摘要：修改的實現，實現接口在改造筆記一整合到中修改實現，添加對的實現如下負載過大，處理不過來時，會回調該方法例如可以發生郵件通知相關人員改造筆記四解決中的調用兩次

在io.moquette.spi.impl.BrokerInterceptor的構造函數中，新建了一個線程池，代碼如下：

private BrokerInterceptor(int poolSize, List handlers) {
        LOG.info("Initializing broker interceptor. InterceptorIds={}", getInterceptorIds(handlers));
        this.handlers = new HashMap<>();
        for (Class messageType : InterceptHandler.ALL_MESSAGE_TYPES) {
            this.handlers.put(messageType, new CopyOnWriteArrayList());
        }
        for (InterceptHandler handler : handlers) {
            this.addInterceptHandler(handler);
        }
        executor = Executors.newFixedThreadPool(poolSize);
    }

executor = Executors.newFixedThreadPool(poolSize);這句代碼雖然創建了一個固定線程數量的線程池，但是線程池的任務隊列并沒有做限制，一旦某個InterceptHandler中的某個方法進行了耗時處理，在高并發的情況下，會很容易導致線程池的隊列堆積大量待處理的任務，進而可能造成內存溢出。

分別添加以下類和接口

public class ThreadPoolHelper {
    public static ExecutorService createFixedExecutor(int threadNum,int capacity,String threadFactoryName) {
        return new ThreadPoolExecutor(
                threadNum,
                threadNum,
                30,
                TimeUnit.SECONDS,
                new LinkedBlockingDeque(capacity),
                new SimpleThreadFactory(threadFactoryName),
                new LogDiscardRejectPolicy()
        );
    }
}

public class SimpleThreadFactory implements ThreadFactory {
    private static final String NAME_FORMAT = "%s-%s";
    private String threadNamePrefix;

    public SimpleThreadFactory(String threadNamePrefix) {
        this.threadNamePrefix = threadNamePrefix;
    }

    @Override
    public Thread newThread(Runnable runnable) {
        Thread thread = new Thread(runnable);
        thread.setName(String.format(NAME_FORMAT, threadNamePrefix, System.currentTimeMillis()));
        return thread;
    }
}


public class LogDiscardRejectPolicy implements RejectedExecutionHandler {
    private static final Logger LOG = LoggerFactory.getLogger(LogDiscardRejectPolicy.class);

    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        LOG.error("executor:{} task queue has full, runnable:{} discarded",executor,r);
        if (!(r instanceof PublishTask)) {
            return;
        }

        PublishTask publishTask = (PublishTask) r;
        InterceptHandler interceptHandler = publishTask.getInterceptHandler();
        if (!(interceptHandler instanceof RejectHandler)) {
            return;
        }

        ((RejectHandler)interceptHandler).rejectedExecution(r,executor);
    }
}


public interface RejectHandler {
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor);
}

BrokerInterceptor 創建線程池的邏輯改為

private BrokerInterceptor(int poolSize, int capacity, List handlers) {
        LOG.info("Initializing broker interceptor. InterceptorIds={}", getInterceptorIds(handlers));
        this.handlers = new HashMap<>();
        for (Class messageType : InterceptHandler.ALL_MESSAGE_TYPES) {
            this.handlers.put(messageType, new CopyOnWriteArrayList());
        }
        for (InterceptHandler handler : handlers) {
            this.addInterceptHandler(handler);
        }

        /** modify by liuhh */
        executor = ThreadPoolHelper.createFixedExecutor(poolSize, capacity, THREAD_POOL_NAME);
        //executor = Executors.newFixedThreadPool(poolSize);

    }

解釋：
（1）ThreadPoolHelper中的createFixedExecutor()方法為新建的線程池指定任務隊列大小和拒絕策略LogDiscardRejectPolicy
（2）在LogDiscardRejectPolicy中，首先將被拒絕的任務log一遍，對于PublishTask（moquette改造筆記(二)：優化BrokerInterceptor notifyTopicPublished()邏輯）做特殊處理，會交給實現RejectHandler的InterceptHandler處理，由業務邏輯決定，出現任務太多處理不完被遺棄的任務該如何處理。

在 moquette改造筆記(一)：整合到SpringBoot 中修改SafetyInterceptHandler實現，添加對RejectHandler的實現如下

@Slf4j
@Component
public class SafetyInterceptHandler extends AbstractInterceptHandler{

    @Override
    public String getID() {
        return SafetyInterceptHandler.class.getName();
    }

    @Override
    public void onConnect(InterceptConnectMessage msg) {
        
    }

    @Override
    public void onConnectionLost(InterceptConnectionLostMessage msg) {
       
    }


    @Override
    public void onPublish(InterceptPublishMessage msg) {
       
    }


    @Override
    public void onMessageAcknowledged(InterceptAcknowledgedMessage msg) {
        
    }
    
    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        /**MQTT SERVICE 負載過大，處理不過來時，會回調該方法*/
        //例如可以發生郵件通知相關人員
    }

}

moquette改造筆記(四)：解決InterceptHandler中的onConnectionLost()調用兩次