Suggest a new sub-interface of Appender:

public interface FlushableAppender<E> extends Appender<E>, java.io.Flushable
{
}

Then, WriterAppender could be defined to implement FlushableAppender, with this simple implementation:

public void flush() throws IOException

{ writer.flush(); }

This would allow manual flushing of the appenders. This is particularly useful when buffered IO is used, obviously. It allows, for instance, to manually flush all appenders when a request has been fully processed, ensuring that we retain the benefits of buffered IO while also having the full logs after request processing.

Here's sample code I used to get all appenders (run once after Logback configuration):

public static Set<Appender> getAllAppenders()
{
ContextSelector selector = StaticLoggerBinder.SINGLETON.getContextSelector();
LoggerContext loggerContext = selector.getLoggerContext();

Map<String, Appender> appenders = newHashMap();

// loop through all Loggers
for ( Logger logger : loggerContext.getLoggerList() )
{
// for each logger, loop through all its appenders
Iterator iter = logger.iteratorForAppenders();
while ( iter.hasNext() )

{ // appenders are uniquely identified by name, so store them in the Map thus // this will overwrite the same entry in the Map many times (with the same reference) Appender appender = ( Appender ) iter.next(); appenders.put( appender.getName(), appender ); }

}

return newHashSet( appenders.values() );
}

The below bean is used in Spring, calling flush() forces all appenders to be flushed:

public class LogbackFlushBean implements Flushable
{
protected final Logger log = LoggerFactory.getLogger( getClass() );

private final Collection<FlushableAppender> flushableAppenders = newLinkedList();

@PostConstruct
public void loadFlushableAppenders()
{
for ( Appender appender : LogbackConfigurer.getAllAppenders() )
{
if ( appender instanceof FlushableAppender )

{ flushableAppenders.add( ( FlushableAppender ) appender ); }

else
{
log.debug( "appender {} is not Flushable, skipping", appender.getName() );
}
}
}

public void flush() throws IOException
{
for ( FlushableAppender appender : flushableAppenders )
{
log.debug( "flushing appender {}", appender.getName() );
appender.flush();
}
}
}