Question

Given a string with replacement keys in it, how can I most efficiently replace these keys with runtime values, using Java? I need to do this often, fast, and on reasonably long strings (say, on average, 1-2kb). The form of the keys is my choice, since I’m providing the templates here too.

Here’s an example (please don’t get hung up on it being XML; I want to do this, if possible, cheaper than using XSL or DOM operations). I’d want to replace all @[^@]*?@ patterns in this with property values from bean properties, true Property properties, and some other sources. The key here is fast. Any ideas?

<?xml version='1.0' encoding='utf-8'?>  <envelope version='2.3'>    <delivery_instructions>      <delivery_channel>       <channel_type>@CHANNEL_TYPE@</channel_type>     </delivery_channel>      <delivery_envelope>       <chan_delivery_envelope>     <queue_name>@ADDRESS@</queue_name>       </chan_delivery_envelope>     </delivery_envelope>    </delivery_instructions>    <composition_instructions>     <mime_part content_type='application/xml'>       <content><external_uri>@URI@</external_uri></content>     </mime_part>   </composition_instructions>  </envelope> 

The naive implementation is to use String.replaceAll() but I can’t help but think that’s less than ideal. If I can avoid adding new third-party dependencies, so much the better.

Answer 1

The appendReplacement method in Matcher looks like it might be useful, although I can’t vouch for its speed.

Here’s the sample code from the Javadoc:

Pattern p = Pattern.compile('cat'); Matcher m = p.matcher('one cat two cats in the yard'); StringBuffer sb = new StringBuffer(); while (m.find()) {     m.appendReplacement(sb, 'dog'); } m.appendTail(sb); System.out.println(sb.toString()); 

EDIT: If this is as complicated as it gets, you could probably implement your own state machine fairly easily. You’d pretty much be doing what appendReplacement is already doing, although a specialized implementation might be faster.