AdaptorFactory.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.hadoop.chukwa.datacollection.agent;


import org.apache.hadoop.chukwa.datacollection.adaptor.Adaptor;
import org.apache.log4j.Logger;

/**
 * Produces new unconfigured adaptors, given the class name of the appender type.
 *  Will try the name both in the default package, and then with 
 *  'org.apache.hadoop.chukwa.datacollection.adaptor' prepended.
 *  
 */
public class AdaptorFactory {
  public static final String PREPENDED_PACKAGE = "org.apache.hadoop.chukwa.datacollection.adaptor.";
  static Logger log = Logger.getLogger(ChukwaAgent.class);

  /**
   * Instantiate an adaptor that can be added by the {@link ChukwaAgent}
   * 
   * @param className the name of the {@link Adaptor} class to instantiate
   * @return an Adaptor of the specified type
   */
  static public Adaptor createAdaptor(String className) {
    Object obj = null;
    try {
      // the following reflection business for type checking is probably
      // unnecessary
      // since it will just throw a ClassCastException on error anyway.
      obj = Class.forName(className).newInstance();
      if (Adaptor.class.isInstance(obj)) {
        return (Adaptor) obj;
      } else
        return null;
    } catch (Exception e1) {
      log.debug("Error instantiating new adaptor by class name, "
              + "attempting again, but with default chukwa package prepended, i.e. "
              + PREPENDED_PACKAGE + className
              + ". " + e1);
      try {
        // if failed, try adding default class prefix
        Object obj2 = Class.forName(
            PREPENDED_PACKAGE + className)
            .newInstance();
        if (Adaptor.class.isInstance(obj2)) {
          log.debug("Succeeded in finding class by adding default adaptor "
              + "namespace prefix to class name profided");
          return (Adaptor) obj2;
        } else
          return null;
      } catch (Exception e2) {
        log.warn("Error instantiating new adaptor "+ className +  " by classname"
            + " and also with \"o.a.h.c.datacollection.adaptor\" prefix added", e2);
        return null;
      }
    }
  }

}