Example Web Application in Clojure

This is a simple web application using Component, Ring, Compojure, and Selmer connected to a local SQLite database.

Clojure beginners often ask for a "complete" example that they can look at to see how these common libraries fit together and for a long time I pointed them at the User Manager example in the Framework One for Clojure repo -- but since I EOL'd that framework and I'd already rewritten the example app to no longer use the framework, it's just confusing to point them there, so this is a self-contained repo containing just that web app example.

A variant using Integrant and Reitit (instead of Component and Compojure), inspired by this example repo, can be found in Michaël Salihi's repo.

A version of this application that uses the Polylith architecture is also available, on the polylith branch.

A version of this application that uses the XTDB 2 database instead of SQLite/H2 is also available, on the xtdb branch.

Aditya Athalye has created a stripped version, using core functions and helper functions instead of several libraries that this version uses: usermanager-example from first principles. Comparing that version and this version is a good exercise in understanding the basic machinery that a web app needs, and what those libraries are doing for you.

Quickstart via Devcontainers or Github Codespaces

If you have configured your Github account, you can start the project without any other setup. It will open a web-based vscode editor backed by a Github Codespace VM. (Codespaces is Github's hosted Devcontainer solution)

You can also clone this repo locally, and using vscode (with the devcontainer plugin), and Docker Desktop, run an isolated, fully setup version of this application locally. Open the repo in your editor and run the command Dev Containers: Open Folder in Container....

Requirements

This example assumes that you have a recent version of the Clojure CLI installed (at least 1.10.3.933), and provides a deps.edn file, and a build.clj file.

Clojure 1.10 (or later) is required. The "model" of this example app uses namespace-qualified keys in hash maps. It uses next.jdbc -- the "next generation" JDBC library for Clojure -- which produces namespace-qualified hash maps from result sets.

Usage

Clone the repo, cd into it, then follow below to Run the Application or Run the application in REPL or Run the tests or Build an Uberjar.

Run the Application

clojure -M -m usermanager.main

It should create a SQLite database (usermanager_db) and populate two tables (department and addressbook) and start a Jetty instance on port 8080.

If that port is in use, start it on a different port. For example, port 8100:

clojure -M -m usermanager.main 8100

Run the Application in REPL

Start REPL

$ clj

Once REPL starts, start the server as an example on port 8888:

user=> (require 'usermanager.main)                             ; load the code
user=> (in-ns 'usermanager.main)                               ; move to the namespace
usermanager.main=> (def system (new-system 8888))              ; specify port
usermanager.main=> (alter-var-root #'system component/start)   ; start the server

Run the tests with:

clojure -T:build test

You should see something like this:

Running task for: test

Running tests in #{"test"}
2023-01-24 22:31:01.269:INFO::main: Logging initialized @4050ms to org.eclipse.jetty.util.log.StdErrLog

Testing usermanager.model.user-manager-test
Created database and addressbook table!
Populated database with initial data!

Ran 3 tests containing 9 assertions.
0 failures, 0 errors.

This uses the :build alias to load the build.clj file, based on tools.build, and run the test task.

Build an Uberjar

For production deployment, you typically want to build an "uberjar" -- a .jar file that contains Clojure itself and all of the code from your application and its dependencies, so that you can run it with the java -jar command.

The build.clj file -- mentioned above -- contains a ci task that:

• runs all the tests
• cleans up the target folder
• compiles the application (sometimes called "AOT compilation")
• produces a standalone .jar file

clojure -T:build ci

That should produce the same output as test above, followed by something like:

Copying source...

Compiling usermanager.main...
2023-01-24 22:35:37.922:INFO::main: Logging initialized @2581ms to org.eclipse.jetty.util.log.StdErrLog

Building JAR...

The target folder will be created if it doesn't exist and it will include a classes folder containing all of the compiled Clojure source code from the usermanager application and all of its dependencies including Clojure itself:

$ ls target/classes/
camel_snake_kebab  clout  compojure  instaparse  medley  public  selmer       views
clojure            com    crypto     layouts     next    ring    usermanager

It will also include the standalone .jar file which you can run like this:

java -jar target/usermanager/example-standalone.jar

This should behave the same as the Run the Application example above.

This JAR file can be deployed to any server that have Java installed and run with no other external dependencies or files.

Stuff I Need To Do

• I might add a datafy/nav example.

License & Copyright

Copyright (c) 2015-2023 Sean Corfield.

Distributed under the Apache Source License 2.0.