When to Use

Load this skill when:

• Building a Spring Boot 3.3+ service or API

• Wiring beans with dependency injection

• Defining configuration properties and validation

• Implementing REST controllers and service layers

Critical Patterns

Pattern 1: Constructor injection only

Always use constructor injection; avoid field injection.

Pattern 2: Typed configuration properties

Use @ConfigurationProperties with validation, not scattered @Value.

Pattern 3: Transaction boundaries at service layer

Apply @Transactional on application services, not controllers.

Code Examples

Example 1: Configuration properties with validation

package com.acme.config;

import jakarta.validation.constraints.NotBlank; import org.springframework.boot.context.properties.ConfigurationProperties; import org.springframework.validation.annotation.Validated;

@Validated @ConfigurationProperties(prefix = "payment") public record PaymentProperties( @NotBlank String provider, @NotBlank String apiKey ) { }

package com.acme;

import org.springframework.boot.context.properties.ConfigurationPropertiesScan; import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication @ConfigurationPropertiesScan public class Application { }

Example 2: Service with constructor injection + transaction

package com.acme.order.application;

import org.springframework.stereotype.Service; import org.springframework.transaction.annotation.Transactional;

@Service public final class OrderService { private final OrderRepository repository;

public OrderService(OrderRepository repository) { this.repository = repository; }

@Transactional public void placeOrder(OrderCommand command) { repository.save(command.toEntity()); } }

Example 3: REST controller with DTO records

package com.acme.order.api;

import org.springframework.http.ResponseEntity; import org.springframework.web.bind.annotation.*;

@RestController @RequestMapping("/orders") public final class OrderController { private final OrderService service;

public OrderController(OrderService service) { this.service = service; }

@PostMapping public ResponseEntity<OrderResponse> place(@RequestBody OrderRequest request) { service.placeOrder(request.toCommand()); return ResponseEntity.ok(new OrderResponse("ok")); }

public record OrderRequest(String sku, int qty) { public OrderCommand toCommand() { return new OrderCommand(sku, qty); } }

public record OrderResponse(String status) { } }

Anti-Patterns

Don't: Use field injection

// BAD: field injection @Service public class OrderService { @org.springframework.beans.factory.annotation.Autowired private OrderRepository repository; }

Don't: Scatter configuration with @Value

// BAD: hard to validate and test @Service public class PaymentService { @org.springframework.beans.factory.annotation.Value("${payment.apiKey}") private String apiKey; }

Quick Reference

Task Pattern

Inject dependencies Constructor injection only

Read config @ConfigurationProperties + @Validated

Transactions @Transactional on services

Resources

• Spring Boot Reference: https://docs.spring.io/spring-boot/docs/current/reference/html/

• Spring Framework Reference: https://docs.spring.io/spring-framework/reference/