What is the good starting point to developing RESTful web service in Clojure?

I am looking into something lightweight, that, at a minimum should support the following features:

• Support for easy definition of actions through metadata
• Wrapper that extracts parameters from request into clojure map, or as function parameters
• Support for multiple forms of authentication (basic, form, cookie)
• basic authorization based of api met开发者_开发百科hod metadata
• session object wrapped in clojure map
• live coding from REPL (no need to restart server)
• automatic serialization of return value to json and xml
• have nice (pluggable) url parameter handling (eg /action/par1/par2 instead of /action?par1=val1&par2=val2)

I know it is relatively easy to roll my own micro-framework for each one of these options, but why reinvent the wheel if something like that already exists? Especially if it is:

• Active project with rising number of contributors/users
• Have at least basic documentation and tutorial online.

First of all, I think that you are unlikely to find a single shrinkwrapped solution to do all this in Clojure (except in the form of a Java library to be used through interop). What is becoming Clojure's standard Web stack comprises a number of libraries which people mix and match in all sorts of ways (since they happily tend to be perfectly compatible).¹

Here's a list of some building blocks which you might find useful:

1. Ring -- Clojure's basic HTTP request handling library; all the other webby libraries (for writing routes &c.) that I know of are compatible with Ring. Ring is being actively developed, has a robust community, is very well-written and has a nice SPEC document detailing its design philosophy. This blog post provides a nice example of how it might be used (reacting to GitHub commits).

2. Sandbar -- currently an authentication library, more types of functionality planned; under development.

3. Compojure -- a mature and robust library which provides a nice DSL for writing routes to be used on top of Ring. This will give you the nice URL parameter handling.

4. Compojure-rest -- "a library for building RESTful applications on top of Compojure". Compojure-rest is, as far as I can tell, in its early stages of development; perhaps you might see this as an opportunity to influence its design. :-)

5. For dealing with XML, there's clojure.contrib.lazy-xml (and the helper library clojure.contrib.zip-filter.xml) and Enlive (the built-in clojure.xml namespace is currently not very usable); these would be used in tandem (though for your purposes the former might suffice).

6. For JSON, there a library in contrib and clojure-json (and I think there was at least one other lib I seem to be forgetting now...); pick the one you like best.

All of will be perfectly happy with a REPL-driven development style (see the accepted answer to this SO question for a Ring trick which is very much to the purpose here). I suppose the above collection of links does leave a few blind spots (in particular, the authentication story is still being ironed out, as far as I can tell), but hopefully it's a good start.

¹The only single-package solution for building webapps in Clojure that I know of is Conjure, inspired by Rails; unfortunately I have to admit that I don't know much about it, so if you feel interested, follow the link and look around the sources, wiki &c.

While building my first Clojure rest service I found myself asking often the same question. The Clojure Toolbox helped me a lot: http://www.clojure-toolbox.com/

If you are looking for some sample, real-world, illustrative code to get you started, then you could study this clojure-news-feed on github project which demonstrates how to implement a non-trivial RESTful web service with compojure/ring that wraps both SQL (postgresql or mysql) and NoSQL (cassandra), search (solr), caching (redis), event logging (kafka), connection pooling (c3po), and real-time metrics via JMX.

This blog about Building a Scalable News Feed Web Service in Clojure provides a good introduction. I ran some load tests against this service on a humble AWS deployment and got about eighty transactions per second with less than a half second average latency per transaction.

Take a look at liberator library http://clojure-liberator.github.io/liberator/ It's noy a standalone solution, buy very good for rest service definition.

Just to provide an updated answer to this old question, currently (in 2018) I think Luminus provides an excellent starting point. It's using many of the libraries (ring, compojure, etc.) mentioned in previous answers, is modular and as close to "single package" as you can get with Clojure. Specifically for REST, take a look at compojure-api. Luminus recommends buddy for authentication, I've had good success using it both for traditional session-based auth as well as Oauth and stateless JWTs.