import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Test6 {

    public static void main(String[] args) {
        String str = "222.96.22.5";
        
        // 方法 1（推荐）
        Pattern pattern = Pattern.compile("(?<=^|\\.)(?:(\\d{2})|(\\d))(?!\\d)");
        Matcher matcher = pattern.matcher(str);
        StringBuffer sb = new StringBuffer();
        while (matcher.find()) {
            if (matcher.start(1) > 0) {
                matcher.appendReplacement(sb, "0$1");
            } else if (matcher.start(2) > 0) {
                matcher.appendReplacement(sb, "00$2");
            }
        }
        matcher.appendTail(sb);
        System.out.println(sb.toString());
        
        // 方法 2
        str = str.replaceAll("(?<=^|\\.)(\\d{1,2})(?!\\d)", "0$1")
                 .replaceAll("(?<=^|\\.)(\\d{2})(?!\\d)", "0$1");
        System.out.println(str);
    }
}