Logging in Clojure

Question

For Java development, I use Slf4j and Logback.

Logger logger = LoggerFactory.getLogger(HelloWorld.class);
logger.debug("Hello world.");

How to use these two libs in Clojure programs? Majority of Clojure programming doesn't has .class concept (possible of course via AOT).

What do you use for logging in Clojure?

Balbinder

There are two overloads for getLog(): one uses a Class, the other takes a String. You could simply use the String one. – Arawak

Answer 1

Clojure comes with a logging core library in tools.logging. Add [org.clojure/tools.logging "0.2.3"] to your leiningen project.clj and run $lein deps as usual.

Once you use the library you can start logging away

(use 'clojure.tools.logging)
(warn "something bad happened") 

Now you can also access the logger object and set the required fields, refer to the following article for this (written for the older contrib-lib but the same ideas apply):

http://www.paullegato.com/blog/setting-clojure-log-level/

Seibel

contrib is deprecated in favor of tools.logging github.com/clojure/tools.logging – Shilohshim

Answer 2

Look at this as well https://github.com/ptaoussanis/timbre . It looks very simple and nicely done.

Matchlock

Actually timbre is what I prefer as out of the box logging! spy and other functionality is very helpful. – Kafiristan

Here is another question that covers Timbre logging in more detail: #32311119 – Vaudevillian

Answer 3

tools.logging. For details, refer to tools.logging vs clojure.contrib.logging

Nickelson

Answer 4

some excerpts from a one of my projects that uses log4j:

log.clj:

(ns 
    #^{:author "Arthur Ulfeldt", 
       :doc "Polynomial threshold encryption"}
  com.cryptovide.log
  (:gen-class)
  (:use
   clojure.contrib.logging))

...

(def logger (org.apache.log4j.Logger/getLogger "A1"))
(def log-levels (vec ( org.apache.log4j.Level/getAllPossiblePriorities)))

...

(defn start-logging []
  (org.apache.log4j.BasicConfigurator/configure))

main.clj:

(start-logging)
(. logger setLevel (log-levels verbose-level))

Bacteriostat

Answer 5

Mulog is library that defines log events as data, with a wide range of publisher for popular log aggregation services, e.g. Elastic Search, Cloudwatch, Kinesis, Prometheus, etc.)

As each event log is data, then searching through logs is far simpler to filter on specific keys (compared to when logs are strings).

mulog/log function is used to define an event message. The first argument is a unique event name, followed by any key/value pairs that are useful to define the contents of the log message.

An example of a simple Mulog event:

mulog/log ::dev-user-ns :message "Example event message" :ns (ns-publics *ns*))

Using a custom publisher, Mulog events can automatically be sent to data inspectors such as Portal.

Weymouth