Is Maven mandatory for Clojure on the JVM?

Question

I'm a bit surprised at the sheer number of articles / blogs / questions / answers about Clojure mentioning Maven.

In about ten years working as a Java dev, working on both desktop apps and webapps, I've never ever used Maven once (typically --and that's a personal opinion but I know some people do think the same-- the projects I've seen using Maven where including the "kitchen sink" whereas the ones built with a more "controlled" build process where way "cleaner" and producing smaller jars, faster build time, etc.).

Is Maven a requirement when you want to build a Clojure app?

Is Maven mandatory when you want to use Leiningen? For example, can I add external jars as dependencies to a leiningen project "manually", without needing Maven?

I think my question boils down to this: can you, in the Clojure/JVM world get away without ever using Maven, just like you can build, test, package and ship both Java desktop, webapps and Android apps without ever needing Maven?

Answer 1

Short answer: No. Clojure's just a jar and you can use it as "raw" as you like, just like any other Java library.

Longer answer: Maven's not a requirement, but the tooling around Clojure, especially Leiningen, is highly Maven-aligned so your life will be easier if you just submit to Maven's will. But, with a little work, it's not that hard to get along without Maven. At work, I use a mix of Leiningen and our existing Ant/Ivy-based build infrastructure. I use Ant to resolve dependencies (from our curated internal repo) and then use a hack of Leiningen's :resource-paths to get it to pick up the non-Maven jars. At some point I'll make a true plugin to do this stuff, but it's been working fine for me so far.

Also, if you're an Eclipse person and use CounterClockwise, you can treat your project like any other Java project in Eclipse, managing the classpath manually. It just happens that you've got some Clojure code in there as well.

Of course, the drawback in either approach is that if you want to grab something that's available from either Maven central or Clojars, you'll either have to set up some kind of mirror for your infrastructure, or manually pull down the transitive dependencies and add them to your project.

Answer 2

You do not have to use maven, or leiningen, for that matter. You can run the clojure REPL with

 java -jar clojure-1.3.0.jar

and it will work just fine. I know where you're coming from, because a year ago, I was in the same boat as you. never used maven, seen a couple of less than great projects that used it poorly, and generally distrusted maven. Ant+ivy works great, who needs maven?

As a result of using leiningen, and starting a new job where we have a very well setup maven config, I've changed my tune completely; I now think maven is great, and far prefer it to ant, which I've used for a long time.

Specifically with clojure, some advantages of leiningen are:

• automagic project scaffolding: "lein new" sets up a new project for you. convention is important, it helps other developers understand your project and quickly ramp up on it.
• dependency and plugin management. adding a dependency is trivial, and there isn't a great way that I am aware of to do non-maven dependency management that is tightly integrated with clojure.
• "lein repl" sets up your classpath and everything correctly, so you don't have to fool with it, you can just start and run a REPL.
• artifact creation: building a fat jar (lein uberjar) is straightforward, and already set up for you.

So, while it's definitely possible to use clojure without leiningen, I honestly don't see why you would want to. There are too many niceities for day to day development not to use it, in my opinion.

Answer 3

regarding "Is Maven mandatory when you want to use Leiningen?"

leiningen uses and wraps Maven so you can't truly avoid it, though you don't ever need to touch any XML

Answer 4

Maven is not mandatory for Clojure as others have rightly pointed out.

However, I would like to encourage you to embrace Maven (either directly or via leiningen). It has some big advantages in the Clojure world:

• You will be more productive in the long run - once you've got it set up, it is pretty impressive to see a complex build, test and deployment execute in a single command. Do you really want to be manually setting classpaths, downloading dependencies, incrementing version numbers, uploading to FTP sites etc.?
• One of the biggest advantages of using Clojure on the JVM is access to the Java library ecosystem. Maven is the tool of choice for automatically managing dependencies on Java libraries. Nearly everything you are likely to need will be in either the Maven Central or Clojars repositories.
• Clojure tends to have small focused libraries - this is good because they are "simple" and you can pick and choose the functionality you like. At the same time, it also means that you are likely to have numerically more library dependencies. Hence a build management system is going to be more useful.
• You can make Maven builds as "lean" as you like. Obviously you can pull in every dependency under the sun if you like, but you can also create very lean jars by excluding the unnecessary cruft. That's your choice.
• It is the de-facto standard in the Clojure world. If nothing else, using it means that you will be able to collaborate with others more easily.

P.S. Like you, I didn't really see the point of Maven 5 years ago. Then I gave it a go and saw how powerful it could be for my workflow. Now I'm a convert :-)