Skip to content
Carica is a flexible configuration library.
Find file
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.


Carica is a flexible configuration library.

It offers:

  • a simple lookup syntax
  • support for both Clojure and JSON config files
  • config file merging (if you have more than one config file)
    • Even if one is a Clojure file and the other is JSON
  • code evaluation in Clojure files
  • runtime override capabilities for testing
  • easy default config file names (config.clj and config.json)
    • ability to override the defaults


[sonian/carica "1.0.2"]
;; carica is compatible with clojure 1.4+

Carica looks for the config files on the classpath.

Leiningen will add a directory called "resources" to the classpath even though the directory is not created by default, so create a "resources" directory at the root of your project. Now, create and open "resources/config.clj" in your favorite editor.

{:foobar-timeout 300 #_"In seconds"
 :favorite-hour-of-day 8 #_"0-23"
 :blacklist nil
 :export-dir "/mnt/export"
 :timeout-ms (* 20 60 1000) #_"20 minutes"
 :db {:classname "org.postgresql.Driver"
      :subprotocol "postgresql"
      :subname "//localhost/test"
      :username "cosmo"
      :password "toomanysecrets"}}

(If you're wondering about the #_"" comments, we've found that they're less prone to errors in the configuration files. That is, from accidental newlines or from pulling up the closing brace into a line with a ;; comment.)


Now, with all of that in place, open a new REPL session:

(use '[carica.core])

(config :export-dir)
;;=> "/mnt/export"

(config :db :username)
;;=> "cosmo"

(config :blacklist)
;;=> nil

(config :non-existent-key)
;;=> nil (with a warning message logged)

That's it!

Overriding the defaults

Maybe you already have a config file with a different name, or a config.clj that you use for a different purpose. No problem. To override what files Carica loads you can create your own config function using the configurer function.

(ns my-proj.config
  (:require [carica.core :refer [configurer

(def config (configurer (resources "proj_config.clj")))

Calling my-proj.config/config will work the same as calling carica.core/config except that it will use your config file.


You can change the resulting config map in Carica by adding middleware. For instance, if you trust the data you are reading and want to have it evaluated, there is an eval-config middleware provided. If you want the config to be read only once from disk, you can use the cache-config middleware.

(ns my-proj.config
  (:require [carica.core :refer [configurer

(def config (configurer (resources "proj_config.clj")

In typical middleware fashion, eval-config and cache-config are functions that take a function as their only argument and return a function that takes a list of resources as its only input. For instance, the cache-config function:

(defn cache-config
  "Config middleware that will cache the config map so that it is
  loaded only once."
  (memoize (fn [resources]
             (f resources))))


Sometimes, during tests, it's handy to be able to override config values:

(with-redefs [config (override-config :db :password "swordfish")]

  (config :db :password)
  ;;=> "swordfish"

  (config :db :username))
  ;;=> "cosmo"


(with-redefs [config (override-config :db {:username "wagstaff"
                                           :password "swordfish"})]
  (config :db :password)
  ;;=> "swordfish"

  (config :db :username))
  ;;=> "wagstaff"

Only the provided values will be overwritten.

Mind the Classpath

Carica looks for resources on the classpath and merges them in order, meaning that configuration files earlier in the classpath will take precedence over those that come later.

When using Leiningen the classpath is built such that test comes first, then src, followed by resources-path. Keep the order in mind when dealing with multiple configuration files with Leiningen and when building the classpath by hand.

Optional Dependencies

Carica only uses Cheshire for JSON config parsing, so if you aren't using that feature, then you can exclude Cheshire from your dependencies, like this:

[sonian/carica "1.0.2" :exclusions [[cheshire]]]


Copyright (C) 2013 Sonian, Inc.

Distributed under the Eclipse Public License, the same as Clojure.

Something went wrong with that request. Please try again.