Groovy overview, DSLs and ecosystem - Mars JUG - 2010

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Groovy
Overview, DSLs, ecosystem

...

Guillaume Laforge

• Groovy Project Manager
• JSR-241 Spec Lead
• Head of Groovy Development
at SpringSource...

Contact information

• Email
– glaforge@gmail.com

• Twitter
– @glaforge

• Blog
...

A little story

Copyright 2010 SpringSource. Copying, publishing or distributing without express written permission is ...

nd a
Ag e • Int...

nd a
Ag e • Int...

Groovy in a few words

• Groovy is a dynamic language for the JVM
– with a Meta Object Protocol
–...

Most popular alternative
language for the JVM

• In terms of...
– Poll and survey popularity
– ...

In terms of polls & surveys

Copyright 2010 SpringSource. Copying, publishing or distributing without express written p...

In terms of books

Copyright 2010 SpringSource. Copying, publishing or distributing without express written permission ...

In terms of jobs

Copyright 2010 SpringSource. Copying, publishing or distributing without express written permission i...

In terms of integration in
other projects and products

• Groovy is integrated in many Open Source projects
and ...

In terms of download numbers

• Number of downloads per month
– 2003: a few hundreds
...

In terms of community activity

• Very high traffic on the mailing-lists
– 1500+ members
• Dedicated conf...

In terms of innovation

• JAX Innovation Award
– Biggest German Java conference
• Groovy won first prize ...

Features at a glance

• Fully Object-Oriented: same as Java
• Closures: reusable/assignable code blocks
• Propert...

Mandatory Hello World

• Java public class HelloWorld {
...

Mandatory Hello World

• Groovy public class HelloWorld {
...

Mandatory Hello World

• Groovy
style...

...

Syntax basics

• Grammar deriving from Java 5
– annotations, enums, static imports, generics...
• Usual J...

On Java interoperability

• Groovy is the alternative JVM language providing
the best integration with Java ...

Native syntax constructs

• Lists
def someNumbers = [1, 2, 3, 5, 7, 11]

• Ranges
def range = 1..18

...

GStrings

• Sexiest feature of the language!

• Ability to embed variables
inside strings

def firstna...

Closures

• A reusable / assignable code block
– CS 101 for a proper definition

...

Time savers

• The «Groovy Truth»

def blank = ""; assert !blank
...

GDK: Groovy Development Kit

• Thanks to Groovy’s dynamic nature, we «decorate»
existing JDK classes to add new ha...

Now onto APIs!

• After this language crash course,
let’s have a look at the APIs Groovy provides:

– M...

Markup builder

• Producing markup content
new MarkupBuilder().languages {
...

XML slurper

• Easily parsing and consumming XML content
• Navigating through the nodes as an object graph

...

Swing builder

• Creating Swing UI with a programmatic descriptive
Domain-Specific Language
import ...

Template engine

• Templating capabilities, with embedded GStrings,
and scriptlet notation
...

JDBC facilities

• Transparent resource handling thanks to closures
...

JMX Builder

• Expose, configure JMX beans, export operations,
create timers, event handling with closures, and
...

Ant builder

• Script and reuse any Ant task
– FTP, SSH, Javac, file handling, etc.

new Ant...

Grape: a great way for sharing
Groovy scripts

• Grape: Groovy Advanced Packagning Engine

• You can «grab» depend...

Benefits of the Groovy APIs

• Easily share scripts thanks to Grape
– no need to package JARs
–au...

Spring integration (1/2)

•Groovy integrated in Spring since 2.0
–ability to define beans in Groovy
...

Spring integration (2/2)

• Grails provides a Spring bean builder
– for programmatically define Spring confi...

Question & Answers

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Ag e • Dom...

The Context

Subject Matter Expers,
Business Analysts...

Developer producing LOLCODE

HAI
CAN HAS STDIO?
I HAS A VAR
IM IN YR LOOP
UP VAR!!1
VISIBLE VAR
IZ VAR BIGGER ...

Lots of Languages...

And in the end...
nobody understands
each other

Expressing Requirements...

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DSL: a potential solution?

•Use a more expressive language
than a general purpose one

•Share a common metaphore o...

Towards more readibility (1)

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Towards more readibility (1)

Copyright 2010 SpringSource. Copying, publishing or distributing without express written ...

Towards more readibility (1)

...

Towards more readibility (2)

Copyright 2010 SpringSource. Copying, publishing or distributing without express written ...

Towards more readibility (2)

Copyright 2010 SpringSource. Copying, publishing or distributing without express written ...

Towards more readibility (2)

...

A collection of DSLs

• In our everyday life, we’re surrounded by DSLs

– Technical dialects

– ...

Technical dialects

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SQL

$^[w-.]+@([w-]){2,4}$ Copyright 2010 SpringSource. Copying, publishing or distributing without express written permissi...$

Notations

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1. e4 e5
2. Nf3 Nc6
3. Bb5 a6

L2 U F-1 B L2 F B -1 U L2

Visual!

Real-life Groovy examples

• Anti-malaria drug resistance simulation
• Human Resources employee skills representatio...

Three levels of techniques

Flexible & Meta- ...

A flexible & malleable syntax

• No need to write full-blown classes, use scripts
• Optional typing (def)
...

Scripts vs classes

• Hide all the boilerplate technical code
– an end-user doesn’t need to know about class...

Optional typing

• No need to bother with types or even generics
– unless you want to!

• Imagine an i...

Native syntax constructs

• Lists
– [Monday, Tuesday, Wednesday]

• Maps
– [CA: ‘California’, ...

Optional parens & semis

• Make statements and expressions
look more like natural languages

– move(...

Named arguments

• In Groovy you can mix named and unnamed
arguments for method parameters
– named para...

BigDecimal by default

• Main reason why financial institutions often decide
to use Groovy for their business rule...

Custom control structures,
thanks to closures

• When closures are last, they can be put “out” of the
parenthese...

Operator overloading

a + b
a - b
a.plus(b)
a.minus(b)
...

The MOP
(Meta-Object Protocol)

Groovy’s MOP

• All the accesses to methods, properties,
constructors, operators, etc. can be intercepted
tha...

GroovyObject

• All instances of classes created in Groovy
implement the GroovyObject interface:

–get/...

MetaClass

• The core of Groovy’s MOP system
–invokeConstructor()
–invokeMethod() and invokeStati...

ExpandoMetaClass

• A DSL for MetaClasses!
• MoneyAmount.metaClass.constructor = { ... }
Number.metaClass.getDo...

The Builder pattern

A builder for HR

• softskills {
ideas {
capture 2
formulate 3
}
....

A builder for HR

• softskills {
ideas {
capture 2
formulate 3
}
....

Builders

• Builders are...
– a mechanism for creating any tree-structered graph
– the realization of the GoF bu...

The clever trick

• GroovyObject#invokeMethod() is used to catch all
non-existing method calls in the context of t...

Adding properties to numbers

• Three possible approaches

– create a Category
•a category...

With a Category

• class DistanceCategory {
static Distance getMeters(Integer self) {
new Distanc...

With an ExpandoMetaClass

• Number.metaClass.getMeters = {->
new Distance(delegate, Unit.METERS)
}

...

Compile-time
metaprogramming

• Groovy 1.6 introduced AST Transformations
• Compile-time == No runtime performance...

Compile-time
metaprogramming

• With metaprogramming, Groovy’s able to modify
the behaviour of programs... at ru...

AST Transformations

• Two kinds of transformations

– Global transformations
•applicable...

AST Transformations
in Groovy 1.6

• Several (local) transformations finds their way
– @Singleton — okay, ...

The @Singleton anti-pattern

•The evil Java singleton
public class Evil {
...

@Immutable

• To properly implement immutable classes
– No mutators (state musn’t change)
– Priva...

@Lazy, not just for lazy dudes!

• When you need to lazily evaluate or instantiate
complex data structures for cla...

@Delegate
Not just for managers!

•You can delegate to fields of your class
–Think multiple inheritance

...

Global transformations

• Implement ASTTransformation
• Annotate the transfo specifying a compilation phase

• @G...

Local transformations

• Same approach as Globale transformations
• But you don’t need the META-INF file
• Instea...

Example: the Spock
framework

• Changing the semantics of the original code
• But keeping a valid Groovy syntax
...

Various integration
mechanisms

• Java 6’s javax.script.* APIs (aka JSR-223)
• Spring’s language namespace
• Gr...

Java 6’s javax.script.* API

• Groovy 1.6 provides its own implementation of the
javax.script.* API

• ScriptEn...

Spring’s lang namespace

• POGOs (Plain Old Groovy Objects) can be pre-
compiled as any POJO and used interchangea...

Groovy’s own mechanisms

• Eval
– for evaluating simple expressions

• GroovyShell
– for more...

Eval

• Simple mechanism to evaluate math-like formulas

• Eval.me ( ...

GroovyShell

• A Binding provides a context of execution
– can implement lazy evaluation if needed

• A ...

GroovyClassLoader

• Most powerful mechanism
– could also visit or change the AST
– scripts & cla...

Externalize business rules

• Although Groovy DSLs can be embedded in normal
Groovy classes, you should externaliz...

A few considerations

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Start small, with key concepts
Beware over-engineering!

Grow your language
progressively

Get your hands dirty
Play with the end-users

Let your DSL fly,
it’s not yours, it’s theirs!

Tight feedback loop
Iterative process

Stay humble,
You can’t get it right the 1st time.

Don’t design alone at your desk
Involve the end users from the start

Playing it safe in a sandbox

Various levels
of sandboxing

• Groovy supports the usual
Java Security Managers

• Use metaprogramming tric...

Test, test, test!

• Don’t just test for nominal cases
– Explicitely test for errors!

• Ensure end-use...

Question & Answers

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Ag e • The...

The Groovy Ecosystem

• Many projects based on Groovy

• Serve various purposes:
– build applications (ie...

Gaelyk

•Groovy on Google App Engine
– Lightweight Groovy tooking for writing
applications in G...

GPars

• Actors, dataflow,
concurrency, and more
– for harnessing our
multicore platforms
...

Easyb (1/4)

• From the website:
– « Easyb is a behavior driven development (BDD)
framework for...

Easyb (2/4)

• First, let’s write a story

given "an invalid zip code"
...

Easyb (3/4)

• Let’s write the test itself

given "an invalid zip code", {
...

Easyb (4/4)

• There’s also the specification format

...

Spock (1/3)

• From the horse’s mouth:
– « Spock is a testing and specification framework for Java
...

Spock (2/3)

• Extensible (but transparent) use of AST
transformations to «pervert» the Groovy language
...

Spock (3/3)

• Another example of the expressive language

...

GMock (1/3)

• GMock is a mocking framework for Groovy
...

GMock (2/3)

• Mocking method calls
def loader = mock()
loader.put("f...

GMock (3/3)

• Expecting exceptions
ception, "an excepti...

Gant

• Gant is a tool for scripting Ant tasks using Groovy
instead of XML to specify the logic
...

Gradle (1/2)

• From the website:

« Gradle is an enterprise-grade build system providing:
– A very...

Gradle (2/2)

• For example, for a classical Java project

usePlugin ‘java’

reposit...

Other build and quality tools

• You can use Ant, Gant, Maven (GMaven plugin) or
Gradle to build your projects
...

HTTPBuilder (1/3)

• HTTPBuilder provides a convenient builder API for
complex HTTP requests
...

HTTPBuilder (2/3)

• Posting to a URL

import groovyx.net.http.HTTPBuilder
...

HTTPBuilder (3/3)

• Posting XML content to a URL

http.request(POST...

GroovyWS (1/2)

• Publishing and consuming WS-I
compliant SOAP web services
import groovyx.net.ws...

GroovyWS (2/2)

• Publishing a service
– considering a service

class MathService { ...

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Make your life easier

Great fit for
Domain-Specific
Languages

Rich and active
ecosystem

Question & Answers

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Picture credits
• http://www.flickr.com/photos/featheredtar/2305070061/ ...