Question

I need a regular expression that will replace odd number of slashes with even number of slashes while leave the even number of slashes intact.

For Example:

• Test/123 –> Test//123
• Test//123 –> Test//123
• Test///123 –> Test//////123

Answer 1

  Pattern p = Pattern.compile("(?<!/)/(//)*(?!/)");
  Matcher m = p.matcher(inputString);
  String outputStr = m.replaceAll("$0$0");

• (?<!/) makes sure there are no slashes right before the match;
• /(//)* matches an odd number of slashes;
• (?!/) makes sure there are no slashes right after the match.

The replacement string is $0$0, which doubles up the matched slashes.

I’ve tested this on your inputs, and it works exactly as per your spec.