Replacing multiple substrings in Java when replacement text overlaps search text

Question

Say you have the following string:

cat dog fish dog fish cat

You want to replace all cats with dogs, all do

Answer 1

String rep = str.replace("cat","§1§").replace("dog","§2§")
                .replace("fish","§3§").replace("§1§","dog")
                .replace("§2§","fish").replace("§3§","cat");

Ugly and inefficient as hell, but works.

---

OK, here's a more elaborate and generic version. I prefer using a regular expression rather than a scanner. That way I can replace arbitrary Strings, not just words (which can be better or worse). Anyway, here goes:

public static String replace(
    final String input, final Map replacements) {

    if (input == null || "".equals(input) || replacements == null 
        || replacements.isEmpty()) {
        return input;
    }
    StringBuilder regexBuilder = new StringBuilder();
    Iterator it = replacements.keySet().iterator();
    regexBuilder.append(Pattern.quote(it.next()));
    while (it.hasNext()) {
        regexBuilder.append('|').append(Pattern.quote(it.next()));
    }
    Matcher matcher = Pattern.compile(regexBuilder.toString()).matcher(input);
    StringBuffer out = new StringBuffer(input.length() + (input.length() / 10));
    while (matcher.find()) {
        matcher.appendReplacement(out, replacements.get(matcher.group()));
    }
    matcher.appendTail(out);
    return out.toString();
}

Test Code:

System.out.println(replace("cat dog fish dog fish cat",
    ImmutableMap.of("cat", "dog", "dog", "fish", "fish", "cat")));

Output:

dog fish cat fish cat dog

Obviously this solution only makes sense for many replacements, otherwise it's a huge overkill.