Java POJO与业务逻辑：深度解析与最佳实践

public class Order {
    private String orderId;
    private List<LineItem> lineItems;
    private BigDecimal totalAmount;
    private OrderStatus status;

    // 构造函数
    public Order(String orderId, List<LineItem> lineItems) {
        this.orderId = orderId;
        this.lineItems = new ArrayList<>(lineItems);
        this.status = OrderStatus.PENDING;
        calculateTotalAmount(); // 业务逻辑：计算总金额
    }

    // Getter方法
    public String getOrderId() { return orderId; }
    public List<LineItem> getLineItems() { return Collections.unmodifiableList(lineItems); }
    public BigDecimal getTotalAmount() { return totalAmount; }
    public OrderStatus getStatus() { return status; }

    // 业务逻辑方法：计算订单总金额
    private void calculateTotalAmount() {
        this.totalAmount = lineItems.stream()
                                    .map(item -> item.getPrice().multiply(BigDecimal.valueOf(item.getQuantity())))
                                    .reduce(BigDecimal.ZERO, BigDecimal::add);
    }

    // 业务逻辑方法：放置订单
    public void placeOrder() {
        if (this.status == OrderStatus.PENDING) {
            this.status = OrderStatus.PLACED;
            System.out.println("Order " + orderId + " has been placed. Total: " + totalAmount);
            // 可以在此处触发事件通知其他服务
        } else {
            throw new IllegalStateException("Order cannot be placed from status: " + status);
        }
    }

    // 业务逻辑方法：取消订单
    public void cancelOrder() {
        if (this.status == OrderStatus.PLACED || this.status == OrderStatus.PENDING) {
            this.status = OrderStatus.CANCELLED;
            System.out.println("Order " + orderId + " has been cancelled.");
            // 可以在此处触发事件通知其他服务
        } else {
            throw new IllegalStateException("Order cannot be cancelled from status: " + status);
        }
    }

    // 内部枚举
    public enum OrderStatus {
        PENDING, PLACED, SHIPPED, DELIVERED, CANCELLED
    }
}

class LineItem {
    private String productId;
    private int quantity;
    private BigDecimal price;

    public LineItem(String productId, int quantity, BigDecimal price) {
        this.productId = productId;
        this.quantity = quantity;
        this.price = price;
    }

    public String getProductId() { return productId; }
    public int getQuantity() { return quantity; }
    public BigDecimal getPrice() { return price; }
}

public record Employee(String firstName, String lastName, LocalDate hiredDate) {
    // Records可以添加额外的构造函数或方法，但通常保持其数据载体特性
    public String getFullName() {
        return firstName + " " + lastName;
    }
}