code: public static String getMapperSql(SqlSession session, String fullMapperMethodName, Object... args) {
          if (args == null || args.length == 0) {
              return getNamespaceSql(session, fullMapperMethodName, null);
          }
          String methodName = fullMapperMethodName.substring(fullMapperMethodName.lastIndexOf('.') + 1);
          Class<?> mapperInterface = null;
          try {
              mapperInterface = Class.forName(fullMapperMethodName.substring(0, fullMapperMethodName
                      .lastIndexOf('.')));
              return getMapperSql(session, mapperInterface, methodName, args);
          } catch (ClassNotFoundException e) {
              throw new IllegalArgumentException("参数" + fullMapperMethodName + "无效！");
          }
      }
docs: 通过Mapper方法名获取sql