groovy-snippets.md

Intro and Tools

Resources

• Cheatsheets - http://geek.starbean.net/?page_id=202
• Devops in the cloud - http://www.slideshare.net/aestasit/groovy-dev-ops-in-the-cloud
• Groovy JavaOne - http://www.slideshare.net/jimdriscoll/groovy-dsls-javaone-presentation
• Going to Mars - http://www.slideshare.net/glaforge/going-to-mars-with-groovy-domainspecific-languages

Libraries

• Groovy Rules - http://www.slideshare.net/paulk_asert/groovy-rules
• Concurreny (GPars) - http://www.slideshare.net/paulk_asert/concurrency-gpars
• Popper (Junit Theories) - http://groovy.codehaus.org/Using+Popper+with+Groovy
• Instinct (BDD) - http://groovy.codehaus.org/Using+Instinct+with+Groovy
• Choco (Constraint Programming) - http://groovy.codehaus.org/Constraint+Programming

Build Tools

• Grape - dependency management - http://groovy.codehaus.org/Grape
• Install gvm - Groovy Environment Manager (http://gvmtool.net/)

and use that to install Gradle, Grails etc...

• IDE - http://grails.org/products/ggts

Sample build.gradle

apply plugin: 'java'

repositories {
    mavenCentral()
}

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.+'
}

REPL - groovysh
Compile with:

gradle build
gradle tasks

http://www.gradle.org/docs/current/userguide/tutorial_using_tasks.html

Integration

http://groovy.codehaus.org/Embedding+Groovy

Integration occurs through a number of mechanisms:

• GroovyShell - use Binding to pass variables
• GroovyClassLoader - dynamic loading of scripts http://groovy.codehaus.org/api/groovy/lang/GroovyClassLoader.html
• GroovyScriptEngine - most complete solution
• Eval

Java 6 provides a JSR-233 implementation for script loading

Dynamic Language Scripts in Spring - http://groovy.codehaus.org/Dynamic+language+beans+in+Spring

Embedding a Groovy Console - http://groovy.codehaus.org/Embedding+a+Groovy+Console+in+a+Java+Server+Application

Bindings and Compiler Customisations

• ImportCustomizer
• ASTTransformationCustomizer
• SecureASTCustomizer

Scripts

Extending BaseScript (adding default methods) - http://jamesgdriscoll.wordpress.com/2012/04/22/adding-default-methods-with-a-groovy-basescript/

• Use Compilerconfiguration to set this

invokeMethod - allows for interception of a method call

• Can also implement GroovyInterceptable
• For property interception you can override getProperty() and setProperty()

Language

Data Structures

Defining data structures:

Map

def storage = [:]

List

list = []

Filtering

Find all matching a predicate:

[2, 3, 5, 7, 11].findAll { 
    it > 6 
}

Perform a map operation:

[2, 3, 5, 7].collect { 
    it+1 
}

Join all elements together:

[2, 3, 5, 7].join(" ")

Looping

List:

[2, 3, 5, 7, 11].each { 
    println it 
}

Map:

storage.each() { key, value -> 
    println "${key} == ${value}" 
};

With an index:

[2, 3, 5].eachWithIndex { p, i -> 
    println "$i: $p" 
}

I/O

Read a file line by line:

new File("test.txt").eachLine { 
    println it 
}

Strings and Pattern Matching

~ - pattern = - find ==

MarkupBuilder

MarkupBuilder provides a way to output XML/HTML:

    import groovy.xml.*

    def page = new MarkupBuilder()
    page.html {
    	head {title 'Hello'}
    	body {
    		ul {
    			for (count in 1..5) {
    				li "world $count"
    			}
    		}
    	}
    }

Closures

See - http://groovy.codehaus.org/Closures

    def printsum = { a,b -> print a + b}

You can define a free variable (variable not listed in the parameter list) also with a closure:

    def amount = 5
    def incAmount = { num -> num + amount }
    incAmount(10)

Single argument, you can omit the parameter

    def incAmount = { num -> num + amount }

this, owner, delegate

    TODO 

Can define a method as having a closure as the last thing with:

    def clos = { it.toUpperCase() }
    list.collect( newlist, clos )

shorthand, this is much cleaner though, although implicit:

    list.collect( newlist ) {
        it.toUpperCase()
    }

Annotations

Processing annotations - http://groovy.codehaus.org/Annotations+with+Groovy

There are a number of ways of doing AST's as well with the following examples:

@Immutable class Person {
    String firstname, surname
}

@Singleton
@Lazy - mark a field so that any complex computation can be done as late as possible
@Delegate - (awesome).  Specify that a object inherit methods from another class - @Delegate Date when
@Newify - new way of constructing new objects
@Category - specify an operation, then use @Mixin to include your categories
@PackageScope - 

Category and Mixin Transformations

http://groovy.codehaus.org/Category+and+Mixin+transformations