feat: Spring Boot 学习脚手架 v2.0

- 新增 IoC 容器学习模块
- 新增 AOP 切面编程学习模块
- 新增 MyBatis 集成学习模块
- 新增事务管理学习模块
- 新增用户/产品/订单 CRUD
- 新增 7 个交互式学习页面
- 集成性能监控切面

src/main/java/com/example/scaffold/service/impl/OrderService.java

@@ -0,0 +1,126 @@
+package com.example.scaffold.service.impl;
+
+import com.example.scaffold.entity.Order;
+import com.example.scaffold.entity.Product;
+import com.example.scaffold.mapper.OrderMapper;
+import com.example.scaffold.mapper.ProductMapper;
+import com.example.scaffold.mapper.UserMapper;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Isolation;
+import org.springframework.transaction.annotation.Propagation;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.math.BigDecimal;
+import java.util.List;
+
+/**
+ * 订单服务 - 演示事务传播和隔离级别
+ * 
+ * 学习要点：
+ * 1. 事务传播行为 - Propagation
+ * 2. 事务隔离级别 - Isolation
+ * 3. 事务回滚 - rollbackFor
+ */
+@Slf4j
+@Service
+@RequiredArgsConstructor
+public class OrderService {
+    
+    private final OrderMapper orderMapper;
+    private final ProductMapper productMapper;
+    private final UserMapper userMapper;
+    
+    /**
+     * 创建订单 - 演示事务
+     * REQUIRED: 有事务则加入，无则新建
+     */
+    @Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class)
+    public Order createOrder(Long userId, Long productId, Integer quantity) {
+        log.info("📦 [OrderService] 创建订单: userId={}, productId={}, quantity={}", userId, productId, quantity);
+        
+        // 检查用户
+        if (userMapper.findById(userId) == null) {
+            throw new RuntimeException("用户不存在: " + userId);
+        }
+        
+        // 检查产品
+        Product product = productMapper.findById(productId);
+        if (product == null) {
+            throw new RuntimeException("产品不存在: " + productId);
+        }
+        
+        // 扣减库存
+        int rows = productMapper.decreaseStock(productId, quantity);
+        if (rows == 0) {
+            throw new RuntimeException("库存不足");
+        }
+        
+        // 创建订单
+        Order order = new Order();
+        order.setUserId(userId);
+        order.setProductId(productId);
+        order.setQuantity(quantity);
+        order.setTotalPrice(product.getPrice().multiply(BigDecimal.valueOf(quantity)));
+        order.setStatus("PENDING");
+        
+        orderMapper.insert(order);
+        log.info("✅ [OrderService] 订单创建成功: orderId={}", order.getId());
+        
+        return order;
+    }
+    
+    /**
+     * 模拟事务回滚
+     */
+    @Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class)
+    public Order createOrderWithRollback(Long userId, Long productId, Integer quantity, boolean shouldRollback) {
+        log.info("📦 [OrderService] 创建订单(可能回滚): userId={}, shouldRollback={}", userId, shouldRollback);
+        
+        Order order = createOrder(userId, productId, quantity);
+        
+        if (shouldRollback) {
+            log.warn("⚠️ [OrderService] 触发回滚!");
+            throw new RuntimeException("模拟事务回滚");
+        }
+        
+        return order;
+    }
+    
+    /**
+     * REQUIRES_NEW - 挂起当前事务，创建新事务
+     */
+    @Transactional(propagation = Propagation.REQUIRES_NEW)
+    public void logOrderOperation(Long orderId, String operation) {
+        log.info("📝 [OrderService] 记录订单操作: orderId={}, operation={}", orderId, operation);
+        // 这个方法会在独立事务中执行
+        // 即使外部事务回滚，这里的记录也会保留
+    }
+    
+    /**
+     * 使用隔离级别 READ_COMMITTED
+     */
+    @Transactional(isolation = Isolation.READ_COMMITTED)
+    public Order getOrder(Long id) {
+        return orderMapper.findById(id);
+    }
+    
+    public List<Order> findAll() {
+        return orderMapper.findAll();
+    }
+    
+    public List<Order> findByUserId(Long userId) {
+        return orderMapper.findByUserId(userId);
+    }
+    
+    @Transactional
+    public void updateStatus(Long id, String status) {
+        orderMapper.updateStatus(id, status);
+    }
+    
+    @Transactional
+    public void deleteById(Long id) {
+        orderMapper.deleteById(id);
+    }
+}