ReplicaSelectorFactory.java

/**
 *  Copyright 2007-2008 University Of Southern California
 *
 *  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 edu.isi.pegasus.planner.selector.replica;

import edu.isi.pegasus.planner.selector.ReplicaSelector;

import edu.isi.pegasus.planner.common.PegasusProperties;

import edu.isi.pegasus.common.util.DynamicLoader;


/**
 * A factory class to load the appropriate type of Replica Selector, as
 * specified by the user at runtime in properties. Each invocation of the
 * factory results in a ReplicaSelector being instantiated.
 *
 * @author Karan Vahi
 * @version $Revision$
 */

public class ReplicaSelectorFactory {

    /**
     * The default package where the all the implementing classes provided with
     * the VDS reside.
     */
    public static final String DEFAULT_PACKAGE_NAME =
                                        "edu.isi.pegasus.planner.selector.replica";

    /**
     * The name of the class in the DEFAULT package, that corresponds to the
     * default replica selector.
     */
    public static final String DEFAULT_REPLICA_SELECTOR = "Default";

    /**
     * A no hassle factory method that loads the replica selector specified
     * in the properties. The properties are obtained from the property
     * singleton. A default replica selector is loaded if property is not
     * specified in the properties.
     *
     * @return the instance of the class implementing this interface.
     *
     * @exception ReplicaSelectorFactoryException that chains any error that
     *            might occur during the instantiation
     *
     * @see #DEFAULT_PACKAGE_NAME
     * @see #DEFAULT_REPLICA_SELECTOR
     */
    public static ReplicaSelector loadInstance()
                                      throws ReplicaSelectorFactoryException {


        return loadInstance( PegasusProperties.getInstance());
    }


    /**
     * Loads the implementing class corresponding to the mode specified by the user
     * at runtime in the properties file. A default replica selector is loaded
     * if property is not specified in the properties.
     *
     * @param properties the <code>PegasusProperties</code> object containing all
     *                   the properties required by Pegasus.
     *
     * @return the instance of the class implementing this interface.
     *
     * @exception ReplicaSelectorFactoryException that chains any error that
     *            might occur during the instantiation
     *
     * @see #DEFAULT_PACKAGE_NAME
     * @see #DEFAULT_REPLICA_SELECTOR
     */
    public static ReplicaSelector loadInstance(PegasusProperties properties)
                                      throws ReplicaSelectorFactoryException {

        String className = null;
        //sanity check
        try{
            if(properties == null){
                throw new RuntimeException("Invalid properties passed");
            }

            //figure out the implementing class
            //that needs to be instantiated.
            className = properties.getReplicaSelector();
            className = (className == null || className.trim().length() < 2)?
                         DEFAULT_REPLICA_SELECTOR:
                         className;
        }
        catch( Exception e ){
            throw new
            ReplicaSelectorFactoryException( "Instantiating ReplicaSelector ",e );

        }

        return loadInstance(properties,className);
    }


    /**
     * Loads the implementing class corresponding to the class. If the package
     * name is not specified with the class, then class is assumed to be
     * in the DEFAULT_PACKAGE. The properties object passed should not be null.
     *
     * @param className  the name of the class that implements the mode. It is the
     *                   name of the class, not the complete name with package. That
     *                   is added by itself.
     * @param properties the <code>PegasusProperties</code> object containing all
     *                   the properties required by Pegasus.
     *
     * @return the instance of the class implementing this interface.
     *
     * @exception ReplicaSelectorFactoryException that chains any error that
     *            might occur during the instantiation
     *
     * @see #DEFAULT_PACKAGE_NAME
     */
    public static ReplicaSelector loadInstance(PegasusProperties properties,
                                       String className)
                                       throws ReplicaSelectorFactoryException{


        ReplicaSelector rs = null;

        try{
            //some sanity checks
            if(properties == null){
                throw new RuntimeException("Invalid properties passed");
            }
            if(className == null){
                throw new RuntimeException("Invalid className specified");
            }

            //prepend the package name
            className = (className.indexOf('.') == -1)?
                        //pick up from the default package
                        DEFAULT_PACKAGE_NAME + "." + className:
                        //load directly
                        className;

            //try loading the class dynamically
            DynamicLoader dl = new DynamicLoader(className);
            Object argList[] = new Object[1];
            argList[0] = properties;
            rs = (ReplicaSelector) dl.instantiate(argList);
        }
        catch(Exception e){
            //chain the exception caught into the appropriate Factory Exception
            throw new
                ReplicaSelectorFactoryException( "Instantiating ReplicaSelector ",
                                                 className, e );
        }

        return rs;
    }


}