title: Does the contents of rt.jar change across different JVM vendors?
body: <p>I've inheirited support for a legacy web app which is directly using the **.internal.** apache xerces classes within the rt.jar. I think the history is that this code (back in java1.4) used to explicitly use xerces and at some point when moving to java5 use of the xerces jar was dropped and those classes were referenced out of rt.jar as the <em>internal</em> equivalents.</p>
  
  <p>I'm trying to understand what the impact of running this project on various web containers will be (e.g Websphere versus Tomcat etc).</p>
  
  <ul>
  <li>Is rt.jar supplied by SUN or the JVM/JRE vendor?</li>
  <li>Do alternate vendors continue to use xerces internally or are there other XML implementations?</li>
  </ul>
  
  <p>At some point (resource permitting) this code will need to be changed to use the standard java APIs, I was want to get a handle on how big a problem this might be.</p>
  
  <p>Thanks, Rob</p>