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A library used at otto.de to implement Spring Boot based event-sourcing microserivces.
There is a newer version: 0.10.1
package de.otto.synapse.compaction.aws;

import de.otto.synapse.channel.ChannelPosition;
import de.otto.synapse.consumer.DefaultMessageConsumer;
import de.otto.synapse.endpoint.receiver.MessageLogReceiverEndpoint;
import de.otto.synapse.endpoint.receiver.MessageLogReceiverEndpointFactory;
import de.otto.synapse.eventsource.EventSource;
import de.otto.synapse.eventsource.EventSourceBuilder;
import de.otto.synapse.state.StateRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.time.Clock;

import static java.time.Instant.now;

public class CompactionService {

    private static final Logger LOG = LoggerFactory.getLogger(CompactionService.class);

    private final StateRepository stateRepository;
    private final SnapshotWriteService snapshotWriteService;
    private final EventSourceBuilder eventSourceBuilder;
    private final MessageLogReceiverEndpointFactory messageLogReceiverEndpointFactory;
    private final Clock clock;

    public CompactionService(final SnapshotWriteService snapshotWriteService,
                             final StateRepository stateRepository,
                             final EventSourceBuilder eventSourceBuilder,
                             final MessageLogReceiverEndpointFactory messageLogReceiverEndpointFactory)
    {
        this(snapshotWriteService, stateRepository, eventSourceBuilder, messageLogReceiverEndpointFactory, Clock.systemDefaultZone());
    }

    public CompactionService(final SnapshotWriteService snapshotWriteService,
                             final StateRepository stateRepository,
                             final EventSourceBuilder eventSourceBuilder,
                             final MessageLogReceiverEndpointFactory messageLogReceiverEndpointFactory,
                             final Clock clock)
    {
        this.snapshotWriteService = snapshotWriteService;
        this.stateRepository = stateRepository;
        this.eventSourceBuilder = eventSourceBuilder;
        this.messageLogReceiverEndpointFactory = messageLogReceiverEndpointFactory;
        this.clock = clock;
    }

    public String compact(final String channelName) {
        LOG.info("Start compacting channel {}", channelName);
        stateRepository.clear();

        LOG.info("Start loading entries into inMemoryCache from snapshot");
        final MessageLogReceiverEndpoint messageLog = messageLogReceiverEndpointFactory.create(channelName);
        final EventSource compactingKinesisEventSource = eventSourceBuilder.buildEventSource(messageLog);
        compactingKinesisEventSource.register(
                new DefaultMessageConsumer<>(".*", String.class, stateRepository)
        );

        try {
            final ChannelPosition currentPosition = compactingKinesisEventSource.consumeUntil(now(clock)).get();

            LOG.info("Finished updating snapshot data. StateRepository now holds {} entries.", stateRepository.size());

            return snapshotWriteService.writeSnapshot(channelName, currentPosition, stateRepository);
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            stateRepository.clear();
        }
    }

}