The document summarizes Ratpack, an open source web framework for the JVM. It provides an overview of Ratpack's features such as its non-blocking architecture, support for templates, microservices, HTTP client, metrics, and more. It describes Ratpack's execution model using promises to provide deterministic processing for asynchronous code. The document also covers Ratpack's use of registries for dependency injection and blocking support.

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Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a Creative Commons Attributio n-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Ratpack Web Framework
By Dan Woods
@danveloper

2. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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About Me
• Member of the Ratpack Web core team
• Author of “Learning Ratpack”, O’Reilly
• http://shop.oreilly.com/product/0636920037545.do
• Senior Engineer, The Groundwork
• https://github.com/danveloper
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1st Four Chapters Available Today!

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Ratpack Team on Twitter
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Follow this crew!
• @ldaley
• @varzof
• @rus_hart
• @beckje01
• @marcinerdmann
• @zedar185
• @Lspacewalker
• @johnrengelman

4. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Brief History of Ratpack
• Ratpack started out as a Groovy DSL implementation example (2010)
• Evolved steadily into a JVM Sinatra clone (2010-2011)
• Dumped Sinatra legacy and started focusing on NIO/performance (2012)
• Under steady development in its modern form for 3 full years!
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GroovyDSLImplementation
JVMSinatraClone
Drop“Sinatra”,NIO/Perf
DropsServletsforVert.x
CorerewritteninJava
Movestoorg.ratpackpackages
ExecutionModelIntroduced
Bootstraping,Config
Registryisintroduced
MovefromVert.xtoNetty
Stable,ProductionReady–1.0

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Overview of Ratpack
• Ratpack is now at version 1.0.0
• Production-ready, API-stable
• Can safely adopt without fear of breaking API changes
• Great option for building microservices
• Can also be integrated into legacy apps through its robust test fixtures
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6. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Overview of Ratpack
• A high performance web framework
• Built on a non-blocking network stack
• Provides low-level constructs for working with async APIs
• Core is written in Java (requires Java 8)
• Integrated support for building Groovy-based applications
• Emphasis on developer productivity
• As few opinions as possible
• Fast, self-contained, light-weight deployables
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Simplest Hello World Example
• Just a few lines of Groovy code required!
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Simplest Hello World Example
• Totally Tweetable! https://twitter.com/danveloper/status/608298173208100864
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Java Hello World Example
• Still, not very much needed at all…
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Overview of Ratpack
• Support for HTML templates with Groovy and Handlebars
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Overview of Ratpack
• Great for microservices!
• First-class support for language agnostic transport
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Overview of Ratpack
• Non-blocking HTTP client
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Overview of Ratpack
• Fault tolerance for building distributed systems
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Overview of Ratpack
• Support for metric reporting with Dropwizard Metrics
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Overview of Ratpack
• Comprehensive configuration model
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Overview of Ratpack
• Support for persistent sessions
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Overview of Ratpack
• Robust security with Pac4j
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Overview of Ratpack
• Out of the box SSL support
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Performance
• Like most frameworks, Ratpack is CPU-bound (the more CPUs, the better)
• Unlike most frameworks, Ratpack efficiently processes on each CPU
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https://gist.github.com/danveloper/db888be3519966976368

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Execution Model
• The execution model in Ratpack is borne from the fact that the JVM has no
inherent support for Continuations
• Asynchronous programming is difficult
• Async processing introduces non-determinism
• Web applications require deterministic processing
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21. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Execution Model
• Ratpack wants to make Async processing and programming a reliable and
usable model for the JVM
• By fitting into the execution model, applications garner confidence from a
deterministic processing flow
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TPR/TPC Processing Model
• How most JVM web frameworks work
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Internet Web App
new Thread().start()
Blocking
Processing
Process and wait

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TPR/TPC Processing Model
• In the thread-per-request (or thread-per-connection) model, you are limited by
the amount of threads that you can create
• Bringing the data from a request-taking thread and placing it into a processing
thread incurs a context switch
• The processing thread is where all your work is done, and is established until
you respond
• This is not performant at all, but it is an easy model to program in, and that’s
why people use it
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24. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Ratpack Processing Model
• How Ratpack works (4 CPU example)
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Internet Event Loop
Event Loop
Event Loop
Event Loop
Handler
Waiting for something?
(db call, call to remote)
Return thread to
request-taking pool
while we wait
Respond
One thread per CPU core

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Ratpack Processing Model
• Only establishes a single thread per CPU core
• Processing doesn’t block the thread (if it needs to, then we can schedule it to
the blocking thread pool)
• While we wait for async responses to be fulfilled, the thread is able to process
other requests
• When we get the async response, processing continues on the same thread
• No context switching in computation handlers, async processing responds when
its work is done
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26. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Problems with Async Programming
• Callbacks are obnoxious to work with
• No good way to detect when waiting for async responses
• Represents a temporal disconnect from the processing flow
• Most async web frameworks start a timer when a request comes in, and if you
don’t respond by the time that’s over, then it assumes you’re not going to
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Problems with Async Programming
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Callback
HELL

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Problems with Async Programming
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With Ratpack Promises, you
get guaranteed execution
order without the need
scoped callbacks.
<1> - definitely happens 1st
<2> - definitely happens 2nd
<3> - definitely happens 3rd
<4> - definitely happens 4th
<5> - definitely happens 5th

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Problems with Async Programming
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In other async web
frameworks:
The clock is ticking for you
to get that response out
before the framework
shuts you down

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Problems with Async Programming
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Execution
|__stream
|__marker
|__flatMap(..)
|__findByUsername
|__stream
|__marker
|__flatMap(..)
|__loadProfile
|__stream
|__marker
|__flatMap(..)
|__loadFriends
|__stream
|__marker
|__flatMap(..)
|__loadFriendPhotos
|__stream
|__marker
|__render(..)
|__then(..)

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Execution Model
• The overall execution is a parallel to the construct of a continuation
• Each of the calls to a Promise represent a frame in the execution
• Each of the Promise types represents a new processing stream in the
execution
• While async processing is taking place (ie. Promise is not fulfilled), the
execution is suspended
• When the execution is suspended, the processing thread is given back to the
event loop to continue processing requests
• When an async call returns, the execution is resumed
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32. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Execution Model
• Most importantly, we know that when we hit the marker on a processing stream
that the stream is done computing
• The processing streams are supervised by Ratpack to know that a request is
still processing
• If your code doesn’t respond to a request, we don’t need to wait until the
request times out to inform the client
• If all the streams are done computing but no response has been sent, we are
aware of that and can send an appropriate error back (no response sent) to the
client
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33. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Execution Model
• Ratpack’s execution model gives you much higher confidence in working with
async programming
• The Promise type makes async programming easier
• Deterministic async processing gives added benefits for concurrency
• You have better confidence when programming to async APIs with Ratpack
• Fun fact: any API can be made asynchronous in Ratpack
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34. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Blocking Done Right
• To make use of most 3rd party Java libraries, blocking will need to take place at
some point
• A prime example here is using JDBC
• Since you can’t block on the request-taking thread, you will need to do blocking
on a separate thread
• Any non-trivial application will need to do blocking at some point…
• Ratpack provides easy fixtures for Promise types to be scheduled for
computation or blocking
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35. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Blocking Done Right
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Dependency Injection
• Ratpack is not tied to any particular dependency injection framework
• DI is an abstract concept in Ratpack, components are registered via a Registry
• Ratpack apps can be built entirely without any DI
• Framework modularity is accomplished via Guice
• 1st class support for Guice and Spring Boot
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37. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Registry
• There are multiple registries in Ratpack
• Provide components at different layers of the framework
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Server Registry
User Registry
Context Registry
Request Registry

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Registry
• Components can be bound to the user registry at start time
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Registry
• Registries can be built and cascaded at request time, and according to request
attributes
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Registry
• Registries can be backed by Guice…
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Registry
• … or by Spring Boot…
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Registry
• … or both …
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Dependency Injection
• In Groovy, dependency injection can be accomplished by simply specifying the
type as a closure argument
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44. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Dependency Injection
• Taking a completely unopinionated approach to dependency injection allows
implementations to be flexible
• Can support nearly every component-providing backend
• Gives you the ability to leverage the best parts of all available ecosystems
• New Ratpack apps can readily fit into legacy infrastructures that do have
opinions about this stuff
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45. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Build System Support
• Ratpack is just a set of libraries, so any Java build system can build your project
• Advanced integration with Gradle is provided through the ratpack-gradle plugin
• Using Gradle is the easiest way to get started
• Gradle plugin provides version-proper dependency resolution, so you don’t
need to update versions as you upgrade your project
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46. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Build System Support
• Just a set of libraries…
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47. Unless otherwise indicated, these slides are © 2013 -2015 Pivotal Software, Inc. and licensed under a
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Build System Support
• Advanced integration with Gradle…
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Build System Support
• Ratpack apps can be easily packaged for deployment with Gradle
• Multiple options: fat jar, tarball, zip file
• Gradle plugin applies the application plugin, so distributions and dependencies
can easily be built and shipped with os start scripts
• Fat JAR building is accomplished via the ShadowJar plugin
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Developer Productivity
• Development time hot reloading is provided via Gradle’s “continuous build”
mode
• Standalone Ratpack Groovy scripts are able to be reloaded when the
development serverConfig option is true
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The Handler Chain
• Denotes the edge of your application
• Requests flow through the chain until reaching a handler than can provide a
response
• Two types of handlers: request flow and terminal
• Request Flow handlers manage the direction the request takes through the
chain
• Terminal handlers process a request and respond to it
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The Handler Chain
• Request flow handler
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The Handler Chain
• Terminal handler
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The Handler Chain
• Chain API provides semantic methods to bind a handler to an HTTP verb and
optionally a path
• get(..), post(..), put(..), patch(..), delete(..) methods will bind accordingly
• Can also bind a handler that will be called for every incoming request with the
all(..) and path(..) chain methods
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Live Coding Demo Time
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Questions?
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Join the Community
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http://slack-signup.ratpack.io/