验证空变量正则表达式

Question

I have a regex scipt which validate a field variable for some extensions (pdf, doc, jpeg, jpg, and png). But sometimes, this field can be empty. I see on some topics that "^$" can solved my problem. I try a lot of combinaisons (cause I do not know regex) but it doesn't work. I give you my current code:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

String REGEX = "([^#@]+(\\.(?i)(pdf|doc|docx|jpeg|mp3|jpg|png))\$)";
Pattern pattern = Pattern.compile(REGEX);
Matcher matcher = pattern.matcher(field_Fichier1.getFileName());
return matcher.matches();

Thanks for your help

Answer 1

// Mine = doesn't work for empty field
//String REGEX = "([^#@]+(\\.(?i)(pdf|doc|docx|jpeg|mp3|jpg|png))\$)";

// Anubhava = doesn't work for empty field
//String REGEX = "([^#@]+(\\.(?i)(pdf|doc|docx|jpeg|mp3|jpg|png)))?";
//        or
//String REGEX = "([^#@]+(\\.(?i)(pdf|doc|docx|jpeg|mp3|jpg|png)))";

// Bohemian = can't be run = error: "Groovy:illegal string body character after dollar sign;"
String REGEX = "^$|([^#@]+(\\.(?i)(pdf|doc|docx|jpeg|mp3|jpg|png))\$)";

Answer 2

Why do you have \\$ in your regex. You can just make your whole regex optional to allow for empty string match:

String REGEX = "([^#@]+(\\.(?i)(pdf|doc|docx|jpeg|mp3|jpg|png)))?";

? in the end will make whole regex match optional thus allowing it match "" as well.

Answer 3

Just add ^$| to the front of your regex:

String REGEX = "^$|([^#@]+(\\.(?i)(pdf|doc|docx|jpeg|mp3|jpg|png))\$)";

Note that I haven't checked your existing regex - I'm assuming it works for non-blank input.