I am new to exist  and i find some code for importing exist servlet and i have sme code for
retrieving xml  from DB,

import org.xmldb.api.base.*;
import org.xmldb.api.modules.*;
import org.xmldb.api.*;
public class Example1 {
   public static void main(String[] args) throws Exception {
      Collection col = null;
      try {
         String driver = "org.dbxml.client.xmldb.DatabaseImpl";
         Class c = Class.forName(driver);

         Database database = (Database) c.newInstance();
         DatabaseManager.registerDatabase(database);
         col =
            DatabaseManager.getCollection("xmldb:dbxml:///db/addresses");

         String xpath = "/address[@id = 1]";
         XPathQueryService service =
            (XPathQueryService) col.getService("XPathQueryService", "1.0");
         ResourceSet resultSet = service.query(xpath);
         ResourceIterator results = resultSet.getIterator();

         while (results.hasMoreResources()) {
            Resource res = results.nextResource();
            System.out.println((String) res.getContent());
         }
      }
      catch (XMLDBException e) {
         System.err.println("XML:DB Exception occurred " + e.errorCode + " " + 
            e.getMessage());
      }
      finally {
         if (col != null) {
            col.close();
         }}}}
but i want to know how can i update  my xml doc? for updating my doc i must execute some query like this:
for $address in //address
return
    (: Move lname and fname into a new name element :)
    update replace $address with
        <address>
            <name>
                <family>{$address/lname/text()}</family>
                <given>{$address/fname/text()}</given>
            </name>
            {$address/city, $address/email}
        </address>
or this:
<xupdate:modifications version="1.0"
      xmlns:xupdate="http://www.xmldb.org/xupdate">
   <xupdate:update select="/address[@id = 1]/name/last">Herman</xupdate:update>
</xupdate:modifications>