Question

I need java pattern for string not bounded by a character.

I have a string (as mentioned below), with some curly brackets bounded by single quotes and other curly brackets that are not. I want to replace the curly brackets that are not bounded by single quotes, with another string.

Original string:

this is single-quoted curly '{'something'}' and this is {not} end

Needs to be converted to

this is single-quoted curly '{'something'}' and this is <<not>> end

Notice that the curly brackets { } that are not bounded by single quotes have been replaced with << >>.

However, my code prints (character gets eaten up) the text as

this is single-quoted curly '{'something'}' and this is<<no>> end

when I use the pattern

[^']([{}])

My code is

String regex = "[^']([{}])";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(str);

while (matcher.find()) {
    if ( "{".equals(matcher.group(1)) ) {
        matcher.appendReplacement(strBuffer, "<<");
    } else if ( "}".equals(matcher.group(1))) {
        matcher.appendReplacement(strBuffer, ">>");
    }
}
matcher.appendTail(strBuffer);

Answer 1

This is a clear use case for zero-width assertions. The regex you need isn’t very complex:

String 
   input = "this is single-quoted curly '{'something'}' and this is {not} end",
  output = "this is single-quoted curly '{'something'}' and this is <<not>> end";
System.out.println(input.replaceAll("(?<!')\\{(.*?)\\}(?!')", "<<$1>>")
                        .equals(output));

prints

true