best way of replacing all tags in a string with java

Question

I have a service method that takes a String and then replaces tags in the String with items from a tag library. As follows:

for( MetaDataDTO tag : tagValues )
{
    message = message.replace( tag.getKey(), tag.getText1() );
}

Obviously; this make heaps of new strings and is BAD. But the StringBuilder replace method is cumbersome to use for multiple strings inside one string. How can I make my method more efficient?

It is for use with blocks of text such as:

Dear #firstName#, your application for #applicationType# has been #approvedRejected# sorry.

Where #firstName#, etc are the keys in a meta data database. It is also possible that tags may not be surrounded by hash characters.

Answer 1

Thanks for your help guys. Certainly learned more about java. Here is my solution. It is this way to support different looking tags and tags within tags:

private static String replaceAllTags(String message, Map< String, String > tags)
{
    StringBuilder sb = new StringBuilder( message );
    boolean tagFound = false;
    /**
     * prevent endless circular text replacement loops
     */
    long recurrancyChecker = 5000;

    do
    {
        tagFound = false;
        Iterator it = tags.entrySet().iterator();
        while( it.hasNext() )
        {
            Map.Entry pairs = (Map.Entry) it.next();

            int start = sb.indexOf( pairs.getKey().toString() );

            while( start > -1 && --recurrancyChecker > 0 )
            {
                int length = pairs.getKey().toString().length();
                sb.replace( start, start + length, pairs.getValue().toString() );
                start = sb.indexOf( pairs.getKey().toString() );
                tagFound = true;
            }
        }
    }
    while( tagFound && --recurrancyChecker > 0 );
    return sb.toString();
}

Answer 2

Basically you want to copy the execution of Matcher.replaceAll() like so:

public static String replaceTags(String message, Map<String, String> tags) {
  Pattern p = Pattern.compile("#(\\w+)#");
  Matcher m = p.matcher(message);
  boolean result = m.find();
  if (result) {
    StringBuffer sb = new StringBuffer();
    do {
      m.appendReplacement(sb, tags.containsKey(m.group(1) ? tags.get(m.group(1)) : "");
      result = m.find();
    } while (result);
    m.appendTail(sb);
    message = sb.toString();
  }
  return message;
}

Note: I've made an assumption about the valid tag (namely \w in the regex). You will need to cater this for what's really valid (eg "#([\w_]+)#").

I've also assumed the tags above looks something like:

Map<String, String> tags = new HashMap<String, String>();
tags.add("firstName", "Skippy");

and not:

tags.add("#firstName#", "Skippy");

If the second is correct you'll need to adjust accordingly.

This method makes exactly one pass across the message string so it doesn't get much more efficient than this.