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package com.soento.logback.kafka.keying;

import ch.qos.logback.core.Context;
import ch.qos.logback.core.CoreConstants;
import ch.qos.logback.core.spi.ContextAwareBase;
import ch.qos.logback.core.spi.LifeCycle;

import java.nio.ByteBuffer;

/**
 * This strategy uses the HOSTNAME as kafka message key.
 * This is useful because it ensures that all log messages issued by this host will remain in the correct order for any consumer.
 * But this strategy can lead to uneven log distribution for a small number of hosts (compared to the number of partitions).
 * @since 0.0.1
 */
public class HostNameKeyingStrategy extends ContextAwareBase implements KeyingStrategy, LifeCycle {

    private byte[] hostnameHash = null;
    private boolean errorWasShown = false;

    @Override
    public void setContext(Context context) {
        super.setContext(context);
        final String hostname = context.getProperty(CoreConstants.HOSTNAME_KEY);
        if (hostname == null) {
            if (!errorWasShown) {
            addError("Hostname could not be found in context. HostNamePartitioningStrategy will not work.");
                errorWasShown = true;
            }
        } else {
            hostnameHash = ByteBuffer.allocate(4).putInt(hostname.hashCode()).array();
        }
    }

    @Override
    public byte[] createKey(Object e) {
        return hostnameHash;
    }

    @Override
    public void start() { }

    @Override
    public void stop() {
        errorWasShown = false;
    }

    @Override
    public boolean isStarted() { return true; }
}
    

    

    

            

    

            



    
    






    
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