/*

  * 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.commons.classscan.util;

 import java.util.Iterator;

 import java.util.ServiceConfigurationError;

 import java.util.ServiceLoader;

 import org.slf4j.Logger;

 import org.slf4j.LoggerFactory;

 /**

  * Visit the provider instances specified in the META-INF/services directories

  * 

  * @param <T> The type of the provider

  */

 public abstract class ServiceVisitor<T> {

     private static final Logger logger = LoggerFactory.getLogger(ServiceVisitor.class);

     /**

      * Visit the service provider available for the given interface and ClassLoader

      * 

      * @param serviceInterface The interface of the service

      * @param classLoader The ClassLoader which will load the service

      */

         public void visitProviders(Class<T> serviceInterface, ClassLoader classLoader) {

                 Iterator<T> factories = ServiceLoader.load(serviceInterface, classLoader).iterator();

                 for(;;) {

                         // this odd loop is due to the possibility of the iterator throwing

                         // ServiceConfigurationError from either hasNext() or next()

                         try {

                                 if(!factories.hasNext()) {

                                         break;

                                 }

                                 T factory = factories.next();

                             if(!visit(factory)) {

                                     break;

                             }

                         }

                         catch(ServiceConfigurationError error) {

                                 logger.warn("Ignoring configuration error", error);

                         }

                 }

         }

         /**

          * The callback method which is invoked upon finding a service provider

          * 

          * @param serviceProvider An instance of the service provider

          * @return true, if additional service providers desired; false, stop the visiting

          */

         abstract protected boolean visit(T serviceProvider);

 }