public LogWriter build() {
        return new DefaultLogWriter(firstNonNull(logger, DefaultLogWriter.defaultLogger),
                                    requestLogLevelMapper(), responseLogLevelMapper(),
                                    responseCauseFilter, logFormatter);
    }
Returns a newly-created {@link LogWriter} based on the properties of this builder.
core/src/main/java/com/linecorp/armeria/common/logging/LogWriterBuilder.java