LAFFactory.java

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 *
 * Pentaho Data Integration
 *
 * Copyright (C) 2002-2013 by Pentaho : http://www.pentaho.com
 *
 *******************************************************************************
 *
 * 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
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package org.pentaho.di.laf;

import java.util.HashMap;

import org.pentaho.di.i18n.MessageHandler;

/**
 * the LAFFactory provides a mechanism whereby @see Handler s can be dynamically replaced to enable user driven
 * replacement of dynamic resolvers whether ImageHandlers, MessageHandlers, or other elements of Look and Feel.
 *
 * @author dhushon
 *
 */
public class LAFFactory {

  static Class<? extends Handler> _defMessageHandler = org.pentaho.di.i18n.LAFMessageHandler.class;
  static Class<? extends Handler> _defPropertyHandler = org.pentaho.di.laf.OverlayPropertyHandler.class;

  // Registry of Delegates that know how to load the appropriate handlers
  private static HashMap<Class<? extends Handler>, LAFDelegate<? extends Handler>> delegateRegistry =
    new HashMap<Class<? extends Handler>, LAFDelegate<? extends Handler>>();

  // Map an abstract ClassName (by String) to an implementing Class
  private static HashMap<String, Class<? extends Handler>> handlerRef =
    new HashMap<String, Class<? extends Handler>>();
  static {
    // handlers.put(MessageHandler.class.), (Handler)_defMessageHandler.newInstance());
    handlerRef.put( MessageHandler.class.getName(), _defMessageHandler );
    handlerRef.put( PropertyHandler.class.getName(), _defPropertyHandler );
  }

  @SuppressWarnings( "unchecked" )
  protected static synchronized <V extends Handler> LAFDelegate<V> getDelegate( Class<V> handler ) {
    LAFDelegate<V> l = (LAFDelegate<V>) delegateRegistry.get( handler );
    if ( l == null ) {
      // TODO: check subclasses
      Class<V> defaultHandler = (Class<V>) handlerRef.get( handler.getName() );
      l = new LAFDelegate<V>( handler, defaultHandler );
      delegateRegistry.put( handler, l );
    }
    return l;
  }

  /**
   * Return an instance of the class that has been designated as the implementor of the requested Interface, will return
   * null if there is no implementor.
   *
   * @param <V>
   * @param handler
   * @return
   */
  public static <V extends Handler> V getHandler( Class<V> handler ) {
    LAFDelegate<V> l = getDelegate( handler );
    return l.getHandler();
  }

}