Regex replace all match with symbol with same length

Question

My application currently logs sensitive information, which I need to mask.

A current log line looks like:

<Unable to fetch user info combination of dob=[20001231] and pan=[ABCD1234Z]

But should be changed to something like

<Unable to fetch user info combination of dob=******** and pan=********>

I tried to mask this using

str.replaceAll("\\[.*?\\]", "*")

but it changed it to:

<Unable to fetch user info combination of dob=* and pan=*>

How can I preserve the quantity of characters when masking characters between square brackets?

Answer 1

It can be done in one line:

str = str.replaceAll("(?=[^\\[]+]).", "*");

See live regex demo and/or live Java demo.

This preserves the square brackets. To omit them from the result, use this:

str = str.replaceAll("\\[?(?=[^\\[]*]).]?", "*");

See live Java demo.

Answer 2

You can manipulate Pattern and Matcher to do this. For example like this:

String log = "<Unable to fetch user info combination of dob=[20001231] and pan=[ABCD1234Z]>";
Pattern pattern = Pattern.compile("\\[.*?\\]");
Matcher  matcher = pattern.matcher(log);
String match="";
while (matcher.find()){
    match=matcher.group();
    char[] symbols = new char[match.length()];
    Arrays.fill(symbols, '*');
    log = log.replace(match, new String(symbols));  
}
System.out.println(log);   

Output:

<Unable to fetch user info combination of dob=******** and pan=********>

There might be some performance issue in the example above, but at least you got the idea.