Sparkler is an attempt to bring developer-friendliness to Java web development by using Rails/Sinatra-style Java libraries/frameworks together with Xtend to provide syntactic sugar and other fun language features (like extension methods and lambdas).
Xtend Shell HTML
Latest commit 8793037 Mar 14, 2017 @tobykurien updated for gradle build
Failed to load latest commit information.
libs updated for gradle build Mar 14, 2017
.project initial version Nov 21, 2013
Todo.txt upgraded to Xtend 2.5.0 Dec 13, 2013
pom.xml updated mainclass Jan 8, 2014

Sparkler web framework

As evident from the TechEmpower Benchmarks, Java is significantly (often orders of magnitude) faster than other, more developer-friendly web frameworks like Django, Rails, or node.js. This means that you disadvantage yourself by creating web startups using these technologies, as scaling becomes a problem quite quickly, and scaling is not an easy problem to solve.

Sparkler is an attempt to bring developer-friendliness to Java web development by using Rails/Sinatra-style Java libraries/frameworks together with Xtend to provide syntactic sugar and other fun language features (like extension methods and lambdas). The result should be the best of both worlds: incredible performance with a developer-friendly framework. The idea is that Sparkler will be fun enough for use in hackathons, as a web startup prototyping tool, and a quick way to get RESTful JSON backends up.


Sparkler uses best-of-breed technologies and is (currently) based on:

  • Xtend a flexible and expressive dialect of Java, which compiles into readable Java 5 compatible source code. Think: CoffeeScript for Java
  • Spark high-performance Sinatra-inspired web micro-framework
  • Jetty high-performance embedded server (supports servlets, SPDY, WebSockets)
  • for logic-less templating (with Django-style template inheritance)
  • ActiveJDBC ActiveRecord-style ORM library (using a modified fork)
  • Apache DBCP database connection pooling
  • Jackson high-performance JSON processor


  • Quick startup: simply Run/Debug as Java Application and it runs using an embedded Jetty server
  • Quick turn-around: in Debug mode, hot code replacement is supported. Simply edit your code and reload the web page.
  • Ruby-like code syntax thanks to Xtend
  • Full IDE support in Eclipse (code-completion, refactoring, code formatting, etc.)
  • High-performance: based on components like Spark, Jetty and Jackson that have proven themselves in the TechEmpower Benchmarks.



Here's a basic (but complete) example of using Sparkler:

import static extension com.tobykurien.sparkler.Sparkler.*

class Main {
   def static void main(String[] args) {
      // Simplest example
      get("/") [req, res|
         "Hi there!"
      // Using named parameters
      get("/hello/:name") [req, res|
         "Well hello, " + req.params("name")


An example of using the templating system:

   // Rendering a Mustache template
   get("/example1/:message") [req, res|
      render("templates/example1.html", #{ 
         "message" -> req.params("message"),
         "items" -> #[
            #{ "name" -> "Alice" },
            #{ "name" -> "Bob" }

And in templates/example1.html:

<head><title>Example 1</title></head>
   The message is: {{message}}
   Some additional stuff:
        <li> Name: {{name}}

Run it and access http://localhost:4567/example1/hello to get the output, which looks like:

 The message is: hello

 Some additional stuff:

    1. Name: Alice
    2. Name: Bob 


You can include a template into another template, for example in templates/main.html:

{{> my_partial}}

This would evaluate and include the contents of templates/my_partial.html, which would have access to all the variables in scope within templates/main.html.

Template Inheritance

Template inheritance is also supported by You can create templates/base.html with:

<head><title>{{$title}}Sparkler examples{{/title}}</title></head>
   <b>Header from base</b>
     Default base content.
   Footer from base.

You can now use that as a layout in templates/example1.html as follows:

{{< base}}

{{$title}}Example 1{{/title}}

  The overridden content


This works like the Jinja2 templating engine, where named blocks from the base file are overriden by the sub-template.


You can add before and after filters to your routes for things like authentication. An example filter:

   before("/admin") [ req, res, filter |
      var password = req.queryParams("password")
      if (!password.equals("openSesame")) {
         filter.haltFilter(401, "You are not welcome here!!!")

JSON RESTful API interfaces

You can quickly and easily create JSON RESTful API for data stored in a database as follows:

class Book extends Model {
   // data model is inferred from the database

class JsonRestApi {
   def static void main(String[] args) {
      DatabaseManager.init( // init db with package containing db models
      val book = Model.with(Book) // get reference to ModelContext for Book
      // Gets all available book resources (id's)
      get(new JsonTransformer("/books") [req, res|
      // Creates a new book resource
      // author and title are sent as query parameters e.g. /books?author=Foo&title=Bar
      put(new JsonTransformer("/books") [req, res|
            "title", req.queryParams("title"),
            "author", req.queryParams("author"))     
      // and so on for update, delete (see Example 2)      

The JsonTransformer class provides the database connection, and will automatically convert Model objects (and lists, or any other type of object) into JSON, as well as handle errors, etc.

To configure the database, edit the /config/database.yml file. By default, Sparkler will use the embedded H2 database (which works like Sqlite). Running java -jar libs/h2-1.3.174.jar from the project root will allow you to manage your database.


You can run Sparkler in various environments, e.g. development, test, or production. By default, Sparkler runs in "production" mode. To run in "development" mode, add -Denvironment=development to your java startup arguments.


You can test using JUnit and JSpec. To write a test, simply create a class that extends TestSupport:

class Example2Test extends TestSupport {
   override getModelPackageName() {
      return  // package containing our Model classes
   def simpleTest() {
      val book = Model.with(Book)
      var newBook = book.createIt("title", "Test", "Author", "Toby Kurien")
      a(newBook.get("author")).shouldBeEqual("Toby Kurien")

You can now right-click the class and select Run As > JUnit Test. Each time the tests are run, the database defined in the test environment in config/database.yml is reset (all tables dropped and the database schema reloaded). This currently happens for each test in your class.

Getting Started

To use Sparkler in it's current state:

  • Install Eclipse with the Xtend compiler (
  • Download a ZIP release from the releases folder (
  • Unzip this into a folder
  • From the unzipped folder, run: ./scripts/ app:init com.yourpackage.MainClassName
  • A Sparkler project is now created for you. At this point, you should import the project into Eclipse and open the MainClassName.xtend and examine it. It should now compile, creating a src/main/xtend-gen source folder.
  • You can now run your app from the command line: ./scripts/ or from Eclipse by right-clicking your MainClassName.xtend class and selecting Run As > Java Application (don't forget to add the -Denvironment=development to the run configuration's VM arguments if you are developing).


  • You can create a database schema by defining the CREATE SQL statements in config/database.schema
  • Now create the database by running ./scripts/ db:init development. If you haven't changed config.database.yml, this should create an H2 database in db/development.db
  • You can now use the database as per Example 2. (
  • To manage the H2 database, from the project root, run java -jar libs/h2-1.3.174.jar


Sparkler applications are self-contained, so they can be copied to a server that has Java 1.7+, and run from there using the embedded Jetty. You can also deploy the application into a servlet container like Tomcat/Resin/Jetty - see here for details:


Refer to the following links for documentation on the various technologies used in Sparkler that you can access:


Sparkler is currently work-in-progress. Here are some notable limitations:

  • Maven build doesn't currently work. You need to use Eclipse with Xtend compiler installed, or use the pre-build releases.
  • Migrations not yet supported.
  • No REPL.
  • No support for fixtures in tests.