org.apache.apex.api.plugin.Plugin Maven / Gradle / Ivy
/**
* 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 plugin context type
*
* @since 3.6.0
*/
@Evolving
public interface Plugin extends Component
{
/**
* 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 the type of the Event.Type
* @param the event type
*/
@Evolving
interface PluginContext> 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 handler);
}
/**
* A handler that handles an event in the Apex engine. Plugins register interest in events by registering handlers
* using the PluginContext.
* @param The event type
*/
@Evolving
interface EventHandler
{
/**
* Handle a event.
*
* This method is called when the event occurs.
*
* @param event
*/
void handle(E event);
}
}