How does SLF4J support structured logging

Question

Anyone knows how structured logging is usually implemented with SLF4J?

Is there any open source already out there handling this?

Answer 1

If you use SLF4J in conjunction with Logback and Logstash, structured logging is supported with StructuredArguments. You can find documentation about this on the logstash logback encoder page on Github.

A simple example of how it works. This log line..

log.debug("Retrieved file {}", StructuredArguments.value("filename", upload.getOriginalFilename()))

..yields the following log json output:

{
  "filename": "simple.zip",
  "@timestamp": "2019-02-12T14:31:31.631+00:00",
  "severity": "DEBUG",
  "service": "upload",
  "thread": "http-nio-9091-exec-1",
  "logger": "some.great.ClassName",
  "message": "Retrieved file simple.zip"
}