Magic with groovy & grails

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Magic with Groovy & Grails
The Search is over
© Catalysts GmbH

What is Groovy?
•

Dynamic language

•

It can leverage Java's enterprise capabilities but also has cool productivity
features like closures, builders and dynamic typing

•

1.0 released on 02.01.2007

•

Dynamically compiled to JVM bytecode

•

99% of Java code is also valid

•

Groovy = Java +
dynamic typing +

additional methods & operators + closures
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Dynamic Typing
Java
ArrayList<String> list = new ArrayList<String>() {
{

Groovy
add("A");
add("B");
add("C");

}
};
HashMap<Integer, String> map = new HashMap<Integer, String>() {
{
put(1, "A");
put(2, "B");
put(3, "C");
}
};

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?

Dynamic Method Invocation
class Dog {
def bark() { println "woof!" }
def sit() { println "(sitting)" }
def jump() { println "boing!" }
}
def doAction( animal, action ) {
animal."$action"() //action name is passed at invocation
}
def rex = new Dog()
doAction( rex, "bark" ) //prints 'woof!'
doAction( rex, "jump" ) //prints 'boing!'

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Additional Operators
•

Spread *.

parent*.action //equivalent to:

parent.collect{ child -> child?.action }
•

Elvis ?:

assert ['cat', 'elephant']*.size() == [3, 8]
•

Safe navigation ?.

•

Equals ==

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Closures
“A Groovy Closure is like a ‘code block’ or a method pointer. It is a piece of
code that is defined and then executed at a later point.”

http://groovy.codehaus.org/Closures

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Functional Programming(1)
•

Closures as functions

def multiply = { x, y -> return x * y }

println multiply.call(3, 4)
def triple = {x -> return 3*x }
•

Closures as function compositions

//like LISP, Haskell lambda functions
def composition = { f, g, x, y-> return f(g(x, y)) }
composition.call(triple, multiply, 5, 6)

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Functional Programming(2)
•

Fibonacci

def fibonacci

fibonacci = { n ->
n <= 1 ? n : fibonacci(n-1) + fibonacci(n-2)
}.memoize()
println fibonacci.call(35)

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What is Grails?
Grails is a full stack framework and attempts to solve as many pieces of the web development puzzle through the core technology
and its associated plugins. Included out the box are things like:
1. An easy to use Object Relational Mapping (ORM) layer built on Hibernate

2. An expressive view technology called Groovy Server Pages (GSP) ~ JSP
3. A controller layer built on Spring MVC
4. A command line scripting environment built on the Groovy-powered Gant
5. An embedded Tomcat container which is configured for on the fly reloading

6. Dependency injection with the inbuilt Spring container
7. Support for internationalization (i18n) built on Spring's core MessageSource concept
8. A transactional service layer built on Spring's transaction abstraction
All of these are made easy to use through the power of the Groovy language and the extensive
use of Domain Specific Languages (DSLs)

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What is Grails?
•

Web application framework

•

Convention over configuration

•

Spring MVC

•

Fast prototyping and development

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Convention over configuration
This typically means that the name and location of files is used instead of explicit configuration

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What does all these means?(1)
What does mean all these features of Grails?
1. An easy to use Object Relational

Mapping (ORM) layer built on

Hibernate
That means that you just have to define your domain classes, with all the attributes that you
want. These domain classes will be automatically mapped by Hibernate to tables inside the
database you have specified in Datasource.groovy, and the domain class attributes will be
mapped to table fields.
Having this domain classes mapped, you can now perform all CRUD operations on them, with
the usage of dynamic methods added by GORM to the domain classes such as “save(),
delete(), findAll, findAllBy, findAllWhere, count etc.”
These dynamic methods instantly boost your productivity since you dont have to worry anymore
about writing sql queries or managing the data layer. Grails does all of these for you! (*
however if you still want to customize how things are mapped, sql queries, you can dive into the
deep of Hibernate configs)
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2. An expressive view technology called
Groovyall these features of Grails? (GSP)
Server Pages
What does mean
Groovy Servers Pages (or GSP for short) is Grails' view technology. It is designed to be familiar
for users of technologies such as ASP and JSP, but to be far more flexible and intuitive.
You can be more flexible because you can use groovy code inside the pages, that is executed
before the page is sent, or use specific reusable componets - taglibs.

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3. A controller layer built on Spring MVC

Controllers are the classes that responds and handle requests from the
front-end.
A controller can generate the response directly or delegate it to a view.
Controller methods and views are tightened together, thus a controller
method called “search” will by default render the view “search”.

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4. A command line scripting environment
built on the Groovy-powered Gant
That means that you can use groovy console to run the application, the
tests, install plugins and so on.

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5. An embedded Tomcat container which
is configured for on the fly reloading
Grails provides an embedded Tomcat instance, where your application is
deployed automatically when you want it to run. This means that you don't
have to worry about a separate Tomcat container and deploy
configurations that takes time.
Also, you can make changes to your application on the fly, without the
need to redeploy the app. However, when changing domain classes, the
database will change too, so the application has to be deployed again.

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6. Dependency injection with the inbuilt
Spring container
Grails leverages Spring MVC in the following areas:
Basic controller logic - Grails subclasses Spring's DispatcherServlet and uses it
to delegate to Grails controllers
Data Binding and Validation - Grails' validation and data binding capabilities are
built on those provided by Spring
Runtime configuration - Grails' entire runtime convention based system is wired
together by a Spring ApplicationContext
Transactions - Grails uses Spring's transaction management in GORM
In other words Grails has Spring embedded running all the way through it.

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7. Support for internationalization (i18n)
built on Spring's core MessageSource
This means that your application can be written in as many languages as you want.
All you have to do is to use specific codes for each message that you use, and
provide different translations for these codes.
You can split and organise your language files as you like.

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8. A transactional service layer built on
Spring's transaction abstraction
The Grails team discourages the embedding of core application logic inside
controllers, as it does not promote reuse and a clean separation of concerns.

Services in Grails are the place to put the majority of the logic in your application,
leaving controllers responsible for handling request flow with redirects and so on.
Services are transactional by default. This means that if an operation on the
database fails, and this operations is performed in a service, that operation will be
automatically rolled back due to default transactional behaviour of services.

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Why would I use it?
1- Grails is Spring and Hibernate
Grails was a good replacement for vanilla Spring/Hibernate, but it’s even better. In
the real world it means that you can bootstrap a new project very quickly by using
default settings, but you have all the power of Spring and Hibernate under the
hood. If you really need to do some really specific stuff, you can easily go into deep
of configurations.
The best of both worlds! And it also means that you can use all the Spring modules
you already love and integrate with all the databases you are used to, without any
problem.
You just have to define your domain classes and with the usage of dynamic
scaffolding your application is ready to go with all the CRUD operations (views,
controllers ) already implemented.

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Why would I use it?
2- Groovy is actually Java
Java is a statically-typed language and it was designed to be, because it’s just easier to
understand. But recently, we have all come to envy the expressivity and power of dynamic
languages like Ruby and Python. The problem is that they are completely new languages,
which means 2 things: the learning curve is pretty steep, and it’s hard to find good developers
for those languages. Well, fear no more, because Groovy is here to save you.
Groovy is essentially a superset of Java as a language, which means that you don’t need to
learn an entirely new language, and it’s really easy to turn any Java developer into a Groovy
developer. Sure Groovy offers much more than Java in terms of power, and it can take some
time to get a good grasp of all the ins and outs of closures, dynamic typing or even metaprogramming.
But the good news is that you don’t need to master all those right away in order to leverage a lot
of the productivity you can get out of Groovy.
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Why would I use it?
3- And it runs on the JVM
And it gets even further than that: Groovy is so Java-rooted that it actually compiles
to run on a Java runtime. Groovy code compiles into JVM bytecode, which means
you can still make Groovy and Grails applications run on your favorite application
server (simplest is Tomcat, but I’ve made it run on JBoss and even Weblogic) AND
you can reuse all the awesome libraries available in the Java ecosystem in an
instant.
Just plug your environment with your Maven or Ivy repository of choice, or copy
some JARs over and you’re good to go! How amazing is that?

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Why would I use it?
4- Groovy is not just for scripting
I mean sure, Groovy is great for system scripting, in the same way as Ruby and
Python are. Not everything needs to be a class so you can write scripts in no time.
But a lot of people use Groovy just for that, and think it’s not ready for prime-time
big-fuss applications yet
Yes, Groovy is a dynamic language, which also means that there is a lot less stuff
checked at compilation time than with mere Java, but since your code is much
more expressive, there is a lot less opportunity for errors too, and unit tests are a
lot easier to write, especially thanks to DSL’s.

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Why would I use it?
5- A very dynamic ecosystem
Every experienced developer knows that a good framework is nothing without good
documentation, serious support and a large community of contributors.
Well, of course Groovy and Grails have all that. First of all, they are part of the portfolio of
SpringSource, the very company that brought you the Spring Framework and that is now a
division of VMWare. The documentation is really good, like most Spring documentations by the
way, and there are some excellent books out there. As for helpers and contributors, whether it is
on the mailing list or on StackOverflow, helpers are everywhere.
And in terms of ecosystem: Grails has a plugin mechanism that makes it really easy to extend
the framework in a lot of different ways. Now I won’t lie, all of the available plugins are not
necessarily supported or kept up-to-date on the long run, but they are so easy to write and fix,
that it’s not really an issue.

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Why would I use it?
Liquibase integration

When you already have your application in production, you need a way to modify your db
automatically, thus Liquibase.

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Magic with groovy & grails

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