七种方法增强代码可扩展性（多图详解）

/**
 * 用户角色枚举
 *
 * @author 微信公众号「JAVA前线」
 *
 */
public enum UserRoleEnum {

    // 1 -> 00000001
    NORMAL(1, "普通用户"),

    // 2 -> 00000010
    MANAGER(1 << 1, "管理员"),

    // 4 -> 00000100
    SUPER(1 << 2, "超级管理员")

    ;

    private int code;
    private String description;

    private UserRoleEnum(Integer code, String description) {
        this.code = code;
        this.description = description;
    }

    public String getDescription() {
        return description;
    }

    public int getCode() {
        return this.code;
    }
}

/**
 * 用户角色枚举
 *
 * @author 微信公众号「JAVA前线」
 *
 */
public enum UserRoleEnum {

    // 1 -> 00000001
    NORMAL(1, "普通用户"),

    // 2 -> 00000010
    MANAGER(1 << 1, "管理员"),

    // 4 -> 00000100
    SUPER(1 << 2, "超级管理员")

    ;

    // 新增角色 -> 位或操作
    // oldRole -> 00000001 -> 普通用户
    // addRole -> 00000010 -> 新增管理员
    // newRole -> 00000011 -> 普通用户和管理员
    public static Integer addRole(Integer oldRole, Integer addRole) {
        return oldRole | addRole;
    }

    // 删除角色 -> 位异或操作
    // oldRole -> 00000011 -> 普通用户和管理员
    // delRole -> 00000010 -> 删除管理员
    // newRole -> 00000001 -> 普通用户
    public static Integer removeRole(Integer oldRole, Integer delRole) {
        return oldRole ^ delRole;
    }

    // 是否有某种角色 -> 位与操作
    // allRole -> 00000011 -> 普通用户和管理员
    // qryRole -> 00000001 -> 是否有管理员角色
    // resRole -> 00000001 -> 有普通用户角色
    public static boolean hasRole(Integer allRole, Integer qryRole) {
        return qryRole == (role & qryRole);
    }

    private int code;
    private String description;

    private UserRoleEnum(Integer code, String description) {
        this.code = code;
        this.description = description;
    }

    public String getDescription() {
        return description;
    }

    public int getCode() {
        return this.code;
    }

    public static void main(String[] args) {
        System.out.println(addRole(1, 2));
        System.out.println(removeRole(3, 1));
        System.out.println(hasRole(3, 1));
    }
}

select * from user_role where (user_flag & 1) = user_flag;
select * from user_role where (user_flag & b'0001') = user_flag;

<select id="selectByUserRole" resultMap="BaseResultMap" parameterType="java.util.Map">
  select * from user_role 
  where user_flag & #{userFlag} = #{userFlag}
</select>

<select id="selectByUserIdAndRole" resultMap="BaseResultMap" parameterType="java.util.Map">
  select * from user_role 
  where id = #{userId} and user_flag & #{userFlag} = #{userFlag}
</select>

public class OrderDTO {
    private Integer bizType;
    private Integer bizSubType;
    private Long amount;
    private String goodsId;
}

public Response<String> createOrder(OrderDTO order);

public class OrderDTO {
    private Integer bizType;
    private Integer bizSubType;
    private Long amount;
    private String goodsId;
    private Map<String, String> params;
}

public Response<String> createOrder(OrderDTO order);

/order/1.0/createOrder
/order/1.1/createOrder

public class OrderServiceImpl implements OrderService {

    @Resource
    private OrderMapper orderMapper;

    @Override
    public void createOrder(OrderBO orderBO) {
        if (null == orderBO) {
            throw new RuntimeException("参数异常");
        }
        if (OrderTypeEnum.isNotValid(orderBO.getType())) {
            throw new RuntimeException("参数异常");
        }
        // A类型订单
        if (OrderTypeEnum.A_TYPE.getCode().equals(orderBO.getType())) {
            orderBO.setPrice(orderBO.getPrice() * 0.9);
            if (orderBO.getWeight() > 9) {
                throw new RuntimeException("超过物流最大重量");
            }
            orderBO.setRefundSupport(Boolean.FALSE);
        }
        // B类型订单
        else if (OrderTypeEnum.B_TYPE.getCode().equals(orderBO.getType())) {
            orderBO.setPrice(orderBO.getPrice() * 0.8);
            if (orderBO.getWeight() > 8) {
                throw new RuntimeException("超过物流最大重量");
            }
            orderBO.setRefundSupport(Boolean.TRUE);
        }
        // C类型订单
        else if (OrderTypeEnum.C_TYPE.getCode().equals(orderBO.getType())) {
            orderBO.setPrice(orderBO.getPrice() * 0.7);
            if (orderBO.getWeight() > 7) {
                throw new RuntimeException("超过物流最大重量");
            }
            orderBO.setRefundSupport(Boolean.TRUE);
        }
        // 保存数据
        OrderDO orderDO = new OrderDO();
        BeanUtils.copyProperties(orderBO, orderDO);
        orderMapper.insert(orderDO);
    }
}

// 优惠策略
public interface DiscountStrategy {
    public void discount(OrderBO orderBO);
}

// A类型优惠策略
@Component
public class TypeADiscountStrategy implements DiscountStrategy {

    @Override
    public void discount(OrderBO orderBO) {
        orderBO.setPrice(orderBO.getPrice() * 0.9);
    }
}

// B类型优惠策略
@Component
public class TypeBDiscountStrategy implements DiscountStrategy {

    @Override
    public void discount(OrderBO orderBO) {
        orderBO.setPrice(orderBO.getPrice() * 0.8);
    }
}

// C类型优惠策略
@Component
public class TypeCDiscountStrategy implements DiscountStrategy {

    @Override
    public void discount(OrderBO orderBO) {
        orderBO.setPrice(orderBO.getPrice() * 0.7);
    }
}

// 优惠策略工厂
@Component
public class DiscountStrategyFactory implements InitializingBean {
    private Map<String, DiscountStrategy> strategyMap = new HashMap<>();

    @Resource
    private TypeADiscountStrategy typeADiscountStrategy;
    @Resource
    private TypeBDiscountStrategy typeBDiscountStrategy;
    @Resource
    private TypeCDiscountStrategy typeCDiscountStrategy;

    public DiscountStrategy getStrategy(String type) {
        return strategyMap.get(type);
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        strategyMap.put(OrderTypeEnum.A_TYPE.getCode(), typeADiscountStrategy);
        strategyMap.put(OrderTypeEnum.B_TYPE.getCode(), typeBDiscountStrategy);
        strategyMap.put(OrderTypeEnum.C_TYPE.getCode(), typeCDiscountStrategy);
    }
}

// 优惠策略执行
@Component
public class DiscountStrategyExecutor {
    private DiscountStrategyFactory discountStrategyFactory;

    public void discount(OrderBO orderBO) {
        DiscountStrategy discountStrategy = discountStrategyFactory.getStrategy(orderBO.getType());
        if (null == discountStrategy) {
            throw new RuntimeException("无优惠策略");
        }
        discountStrategy.discount(orderBO);
    }
}

// 创建订单服务
public interface CreateOrderService {
    public void createOrder(OrderBO orderBO);
}

// 抽象创建订单流程
public abstract class AbstractCreateOrderFlow {

    @Resource
    private OrderMapper orderMapper;

    public void createOrder(OrderBO orderBO) {
        // 参数校验
        if (null == orderBO) {
            throw new RuntimeException("参数异常");
        }
        if (OrderTypeEnum.isNotValid(orderBO.getType())) {
            throw new RuntimeException("参数异常");
        }
        // 计算优惠
        discount(orderBO);
        // 计算重量
        weighing(orderBO);
        // 退款支持
        supportRefund(orderBO);
        // 保存数据
        OrderDO orderDO = new OrderDO();
        BeanUtils.copyProperties(orderBO, orderDO);
        orderMapper.insert(orderDO);
    }

    public abstract void discount(OrderBO orderBO);

    public abstract void weighing(OrderBO orderBO);

    public abstract void supportRefund(OrderBO orderBO);
}

// 实现创建订单流程
@Service
public class CreateOrderFlow extends AbstractCreateOrderFlow {

    @Resource
    private DiscountStrategyExecutor discountStrategyExecutor;
    @Resource
    private ExpressStrategyExecutor expressStrategyExecutor;
    @Resource
    private RefundStrategyExecutor refundStrategyExecutor;

    @Override
    public void discount(OrderBO orderBO) {
        discountStrategyExecutor.discount(orderBO);
    }

    @Override
    public void weighing(OrderBO orderBO) {
        expressStrategyExecutor.weighing(orderBO);
    }

    @Override
    public void supportRefund(OrderBO orderBO) {
        refundStrategyExecutor.supportRefund(orderBO);
    }
}