Your First Application


  1. Guestbook Application
  2. Installing JDK
  3. Installing Leiningen
  4. Creating a new application
  5. Anatomy of a Luminus application
  6. The Source Directory
  7. The Env Directory
  8. The Test Directory
  9. The Resources Directory
  10. The Project File
  11. Creating the Database
  12. Accessing The Database
  13. Running the Application
  14. Creating Pages and Handling Form Input
  15. Packaging the application

Guestbook Application

This tutorial will guide you through building a simple guestbook application using Luminus. The guestbook allows users to leave a message and to view a list of messages left by others. The application will demonstrate the basics of HTML templating, database access, and project architecture.

If you don't have a preferred Clojure editor already, then it's recommended that you use Light Table to follow along with this tutorial.

Installing JDK

Clojure runs on the JVM and requires a copy of JDK to be installed. IF you don't have JDK already on your system then OpenJDK is recommended and can be downloaded here. Note that Luminus requires JDK 8 to work with the default settings.

Installing Leiningen

You need to have Leiningen installed in order to work with Luminus. Installing Leiningen is accomplished by following the step below.

  1. Download the script.
  2. Set it to be executable. (eg: chmod +x lein)
  3. Place it on your $PATH. (eg: ~/bin)
  4. Run lein and wait for the self-installation to complete.
chmod +x lein
mv lein ~/bin

Creating a new application

Once you have Leiningen installed you can run the following command in your terminal to initialize your application:

lein new luminus guestbook +h2
cd guestbook

The above will create a new template project with the support for H2 embedded database engine.

Anatomy of a Luminus application

The newly created application has the following structure:

| |____guestbook
|   |____core.clj
|   |____handler.clj
|   |____layout.clj
|   |____middleware.clj
|   |____routes
|   | |____home.clj
|   |____db
|     |____core.clj
|     |____migrations.clj
| |____dev
| | |____clj
| | |  |____guestbook
| | |   |____config.clj
| | |   |____dev_middleware.clj.clj
| | |___resources
| |      |
| |____prod
|   |____clj
|   | |____guestbook
|   |   |____config.clj
|   |___resources
|        |
| |____guestbook
|   |____test
|     |____handler.clj
  | |____about.html
  | |____base.html
  | |____home.html
  | |____error.html
  | |____css
  | | |____screen.css
  | |____img
  | |____js
  | |
  | |____20150718103127-add-users-table.down.sql
  | |____20150718103127-add-users-table.up.sql

Let's take a look at what the files in the root folder of the application do:

  • Procfile - used to facilitate Heroku deployments
  • - where documentation for the application is conventionally put
  • project.clj - used to manage the project configuration and dependencies by Leiningen
  • profiles.clj - used for local configuration that should not be checked into the code repository
  • .gitignore - a list of assets, such as build generated files, to exclude from Git

The Source Directory

All our code lives under the src folder. Since our application is called guestbook, this is the root namespace for the project. Let's take a look at all the namespaces that have been created for us.


  • core.clj - this is the entry point for the application that contains the logic for starting and stopping the server
  • handler.clj - defines the base routes for the application, this is the entry point into the application
  • layout.clj - a namespace for the layout helpers used to render the content for our pages
  • middleware.clj - a namespace that contains custom middleware for the application


The db namespace is used to define the model for the application and handle the persistence layer.

  • core.clj - used to house the functions for interacting with the database
  • migrations.clj - used to run the database migrations


The routes namespace is where the routes and controllers for our home and about pages are located. When you add more routes, such as authentication, or specific workflows you should create namespaces for them here.

  • home.clj - a namespace that defines the home and about pages of the application

The Env Directory

This source folder contains environment dependent code. The dev configuration will be used during development, while the prod configuration will be used when the application is compiled for production.

  • config.clj - contains the development configuration defaults
  • dev_middleware.clj - contains middleware used for development that should not be compiled in production

The Test Directory

Here is where we put tests for our application, a couple of sample tests have already been defined for us.

The Resources Directory

This is where we put all the static resources for our application. Content in the public directory under resources will be served to the clients by the server. We can see that some CSS resources have already been created for us.

HTML templates

The templates directory is reserved for the Selmer templates that represent the application pages.

  • about.html - the about page
  • base.html - the base layout for the site
  • home.html - the home page

SQL Queries

The SQL queries are found in the resources/sql folder.

  • queries.sql - defines the SQL queries and their associated function names

The Migrations Directory

Luminus uses Migratus for managing migrations. Migrations are managed using up and down SQL files. The files are conventionally versioned using the date and will be applied in order.

  • 20150718103127-add-users-table.up.sql - migrations file to create the tables
  • 20150718103127-add-users-table.down.sql - migrations file to drop the tables

The Project File

As was noted above, all the dependencies are managed via updating the project.clj file. The project file of the application we've created is found in its root folder and should look as follows:

(defproject guestbook "0.1.0-SNAPSHOT"

  :description "FIXME: write description"
  :url ""

:dependencies [[org.clojure/clojure "1.7.0"]
               [selmer "0.9.6"]
               [org.clojure/tools.logging "0.3.1"]
               [org.slf4j/slf4j-log4j12 "1.7.13"]
               [org.apache.logging.log4j/log4j-core "2.5"]
               [com.taoensso/tower "3.0.2"]
               [markdown-clj "0.9.84"]
               [luminus/config "0.3"]
               [compojure "1.4.0"]
               [ring-webjars "0.1.1"]
               [ring/ring-defaults "0.1.5"]               
               [ring "1.4.0"
                :exclusions [ring/ring-jetty-adapter]]
               [metosin/ring-middleware-format "0.6.0"]
               [metosin/ring-http-response "0.6.3"]
               [bouncer "0.3.3"]
               [prone "0.8.2"]
               [org.clojure/tools.nrepl "0.2.10"]
               [org.webjars/bootstrap "3.3.5"]
               [org.webjars/jquery "2.1.4"]
               [migratus "0.8.2"]
               [conman "0.2.7"]               
               [com.h2database/h2 "1.4.187"]
               [org.immutant/web "2.1.1"
                :exclusions ['ch.qos.logback/logback-classic]]]

  :min-lein-version "2.0.0"
  :uberjar-name "guestbook.jar"
  :jvm-opts ["-server"]

  :main guestbook.core
  :migratus {:store :database}

  :plugins [[lein-environ "1.0.1"]
            [lein-ancient "0.6.5"]
            [migratus-lein "0.1.5"]]
  {:uberjar {:omit-source true
             :env {:production true}
             :aot :all}
   :dev           [:project/dev :profiles/dev]
   :test          [:project/test :profiles/test]
   :project/dev  {:dependencies [[ring/ring-mock "0.2.0"]
                                 [ring/ring-devel "1.4.0"]
                                 [pjstadig/humane-test-output "0.7.0"]
                                 [mvxcvi/puget "0.8.1"]]

                  :repl-options {:init-ns guestbook.core}
                  :injections [(require 'pjstadig.humane-test-output)
                  ;;when :nrepl-port is set the application starts the nREPL server on load
                  :env {:dev        true
                        :port       3000
                        :nrepl-port 7000}}
   :project/test {:env {:test       true
                        :port       3001
                        :nrepl-port 7001}}
   :profiles/dev {}
   :profiles/test {}})

As you can see the project.clj is simply a Clojure list containing key/value pairs describing different aspects of the application.

The most common task is adding new libraries to the project. These libraries are specified using the :dependencies vector. In order to use a new library in our project we simply have to add its dependency here.

The items in the :plugins vector can be used to provide additional functionality such as reading environment variables via Environ plugin.

The :profiles contain a map of different project configurations that are used to initialize it for either development or production builds.

Note that the project sets up composite profiles for :dev and :test. These profiles contain the variables from :project/dev and :project/test profiles, as well as from :profiles/dev and :profiles/test found in the profiles.clj. The latter should contain local environment variables that are not meant to be checked into the shared code repository.

Please refer to the official Leiningen documentation for further details on structuring the project.clj build file.

Creating the Database

First, we will create a model for our application, to do that we'll open up the <date>-add-users-table.up.sql file located under the migrations folder. The file has the following contents:

 first_name VARCHAR(30),
 last_name VARCHAR(30),
 email VARCHAR(30),
 admin BOOLEAN,
 last_login TIME,
 is_active BOOLEAN,
 pass VARCHAR(100));

We'll replace the users table with one that's more appropriate for our application:

CREATE TABLE guestbook
 name VARCHAR(30),
 message VARCHAR(200),
 timestamp TIMESTAMP);

The guestbook table will store all the fields describing the message, such as the name of the commenter, the content of the message and a timestamp. We'll save the file and run the following command from the root of our project:

lein run migrate

If everything went well we should now have our database initialized.

Accessing The Database

Next, we'll take a look at the src/guestbook/db/core.clj file. Here, we can see that we already have the definition for our database connection.

(ns guestbook.db.core
    [yesql.core :refer [defqueries]]
    [environ.core :refer [env]]))

(def conn
  {:classname   "org.h2.Driver"
   :connection-uri (:database-url env)
   :make-pool?     true
   :naming         {:keys   clojure.string/lower-case
                    :fields clojure.string/upper-case}})

(defqueries "sql/queries.sql" {:connection conn})

The database connection is read from the :database-url environment variable at runtime. This variable is populated from the profiles.clj file during development and has to be set as an environment variable for production, e.g:

export DATABASE_URL="jdbc:h2:./guestbook.db"

Since we're using the embedded H2 database, the data is stored in a file specified in the URL that's found in the path relative to where the project is run.

The functions that map to database queries are generated when defqueries is called. As we can see it references the sql/queries.sql file. This location is found under the resources folder. Let's open up this file and take a look inside.

-- name: create-user!
-- creates a new user record
(id, first_name, last_name, email, pass)
VALUES (:id, :first_name, :last_name, :email, :pass)

-- name: update-user!
-- update an existing user record
UPDATE users
SET first_name = :first_name, last_name = :last_name, email = :email
WHERE id = :id

-- name: get-user
-- retrieve a user given the id.
WHERE id = :id

As we can see each function is defined using the comment that starts with –name: followed by the name of the function. The next comment provides the doc string for the function and finally we have the body that's plain SQL. The parameters are denoted using : notation. Let's replace the existing queries with some of our own:

-- name:save-message!
-- creates a new message
INSERT INTO guestbook
(name, message, timestamp)
VALUES (:name, :message, :timestamp)

-- name:get-messages
-- selects all available messages
SELECT * from guestbook

Finally, the namespace provides a helper function called run. This function will execute the query functions using the database connection found in the conn atom.

Running the Application

We can run our application in development mode as follows:

>lein run
00:49:54.865 [main] DEBUG org.jboss.logging - Logging Provider: org.jboss.logging.Slf4jLoggerProvider
15-Jul-19 00:49:55 Nyx INFO [guestbook.handler] - nREPL server started on port 7000
15-Jul-19 00:49:55 Nyx INFO [guestbook.handler] -
-=[guestbook started successfullyusing the development profile]=-
00:49:55.772 INFO  [org.projectodd.wunderboss.web.Web] (main) Registered web context /
15-Jul-19 00:49:55 Nyx INFO [guestbook.core] - server started on port: 3000

Once server starts, you should be able to navigate to http://localhost:3000 and see the app running. The server can be started on an alternate port by either passing it as a parameter as seen below, or setting the PORT environment variable.

lein run 8000

Note that the page is prompting us to run the migrations in order to initialize the database. However, since we've already done that earlier and we won't need to do that again.

Creating Pages and Handling Form Input

Our routes are defined in the guestbook.routes.home namespace. Let's open it up and add the logic for rendering the messages from the database. We'll first need to add a reference to our db namespace along with references for Bouncer validators and ring.util.response

(ns guestbook.routes.home
    [guestbook.db.core :as db]
    [bouncer.core :as b]
    [bouncer.validators :as v]
    [ring.util.response :refer [redirect]]))

Next, we'll create a function to validate the form parameters.

(defn validate-message [params]
      :name v/required
      :message [v/required [v/min-count 10]])))

The function uses the Bouncer validate function to check that the :name and the :message keys conform to the rules we specified. Specifically, the name is required and the message must contain at least 10 characters. Bouncer uses vector syntax to pass multiple rules to a validator as is the case with the message validator.

When a validator takes additional parameters as is the case with min-count the vector syntax is used as well. The value will be passed in implicitly as the first parameter to the validator.

We'll now add a function to validate and save messages:

(defn save-message! [{:keys [params]}]
  (if-let [errors (validate-message params)]
    (-> (redirect "/")
        (assoc :flash (assoc params :errors errors)))
       (assoc params :timestamp (java.util.Date.)))
      (redirect "/"))))

The function will grab the :params key from the request that contains the form parameters. When the validate-message functions returns errors we'll redirect back to /, we'll associate a :flash key with the response where we'll put the supplied parameters along with the errors. Otherwise, we'll save the message in our database and redirect.

Finally, we'll change the home-page handler function to look as follows:

(defn home-page [{:keys [flash]}]
   (merge {:messages (db/get-messages)}
          (select-keys flash [:name :message :errors]))))

The function renders the home page template and passes it the currently stored messages along with any parameters from the :flash session, such as validation errors.

Our routes will now have to pass the request to both the home-page and the save-message! handlers:

(defroutes home-routes
  (GET "/" request (home-page request))
  (POST "/" request (save-message! request))
  (GET "/about" [] (about-page)))

Don't forget to refer POST from compojure.core

(ns guestbook.routes.home
  (:require ...
            [compojure.core :refer [defroutes GET POST]]

Now that we have our controllers setup, let's open the home.html template located under the resources/templates directory. Currently, it simply renders the contents of the content variable inside the content block:

{% extends "base.html" %}
{% block content %}
  <div class="jumbotron">
    <h1>Welcome to guestbook</h1>
    <p>Time to start building your site!</p>
    <p><a class="btn btn-primary btn-lg" href="">Learn more &raquo;</a></p>

  <div class="row">
    <div class="span12">
{% endblock %}

We'll update our content block to iterate over the messages and print each one in a list:

{% extends "base.html" %}
{% block content %}
  <div class="jumbotron">
    <h1>Welcome to guestbook</h1>
    <p>Time to start building your site!</p>
    <p><a class="btn btn-primary btn-lg" href="">Learn more &raquo;</a></p>

  <div class="row">
    <div class="span12">
        <ul class="messages">
            {% for item in messages %}
                <time>{{item.timestamp|date:"yyyy-MM-dd HH:mm"}}</time>
                <p> - {{}}</p>
            {% endfor %}
{% endblock %}

As you can see above, we use a for iterator to walk the messages. Since each message is a map with the message, name, and timestamp keys, we can access them by name. Also, notice the use of the date filter to format the timestamps into a human readable form.

Finally, we'll create a form to allow users to submit their messages. We'll populate the name and message values if they're supplied and render any errors associated with them. Note that the forms also uses the csrf-field tag that's required for cross-site request forgery protection.

<div class="row">
    <div class="span12">
        <form method="POST" action="/">
                {% csrf-field %}
                    <input class="form-control"
                           value="{{name}}" />
                {% if %}
                <div class="alert alert-danger">{{|join}}</div>
                {% endif %}
                <textarea class="form-control"
                {% if errors.message %}
                <div class="alert alert-danger">{{errors.message|join}}</div>
                {% endif %}
                <input type="submit" class="btn btn-primary" value="comment" />

Our final home.html template should look as follows:

{% extends "base.html" %}
{% block content %}
<div class="row">
    <div class="span12">
        <ul class="messages">
            {% for item in messages %}
                <time>{{item.timestamp|date:"yyyy-MM-dd HH:mm"}}</time>
                <p> - {{}}</p>
            {% endfor %}
<div class="row">
    <div class="span12">
        <form method="POST" action="/">
                {% csrf-field %}
                    <input class="form-control"
                           value="{{name}}" />
                {% if %}
                <div class="alert alert-danger">{{|join}}</div>
                {% endif %}
                <textarea class="form-control"
                {% if errors.message %}
                <div class="alert alert-danger">{{errors.message|join}}</div>
                {% endif %}
                <input type="submit" class="btn btn-primary" value="comment" />
{% endblock %}

Finally, we can update the screen.css file located in the resources/public/css folder to format our form nicer:

body {
	height: 100%;
	padding-top: 70px;
	font: 14px 'Helvetica Neue', Helvetica, Arial, sans-serif;
	line-height: 1.4em;
	background: #eaeaea;
	width: 550px;
	margin: 0 auto;

.messages {
  background: white;
  width: 520px;
ul {
	list-style: none;

ul.messages li {
	position: relative;
	font-size: 16px;
	padding: 5px;
	border-bottom: 1px dotted #ccc;

li:last-child {
	border-bottom: none;

li time {
	font-size: 12px;
	padding-bottom: 20px;

form, .error {
	width: 520px;
	padding: 30px;
	margin-bottom: 50px;
	position: relative;
  background: white;

When we reload the page in the browser we should be greeted by the guestbook page. We can test that everything is working as expected by adding a comment in our comment form.

Packaging the application

The application can be packaged for standalone deployment by running the following command:

lein uberjar

This will create a runnable jar that can be run as seen below:

java -jar target/guestbook.jar

Complete source listing for the tutorial is available here. For a more complete example you can see the source for this site on Github.