Regular expression extracting a string from url

Question

What I am trying is to extract my account id from a url for other validations. see my URL samples.

http://localhost:8024/accounts/u8m21ercgelj/
http://localhost:8024/accounts/u8m21ercgelj
http://localhost:8024/accounts/u8m21ercgelj/users?

What I required is to extract u8m21ercgelj from the url. I tried it with below code but it fails for the cases like http://localhost:8024/accounts/u8m21ercgelj i.e with out a / at the end.

public  String extractAccountIdFromURL(String url) {
        String accountId = null;
        if ( url.contains("accounts")) {
            Pattern pattern = Pattern.compile("[accounts]/(.*?)/");
            Matcher matcher = pattern.matcher(url);
            while (matcher.find()) {

                accountId = matcher.group(1);
            }
        }
        return accountId;
    }

Can any one help me?

Pshemo · Accepted Answer · 2017-06-30 11:16:37Z

[accounts] doesn't try to find accounts word, but one character which is either a, c (repetition of character doesn't change anything), o, u, n, t or s because [...] is character class. So get rid of those [ and ] and replace them with / since you most likely don't want to accept cases like /specialaccounts/ but only /accounts/.
It looks like you just want to find next non-/ section after /accounts/. In that case you can just use /accounts/([^/]+)
If you are sure that there will be only one /accounts/ section in URL you can (and for more readable code should) change your while to if or even conditional operator. Also there is no need for contains("/accounts/") since it just adds additional traversing over entire string which can be done in find().
It doesn't look like your method is using any data held by your class (any fields) so it could be static.

Demo:

//we should resuse once compiled regex, there is no point in compiling it many times
private static Pattern pattern = Pattern.compile("/accounts/([^/]+)");
public static String extractAccountIdFromURL(String url) {
    Matcher matcher = pattern.matcher(url);
    return matcher.find() ? matcher.group(1) : null;
}

public static void main(java.lang.String[] args) throws Exception {
    String examples = 
            "http://localhost:8024/accounts/u8m21ercgelj/\r\n" + 
            "http://localhost:8024/accounts/u8m21ercgelj\r\n" + 
            "http://localhost:8024/accounts/u8m21ercgelj/users?";
    for (String url : examples.split("\\R")){// split on line separator like `\r\n`
        System.out.println(extractAccountIdFromURL(url));
    }
}

Output:

u8m21ercgelj
u8m21ercgelj
u8m21ercgelj

@ANP I am wondering why you uses while instead of if. Are you assuming that there can be more than one /accounts/ in URL? If not then to not confuse people who will maintain this code you should change it to if. But if url can have many /accounts/ then posted solution may fail for cases like /accounts/accounts/foo (I could try to correct it, so let me know if correction is needed).
Good point, I didn't even look at the [accounts] part of it in my answer. +1 for this answer.
HI All, Only one account will be there in my URL. I will correct the snippet .Thank you All

Daniel Bernsons · Accepted Answer · 2017-06-30 00:25:46Z

3

Your regex is written as such that it is expecting to receive a trailing slash - that's what the slash after the (.*?) means.

You should change this so that it can accept either the trailing slash, or the end of the string. (/|$) should work in this case, meaning your regex would be [accounts]/(.*?)(/|$)

answered Jun 30, 2017 at 0:25

Daniel Bernsons

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