feat(v1): unify API response, validation, exception handling and tests

src/main/java/com/example/demo/service/UserService.java

@@ -1,5 +1,6 @@
 package com.example.demo.service;
 
+import com.example.demo.exception.ResourceNotFoundException;
 import com.example.demo.model.User;
 import org.springframework.stereotype.Service;
 
@@ -8,23 +9,13 @@ import java.util.List;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.stream.Collectors;
 
-/**
- * 用户服务 - 业务逻辑层
- * 
- * 学习点：
- * - @Service: 标记为服务层组件，自动注册为 Bean
- * - 依赖注入：Controller 通过 @Autowired 注入此服务
- * - 分层架构：Controller -> Service -> Repository
- */
 @Service
 public class UserService {
 
-    // 内存存储（演示用，实际项目用数据库）
     private final List<User> users = new ArrayList<>();
     private final AtomicLong idGenerator = new AtomicLong(1);
 
     public UserService() {
-        // 初始化一些测试数据
         users.add(new User(idGenerator.getAndIncrement(), "张三", "zhangsan@example.com", 25));
         users.add(new User(idGenerator.getAndIncrement(), "李四", "lisi@example.com", 30));
         users.add(new User(idGenerator.getAndIncrement(), "王五", "wangwu@example.com", 28));
@@ -38,7 +29,7 @@ public class UserService {
         return users.stream()
                 .filter(u -> u.getId().equals(id))
                 .findFirst()
-                .orElse(null);
+                .orElseThrow(() -> new ResourceNotFoundException("用户不存在: id=" + id));
     }
 
     public List<User> findByName(String name) {
@@ -47,23 +38,28 @@ public class UserService {
                 .collect(Collectors.toList());
     }
 
-    public User save(User user) {
-        if (user.getId() == null) {
-            user.setId(idGenerator.getAndIncrement());
-            users.add(user);
-        } else {
-            // 更新
-            for (int i = 0; i < users.size(); i++) {
-                if (users.get(i).getId().equals(user.getId())) {
-                    users.set(i, user);
-                    break;
-                }
-            }
-        }
+    public User create(User user) {
+        user.setId(idGenerator.getAndIncrement());
+        users.add(user);
         return user;
     }
 
-    public void delete(Long id) {
-        users.removeIf(u -> u.getId().equals(id));
+    public User update(Long id, User user) {
+        findById(id);
+        user.setId(id);
+        for (int i = 0; i < users.size(); i++) {
+            if (users.get(i).getId().equals(id)) {
+                users.set(i, user);
+                return user;
+            }
+        }
+        throw new ResourceNotFoundException("用户不存在: id=" + id);
     }
-}
+
+    public void delete(Long id) {
+        boolean removed = users.removeIf(u -> u.getId().equals(id));
+        if (!removed) {
+            throw new ResourceNotFoundException("用户不存在: id=" + id);
+        }
+    }
+}