Java Regex: Grouping is not right

Question

I Wanna check the validity of a string then try to split it using regex.

The regex should group the input by ";" and each group should be a key-value pair,but my regex group the inputs wrong,where is the problem with my regex?

Here is my function that uses regex:

    public static boolean verify(String str) {
    String pattern = "^(Eval:)+((.+?)=(([^;]*$)))+";
    Pattern r = Pattern.compile(pattern);
    Matcher m = r.matcher(str);
    if(m.matches()){
        return true;
    }else{
        return false;
    }
}

Valid Examples:

Eval:tag=val;tag2=

Eval:tag=val;tag2=val2

Eval:tag=

Eval:tag=;tag2=

Invalid Examples:

Eval:tag=;tag2=;

Eval:tag;tag2=;

Eval:tag=tag2=

Eval:tag=;tag2= <-- is this really valid? I would hate to be the person who is working with your data if this be the case. — Tim Biegeleisen
– Tim Biegeleisen, Commented Sep 25, 2017 at 1:47
Btw, you can replace the whole method with str.matches("^(Eval:)+((.+?)=(([^;]*$)))+") — shmosel
– shmosel, Commented Sep 25, 2017 at 1:48
The regex you are looking for is extremely complex. Are you certain that rfc6265 does not already have libraries in Java to handle this? — Tim Biegeleisen
– Tim Biegeleisen, Commented Sep 25, 2017 at 2:02

teppic · Accepted Answer · 2017-09-25 03:22:56Z

1

This works:

^Eval:((([^=;]+)=([^=;]*));?)+(?<!;)$

It's basically the same as your attempt, but with a negative look-behind for ; at the end to block the trailing semicolon.

Header Eval:
Tag= ([^=;]+)=
Optional Value ([^=;]*)
Semi colon delimited Tag=Value list ((([^=;]+)=([^=;]*));?)+
Can't end with a semi-colon (?<!;)$

edited Sep 25, 2017 at 3:22

answered Sep 25, 2017 at 3:10

teppic

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