code: private void checkToken(String s) {
  		for (int i = 0; i < s.length(); i++) {
  			char ch = s.charAt(i);
  			if (!TOKEN.get(ch)) {
  				throw new IllegalArgumentException("Invalid token character '" + ch + "' in token \"" + s + "\"");
  			}
  		}
  	}
docs: Checks the given token string for illegal characters, as defined in RFC 2616, section 2.2.
  @throws IllegalArgumentException in case of illegal characters
  @see <a href="https://tools.ietf.org/html/rfc2616#section-2.2">HTTP 1.1, section 2.2</a>