docs(zh-CN): sync Chinese docs with latest upstream changes

2026-03-31 22:23:27 +08:00 · 2026-03-21 12:55:58 +08:00
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+---
+paths:
+  - "**/*.java"
+---
+
+# Java 模式
+
+> 本文档扩展了 [common/patterns.md](../common/patterns.md) 中的内容，增加了 Java 特有的部分。
+
+## 仓储模式
+
+将数据访问封装在接口之后：
+
+```java
+public interface OrderRepository {
+    Optional<Order> findById(Long id);
+    List<Order> findAll();
+    Order save(Order order);
+    void deleteById(Long id);
+}
+```
+
+具体的实现类处理存储细节（JPA、JDBC、用于测试的内存存储等）。
+
+## 服务层
+
+业务逻辑放在服务类中；保持控制器和仓储层的精简：
+
+```java
+public class OrderService {
+    private final OrderRepository orderRepository;
+    private final PaymentGateway paymentGateway;
+
+    public OrderService(OrderRepository orderRepository, PaymentGateway paymentGateway) {
+        this.orderRepository = orderRepository;
+        this.paymentGateway = paymentGateway;
+    }
+
+    public OrderSummary placeOrder(CreateOrderRequest request) {
+        var order = Order.from(request);
+        paymentGateway.charge(order.total());
+        var saved = orderRepository.save(order);
+        return OrderSummary.from(saved);
+    }
+}
+```
+
+## 构造函数注入
+
+始终使用构造函数注入 —— 绝不使用字段注入：
+
+```java
+// GOOD — constructor injection (testable, immutable)
+public class NotificationService {
+    private final EmailSender emailSender;
+
+    public NotificationService(EmailSender emailSender) {
+        this.emailSender = emailSender;
+    }
+}
+
+// BAD — field injection (untestable without reflection, requires framework magic)
+public class NotificationService {
+    @Inject // or @Autowired
+    private EmailSender emailSender;
+}
+```
+
+## DTO 映射
+
+使用记录（record）作为 DTO。在服务层/控制器边界进行映射：
+
+```java
+public record OrderResponse(Long id, String customer, BigDecimal total) {
+    public static OrderResponse from(Order order) {
+        return new OrderResponse(order.getId(), order.getCustomerName(), order.getTotal());
+    }
+}
+```
+
+## 建造者模式
+
+用于具有多个可选参数的对象：
+
+```java
+public class SearchCriteria {
+    private final String query;
+    private final int page;
+    private final int size;
+    private final String sortBy;
+
+    private SearchCriteria(Builder builder) {
+        this.query = builder.query;
+        this.page = builder.page;
+        this.size = builder.size;
+        this.sortBy = builder.sortBy;
+    }
+
+    public static class Builder {
+        private String query = "";
+        private int page = 0;
+        private int size = 20;
+        private String sortBy = "id";
+
+        public Builder query(String query) { this.query = query; return this; }
+        public Builder page(int page) { this.page = page; return this; }
+        public Builder size(int size) { this.size = size; return this; }
+        public Builder sortBy(String sortBy) { this.sortBy = sortBy; return this; }
+        public SearchCriteria build() { return new SearchCriteria(this); }
+    }
+}
+```
+
+## 使用密封类型构建领域模型
+
+```java
+public sealed interface PaymentResult permits PaymentSuccess, PaymentFailure {
+    record PaymentSuccess(String transactionId, BigDecimal amount) implements PaymentResult {}
+    record PaymentFailure(String errorCode, String message) implements PaymentResult {}
+}
+
+// Exhaustive handling (Java 21+)
+String message = switch (result) {
+    case PaymentSuccess s -> "Paid: " + s.transactionId();
+    case PaymentFailure f -> "Failed: " + f.errorCode();
+};
+```
+
+## API 响应封装
+
+统一的 API 响应格式：
+
+```java
+public record ApiResponse<T>(boolean success, T data, String error) {
+    public static <T> ApiResponse<T> ok(T data) {
+        return new ApiResponse<>(true, data, null);
+    }
+    public static <T> ApiResponse<T> error(String message) {
+        return new ApiResponse<>(false, null, message);
+    }
+}
+```
+
+## 参考
+
+有关 Spring Boot 架构模式，请参见技能：`springboot-patterns`。
+有关实体设计和查询优化，请参见技能：`jpa-patterns`。