Today I am giving you two new appenders for Logback: one for MongoDB and one which I called recording appender. Just as a reminder, appenders (both in Log4J and Logback) are an abstraction of your application logs destination. The most common are file and console appenders, followed by several others built-in. MongoDB appender is pretty straightforward, so I will start by describing the recording appender.
Recording appender
As you already know, one of the biggest benefits of using logging frameworks are logging levels. By carefully choosing levels for each logging statement we can easily filter which logs should be present in our log files and which shouldn't. Also we can apply different logging strategies for different environments. This is in theory. In practice we often face the choice between: log everything just in case and handle gigabytes of meaningless log files or log only warnings and errors but when they actually occur, they are meaningless as well, lacking important debugging context. The idea isn't new (see [1], [2] and [3] for example), but somehow decent implementation is missing in both Log4J and Logback. And the idea is simple – as long as there is nothing wrong happening with the system: do not log anything or log very little – but silently memorize all debug logs in some cyclic buffer. And whenever disaster occurs (any log with ERROR level, probably an exception), dump the buffer first to provide meaningful context.
Writing custom logging appenders is pretty straightforward. Following is the essence of my recording appender:
