feat(rules): add Java language rules (#645)

Adds Java language rules (coding-style, hooks, patterns, security, testing) following the established language rule conventions.
2026-03-31 06:03:29 +08:00 · 2026-03-20 11:49:21 +08:00
parent a9edf54d2f
commit 9ceb699e9a
5 changed files with 509 additions and 0 deletions
--- a/rules/java/patterns.md
+++ b/rules/java/patterns.md
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+---
+paths:
+  - "**/*.java"
+---
+# Java Patterns
+
+> This file extends [common/patterns.md](../common/patterns.md) with Java-specific content.
+
+## Repository Pattern
+
+Encapsulate data access behind an interface:
+
+```java
+public interface OrderRepository {
+    Optional<Order> findById(Long id);
+    List<Order> findAll();
+    Order save(Order order);
+    void deleteById(Long id);
+}
+```
+
+Concrete implementations handle storage details (JPA, JDBC, in-memory for tests).
+
+## Service Layer
+
+Business logic in service classes; keep controllers and repositories thin:
+
+```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);
+    }
+}
+```
+
+## Constructor Injection
+
+Always use constructor injection — never field injection:
+
+```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 Mapping
+
+Use records for DTOs. Map at service/controller boundaries:
+
+```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());
+    }
+}
+```
+
+## Builder Pattern
+
+Use for objects with many optional parameters:
+
+```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); }
+    }
+}
+```
+
+## Sealed Types for Domain Models
+
+```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 Response Envelope
+
+Consistent API responses:
+
+```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);
+    }
+}
+```
+
+## References
+
+See skill: `springboot-patterns` for Spring Boot architecture patterns.
+See skill: `jpa-patterns` for entity design and query optimization.