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A common publisher-subscriber library.
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/*
 * Copyright 2016 UsefulMilk
 *
 * Licensed 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 com.usefulmilk.pubsub;

import com.usefulmilk.support.Validate;

/**
 * The {@link MilkSubscriber} have to be create to listen specific extension of {@link MilkMessage}.
 * When {@link MilkMessage#publish()} is called, the {@link MilkPublisher} will send the
 * {@link MilkMessage} to this {@link MilkSubscriber} through
 * {@link MilkSubscriber#handleMilkMessage(MilkMessage)} method.
 * Ex:
 * 
 *      class MyMilkMessage extends {@link MilkMessage}{
 *          private String anyMessage;
 *
 *          public MyMilkMessage(MilkPublisher milkPublisher) {
 *              super(milkPublisher);
 *          }
 *
 *          public void setAnyMessage(String anyMessage) {
 *              this.anyMessage = anyMessage;
 *          }
 *
 *          public String getAnyMessage() {
 *              return anyMessage;
 *           }
 *      }
 *
 *      class MyMilkSubscriber extends {@link MilkSubscriber}<MyMilkMessage>}{
 *          protected MyMilkSubscriber() {
 *              super(MyMilkMessage.class);
 *          }
 *
 *          {@literal}@Override
 *          public void handleMilkMessage(MyMilkMessage milkMessage) {
 *              System.out.println(milkMessage.getAnyMessage());
 *          }
 *      }
 * 
 */
public abstract class MilkSubscriber {
    private Class milkMessageClass;

    protected MilkSubscriber(Class milkMessageClass) {
        this.milkMessageClass = Validate.nonNullArgument(milkMessageClass);
    }

    public abstract void handleMilkMessage(T milkMessage);

    Class milkMessageClass() {
        return milkMessageClass;
    }
}