How does SLF4J support structured logging [closed]

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"
}

Answer 2

Slf4j added support for structured logging (and fluent API) with v2.0.0 (Alpha as of Oct 2019):

• http://www.slf4j.org/api/org/slf4j/event/KeyValuePair.html
• http://www.slf4j.org/api/org/slf4j/event/LoggingEvent.html

• http://www.slf4j.org/apidocs/org/slf4j/spi/LoggingEventBuilder.html

  int newT = 15;
  int oldT = 16;
  
  // using classical API
  logger.debug("oldT={} newT={} Temperature changed.", newT, oldT);
  
  // using fluent API
  logger.atDebug()
          .addKeyValue("oldT", oldT)
          .addKeyValue("newT", newT)
          .log("Temperature changed.");