org.apache.flink.streaming.api.functions.windowing.ProcessWindowFunction 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.flink.streaming.api.functions.windowing;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.functions.AbstractRichFunction;
import org.apache.flink.api.common.state.KeyedStateStore;
import org.apache.flink.streaming.api.windowing.windows.Window;
import org.apache.flink.util.Collector;
import org.apache.flink.util.OutputTag;
/**
* Base abstract class for functions that are evaluated over keyed (grouped) windows using a context
* for retrieving extra information.
*
* @param The type of the input value.
* @param The type of the output value.
* @param The type of the key.
* @param The type of {@code Window} that this window function can be applied on.
*/
@PublicEvolving
public abstract class ProcessWindowFunction extends AbstractRichFunction {
private static final long serialVersionUID = 1L;
/**
* Evaluates the window and outputs none or several elements.
*
* @param key The key for which this window is evaluated.
* @param context The context in which the window is being evaluated.
* @param elements The elements in the window being evaluated.
* @param out A collector for emitting elements.
*
* @throws Exception The function may throw exceptions to fail the program and trigger recovery.
*/
public abstract void process(KEY key, Context context, Iterable elements, Collector out) throws Exception;
/**
* Deletes any state in the {@code Context} when the Window is purged.
*
* @param context The context to which the window is being evaluated
* @throws Exception The function may throw exceptions to fail the program and trigger recovery.
*/
public void clear(Context context) throws Exception {}
/**
* The context holding window metadata.
*/
public abstract class Context implements java.io.Serializable {
/**
* Returns the window that is being evaluated.
*/
public abstract W window();
/** Returns the current processing time. */
public abstract long currentProcessingTime();
/** Returns the current event-time watermark. */
public abstract long currentWatermark();
/**
* State accessor for per-key and per-window state.
*
* NOTE:If you use per-window state you have to ensure that you clean it up
* by implementing {@link ProcessWindowFunction#clear(Context)}.
*/
public abstract KeyedStateStore windowState();
/**
* State accessor for per-key global state.
*/
public abstract KeyedStateStore globalState();
/**
* Emits a record to the side output identified by the {@link OutputTag}.
*
* @param outputTag the {@code OutputTag} that identifies the side output to emit to.
* @param value The record to emit.
*/
public abstract void output(OutputTag outputTag, X value);
}
}