使用正则表达式解析正则表达式

Question

I have pattern [a-z0-9]{9}|[a-z0-9]{11}

Here, I have to parse that regex to get 9 and 11 for future message that "U have to input 9 or 11 symbols"

Also I have regex like

[a-z0-9]{9}

[a-z0-9]{9,}

[a-z0-9]{9,11}

I need to write some method,which can parse all that strings to get Number of available symbols.

I did

Pattern.compile(".*\\\\{(\\\\d+)(,?)(\\\\d*)\\\\}(\\\\|.*\\\\{(\\\\d+)\\\\})?");

It find only last number in my first pattern. But other don't recognize.

How to check all strings?

Upd: I can not understand, but in Java first pattern from answer \\{(\\d+)(?:,(\\d*))?\\} doesn't match but find 3 my strings. But first and the longest string it doesn't find.

What is different between matches and find? And why that pattern can find matches in web, but can't in Java? And sometimes I do matcher.find(); // return 2 matcher.group(1); // No match found exception matcher.find(); // return 2 matcher.group(1); // No match found exception

Answer 1

This regex should work for you: [^\\\\](?:\\\\\\\\)*\\{(\\d+)(?:,(\\d*))?\\} .

Part [^\\\\](?:\\\\\\\\)* addresses the case of slash escaping.

Below is Java code example:

public static void main(String[] args) {
    Pattern p = Pattern.compile("[^\\\\](?:\\\\\\\\)*\\{(\\d+)(?:,(\\d*))?\\}");
    String testInput = "[a-z0-9]{1,2}|[a-z0-9]{3,}|[a-z0-9]{4}";
    Matcher matcher = p.matcher(testInput);
    while (matcher.find()){
        System.out.println("Next matching found:");
        if(matcher.group(2) == null){
            System.out.println("Strict: " + matcher.group(1));
        }else {
            System.out.println("Min: "
                    + matcher.group(1)
                    + ", Max: "
                    + ("".equals(matcher.group(2)) ? "Infinte" : matcher.group(2)));
        }
    }
}

Output:

Next matching found:
Min: 1, Max: 2
Next matching found:
Min: 3, Max: Infinte
Next matching found:
Strict: 4