EventAdapterRegistry.java

/*
 * Copyright 2004,2004 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.bsf.util.event;

import java.util.Hashtable;

import org.apache.bsf.util.event.generator.EventAdapterGenerator;

/**
 * The <em>EventAdapterRegistry</em> is the registry of event adapters.
 * If a desired adapter is not found, the adapter will be dynamically
 * generated when lookup is attempted. Set the <code>dynamic</code> property
 * to <code>false</code> to disable this feature.
 * <p>
 * This implementation first looks for an adapter in its lookup table
 * and if it doesn't find one looks for a standard implementation of
 * that adapter in the org.apache.bsf.util.event.adapters package with a
 * standard naming convention. The naming convention it assumes is the
 * following: for event listener type <tt>a.b.c.FooListener</tt>,
 * it loads an adapter of type
 * <tt>org.apache.bsf.util.event.adapters.a_b_c_FooAdapter</tt>.
 * If both the loading and the dynamic generation fail, then a
 * <code>null</code> is returned.
 * <p>
 *
 * @author   Sanjiva Weerawarana
 * @author   Matthew J. Duftler
 * @see      EventAdapter
 */
public class EventAdapterRegistry {
  private static Hashtable reg = new Hashtable ();
  private static ClassLoader cl = null;
  private static String adapterPackage = "org.apache.bsf.util.event.adapters";
  private static String adapterSuffix = "Adapter";
  private static boolean dynamic = true;

  public static Class lookup (Class listenerType) {
	String key = listenerType.getName().replace ('.', '_');
	Class adapterClass = (Class) reg.get (key);

	if (adapterClass == null) {
	  String en = key.substring (0, key.lastIndexOf ("Listener"));
	  String cn = adapterPackage + "." + en + adapterSuffix;

	  try {
		// Try to resolve one.
		// adapterClass = (cl != null) ? cl.loadClass (cn) : Class.forName (cn);
		adapterClass = (cl != null) ? cl.loadClass (cn)
                                            : Thread.currentThread().getContextClassLoader().loadClass (cn); // rgf, 2006-01-05

	  } catch (ClassNotFoundException e) {
		if (dynamic) {
		  // Unable to resolve one, try to generate one.
		  adapterClass = // if second argument is set to 'true', then the class file will be stored in the filesystem
			EventAdapterGenerator.makeEventAdapterClass (listenerType, false);
		}
	  }

	  if (adapterClass != null) {
		reg.put (key, adapterClass);
	  }
	}

	return adapterClass;
  }
  public static void register (Class listenerType, Class eventAdapterClass) {
	String key = listenerType.getName().replace('.', '_');
	reg.put (key, eventAdapterClass);
  }
  /**
   * Class loader to use to load event adapter classes.
   */
  public static void setClassLoader (ClassLoader cloader) {
	cl = cloader;
  }
  /**
   * Indicates whether or not to dynamically generate adapters; default is
   * <code>true</code>.
   * <p>
   * If the <code>dynamic</code> property is set to true, and the
   * <code>ClassLoader</code> is unable to resolve an adapter, one will be
   * dynamically generated.
   *
   * @param dynamic whether or not to dynamically generate adapters.
   */
  public static void setDynamic (boolean dynamic) {
	EventAdapterRegistry.dynamic = dynamic;
  }
}