spring-boot-3

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 { }

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());
  }
}

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) { }
}

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

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