replaceAll for StringBuilder with regex support?

Question

I've looked in the Java API and some common 3rd party libraries but I'm unable to find a suitable method that will do what String.replaceAll does, except for StringBuilder.

I know that with a little work, it can be done for StringBuffer, but I don't want to go down this road because StringBuffer is slower.

Does anyone know of any 3rd party utilies, or if there is a quick piece of code to implement this functionality?

Answer 1

String.replaceAll is just a convenience method for Matcher.replaceAll. Matcher is the "actual" way to use regex in Java and is allows for a lot more sophisticated use cases.

Moreover, anything that can be done with regex methods on String can be done with similar methods on a Matcher. The beauty is, that Matchers work with more than just Strings: Matchers can be obtained for any CharSequence (an interface, which is implemented by StringBuilder, StringBuffer, String and CharBuffer). So you can simply do:

import java.util.regex.*;

...

StringBuilder sb = new StringBuilder();
sb.append("This works with StringBuffers");
Pattern p = Pattern.compile("\\Buffer\\B");
Matcher m = p.matcher(sb);
System.out.println(m.replaceAll("uilder"));

Will output This works with StringBuilders.

Working demo.

Answer 2

Regex does not modify a mutable CharSequence internally. Regex parses a CharSequence to return a String, where String is the result. StringBuffer is an exception as there is special handling - as for StringBuilder being CharSequence, you have to modify it with a match result.

What you can do instead:

// Class
private static final Pattern MY_PATTERN = Pattern.compile("my|regex");

{ // Method
    StringBuilder builder;
    // ...

    Matcher m = MY_PATTERN.matcher(builder);
    builder.replace(0, builder.length(), m.replaceAll("<b>$0</b>"));
}

View a test code demo!

Answer 3

I don't want to go down this road because StringBuffer is slower.

True, but with the usual premature optimization caveat, and more importantly, modern JVMs use escape analysis to remove the StringBuffer/Vector/HashTable locks in certain cases, so once that optimization happens, the performance will be roughly the same.