NullPointerException from GetResource() call

Hello,

I searched around these mail archives for posts about
NullPointerExceptions, but I wasn't able to find a solution to my problem
below.  Any advice on how to find a solution would be greatly appreciated.

Here is the message I receive from XMLDBException.GetMessage() call:
 Failed to execute command 'GetResource' on server:
http://localhost:8080/xindice/, message: java.lang.Exception:
java.lang.NullPointerException

I'm using the following versions:
 Xindice: 1.1b4
 Tomcat:  5.0.25
 JVM:     1.4.2_01-b06
 OS:      Linux 2.4.18-14

Here is the sequence that causes this error:
 1.  User updates web form and post to my Servlet
 2.  My servlet does a GetResource() to pull the current version of the
XML data.
 3.  My servlet updates the XML data.
 4.  My servlet does a createResource() and storeResource() to update the
XML data back into Xindice.
 5.  ... later user repeats steps 1 to 4.

Each time the user updates the form to Add/Update/Delete data.  About one
in every ten cycles the NullPointException will be thrown when I perform
the GetResource().  I tried having my code sleep for 2 seconds after the
first GetResource() failed and then retry to call, but that only solves
the problem once in awhile.

My XML data is usually somewhere in the 5 - 200 Kb range.  A posting said
a storeResource should take about 3ms/KB, so I thought sleeping for 2
seconds should have been enough delay for any of my files.

Thanks for the help,
-Nate

Here is some code snippets.  I create a singleton that owns this class, so
there is only one of these (currently).  Therefore EnableDatabase() is
only executed once the first time that object is used.


/*
 * XindiceGateway.java
 *
 * Created on August 25, 2004, 9:31 PM
 */

package org.test.gateways;

import java.util.Vector;
import org.apache.log4j.Logger;
import org.apache.xindice.client.xmldb.services.CollectionManager;
import org.apache.xindice.xml.dom.DOMParser;
import org.test.commands.DatabaseCommand;
import org.w3c.dom.Node;

import org.xmldb.api.base.*;
import org.xmldb.api.modules.*;
import org.xmldb.api.*;


/**
 *
 * @author  stoddarn
 */
public class XindiceGateway
{
  // Log4j Logger
  static Logger m_logger = Logger.getLogger(XindiceGateway.class);

  // Static mutex on the database
  static String m_databaseMutex = new String ("mutex");

  private boolean m_databaseRegistered = false;

  // Static XINDICE data
  private static String XINDICE_DB_DRIVER = new
String("org.apache.xindice.client.xmldb.DatabaseImpl");

  // The root to the database
  private static String XINDICE_DB_ROOT = new
String("xmldb:xindice://localhost:8080/db/");   // LINUX Penguin

  // Xindice API version
  private static String XINDICE_API_VERSION = new String ("1.0");

  // Xindice file setup
  private static String XINDICE_COMPRESSION_ENABLED = new String ("true");
  private static String XINDICE_FILTER_CLASS = new
String("org.apache.xindice.core.filer.BTreeFiler");


/** Make sure the database is registered */
protected void EnableDatabase ()
       throws ClassNotFoundException, InstantiationException,
IllegalAccessException,
               XMLDBException
{
  // If the database isn't already registered
  if (! m_databaseRegistered)
  {
    m_databaseRegistered = true;

    m_logger.info("Enabling Xindice Database");

    Class c = Class.forName(XINDICE_DB_DRIVER);

    Database database = (Database) c.newInstance();
    DatabaseManager.registerDatabase(database);

    // Update the CodeReview paths
    boolean baseCollectionFound = false;
    boolean projectListingsCollectionFound = false;
    boolean projectListingsFileFound = false;
    boolean projectsCollectionFound = false;

    // Check for "test"
    String [] baseCollection = ListCollections("");
    // Loop to see if there is a match
    for (int bcItr = 0; !baseCollectionFound && bcItr <
baseCollection.length; bcItr++)
    {

      if (baseCollection[bcItr].equals("test"))
      {
        baseCollectionFound = true;
      }
    }
    // If the baseCollection is missing add it
    if (!baseCollectionFound)
    {
      m_logger.info("Create codereview collection required");
      CreateCollection("", "test");
    }

    // Check for "projectlistings" and "projects"
    String [] testCollection = ListCollections("test");
    // Loop to see if there is a match for project listings and projects
    for (int crItr = 0; (!projectListingsCollectionFound ||
!projectsCollectionFound) && crItr < testCollection.length; crItr++)
    {
      if (testCollection[crItr].equals("projectlistings"))
      {
        projectListingsCollectionFound = true;
      }
      else if (testCollection[crItr].equals("projects"))
      {
        projectsCollectionFound = true;
      }
    }
    // If the baseCollection is missing add it
    if (!projectListingsCollectionFound)
    {
      m_logger.info("Create projectlistings collection required");
      CreateCollection("test", "projectlistings");
    }

    // If the baseCollection is missing add it
    if (!projectsCollectionFound)
    {
      m_logger.info("Create projects collection required");
      CreateCollection("test", "projects");
    }
  }
}


/** Add documents to a collection */
public void AddDocument(String collectionName, String documentName, String
documentXML)
{
  Collection col = null;

  String[] documents = null;
  synchronized (m_databaseMutex)
  {
    try {
      EnableDatabase();

      // Get the collection
      col = DatabaseManager.getCollection(XINDICE_DB_ROOT + collectionName);

      XMLResource document = (XMLResource)
col.createResource(documentName, "XMLResource");
      document.setContent(documentXML);
      col.storeResource(document);
    }
    catch (XMLDBException e) {
      m_logger.error("AddDocument: XML:DB Exception occured: " +
e.getMessage());
    }
    catch (Exception e) {
      m_logger.error("AddDocument: Other Exception occured");
    }
    finally
    {
      // If the colletion was created, then make sure we close it
      if (col != null)
      {
        try
        {
          // Close the collection
          col.close();
        }
        catch (Exception e)
        {
          // Catch any issues with closing the exception.
          m_logger.error("Unable to close collection.  " + e.getMessage());
        }
      }
    }
  }
}


/** Read a document */
public String ReadDocument(String collectionName, String documentName)
{
  Collection col = null;
  String returnString = null;

  synchronized (m_databaseMutex)
  {
    try {
      EnableDatabase();

      col = DatabaseManager.getCollection(XINDICE_DB_ROOT + collectionName);

      XMLResource document = (XMLResource) col.getResource(documentName);

      returnString = (String)document.getContent();
    }
    catch (XMLDBException e) {
      m_logger.error("ReadDocument (" + collectionName + "/" +
documentName + "):  " + e.getMessage());
    }
    catch (Exception e) {
      m_logger.error("ReadDocument (" + collectionName + "/" +
documentName + "):  " + e.getMessage());
    }
    finally
    {
      // If the colletion was created, then make sure we close it
      if (col != null)
      {
        try
        {
          // Close the collection
          col.close();
        }
        catch (Exception e)
        {
          // Catch any issues with closing the exception.
          m_logger.error("Unable to close collection.  " + e.getMessage());
        }
      }
    }
  }

   return (returnString);
 }



  /** Creates a new instance of XindiceGateway */
  public XindiceGateway()
  {
  }

}