git clone ''



Logging macros which delegate to a specific logging implementation. At runtime a specific implementation is selected from, in order, slf4j, Apache commons-logging, log4j2, log4j, and finally java.util.logging.

Logging levels are specified by clojure keywords, in increasingly severe order:

:trace, :debug, :info, :warn, :error, :fatal

Logging occurs with the log macro, or the level-specific convenience macros (e.g., debug, debugf). Only when the specified logging level is enabled will the message arguments be evaluated and the underlying logging implementation be invoked. By default that invocation will occur via an agent when inside a running STM transaction.

Unless otherwise specified, the current namespace (as identified by *ns*) will be used as the log-ns (similar to how the java class name is usually used). Note: you should configure your logging implementation to display the name that was passed to it; if it instead performs stack-inspection you'll see some ugly and unhelpful text in your logs.

You can redirect all java writes of System.out and System.err to the log system by calling log-capture!. To bind *out* and *err* to the log system invoke with-logs. In both cases a log-ns value must be specified in order to namespace the output.


The latest API documentation can be found at

The following short example should give you what you need to get started:

(ns example.math
  (:require [ :as log]))

(defn divide [x y]
  (log/info "dividing" x "by" y)
    (log/spyf "result is %s" (/ x y)) ; yields the result
    (catch Exception ex
      (log/error ex "There was an error in calculation"))))

Example repl output using the configuration below:

user=> (use 'my.example)
user=> (divide 1 2)
INFO  example.math: dividing 1 by 2
DEBUG example.math: result is 1/2
user=> (divide 2 0)
INFO  example.math: dividing 2 by 0
ERROR example.math: There was an error in calculation
java.lang.ArithmeticException: Divide by zero
    at clojure.lang.Numbers.divide(

For those new to using a java logging library, the following is a very basic configuration for log4j. Place it in a file called and place that file (and the log4j JAR) on the classpath.

log4j.rootLogger=INFO, console
log4j.appender.console.layout.ConversionPattern=%-5p %c: %m%n

The above will print messages to the console for :debug or higher if one is in the example namespace, and :info or higher in all other namespaces.


Logging is available in Maven central. Add it to your Maven project's pom.xml:


or your leiningen project.clj:

[org.clojure/tools.logging "0.5.0"]

Please note the changelog below.

Building Logging

  1. Clone the repo
  2. Make sure you have maven installed
  3. Run the maven build; run either:
    1. mvn install: This will produce a logging jar file in the target directory, and run all tests with the most recently-released build of Clojure.



Copyright © 2009 Alex Taggart

Licensed under the EPL. (See the file epl.html.)