/*
* 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 java.io.Serializable;
import org.apache.flink.annotation.Public;
import org.apache.flink.api.common.functions.Function;
import org.apache.flink.streaming.api.windowing.windows.Window;
import org.apache.flink.util.Collector;
/**
* Base interface for functions that are evaluated over keyed (grouped) windows.
*
* @param <IN> The type of the input value.
* @param <OUT> The type of the output value.
* @param <KEY> The type of the key.
* @param <W> The type of {@code Window} that this window function can be applied on.
*/
@Public
public interface WindowFunction<IN, OUT, KEY, W extends Window> extends Function, Serializable {
/**
* Evaluates the window and outputs none or several elements.
*
* @param key The key for which this window is evaluated.
* @param window The window that is being evaluated.
* @param input 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.
*/
void apply(KEY key, W window, Iterable<IN> input, Collector<OUT> out) throws Exception;
}