以下为重构后的代码与说明。重构重点：
- 引入策略模式（Strategy）处理折扣计算，消除魔法数与分支膨胀，提升可扩展性。
- 引入仓储模式（Repository）隔离持久化，使用 PreparedStatement 防止 SQL 注入并改进资源管理。
- 提升可维护性与性能：拆分职责、消除拼接字符串、使用 StringBuilder、封装常量、构造函数注入提升可测试性。
- 遵循 Google Java Style：命名、常量、空指针处理、try-with-resources、早返回等。
代码
文件：app/domain/CustomerType.java
package app.domain;
public enum CustomerType {
VIP,
NEW,
STAFF,
REGULAR;
public static CustomerType fromNullable(String type) {
if (type == null) {
return REGULAR;
}
switch (type.trim().toUpperCase()) {
case "VIP":
return VIP;
case "NEW":
return NEW;
case "STAFF":
return STAFF;
default:
return REGULAR;
}
}
}
文件：app/discount/DiscountStrategy.java
package app.discount;
public interface DiscountStrategy {
double calculate(double amount);
}
文件：app/discount/VipDiscountStrategy.java
package app.discount;
public final class VipDiscountStrategy implements DiscountStrategy {
private static final double BASE_RATE = 0.10;
private static final double HIGH_RATE = 0.15;
private static final double THRESHOLD = 1000.0;
@Override
public double calculate(double amount) {
if (amount <= 0.0) {
return 0.0;
}
return amount * (amount > THRESHOLD ? HIGH_RATE : BASE_RATE);
}
}
文件：app/discount/NewUserDiscountStrategy.java
package app.discount;
public final class NewUserDiscountStrategy implements DiscountStrategy {
private static final double WELCOME_CASH = 20.0;
@Override
public double calculate(double amount) {
return WELCOME_CASH;
}
}
文件：app/discount/StaffDiscountStrategy.java
package app.discount;
public final class StaffDiscountStrategy implements DiscountStrategy {
private static final double RATE = 0.30;
@Override
public double calculate(double amount) {
if (amount <= 0.0) {
return 0.0;
}
return amount * RATE;
}
}
文件：app/discount/NoDiscountStrategy.java
package app.discount;
public final class NoDiscountStrategy implements DiscountStrategy {
@Override
public double calculate(double amount) {
return 0.0;
}
}
文件：app/discount/DiscountStrategyFactory.java
package app.discount;
import app.domain.CustomerType;
public final class DiscountStrategyFactory {
private static final DiscountStrategy VIP = new VipDiscountStrategy();
private static final DiscountStrategy NEW_USER = new NewUserDiscountStrategy();
private static final DiscountStrategy STAFF = new StaffDiscountStrategy();
private static final DiscountStrategy NONE = new NoDiscountStrategy();
private DiscountStrategyFactory() {}
public static DiscountStrategy of(CustomerType type) {
switch (type) {
case VIP:
return VIP;
case NEW:
return NEW_USER;
case STAFF:
return STAFF;
case REGULAR:
default:
return NONE;
}
}
}
文件：app/repository/OrderRepository.java
package app.repository;
import java.sql.SQLException;
public interface OrderRepository {
void save(String userId, String productId, int qty) throws SQLException;
int countByUserId(String userId) throws SQLException;
}
文件：app/repository/JdbcOrderRepository.java
package app.repository;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public final class JdbcOrderRepository implements OrderRepository {
private static final String SQL_INSERT =
"INSERT INTO orders(user_id, product_id, qty) VALUES(?, ?, ?)";
private static final String SQL_COUNT_BY_USER =
"SELECT COUNT(*) AS n FROM orders WHERE user_id = ?";
private final Connection connection;
public JdbcOrderRepository(Connection connection) {
this.connection = connection;
}
@Override
public void save(String userId, String productId, int qty) throws SQLException {
try (PreparedStatement ps = connection.prepareStatement(SQL_INSERT)) {
ps.setString(1, userId);
ps.setString(2, productId);
ps.setInt(3, qty);
ps.executeUpdate();
}
}
@Override
public int countByUserId(String userId) throws SQLException {
try (PreparedStatement ps = connection.prepareStatement(SQL_COUNT_BY_USER)) {
ps.setString(1, userId);
try (ResultSet rs = ps.executeQuery()) {
if (rs.next()) {
return rs.getInt("n");
}
return 0;
}
}
}
}
文件：app/service/OrderService.java
package app.service;
import app.discount.DiscountStrategy;
import app.discount.DiscountStrategyFactory;
import app.domain.CustomerType;
import app.repository.JdbcOrderRepository;
import app.repository.OrderRepository;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;
public final class OrderService {
private static final String STATUS_INVALID = "INVALID";
private static final String STATUS_OK_PREFIX = "OK:";
private static final String STATUS_ERR_PREFIX = "ERR:";
private static final String SUMMARY_SEPARATOR = "|";
private static final String SUMMARY_KV_SEPARATOR = ":";
private static final CustomerType SUMMARY_DEFAULT_TYPE = CustomerType.VIP;
private static final double SUMMARY_DEFAULT_AMOUNT = 120.0;
private final OrderRepository orderRepository;
// 推荐：依赖注入仓储以提升可测试性
public OrderService(OrderRepository orderRepository) {
this.orderRepository = orderRepository;
}
// 兼容原构造方式：从 Connection 创建 JDBC 仓储
public OrderService(Connection connection) {
this.orderRepository = new JdbcOrderRepository(connection);
}
// 策略模式：根据类型委派到对应策略
public double calcDiscount(String type, double amount) {
CustomerType customerType = CustomerType.fromNullable(type);
DiscountStrategy strategy = DiscountStrategyFactory.of(customerType);
return strategy.calculate(amount);
}
// 校验与持久化解耦到仓储；使用 PreparedStatement 防注入
public String saveOrder(String userId, String productId, int qty) {
if (isBlank(userId) || isBlank(productId) || qty <= 0) {
return STATUS_INVALID;
}
try {
orderRepository.save(userId, productId, qty);
int count = orderRepository.countByUserId(userId);
return STATUS_OK_PREFIX + count;
} catch (SQLException ex) {
return STATUS_ERR_PREFIX + ex.getMessage();
}
}
// 渲染职责保留在服务层但使用 StringBuilder 提升性能
public String summary(List ids) {
if (ids == null || ids.isEmpty()) {
return "";
}
StringBuilder sb = new StringBuilder(Math.max(32, ids.size() * 16));
for (String id : ids) {
double discount = calcDiscount(SUMMARY_DEFAULT_TYPE.name(), SUMMARY_DEFAULT_AMOUNT);
sb.append(id)
.append(SUMMARY_KV_SEPARATOR)
.append(discount)
.append(SUMMARY_SEPARATOR);
}
return sb.toString();
}
private static boolean isBlank(String s) {
return s == null || s.trim().isEmpty();
}
}
重构说明
-
遵循设计模式
- 折扣计算采用策略模式（Strategy + 简单工厂）。消除了原先 calcDiscount 中的多层 if-else 与魔法数，支持后续在不改动 OrderService 的情况下扩展新折扣类型，符合开闭原则。
- 持久化采用仓储模式（Repository）。OrderService 仅关注用例编排，不关心 SQL 细节，便于替换实现（如切换到 JPA/ORM）。
-
可维护性增强
- 常量命名替代魔法数（VIP 阈值与费率、固定优惠 20、状态前缀、摘要拼接符等）。
- 职责分离：校验、折扣、持久化、渲染各自独立，单元测试更简单；OrderService 支持依赖注入，易于 mock。
- CustomerType 枚举集中管理类型映射与合法性，避免字符串散落。
-
性能优化
- 使用 StringBuilder 构建 summary 字符串，避免重复拼接产生多余临时对象。
- 使用 PreparedStatement 预编译 SQL，减少解析与防止 SQL 注入；try-with-resources 正确释放资源。
- 折扣策略实例在工厂中复用（静态单例），避免重复创建对象。
-
编码规范（Google Java Style）
- 包命名小写、类与枚举命名使用 UpperCamelCase、常量大写下划线。
- 早返回、空值保护、有限制的行宽与缩进、final/不可变语义（不可变常量、不可变依赖）。
兼容性与扩展建议
- 兼容：OrderService 提供 Connection 构造与原方法签名不变，调用方无需调整即可获得更安全与更稳定的实现。
- 扩展：若需要在 summary 中按不同类型或金额渲染，可新增重载 summary(List ids, CustomerType type, double amount) 或注入渲染策略。
- 错误处理：当前保留原返回字符串语义。若允许，可引入 Result 类型或异常映射器以提供更丰富的错误上下文与可观测性。
