code: protected Collection<Field> getSessionFields(Class<?> clazz) {
          Collection<Field> fields = fieldMap.get(clazz);
          if (fields == null) {
              fields = ReflectUtil.getFields(clazz);
              Iterator<Field> iterator = fields.iterator();
              while (iterator.hasNext()) {
                  Field field = iterator.next();
                  if (!field.isAnnotationPresent(Session.class)) {
                      iterator.remove();
                  }
              }
              fieldMap.put(clazz, fields);
          }
          return fields;
      }
docs: Returns all fields with Session annotation for a class.
  @param clazz Class.
  @return All fields with Session annotation for a class.