Java Regex to replace only part of string (url)

I want to replace only numeric section of a string. Most of the cases it's either full URL or part of URL, but it can be just a normal string as well.

• /users/12345 becomes /users/XXXXX
• /users/234567/summary becomes /users/XXXXXX/summary
• /api/v1/summary/5678 becomes /api/v1/summary/XXXX
• http://example.com/api/v1/summary/5678/single becomes http://example.com/api/v1/summary/XXXX/single

Notice that I am not replacing 1 from /api/v1

So far, I have only following which seem to work in most of the cases:

input.replaceAll("/[\\d]+$", "/XXXXX").replaceAll("/[\\d]+/", "/XXXXX/");

But this has 2 problems:

• The replacement size doesn't match with the original string length.
• The replacement character is hardcoded.

Is there a better way to do this?

In Java you can use:

str = str.replaceAll("(/|(?!^)\\G)\\d(?=\\d*(?:/|$))", "$1X");

RegEx Demo

RegEx Details:

• \G asserts position at the end of the previous match or the start of the string for the first match.
• (/|(?!^)\\G): Match / or end of the previous match (but not at start) in capture group #1
• \\d: Match a digit
• (?=\\d*(?:/|$)): Ensure that digits are followed by a / or end.
• Replacement: $1X: replace it with capture group #1 followed by X

Not a Java guy here but the idea should be transferrable. Just capture a /, digits and / optionally, count the length of the second group and but it back again.

So

(/)(\d+)(/?)

becomes

$1XYZ$3

See a demo on regex101.com and this answer for a lambda equivalent to e.g. Python or PHP.

First of all you need something like this :

String new_s1 = s3.replaceAll("(\\/)(\\d)+(\\/)?", "$1XXXXX$3");