ShortenedThrowableConverter: truncate stacktrace based on regex pattern

[brenuart]

The ShortenedThrowableConverter currently allows setting a hard limit on the number of stack trace elements to print (cfr. maxDepthPerThrowable property). Additional elements will not be output and a message indicating how many elements were truncated will be printed instead.

The exact desired length of the stack trace may not always been known up-front and may depend on the stack trace itself. To deal with this situation, it may be desirable to truncate after a line found based on a regex pattern. For instance, users may want to truncate everything below the Spring DispatcherServlet because this information doesn't provide any additional value to them...

This would be configured as follows:

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
    <throwableConverter class="net.logstash.logback.stacktrace.ShortenedThrowableConverter">
        <truncateAfter>^org\.springframework\.web\.servlet\.DispatcherServlet</truncateAfter>
    </throwableConverter>
</encoder>

Everything after the "DispatcherServlet" log line will be truncated and replaced by the usual "frames truncated" message.