Trace Depth Log4j2 Plugin

This is a simple Log4j2 plugin that enables indentation of the log messages based on the "depth" of the traceEntry() and traceExit() pairs.

Log4j2 enables tracing of the method calls (or any "nesting" concepts) by the Logger.traceEntry() and Logger.traceExit() methods. To visualize the nesting it might be handy to log such messages indented by the "depth" of the current nesting "stack". This simple Log4j2 plugin does exactly that.

While this might not be that useful for traditional logging scenarios, it might be useful for trace logging which is intended for the developers to trace the method calls and entry and exit to certain critical sections. In such situations, being able to visually distinguish the sections by depth might help with making sense of the logs.

Usage

Put the jar on the class path, e.g. in Maven:

<dependency>
  <groupId>pw.krejci</groupId>
  <artifactId>tracedepth-log4j2-plugin</artifactId>
  <version>...</version>
</dependency>

In your log4j2.xml configuration file, configure the pattern layout for example like this:

<PatternLayout pattern="%d{HH:mm:ss.SSS} %-5level %traceDepth %logger{1.}.%M - %msg%xEx%n"/>

The log output will then look similar to this:

09:24:37.270 TRACE  o.e.Main.main - Enter main (1)
09:24:37.271 TRACE    o.e.BusinessLayer.process - Enter process
09:24:37.272 TRACE      o.e.BusinessLayer.process - computed the values to store (2)
09:24:37.273 TRACE      o.e.DataLayer.transaction - Enter transaction
09:24:37.273 TRACE        o.e.DataLayer.storeValues - Enter storing the values
09:24:37.275 TRACE        o.e.DataLayer.storeValues - Exit storing the values: 5
09:24:37.276 TRACE      o.e.DataLayer.transaction - Exit transaction: 5 (3)
09:24:37.277 TRACE      o.e.BusinessLayer.process - stored 5 values
09:24:37.277 INFO  o.e.BusinessLayer.process - Processed 5 new values (4)
09:24:37.278 TRACE    o.e.BusinessLayer.process - Exit process
09:24:37.278 TRACE  o.e.Main.main - Exit

1. Logger.traceEntry() called in the main() method

2. The ordinary Logger.trace(String) message will be indented as well

3. Logger.traceExit() called and the indentation of the subsequent trace messages is decreased

4. Other log levels are not affected by the call depth.

Note	The plugin is not smart enough to distinguish unmatched entry/exit pairs. You will get uneven indentation if you mess up.

Configuration

As can be seen above, the call depth is introduced into the log message by using the %traceDepth pattern parameter. The default indentation level is 2 spaces. You can override that by specifying the number of spaces as an option of the parameter, e.g. %traceDepth{4} will indent by 4 spaces.