处理注册异常

src/main/java/com/mathgenerator/service/UserService.java

@@ -1,6 +1,7 @@
 package com.mathgenerator.service;
 
 import com.google.gson.Gson;
+import java.util.Objects;
 import com.google.gson.GsonBuilder;
 import com.google.gson.reflect.TypeToken;
 import com.mathgenerator.model.User;
@@ -81,10 +82,22 @@ public class UserService {
      * @return 成功返回true, 否则返回false
      */
     public boolean register(String username, String email, String password) {
-        if (userDatabase.containsKey(username) ||
-                userDatabase.values().stream().anyMatch(u -> u.email().equals(email))) {
+        // 1. 基础校验：防止 null 或空白输入
+        if (username == null || email == null || password == null ||
+                username.trim().isEmpty() || email.trim().isEmpty() || password.trim().isEmpty()) {
+            return false;
+        }
+
+        // 2. 检查用户名或邮箱是否已存在（使用 Objects.equals 安全比较）
+        boolean usernameExists = userDatabase.containsKey(username);
+        boolean emailExists = userDatabase.values().stream()
+                .anyMatch(u -> Objects.equals(u.email(), email));
+
+        if (usernameExists || emailExists) {
             return false; // 用户名或邮箱已存在
         }
+
+        // 3. 创建新用户并保存
         User newUser = new User(username, email, password);
         userDatabase.put(username, newUser);
         saveUsers();