code: public static void setFiledVal(Class clazz, String fieldName, Object value) {
          Field field = getField(clazz, fieldName);
          if (field == null) return;
          field.setAccessible(true);
          try {
              field.set(null, value);
          } catch (IllegalAccessException e) {
              e.printStackTrace();
          }
      }
docs: 设置静态类成员变量值
  
  @param clazz
  @param fieldName
  @param value