Hazelcast - 集合监听器

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Hazelcast 支持在更新给定集合（例如队列、集合、列表等）时添加侦听器。典型事件包括条目添加和条目删除。

让我们通过一个例子来看看如何实现设置监听器。因此，假设我们想要实现一个监听器来跟踪集合中元素的数量。

例子

因此，我们首先实现 Producer -

public class SetTimedProducer{
   public static void main(String... args) throws IOException,
   InterruptedException {
      //initialize hazelcast instance
      HazelcastInstance hazelcast = Hazelcast.newHazelcastInstance();
      Thread.sleep(5000);
      // create a set
      ISet<String> hzFruits = hazelcast.getSet("fruits");
      hzFruits.add("Mango");
      Thread.sleep(2000);
      hzFruits.add("Apple");
      Thread.sleep(2000);
      hzFruits.add("Banana");
      System.exit(0);
   }
}

现在让我们实现监听器 -

package com.example.demo;

import java.io.IOException;
import com.hazelcast.core.ISet;
import com.hazelcast.core.ItemEvent;
import com.hazelcast.core.ItemListener;
import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.HazelcastInstance;

public class SetListener{
   public static void main(String... args) throws IOException, InterruptedException {
      //initialize hazelcast instance
      HazelcastInstance hazelcast = Hazelcast.newHazelcastInstance();
      // create a set
      ISet<String> hzFruits = hazelcast.getSet("fruits");
      ItemListener<String> listener = new FruitListener<String>();
      hzFruits.addItemListener(listener, true);
      System.exit(0);
   }
   private static class FruitListener<String> implements ItemListener<String> {
      private int count = 0;
      @Override
      public void itemAdded(ItemEvent<String> item) {
         System.out.println("item added" + item);
         count ++;
         System.out.println("Total elements" + count);
      }
      @Override
      public void itemRemoved(ItemEvent<String> item) {
         count --;
      }
   }
}

我们将首先运行生产者 -

java -cp .\target\demo-0.0.1-SNAPSHOT.jar com.example.demo.SetTimedProducer

然后，我们运行监听器并让它无限期地运行 -

java -cp .\target\demo-0.0.1-SNAPSHOT.jar com.example.demo.SetListener

输出

监听器的输出如下-

item added: ItemEvent{
   event=ADDED, item=Mango, member=Member [localhost]:5701-c28a60b7-3259-44bf-8793-54063d244394 this}
Total elements: 1

item added: ItemEvent{
   event=ADDED, item=Apple, member=Member [localhost]:5701-c28a60b7-3259-44bf-8793-54063d244394 this}
Total elements: 2

item added: ItemEvent{
   event=ADDED, item=Banana, member=Member [localhost]:5701-c28a60b7-3259-44bf-8793-54063d244394 this}
Total elements: 3

hzFruits.addItemListener(listener, true) 调用告诉 Hazelcast 提供成员信息。如果设置为 false，我们只会收到添加/删除条目的通知。这有助于避免序列化和反序列化条目以使其可供侦听器访问的需要。