docs: public static String toUnicodeHex(int value) {
  		final StringBuilder builder = new StringBuilder(6);
  
  		builder.append("\\u");
  		String hex = toHex(value);
  		int len = hex.length();
  		if (len < 4) {
  			builder.append("0000", 0, 4 - len);// 不足4位补0
  		}
  		builder.append(hex);
  
  		return builder.toString();
  	}