Example layout for logging ByteBuffers straight to disk

ByteBufferMessageLayout.java

import java.nio.ByteBuffer;

import org.apache.logging.log4j.core.Layout;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.Node;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginFactory;

/**
 * Layout for writing ObjectMessages containing a ByteBuffer to the appender.
 * The ByteBuffer is expected to be ready for reading, with its current position at the start of the data,
 * and its limit at the end of the data.
 */
@Plugin(name = "ByteBufferMessageLayout", category = Node.CATEGORY, elementType = Layout.ELEMENT_TYPE, printObject = true)
public final class ByteBufferMessageLayout extends AbstractLayout<byte[]> {

    private ByteBufferMessageLayout() {
        super(null, null, null);
    }

    /**
     * Creates a ByteBufferMessageLayout.
     * @return A ByteBufferMessageLayout.
     */
    @PluginFactory
    public static ByteBufferMessageLayout createLayout() {
        return new ByteBufferMessageLayout();
    }

    /**
     * Extracts and logs the ByteBuffer from the LogEvent message.
     * Does nothing if the message payload is not a ByteBuffer.
     * <p>
     * The ByteBuffer is expected to be ready for reading, with its current
     * position at the start of the data, and its limit at the end of the data.
     * </p>
     *
     * @param event The LogEvent.
     * @param destination the destination to write the data to
     */
    @Override
    public void encode(final LogEvent event, final ByteBufferDestination destination) {
        final ByteBuffer src = extractByteBuffer(event);
        if (src != null) {
            ByteBuffer dest = destination.getByteBuffer();
            int todo = src.remaining();
            int pos = src.position();
            while (todo > 0) {
                if (dest.remaining() < todo) {
                    dest = destination.drain(dest);
                }
                final int count = Math.min(dest.remaining(), src.remaining());
                src.position(pos);
                src.limit(pos + count);
                dest.put(src);
                todo -= count;
                pos += count;
            }
        }
    }

    private ByteBuffer extractByteBuffer(final LogEvent logEvent) {
        final Object[] params = logEvent.getMessage().getParameters();
        if (params[0] instanceof ByteBuffer) {
            return (ByteBuffer) params[0];
        }
        return null;
    }

    /**
     * Fallback layout method used by appenders if
     * {@link org.apache.logging.log4j.core.util.Constants#ENABLE_DIRECT_ENCODERS} is set to false.
     *
     * @param event The Logging Event.
     * @return the data to write to the appender
     */
    @Override
    public byte[] toByteArray(final LogEvent event) {
        final ByteBuffer byteBuffer = extractByteBuffer(event);
        if (byteBuffer == null) {
            return new byte[0];
        }
        if (byteBuffer.hasArray() && byteBuffer.remaining() == byteBuffer.capacity()) {
            return byteBuffer.array();
        }
        final byte[] result = new byte[byteBuffer.remaining()];
        byteBuffer.get(result);
        return result;
    }

    // not called
    @Override
    public byte[] toSerializable(final LogEvent event) {
        return toByteArray(event);
    }

    /**
     * ByteBufferMessageLayout returns a binary stream.
     * @return The content type.
     */
    @Override
    public String getContentType() {
        return "application/octet-stream";
    }
}