| /** |
| * 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.apex.api.plugin; |
| |
| import org.apache.hadoop.classification.InterfaceStability.Evolving; |
| |
| import com.datatorrent.api.Component; |
| import com.datatorrent.api.Context; |
| |
| /** |
| * An Apex plugin is user code which runs inside the Apex engine. Plugin implementations implement this interface. |
| * |
| * Plugins can identify extension points by registering interest in events in the {@link Component#setup(Context)} |
| * initialization method. They should also cleanup any additional resources created during shutdown such as helper |
| * threads and open files in the {@link Component#teardown()} method. |
| * @param <T> plugin context type |
| * |
| * @since 3.6.0 |
| */ |
| @Evolving |
| public interface Plugin<T extends Plugin.PluginContext> extends Component<T> |
| { |
| |
| /** |
| * An Apex plugin is user code which runs inside the Apex engine. The interaction between plugin and engine is managed |
| * by PluginContext. Plugins can register interest in different events in the engine using the |
| * ${@link PluginContext#register(Event.Type, EventHandler)} method. |
| * |
| * @param <T> the type of the Event.Type |
| * @param <E> the event type |
| */ |
| @Evolving |
| interface PluginContext<T extends Event.Type, E extends Event<T>> extends Context |
| { |
| |
| /** |
| * Register interest in an event. |
| * |
| * Plugins register interest in events using this method. They would need to specify the event type and a handler to |
| * handle the event, that would get called when the event occurs. A plugin can register interest in several events but |
| * should register only a single handler for any specific event. In case register is called multiple times with the |
| * same event type, then the last registered handler will be used. |
| * |
| * When an event occurs the |
| * {@link EventHandler#handle(Event event)} method gets called with the event data. |
| * |
| * @param type The event type |
| * @param handler The event handler |
| */ |
| void register(T type, EventHandler<E> handler); |
| } |
| |
| /** |
| * A handler that handles an event in the Apex engine. Plugins register interest in events by registering handlers |
| * using the PluginContext. |
| * @param <E> The event type |
| */ |
| @Evolving |
| interface EventHandler<E extends Event> |
| { |
| /** |
| * Handle a event. |
| * |
| * This method is called when the event occurs. |
| * |
| * @param event |
| */ |
| void handle(E event); |
| } |
| } |