Can I pick your brains on globally accessing XML resources?

[Chris Corbyn]

In my servlet/JSP app I have a handful of XML files which all sit in /WEB-INF and get accessed from various different places (Filters, Controllers, Beans...). I started out using servletContext.getResourceAsStream() and then using DocumentBuilder to create a new Document object.

The problem with that was that I was:

a) Needing to pass ServletContext around all components which need to read XML files
b) Creating multiple instances of the same Document needlessly.

So with that in mind I set about trying to create a singleton called DocumentFactory which contains ServletContext and a Map of already built Documents.

Early on in the FrontController invoke: DocumentFactory.getInstance().init(servletContext).

/*
 Creates and registers XML resources globally.
 
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation, either version 3 of the License, or
 (at your option) any later version.
 
 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.
 
 You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 */
 
package org.mayo.util;
 
import javax.servlet.ServletContext;
import java.util.Map;
import java.util.HashMap;
import org.w3c.dom.Document;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.InputStream;
 
/**
 * Prevents the overhead of repeatedly opening the same document in XML format
 * by registering created documents for global access.
 * @author Chris Corbyn <[e-mail]>
 */
final public class DocumentFactory {
  
  /** This class as a singleton */
  protected static DocumentFactory instance = null;
  
  /** The current ServletContext where resources can be found */
  protected ServletContext context;
  
  /** The map which holds the registry internally */
  protected Map<String,Document> map;
  
  /**
   * Constructor.
   */
  protected DocumentFactory() {
    setMap(new HashMap<String,Document>());
  }
  
  /**
   * Get the instance of this DocumentFactory.
   * @return DocumentFactory
   */
  public synchronized static DocumentFactory getInstance() {
    if (instance == null) {
      instance = new DocumentFactory();
    }
    return instance;
  }
  
  /**
   * Initialize the DocumentFactory with the ServletContext.
   * @param ServletContext context
   */
  final public void init(ServletContext context) {
    this.setContext(context);
  }
  
  /**
   * Set the Map which holds the registry.
   * @param Map<String,Document> map
   */
  protected void setMap(Map<String,Document> map) {
    this.map = map;
  }
  
  /**
   * Get the Map which holds the registry.
   * @return Map<String,Document>
   */
  protected Map<String,Document> getMap() {
    return map;
  }
  
  /**
   * Set the ServletContext.
   * @param ServletContext context
   */
  protected void setContext(ServletContext context) {
    this.context = context;
  }
  
  /**
   * Get the ServletContext.
   * @return ServletContext
   */
  public ServletContext getContext() {
    return context;
  }
  
  /**
   * Get or create Document from the provided resource path.
   * Null is returned if no resource exists at the given path.
   * @param String path
   * @return Document
   */
  public Document getDocument(String path) {
    Document document = null;
    Map<String,Document> map = getMap();
    if (!map.containsKey(path)) {
      InputStream is = getContext().getResourceAsStream(path);
      if (is == null) {
        return document;
      }
      try {
        DocumentBuilderFactory builder = DocumentBuilderFactory.newInstance();
        document = builder.newDocumentBuilder().parse(is);
        map.put(path, document);
      } catch (Exception e) {
        System.out.println(
            "Document building for path '" + path + "' failed. " + e);
      }
    }
    return map.get(path);
  }
  
  /**
   * Cleanup after this object is no longer needed.
   */
  final public void destroy() {
    getMap().clear();
    instance = null;
  }
  
}

This worked great when I was just working within my servlet. But just recently I tried using it in a JavaBean from a JSP file. It always returns NULL for any document that wasn't used previously. The only difference between trying to use it from a JSP/JavaBean and using it from the servlet is that RequestDispatcher.forward() has been called.

I've pinned the problem down to this line:

      InputStream is = getContext().getResourceAsStream(path);
      if (is == null) {
        return document;
      }

Is there a reason why servletContext (from the Servlet, before forward() was called) will not fetch resources *after* forward() has been called?

Is that a more elegant way to do what I'm trying to do?

Basically I just want a convenience class that can grab me a XML file from WEB-INF and can be accessed from anywhere within the current context.

Thanks for the help if anybody actualy gets to the end of this thread

[Chris Corbyn]

EDIT | Scrap that. Confused
[ September 09, 2007: Message edited by: Chris Corbyn ]

[Chris Corbyn]

Drum roll please.....

<navigation>
...
</naviagtion>

That was the root of my problem. I've got fat fingers. Now suddenly I don't care if I have to put try/catch around every call to DocumentFactory.getDocument() because I'd rather know what the problem is than just having a null return value