Brutally opinionated REST micro-framework.
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.


What is it?

Java for the Web. A brutally opinionated, super-simple REST API framework, plus static file serving.

It's not comprehensive, won't give you the flexibility you want and doesn't really care about your special needs.

For an overview and examples of the framework, head to the restolino-example repo to see a template project.

What it does do is let you work and stays out of your way, because configuring frameworks is a distraction. Java is a great language with loads of support, but it's never been efficient for Web development. This changes that.

Life is hard enough. Complexity will quitetly come and steal your time. Bar the door. Don't go looking for it. If it sits down it won't want to leave.

If you're a Java purist, this is not the framework you are looking for.

And that's it.


Restolino has unreasonable opinions:

  • Web applications should be APIs: data should not be wrapped in markup.
  • HTML/Javascript is youn API client: then you can add mobile apps, IoT devices, etc.
  • Templating is great: do it in Javascript, not server-side.
  • Efficient development: add classes, change interfaces, whatever, then refresh.
  • Immutable releases: single-jar artifact. To make a change to the deployed version, deploy a new version and delete the old vesion (blue-green and all that).
  • Stateless requests: when deployed, you'll probably have multiple nodes. Everything gets reinitialised after each change in development. That makes stetefulness difficult, which is a good thing.
  • Restolino will cause your design to hurt and adapt. You'll be better for it in the long run.
  • Constraints are your path to simplicity. Enjoy them.

How it works

The framework does less than you'd expect, and that's better:

  • Runs an embedded Jetty server with raw Handler classes. No Servlets, no Filters, no Context. No web.xml.
  • Requests that have a file extension are static files. They will be handled by a Jetty ResourceHandler.
  • Requests that do not have a file extension go to your API.
  • APIs consume and return JSON. Accept a parameter of any type, return a result of any type. Serialisation is done for you using Gson.
  • You get direct access to HttpServletRequest and HttpServletResponse.
  • If you need to return something other than Json, use a void method or return null.
  • Unmapped requests go to your implementation of the NotFound interface, or the DefaultNotFound implementation. A 404 status code is set by default.
  • Errored requests go to your implementation of the ServerError interface, or the DefaultServerError implementation. A 500 status code is set by default.
  • Responses are compressed automatically by a Jetty GzipHandler if the client supports gzip encoding.

Getting started

  • You can only GET /. Why would you PUT, POST or DELETE the root? You wouldn't. If you think you would, your design sucks.
  • By default / will give you Json documentation of your API. To change this, implement the Home interface, which provides a single method: get(req, res) (or subclass HomeRedirect).
  • Put all your static files under web - i.e. src/main/resources/web/... (or src/main/web/... and add a resources section to your pom).
  • Annotate your API classes as @Api.
  • API names are lowercased class names. More complexity would need more of your time. Get over it.
  • Annotate your methods with JAX-RS @GET, @PUT, @POST and @DELETE.
  • Method parameters can include HttpServletRequest and HttpServletResponse. You can optionally have one parameter of any type you want. Gson will attempt to deserialise this from the request body.
  • The return type of your method can be any type you want Gson to attempt to serialise into the response. Returns of void and null are fine, in which case Restolino won't change your response.
  • Request and response messages are [de]serialised as JSON using Gson. If you need to add custom type adapters for serialisation, you can access the GsonBuilder via Serialiser.getBuilder(). A few default type adapters (in the json.typeadapters package) and a sensible Javascript isoDate format are set for you by default.
  • There's no context path. Why would you run more than one app in the same server process? The Jetty process is one-to-one with your app.
  • You only need one not-found handler. Implement the NotFound interface. It provides a single method: handle(req, res). A 404 status will be pre-set for you. You can update it if you want.
  • You only need one error handler, but you do need to know where the error occurred. Implement the ServerError interface, which provides a single method handle(req, res, RequestHandler, Throwable). A 500 status will be pre-set for you. You can update it if you want.
  • No clever (read: fiddly and time consuming) path/parameter parsing. Simple helper classes are provided instead: Path, QueryString and Parameter. See the com.github.davidcarboni.restolino.helpers package.
  • OPTIONS will query the configuration and tell you which of GET, PUT, POST and DELETE are implemented for that API. OPTIONS on / will return GET if you have implemented Home or subclassed HomeRedirect.
  • To see the whole framework - all the interfaces and annotations you can use - have a look in the com.github.davidcarboni.restolino.framework package. It's intentionally small.
  • Java 1.7. If you're using anything older, try using Bing to look up SOAP. I know, that's not fair. If you're smart enough to be able to use Google, fork and build from source.
  • There are non-private fields in the classes. Like semi-colons in Javascript, the usual modifiers are visual clutter that provide too little benefit. That's my opinion. I'm not asking you to agree if you don' want to.

Looking under the hood

Restolino aims to be simple enough for you to understand the code. This is not intended as an academic achievement of subtle software engineering prowess. It's meant to be basic, pragmatic, helpful and uncomplicated. Sort of like the girl/boy next door you realise is a far deeper friend than cool kids you've been trying to impress.

Here is the list of packages and what they mean. There are no more than a pizza's worth of classes in each:

  • com.github.davidcarboni.restolino.framework - The stuff you need to define your API - annotations and interfaces.
  • com.github.davidcarboni.restolino.helpers - Convenience classes you may (or may not) want to use to make your life easier.
  • com.github.davidcarboni.restolino.handlers - Default and example Home, NotFound and ServerError handlers.
  • com.github.davidcarboni.restolino.json - Json serialisation
  • com.github.davidcarboni.restolino.api - The classes that set up your API.
  • com.github.davidcarboni.restolino.reload - The classes that detect file changes and trigger reloading.
  • com.github.davidcarboni.restolino.jetty - The Jetty handlers that make up Restolino. MainHandler receives requests, decides whether a request is for an API or a file and delegates to ApiHandler or FilesHandler. There's also a handler for HTTP Basic authentication.
  • com.github.davidcarboni.restolino - The Main and Configuration classes used to start the server.



Maven build

The configuration below provides both a -jar-with-dependencies (for deployment) and a folder of dependencies for reloading in development (${}/dependency). NB this should work if you want to deploy to Heroku.

This also configures your project for Java 1.8. You could do this with profiles if you want to:

			<!-- Standard resources -->
			<!-- Your static content - this will end up in target/web/ -->
			<!-- Java 1.8. You're not still using 1.6 - are you: -->
			<!-- An assembly that includes all dependencies is produced for deployment: -->

			<!-- A folder of dependencies is used in development when reloading classes: -->
						<!-- Default output folder is ${}/dependency -->


NB you could use the maven-shade-plugin if you want finer control of the "uberjar", but jar-with-dependencies is pretty restrictive, which is almost always a good thing - and should help you keep a clean and simple design.


This is what you want, right? Minimum time-to-working. This runs your API on port 8080 with remote debug on 8000.


# Remote debug:
export JAVA_OPTS="-Xdebug -Xrunjdwp:transport=dt_socket,address=8000,server=y,suspend=n"

# File reloading:
export RESTOLINO_STATIC="src/main/web"

# Class reloading
export RESTOLINO_CLASSES="target/classes"
# Optional package prefix:
# export RESTOLINO_PACKAGEPREFIX=com.mycompany.myapp

# Basic authentication
#export USERNAME=java
#export PASSWORD=fortheweb
# Optional: Practically speaking, any value you like that describes your app.
#           see also:
#export REALM=niceapp

mvn clean package && \

# Development: reloadable
java $JAVA_OPTS -Drestolino.files=$RESTOLINO_STATIC -Drestolino.classes=$RESTOLINO_CLASSES -Drestolino.packageprefix=$RESTOLINO_PACKAGEPREFIX -cp "target/dependency/*" com.github.davidcarboni.restolino.Main

# Deployment: non-reloadable
#java $JAVA_OPTS -jar target/*-jar-with-dependencies.jar

Why not reload when deployed? You want to be using containers, but as a minimum you should be designing for stateless, immutable nodes. If something needs to change in your deployment, update a the build using your flavour of continuous delivery. Changing running servers manually is a brew of risk that ends in pain.

FAQ (Frequently Anticipated Questions)

Is it good enough for commercial projects?

I used Restolino to implement a significant Alpha project for the UK government. The focus was on creating a working prototype, so speed of iteration was very important. It worked. The best thing about using Restolino was nobody talked about Restolino - it stayed out of the way and never became the conversation.

Is it fast/secure/productionised?

I don't know. What I do know is that both the server and the framework are doing much less before your code gets to see a request. That's a good indicator for performance (less layers) and security (less places for bugs to hide), so chances are good.

Restolino takes more away (Servlets, Filters, Context, etc.) than it adds. If you trust Jetty and want to make simple things freely, Restolino will probably work for you. (see also

Can I switch to Jersey for production?

Yes. Restolino intentionally doesn't stray too far from JAX-RS. If you add @Path(<classname>) to your classes and @Context to your HttpServletRequest and HttpServletResponse method parameters, your code should slot straight in to a Jersey application.

Why not use interfaces to define request handlers?

I've tried, but it adds complexity, doesn't add value and makes life harder. Why? Because the interface has to take into account that there may or may not be a request message type (so generic varargs would be needed - ever tried that?) and you can return any (or no) response message type (so the retun type is variable). That means either an altogether too generic interface (everything has to be Object, even if you'd prefer void) or individual interfaces for every permutation.

Using reflection to search for methods with either two or three parameters, where the first two are HttpServletRequest and HttpServletResponse turns out to be simpler, cleaner and more easily understood. Like I said, if you're a purist this isn't the framework you're looking for. Try it if you like - if you can come up with an elegant, pragmatic and developer-friendly solution, send me a pull request.

Why aren't my classes reloading / nothing gets configured?

First port of call is to look at the information printed to the console on startup. If you see Reflections URLs: [] you might need to check your restolino.packageprefix setting - I've made this mistake a couple of times. If nothing is happening when you update a class, check the values of classesReloadable and classesInClasspath. It's not possible to reload classes that are on the JVM classpath at startup.

How can I enable logging?

Restolino uses the SLF4J interface for logging. Please refer to the SLF4J documentation for further information on enabling its output.

Is it really this cool?

I'm still aced that I can edit code, adding new fields, methods, annotations - even classes - and it's there when I refresh the browser. After years of productivity-sapping build-redeploy cycles, there's something utterly delicious and deeply freeing about it.

I was able to create a project from scratch and get to a running API in 10 minutes by cutting and pasting the above snippets. For me that's a lot faster than configuring Spring or even Jersey, not to mention the time I've spent debugging config.

Honestly, I originally built this in a day so don't expect a miracles. I hope it gives you a boost with getting stuff done rather than learning to love a fancy framework. Class reloading took longer and I ditched Servlets for embedded Jetty with raw Handlers along the way.

The code isn't perfect, but it should just work - and let you work. Let me know if you like it.