apollo-core/src/main/java/com/ctrip/framework/apollo/core/utils/StringUtils.java/StringUtils/isBlank
class StringUtils:  public static boolean isBlank(String str) {
    int strLen;
    if (str == null || (strLen = str.length()) == 0) {
      return true;
    }
    for (int i = 0; i < strLen; i++) {
      if (!Character.isWhitespace(str.charAt(i))) {
        return false;
      }
    }
    return true;
  }