Replace regex pattern to lowercase in java

I'm trying to replace a url string to lowercase but wanted to keep the certain pattern string as it is.

eg: for input like:

http://BLABLABLA?qUERY=sth&macro1=${MACRO_STR1}&macro2=${macro_str2}

The expected output would be lowercased url but the multiple macros are original:

http://blablabla?query=sth&macro1=${MACRO_STR1}&macro2=${macro_str2}

I was trying to capture the strings using regex but didn't figure out a proper way to do the replacement. Also it seemed using replaceAll() doesn't do the job. Any hint please?

Solution

It looks like you want to change any uppercase character which is not inside ${...} to its lowercase form.

With construct

Matcher matcher = ...

StringBuffer buffer = new StringBuffer();
while (matcher.find()){
    String matchedPart = ...
    ...
    matcher.appendReplacement(buffer, replacement); 
}
matcher.appendTail(buffer);
String result = buffer.toString();

or since Java 9 we can use Matcher#replaceAll(Function<MatchResult,String> replacer) and rewrite it like

String replaced = matcher.replaceAll(m -> {
    String matchedPart = m.group();
    ...
    return replacement;
});

you can dynamically build replacement based on matchedPart.

So you can let your regex first try to match ${...} and later (when ${..} will not be matched because regex cursor will not be placed before it) let it match [A-Z]. While iterating over matches you can decide based on match result (like its length or if it starts with $) if you want to use use as replacement its lowercase form or original form.

BTW regex engine allows us to place in replacement part $x (where x is group id) or ${name} (where name is named group) so we could reuse those parts of match. But if we want to place ${..} as literal in replacement we need to escape \$. To not do it manually we can use Matcher.quoteReplacement.

Demo:

String yourUrlString = "http://BLABLABLA?qUERY=sth&macro1=${MACRO_STR1}&macro2=${macro_str2}";

Pattern p = Pattern.compile("\\$\\{[^}]+\\}|[A-Z]");
Matcher m = p.matcher(yourUrlString);

StringBuffer sb = new StringBuffer();
while(m.find()){
    String match = m.group();
    if (match.length() == 1){
        m.appendReplacement(sb, match.toLowerCase());
    } else {
        m.appendReplacement(sb, Matcher.quoteReplacement(match));
    }
}
m.appendTail(sb);
String replaced = sb.toString();
System.out.println(replaced);

or in Java 9

String replaced = Pattern.compile("\\$\\{[^}]+\\}|[A-Z]")
        .matcher(yourUrlString)
        .replaceAll(m -> {
            String match = m.group();
            if (match.length() == 1)
                return match.toLowerCase();
            else
                return Matcher.quoteReplacement(match); 
        });
System.out.println(replaced);

Output: http://blablabla?query=sth&macro1=${MACRO_STR1}&macro2=${macro_str2}