提高开发效率和代码质量的秘籍：Spring设计模式的有效应用

@Service
public class SingletonDemo {
    // 私有的静态实例
    private static SingletonDemo instance;
    
    // 私有构造方法
    private SingletonDemo() {}
    
    // 全局访问点
    public static SingletonDemo getInstance() {
        if (instance == null) {
            instance = new SingletonDemo();
        }
        return instance;
    }
}

public interface Car {
    void drive();
}

@Component
public class BMW implements Car {
    public void drive() {
        System.out.println("Driving BMW");
    }
}

@Component
public class Audi implements Car {
    public void drive() {
        System.out.println("Driving Audi");
    }
}

@Component
public class CarFactory {
    public Car createCar(String brand) {
        if ("BMW".equals(brand)) {
            return new BMW();
        } else if ("Audi".equals(brand)) {
            return new Audi();
        } else {
            throw new IllegalArgumentException("Invalid brand: " + brand);
        }
    }
}

public interface UserService {
    void saveUser(User user);
}

@Service
public class UserServiceImpl implements UserService {
    @Override
    public void saveUser(User user) {
        // 保存用户逻辑
    }
}

@Component
public class UserServiceProxy implements UserService {
    @Autowired
    private UserServiceImpl userService;
    
    @Override
    public void saveUser(User user) {
        // 执行额外的逻辑，如事务的开始和提交
        userService.saveUser(user);
        // 执行额外的逻辑，如日志的记录
    }
}