聊聊CanalEventDownStreamHandler

序

本文主要研究一下CanalEventDownStreamHandler

CanalEventDownStreamHandler

canal-1.1.4/sink/src/main/java/com/alibaba/otter/canal/sink/CanalEventDownStreamHandler.java

public interface CanalEventDownStreamHandler<T> extends CanalLifeCycle {

    /**
     * 提交到store之前做一下处理，允许替换Event
     */
    public T before(T events);

    /**
     * store处于full后，retry时处理做一下处理
     */
    public T retry(T events);

    /**
     * 提交store成功后做一下处理
     */
    public T after(T events);
}

• CanalEventDownStreamHandler继承了CanalLifeCycle接口，它定义了before、retry、after方法

AbstractCanalEventDownStreamHandler

canal-1.1.4/sink/src/main/java/com/alibaba/otter/canal/sink/AbstractCanalEventDownStreamHandler.java

public class AbstractCanalEventDownStreamHandler<T> extends AbstractCanalLifeCycle implements CanalEventDownStreamHandler<T> {

    public T before(T events) {
        return events;
    }

    public T retry(T events) {
        return events;
    }

    public T after(T events) {
        return events;
    }

}

• AbstractCanalEventDownStreamHandler继承了AbstractCanalLifeCycle，实现了CanalEventDownStreamHandler接口，before、retry、after方法默认返回入参的events

HeartBeatEntryEventHandler

canal-1.1.4/sink/src/main/java/com/alibaba/otter/canal/sink/entry/HeartBeatEntryEventHandler.java

public class HeartBeatEntryEventHandler extends AbstractCanalEventDownStreamHandler<List<Event>> {

    public List<Event> before(List<Event> events) {
        boolean existHeartBeat = false;
        for (Event event : events) {
            if (event.getEntryType() == EntryType.HEARTBEAT) {
                existHeartBeat = true;
            }
        }

        if (!existHeartBeat) {
            return events;
        } else {
            // 目前heartbeat和其他事件是分离的，保险一点还是做一下检查处理
            List<Event> result = new ArrayList<Event>();
            for (Event event : events) {
                if (event.getEntryType() != EntryType.HEARTBEAT) {
                    result.add(event);
                }
            }

            return result;
        }
    }

}

• HeartBeatEntryEventHandler继承了AbstractCanalEventDownStreamHandler，其before方法遍历events判断是否有EntryType.HEARTBEAT类型的event，如果没有则立即返回events，如果有则返回非heartbeat的事件

PrometheusCanalEventDownStreamHandler

canal-1.1.4/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/PrometheusCanalEventDownStreamHandler.java

public class PrometheusCanalEventDownStreamHandler extends AbstractCanalEventDownStreamHandler<List<Event>> {

    private final AtomicLong latestExecuteTime  = new AtomicLong(System.currentTimeMillis());
    private final AtomicLong transactionCounter = new AtomicLong(0L);

    @Override
    public List<Event> before(List<Event> events) {
        long localExecTime = 0L;
        if (events != null && !events.isEmpty()) {
            for (Event e : events) {
                EntryType type = e.getEntryType();
                if (type == null) continue;
                switch (type) {
                    case TRANSACTIONBEGIN: {
                        long exec = e.getExecuteTime();
                        if (exec > 0) localExecTime = exec;
                        break;
                    }
                    case ROWDATA: {
                        long exec = e.getExecuteTime();
                        if (exec > 0) localExecTime = exec;
                        break;
                    }
                    case TRANSACTIONEND: {
                        long exec = e.getExecuteTime();
                        if (exec > 0) localExecTime = exec;
                        transactionCounter.incrementAndGet();
                        break;
                    }
                    case HEARTBEAT:
                        CanalEntry.EventType eventType = e.getEventType();
                        if (eventType == CanalEntry.EventType.MHEARTBEAT) {
                            localExecTime = System.currentTimeMillis();
                        }
                        break;
                    default:
                        break;
                }
            }
            if (localExecTime > 0) {
                latestExecuteTime.lazySet(localExecTime);
            }
        }
        return events;
    }

    @Override
    public void start() {

        super.start();
    }

    @Override
    public void stop() {
        super.stop();
    }

    public AtomicLong getLatestExecuteTime() {
        return latestExecuteTime;
    }

    public AtomicLong getTransactionCounter() {
        return transactionCounter;
    }

}

• PrometheusCanalEventDownStreamHandler继承了AbstractCanalEventDownStreamHandler，其before方法遍历events，然后根据不同的EntryType来更新localExecTime、transactionCounter、latestExecuteTime

小结

CanalEventDownStreamHandler继承了CanalLifeCycle接口，它定义了before、retry、after方法；AbstractCanalEventDownStreamHandler继承了AbstractCanalLifeCycle，实现了CanalEventDownStreamHandler接口，before、retry、after方法默认返回入参的events；目前有HeartBeatEntryEventHandler及PrometheusCanalEventDownStreamHandler继承了AbstractCanalEventDownStreamHandler

doc

• CanalEventDownStreamHandler