src/org/apache/bsf/util/ObjectRegistry.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;

import java.util.Hashtable;

/**
 * The <em>ObjectRegistry</em> is used to do name-to-object reference lookups.
 * If an <em>ObjectRegistry</em> is passed as a constructor argument, then this
 * <em>ObjectRegistry</em> will be a cascading registry: when a lookup is
 * invoked, it will first look in its own table for a name, and if it's not
 * there, it will cascade to the parent <em>ObjectRegistry</em>.
 * All registration is always local. [??]
 * 
 * @author   Sanjiva Weerawarana
 * @author   Matthew J. Duftler
 */
public class ObjectRegistry {
  Hashtable      reg    = new Hashtable ();
  ObjectRegistry parent = null;

  public ObjectRegistry () {
  }
  public ObjectRegistry (ObjectRegistry parent) {
	this.parent = parent;
  }
  // lookup an object: cascade up if needed
  public Object lookup (String name) throws IllegalArgumentException {
	Object obj = reg.get (name);

	if (obj == null && parent != null) {
	  obj = parent.lookup (name);
	}

	if (obj == null) {
	  throw new IllegalArgumentException ("object '" + name + "' not in registry");
	}

	return obj;
  }
  // register an object
  public void register (String name, Object obj) {
	reg.put (name, obj);
  }
  // unregister an object (silent if unknown name)
  public void unregister (String name) {
	reg.remove (name);
  }
}