add

backend/src/main/java/com/car/mapper/UserMapper.java

@@ -0,0 +1,20 @@
+package com.car.mapper;
+
+import com.car.entity.User;
+import org.apache.ibatis.annotations.Mapper;
+import org.apache.ibatis.annotations.Param;
+
+import java.util.List;
+
+@Mapper
+public interface UserMapper {
+    User findByUsername(@Param("username") String username);
+
+    User findById(@Param("id") Long id);
+
+    int insert(User user);
+
+    int update(User user);
+
+    List<User> findAll(@Param("keyword") String keyword);
+}