kafka EmitStrategy 源码

kafka EmitStrategy 代码

文件路径：/streams/src/main/java/org/apache/kafka/streams/kstream/EmitStrategy.java

/*
 * 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.kafka.streams.kstream;

import org.apache.kafka.streams.kstream.internals.UnlimitedWindow;
import org.apache.kafka.streams.kstream.internals.emitstrategy.WindowCloseStrategy;
import org.apache.kafka.streams.kstream.internals.emitstrategy.WindowUpdateStrategy;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.HashMap;
import java.util.Map;

/**
 * This interface controls the strategy that can be used to control how we emit results in a processor.
 */
public interface EmitStrategy {

    Logger log = LoggerFactory.getLogger(EmitStrategy.class);

    enum StrategyType {
        ON_WINDOW_UPDATE(0, new WindowUpdateStrategy()),
        ON_WINDOW_CLOSE(1, new WindowCloseStrategy());

        private final short code;
        private final EmitStrategy strategy;

        private short code() {
            return this.code;
        }

        private EmitStrategy strategy() {
            return this.strategy;
        }

        StrategyType(final int code, final EmitStrategy strategy) {
            this.code = (short) code;
            this.strategy = strategy;
        }

        private final static Map<Short, EmitStrategy> TYPE_TO_STRATEGY = new HashMap<>();

        static {
            for (final StrategyType type : StrategyType.values()) {
                if (TYPE_TO_STRATEGY.put(type.code(), type.strategy()) != null)
                    throw new IllegalStateException("Code " + type.code() + " for type " +
                            type + " has already been used");
            }
        }

        public static EmitStrategy forType(final StrategyType type) {
            return TYPE_TO_STRATEGY.get(type.code());
        }
    }

    /**
     * Returns the strategy type
     * @return Emit strategy type
     */
    StrategyType type();

    /**
     * This strategy indicates that the aggregated result for a window will only be emitted when the
     * window closes instead of when there's an update to the window. Window close means that current
     * event time is larger than (window end time + grace period).
     *
     * <p>This strategy should only be used for windows which can close. An exception will be thrown
     * if it's used with {@link UnlimitedWindow}.
     *
     * @see TimeWindows
     * @see SlidingWindows
     * @see SessionWindows
     * @see UnlimitedWindows
     * @see WindowUpdateStrategy
     *
     * @return WindowCloseStrategy instance
     */
    static EmitStrategy onWindowClose() {
        return new WindowCloseStrategy();
    }

    /**
     * This strategy indicates that the aggregated result for a window will be emitted every time
     * when there's an update to the window instead of when the window closes.
     *
     * @see TimeWindows
     * @see SlidingWindows
     * @see SessionWindows
     * @see UnlimitedWindows
     * @see WindowCloseStrategy
     *
     * @return WindowCloseStrategy instance
     */
    static EmitStrategy onWindowUpdate() {
        return new WindowUpdateStrategy();
    }
}

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