, and stdio/HTTP/SSE transports with Spring AI security.

## When to Use

MCP servers, Spring AI function calling, AI tools, tool calling, custom tool handlers, Spring Boot MCP, resource endpoints, or MCP transport configuration.

## Quick Reference

### Core Annotations

| Annotation | Target | Purpose |
|-----------|--------|---------|
| `@EnableMcpServer` | Class | Enable MCP server auto-configuration |
| `@Tool(description)` | Method | Declare AI-callable tool |
| `@ToolParam(value)` | Parameter | Document tool parameter for AI |
| `@PromptTemplate(name)` | Method | Declare reusable prompt template |
| `@PromptParam(value)` | Parameter | Document prompt parameter |

### Transport Types

| Transport | Use Case | Config |
|-----------|----------|--------|
| `stdio` | Local process / Claude Desktop | Default |
| `http` | Remote HTTP clients | `port`, `path` |
| `sse` | Real-time streaming clients | `port`, `path` |

### Key Dependencies

```xml
<!-- Maven -->
<dependency>
    <groupId>org.springframework.ai</groupId>
    <artifactId>spring-ai-mcp-server</artifactId>
    <version>1.0.0</version>
</dependency>
<dependency>
    <groupId>org.springframework.ai</groupId>
    <artifactId>spring-ai-starter-model-openai</artifactId>
    <version>1.0.0</version>
</dependency>
```

```gradle
// Gradle
implementation 'org.springframework.ai:spring-ai-mcp-server:1.0.0'
implementation 'org.springframework.ai:spring-ai-starter-model-openai:1.0.0'
```

## Instructions

### 1. Project Setup

Add Spring AI MCP dependencies (see Quick Reference above), configure the AI model in `application.properties`, and enable MCP with `@EnableMcpServer`:

```java
@SpringBootApplication
@EnableMcpServer
public class MyMcpApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyMcpApplication.class, args);
    }
}
```

```properties
spring.ai.openai.api-key=${OPENAI_API_KEY}
spring.ai.mcp.enabled=true
spring.ai.mcp.transport.type=stdio
```

### 2. Define Tools

Annotate methods with `@Tool` inside `@Component` beans. Use `@ToolParam` to document parameters:

```java
@Component
public class WeatherTools {

    @Tool(description = "Get current weather for a city")
    public WeatherData getWeather(@ToolParam("City name") String city) {
        return weatherService.getCurrentWeather(city);
    }

    @Tool(description = "Get 5-day forecast for a city")
    public ForecastData getForecast(
            @ToolParam("City name") String city,
            @ToolParam(value = "Unit: celsius or fahrenheit", required = false) String unit) {
        return weatherService.getForecast(city, unit != null ? unit : "celsius");
    }
}
```

See [references/implementation-patterns.md](references/implementation-patterns.md) for database tools, API integration tools, and the `FunctionCallback` low-level pattern.

### 3. Create Prompt Templates

```java
@Component
public class CodeReviewPrompts {

    @PromptTemplate(
        name = "java-code-review",
        description = "Review Java code for best practices and issues"
    )
    public Prompt createCodeReviewPrompt(
            @PromptParam("code") String code,
            @PromptParam(value = "focusAreas", required = false) List<String> focusAreas) {

        String focus = focusAreas != null ? String.join(", ", focusAreas) : "general best practices";
        return Prompt.builder()
                .system("You are an expert Java code reviewer with 20 years of experience.")
                .user("Review the following Java code for " + focus + ":\n```java\n" + code + "\n```")
                .build();
    }
}
```

See [references/implementation-patterns.md](references/implementation-patterns.md) for additional prompt template patterns.

### 4. Configure Transport

```yaml
spring:
  ai:
    mcp:
      enabled: true
      transport:
        type: stdio       # stdio | http | sse
        http:
          port: 8080
          path: /mcp
      server:
        name: my-mcp-server
        version: 1.0.0
```

### 5. Add Security

```java
@Configuration
public class McpSecurityConfig {

    @Bean
    public ToolFilter toolFilter(SecurityService securityService) {
        return (tool, context) -> {
            User user = securityService.getCurrentUser();
            if (tool.name().startsWith("admin_")) {
                return user.hasRole("ADMIN");
            }
            return securityService.isToolAllowed(user, tool.name());
        };
    }
}
```

Use `@PreAuthorize("hasRole('ADMIN')")` on tool methods for method-level security. See [references/implementation-patterns.md](references/implementation-patterns.md) for full security patterns.

### 6. Testing

```java
@SpringBootTest
class WeatherToolsTest {

    @Autowired
    private WeatherTools weatherTools;

    @MockBean
    private WeatherService weatherService;

    @Test
    void testGetWeather_Success() {
        when(weatherService.getCurrentWeather("London"))
            .thenReturn(new WeatherData("London", "Cloudy", 15.0));

        WeatherData result = weatherTools.getWeather("London");

        assertThat(result.city()).isEqualTo("London");
        verify(weatherService).getCurrentWeather("London");
    }
}
```

See [references/testing-guide.md](references/testing-guide.md) for integration tests, Testcontainers, security tests, and slice tests.

## Best Practices

### Tool Design
- Keep tools focused — one operation per tool
- Use clear, action-oriented names (`getWeather`, `executeQuery`)
- Always annotate parameters with `@ToolParam` and descriptive text
- Return structured records/DTOs, not raw strings or maps
- Design tools to be idempotent when possible

### Security
- Validate and sanitize all inputs — AI-generated parameters are untrust