Java PatternSyntaxException: Illegal repetition on string substitution?

Question

In ${fizz}

{ is an indicator to the regex engine that you are about to start a repetition indicator, like {2,4} which means '2 to 4 times of the previous token'. But {f is illegal, because it has to be followed by a number, so it throws an exception.

You need to escape all regex metacharacters (in this case $, { and }) (try using http://docs.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html#quote(java.lang.String) ) or use a different method that substitutes a string for a string, not a regex for a string.

As pointed out by Patashu, the problem is in replaceFirst(token, replacementValue), that expects a regex in the first argument, not a literal. Change it to replaceFirst(Pattern.quote(token), replacementValue) and you will do alright.

I also changed a bit the first regex, as it goes faster with + instead of * but that's not necessary.

static String substituteAllTokens(Map<String,String> tokensMap, String toInspect) {
    String regex = "\\$\\{([^}]+)\\}";
    Pattern pattern = Pattern.compile(regex);
    Matcher matcher = pattern.matcher(toInspect);
    String result = toInspect;
    while(matcher.find()) {
        String token = matcher.group();     // Ex: ${fizz}
        String tokenKey = matcher.group(1); // Ex: fizz
        String replacementValue = null;

        if(tokensMap.containsKey(tokenKey))
            replacementValue = tokensMap.get(tokenKey);
        else
            throw new RuntimeException("String contained an unsupported token.");

        result = result.replaceFirst(Pattern.quote(token), replacementValue);
    }

    return result;
}

Adapted from Matcher.replaceAll

boolean result = matcher.find();
if (result) {
    StringBuffer sb = new StringBuffer();
    do {
        String tokenKey = matcher.group(1); // Ex: fizz
        String replacement = Matcher.quoteReplacement(tokensMap.get(tokenKey));
        matcher.appendReplacement(sb, replacement);
        result = matcher.find();
    } while (result);
    matcher.appendTail(sb);
    return sb.toString();
}

You can make your RegEx a bit ugly, but this will work

String regex = "\\$[\\{]([^}]*)[\\}]";