metracer – Logging via org.slf4j.Logger

New version 1.1.0 of metracer was released: were many experiments, redesigns and code rewrites. Main changes are around tracing output – now it’s done via org.slf4j.Logger. (issue #8)

Decision to use org.slf4.Logger to output entry / exit tags was made because:

  • org.slf4.Logger is one of the standards of logging for JavaEE which allows to interleave application logs and output of metracer in a natural way;
  • System.out.println doesn’t suite well for JavaEE applications because output could be easily redirected at runtime.

Use of org.slf4.Logger  made it necessary to redesign code a bit:

  • new Runtime class was introduced which handles all the logic of logging. Instrumentation now only inserts callbacks to Runtime, there is no heavy logic in a generated code (see TracingCodeInjector class);
  • to fight with the issues of ClassLoaders isolation (enforced e.g. by JBoss‘s ModuleClassLoader) patching of all encountered ClassLoaders was introduced – patching drills a direct hole to App ClassLoader where Runtime class of metracer lives (see TracingCodeInjector.injectDirectAccessToMetracerClasses);
  • since not all instrumented classes have  org.slf4.Logger inside a ‘context sensitive’ discovery method was introduced – we scan a stack trace and take a Logger for the very first class which has the  Logger. If there is no such class on the way we fallback to default System.out.println.

Among the notable changes is a drop of support of annotations  – issue #9. It turned out that there is too few benefits from the use of annotations – the same things could be achieved via some AOP in a more natural way.




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