聊聊BinaryLogClient的EventListener

序

本文主要研究一下BinaryLogClient的EventListener

EventListener

mysql-binlog-connector-java-0.20.1/src/main/java/com/github/shyiko/mysql/binlog/BinaryLogClient.java

    public interface EventListener {

        void onEvent(Event event);
    }

• EventListener接口定义了onEvent方法

BinaryLogClientStatistics

mysql-binlog-connector-java-0.20.1/src/main/java/com/github/shyiko/mysql/binlog/jmx/BinaryLogClientStatistics.java

public class BinaryLogClientStatistics implements BinaryLogClientStatisticsMXBean,
        BinaryLogClient.EventListener, BinaryLogClient.LifecycleListener {

    private AtomicReference<EventHeader> lastEventHeader = new AtomicReference<EventHeader>();
    private AtomicLong timestampOfLastEvent = new AtomicLong();
    private AtomicLong totalNumberOfEventsSeen = new AtomicLong();
    private AtomicLong totalBytesReceived = new AtomicLong();
    private AtomicLong numberOfSkippedEvents = new AtomicLong();
    private AtomicLong numberOfDisconnects = new AtomicLong();

    public BinaryLogClientStatistics() {
    }

    public BinaryLogClientStatistics(BinaryLogClient binaryLogClient) {
        binaryLogClient.registerEventListener(this);
        binaryLogClient.registerLifecycleListener(this);
    }

    @Override
    public String getLastEvent() {
        EventHeader eventHeader = lastEventHeader.get();
        return eventHeader == null ? null : eventHeader.getEventType() + "/" + eventHeader.getTimestamp() +
                " from server " + eventHeader.getServerId();
    }

    @Override
    public long getSecondsSinceLastEvent() {
        long timestamp = timestampOfLastEvent.get();
        return timestamp == 0 ? 0 : (getCurrentTimeMillis() - timestamp) / 1000;
    }

    @Override
    public long getSecondsBehindMaster() {
        // because lastEventHeader and timestampOfLastEvent are not guarded by the common lock
        // we may get some "distorted" results, though shouldn't be a problem given the nature of the final value
        long timestamp = timestampOfLastEvent.get();
        EventHeader eventHeader = lastEventHeader.get();
        if (timestamp == 0 || eventHeader == null) {
            return -1;
        }
        return (timestamp - eventHeader.getTimestamp()) / 1000;
    }

    @Override
    public long getTotalNumberOfEventsSeen() {
        return totalNumberOfEventsSeen.get();
    }

    @Override
    public long getTotalBytesReceived() {
        return totalBytesReceived.get();
    }

    @Override
    public long getNumberOfSkippedEvents() {
        return numberOfSkippedEvents.get();
    }

    @Override
    public long getNumberOfDisconnects() {
        return numberOfDisconnects.get();
    }

    @Override
    public void reset() {
        lastEventHeader.set(null);
        timestampOfLastEvent.set(0);
        totalNumberOfEventsSeen.set(0);
        totalBytesReceived.set(0);
        numberOfSkippedEvents.set(0);
        numberOfDisconnects.set(0);
    }

    @Override
    public void onEvent(Event event) {
        EventHeader header = event.getHeader();
        lastEventHeader.set(header);
        timestampOfLastEvent.set(getCurrentTimeMillis());
        totalNumberOfEventsSeen.getAndIncrement();
        totalBytesReceived.getAndAdd(header.getHeaderLength() + header.getDataLength());
    }

    @Override
    public void onEventDeserializationFailure(BinaryLogClient client, Exception ex) {
        numberOfSkippedEvents.getAndIncrement();
        lastEventHeader.set(null);
        timestampOfLastEvent.set(getCurrentTimeMillis());
        totalNumberOfEventsSeen.getAndIncrement();
    }

    @Override
    public void onDisconnect(BinaryLogClient client) {
        numberOfDisconnects.getAndIncrement();
    }

    @Override
    public void onConnect(BinaryLogClient client) {
    }

    @Override
    public void onCommunicationFailure(BinaryLogClient client, Exception ex) {
    }

    protected long getCurrentTimeMillis() {
        return System.currentTimeMillis();
    }

}

• BinaryLogClientStatistics实现了BinaryLogClient.EventListener接口，其onEvent方法会更新lastEventHeader、timestampOfLastEvent、totalNumberOfEventsSeen、totalBytesReceived

listenForEventPackets

mysql-binlog-connector-java-0.20.1/src/main/java/com/github/shyiko/mysql/binlog/BinaryLogClient.java

public class BinaryLogClient implements BinaryLogClientMXBean {
	
	//......

    private void listenForEventPackets() throws IOException {
        ByteArrayInputStream inputStream = channel.getInputStream();
        boolean completeShutdown = false;
        try {
            while (inputStream.peek() != -1) {
                int packetLength = inputStream.readInteger(3);
                inputStream.skip(1); // 1 byte for sequence
                int marker = inputStream.read();
                if (marker == 0xFF) {
                    ErrorPacket errorPacket = new ErrorPacket(inputStream.read(packetLength - 1));
                    throw new ServerException(errorPacket.getErrorMessage(), errorPacket.getErrorCode(),
                        errorPacket.getSqlState());
                }
                if (marker == 0xFE && !blocking) {
                    completeShutdown = true;
                    break;
                }
                Event event;
                try {
                    event = eventDeserializer.nextEvent(packetLength == MAX_PACKET_LENGTH ?
                        new ByteArrayInputStream(readPacketSplitInChunks(inputStream, packetLength - 1)) :
                        inputStream);
                    if (event == null) {
                        throw new EOFException();
                    }
                } catch (Exception e) {
                    Throwable cause = e instanceof EventDataDeserializationException ? e.getCause() : e;
                    if (cause instanceof EOFException || cause instanceof SocketException) {
                        throw e;
                    }
                    if (isConnected()) {
                        for (LifecycleListener lifecycleListener : lifecycleListeners) {
                            lifecycleListener.onEventDeserializationFailure(this, e);
                        }
                    }
                    continue;
                }
                if (isConnected()) {
                    eventLastSeen = System.currentTimeMillis();
                    updateGtidSet(event);
                    notifyEventListeners(event);
                    updateClientBinlogFilenameAndPosition(event);
                }
            }
        } catch (Exception e) {
            if (isConnected()) {
                for (LifecycleListener lifecycleListener : lifecycleListeners) {
                    lifecycleListener.onCommunicationFailure(this, e);
                }
            }
        } finally {
            if (isConnected()) {
                if (completeShutdown) {
                    disconnect(); // initiate complete shutdown sequence (which includes keep alive thread)
                } else {
                    disconnectChannel();
                }
            }
        }
    }

    private void notifyEventListeners(Event event) {
        if (event.getData() instanceof EventDataWrapper) {
            event = new Event(event.getHeader(), ((EventDataWrapper) event.getData()).getExternal());
        }
        for (EventListener eventListener : eventListeners) {
            try {
                eventListener.onEvent(event);
            } catch (Exception e) {
                if (logger.isLoggable(Level.WARNING)) {
                    logger.log(Level.WARNING, eventListener + " choked on " + event, e);
                }
            }
        }
    }

	//......

}

• listenForEventPackets方法会读取channel.getInputStream()，然后通过eventDeserializer.nextEvent解析为event，之后调用updateGtidSet、notifyEventListeners、updateClientBinlogFilenameAndPosition方法；notifyEventListeners方法会遍历eventListeners挨个执行其onEvent方法

小结

EventListener接口定义了onEvent方法；BinaryLogClientStatistics实现了BinaryLogClient.EventListener接口，其onEvent方法会更新lastEventHeader、timestampOfLastEvent、totalNumberOfEventsSeen、totalBytesReceived

doc

• BinaryLogClient

来源：oschina

链接：https://my.oschina.net/go4it/blog/4255652