# ApplicationEventCreationConcern.java

    /*
     * Copyright 2009-2010 Rickard Öberg AB
     *
     * 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.qi4j.library.eventsourcing.application.factory;

    import java.lang.reflect.Method;
    import org.qi4j.api.common.AppliesTo;
    import org.qi4j.api.concern.GenericConcern;
    import org.qi4j.api.injection.scope.Service;
    import org.qi4j.library.eventsourcing.application.api.ApplicationEvent;

    /**
     * Generate application event for event method
     */
    @AppliesTo(ApplicationEventMethodFilter.class)
    public class ApplicationEventCreationConcern
            extends GenericConcern
    {
        @Service
        ApplicationEventFactory eventFactory;

        @Override
        public Object invoke( Object proxy, Method method, Object[] args ) throws Throwable
        {
            if (args[0] == null)
            {
                // Create application event
                ApplicationEvent event = eventFactory.createEvent( method.getName(), args );
                args[0] = event;
            }

            return next.invoke( proxy, method, args );
        }
    }