diff --git a/src/main/java/xyz/zhouxy/jdbc/JdbcOperationSupport.java b/src/main/java/xyz/zhouxy/jdbc/JdbcOperationSupport.java
index 5e1adab..1b73525 100644
--- a/src/main/java/xyz/zhouxy/jdbc/JdbcOperationSupport.java
+++ b/src/main/java/xyz/zhouxy/jdbc/JdbcOperationSupport.java
@@ -252,7 +252,7 @@ class JdbcOperationSupport {
         try (PreparedStatement stmt = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS)) {
             fillStatement(stmt, params);
             stmt.executeUpdate();
-            try (ResultSet generatedKeys = stmt.getGeneratedKeys();) {
+            try (ResultSet generatedKeys = stmt.getGeneratedKeys()) {
                 int rowNumber = 0;
                 while (generatedKeys.next()) {
                     T e = rowMapper.mapRow(generatedKeys, rowNumber++);
@@ -399,12 +399,13 @@ class JdbcOperationSupport {
     }
 
     /**
-     * 执行查询，将查询结果的第一行数据按照指定逻辑进行处理，返回 {@link Optional}
+     * 执行查询，将查询结果的第一行数据按照指定逻辑进行处理，返回映射结果
      *
      * @param conn      数据库连接
      * @param sql       SQL
      * @param params    参数
      * @param rowMapper 行数据映射逻辑
+     * @return 映射结果。如果查询结果为空，则返回 null
      */
     private static <T> T queryFirstInternal(@Nonnull Connection conn,
                                             @Nonnull String sql,
diff --git a/src/main/java/xyz/zhouxy/jdbc/RowMapper.java b/src/main/java/xyz/zhouxy/jdbc/RowMapper.java
index 10e8fd5..55b93a1 100644
--- a/src/main/java/xyz/zhouxy/jdbc/RowMapper.java
+++ b/src/main/java/xyz/zhouxy/jdbc/RowMapper.java
@@ -37,7 +37,7 @@ public interface RowMapper<T> {
     T mapRow(ResultSet rs, int rowNumber) throws SQLException;
 
     /** 每一行数据转换为 {@link HashMap} */
-    public static final RowMapper<Map<String, Object>> HASH_MAP_MAPPER = (rs, rowNumber) -> {
+    RowMapper<Map<String, Object>> HASH_MAP_MAPPER = (rs, rowNumber) -> {
         Map<String, Object> result = new HashMap<>();
         ResultSetMetaData metaData = rs.getMetaData();
         int columnCount = metaData.getColumnCount();
@@ -49,12 +49,12 @@ public interface RowMapper<T> {
     };
 
     /** 默认实现的将 {@link ResultSet} 转换为 Java Bean 的 {@link RowMapper}。 */
-    public static <T> RowMapper<T> beanRowMapper(Class<T> beanType) throws SQLException {
+    static <T> RowMapper<T> beanRowMapper(Class<T> beanType) throws SQLException {
         return DefaultBeanRowMapper.of(beanType);
     }
 
     /** 默认实现的将 {@link ResultSet} 转换为 Java Bean 的 {@link RowMapper}。 */
-    public static <T> RowMapper<T> beanRowMapper(Class<T> beanType, Map<String, String> propertyColMap)
+    static <T> RowMapper<T> beanRowMapper(Class<T> beanType, Map<String, String> propertyColMap)
             throws SQLException {
         return DefaultBeanRowMapper.of(beanType, propertyColMap);
     }