<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-pool2</artifactId>
    <version>2.7.0</version>
</dependency>

package com.vipsoft.mqtt.pool;
 
public class MqttConnection {

    private String mqttClient;
    ;

    public MqttConnection(String mqttClient) {
        this.mqttClient = mqttClient;
    }

    public String getMqttClient() {
        return mqttClient;
    }

    public void setMqttClient(String mqttClient) {
        this.mqttClient = mqttClient;
    }

    /**
     * 推送方法消息
     */
    public void publish(String msg) throws Exception {
        System.out.println("對象" + mqttClient + ":" + "執(zhí)行任務" + msg);
    }

    @Override
    public String toString() {
        return "MqttConnection{" + "id=" + mqttClient + '}';
    }
}

package com.vipsoft.mqtt.pool;

import org.apache.commons.pool2.BasePooledObjectFactory;
import org.apache.commons.pool2.PooledObject;
import org.apache.commons.pool2.impl.DefaultPooledObject;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.atomic.AtomicInteger;

public class MqttConnectionFactory extends BasePooledObjectFactory<MqttConnection> {

    private static final Logger logger = LoggerFactory.getLogger(MqttConnectionFactory.class);


    // AtomicInteger是一個提供原子操作的Integer類，通過線程安全的方式操作加減
    private AtomicInteger counter = new AtomicInteger();

    /**
     * 在對象池中創(chuàng)建對象
     *
     * @return
     * @throws Exception
     */
    @Override
    public MqttConnection create() throws Exception {

        // 實現(xiàn)線程安全避免在高并發(fā)的場景下出現(xiàn)clientId重復導致無法創(chuàng)建連接的情況
        int count = this.counter.addAndGet(1);
        MqttConnection mqttConnection = new MqttConnection("MqttConnection：" + count);
        logger.info("在對象池中創(chuàng)建對象 {}", mqttConnection.toString());
        return mqttConnection;
    }

    /**
     * common-pool2 中創(chuàng)建了 DefaultPooledObject 對象對對象池中對象進行的包裝。
     * 將我們自定義的對象放置到這個包裝中，工具會統(tǒng)計對象的狀態(tài)、創(chuàng)建時間、更新時間、返回時間、出借時間、使用時間等等信息進行統(tǒng)計
     *
     * @param mqttConnection
     * @return
     */
    @Override
    public PooledObject<MqttConnection> wrap(MqttConnection mqttConnection) {
        logger.info("封裝默認返回類型 {}", mqttConnection.toString());
        return new DefaultPooledObject<>(mqttConnection);
    }

    /**
     * 銷毀對象
     *
     * @param p 對象池
     * @throws Exception 異常
     */
    @Override
    public void destroyObject(PooledObject<MqttConnection> p) throws Exception {
        logger.info("銷毀對象 {}", p.getObject().getMqttClient());
        super.destroyObject(p);
    }

    /**
     * 校驗對象是否可用
     *
     * @param p 對象池
     * @return 對象是否可用結果，boolean
     */
    @Override
    public boolean validateObject(PooledObject<MqttConnection> p) {
        logger.info("校驗對象是否可用 {}", p.getObject().getMqttClient());
        return super.validateObject(p);
    }

    /**
     * 激活鈍化的對象系列操作
     *
     * @param p 對象池
     * @throws Exception 異常信息
     */
    @Override
    public void activateObject(PooledObject<MqttConnection> p) throws Exception {
        logger.info("激活鈍化的對象 {}", p.getObject().getMqttClient());
        super.activateObject(p);
    }

    /**
     * 鈍化未使用的對象
     *
     * @param p 對象池
     * @throws Exception 異常信息
     */
    @Override
    public void passivateObject(PooledObject<MqttConnection> p) throws Exception {
        logger.info("鈍化未使用的對象 {}", p.getObject().getMqttClient());
        super.passivateObject(p);
    }
}

package com.vipsoft.mqtt;

import cn.hutool.core.date.DateUtil;
import com.vipsoft.mqtt.pool.MqttConnection;
import com.vipsoft.mqtt.pool.MqttConnectionFactory;
import org.apache.commons.pool2.impl.GenericObjectPool;
import org.apache.commons.pool2.impl.GenericObjectPoolConfig;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;

@SpringBootTest
public class PoolTest {

    @Test
    void basePooledTest() throws InterruptedException {

        AtomicInteger atomicInteger = new AtomicInteger();

        int excutorCount = 15;
        CountDownLatch countDownLatch = new CountDownLatch(excutorCount);

        // =====================創(chuàng)建線程池=====================
        ExecutorService excutor = Executors.newFixedThreadPool(5);
        // =====================創(chuàng)建對象池 項目中使用了InitializingBean.afterPropertiesSet() 中創(chuàng)建=====================
        // 對象池工廠
        MqttConnectionFactory personPoolFactory = new MqttConnectionFactory();
        // 對象池配置
        GenericObjectPoolConfig<MqttConnection> objectPoolConfig = new GenericObjectPoolConfig<>();
        objectPoolConfig.setMaxTotal(50);
        // 對象池
        GenericObjectPool<MqttConnection> mqttPool = new GenericObjectPool<>(personPoolFactory, objectPoolConfig);
        // =====================測試對象池=====================
        // 循環(huán)100次，從線程池中取多個多線程執(zhí)行任務，來測試對象池
        for (int i = 0; i < excutorCount; i++) {
            excutor.submit(new Thread(() -> {
                // 模擬從對象池取出對象，執(zhí)行任務
                MqttConnection mqtt = null;
                try {
                    // 從對象池取出對象
                    mqtt = mqttPool.borrowObject();
                    // 讓對象工作
                    int count = atomicInteger.addAndGet(1);
                    mqtt.publish("Id:" + count + " Time: " + DateUtil.now());
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    // 回收對象到對象池
                    if (mqtt != null) {
                        mqttPool.returnObject(mqtt);
                    }
                    countDownLatch.countDown();
                }
            }));
        }
        countDownLatch.await();
    }
}