Spring Boot 3 & Java 21 Cursor Rules (.mdc) | Modern Enterprise Java

// Discouraged: Legacy javax namespace, verbose POJO with setters, mutable entity exposure
import javax.persistence.*; // Obsolete in Spring Boot 3!

public class BadOrderDTO {
    private String customerId;
    public void setCustomerId(String id) { this.customerId = id; }
}

package com.example.demo.order;

import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.Positive;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import java.math.BigDecimal;

public record CreateOrderRequest(
    @NotBlank String customerId,
    @Positive BigDecimal amount
) {}

public record OrderResponse(Long id, String customerId, BigDecimal amount) {}

@RestController
@RequestMapping("/api/v1/orders")
public class OrderController {
    private final OrderService orderService;

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

    @PostMapping
    public ResponseEntity<OrderResponse> create(@RequestBody CreateOrderRequest request) {
        OrderResponse response = orderService.processOrder(request);
        return ResponseEntity.ok(response);
    }
}