This document summarizes Adam L. Davis' presentation on writing Groovy domain-specific languages (DSLs). It discusses key Groovy features for building DSLs like command chains, named parameters, operator overloading, categories/extension modules, closures, property/method missing, Groovy scripts, and common Groovy DSL examples including Gradle, JSONBuilder, and GrooCSS. The presentation provides code examples demonstrating how to implement DSL functionality in Groovy.

1. Adam L. Davis
The Solution Design Group, Inc.
@adamldavis.com
thesdg.com
Writing
Groovy DSLs

2. Agenda
●
Command Chains and @NamedParams
●
Operator Overloading
●
Categories, Extension modules
●
Closures, with, delegate, owner
●
propertyMissing, methodMissing
●
Groovy Scripts, GroovyShell
●
Groovy 3.0
●
Common DSLs

3. Command Chains
●
Command Chains allows parenthesis-free
fluent method calls
●
EX: method(param).then(foo) can be written
method param then foo

4. @NamedParams
● Mainly to give IDE hints for mapped parameters
● @NamedParams([array of @NamedParam])
● Can optionally tell what type is expected
Task task(@NamedParams([
@NamedParam(value = "name", type = String.class),
@NamedParam(value = "type", type = Class.class),
@NamedParam(value = "doLast", type = Closure.class),
@NamedParam(value = "doFirst", type = Closure.class),
@NamedParam(value = "depends", type = List.class)
]) Map<String, Object> map)

5. Operator Overloading

6. Demo 0

7. Categories, Extension modules
●
Category
– use(YourCategory) { *DSL* }
– YourCategory has static methods, first parameter is
class to decorate
– Unlike using metaclass, allows static compilation
●
Extension Modules!
– Much like Category but everywhere
– Put file in META-INF/groovy/
– “org.codehaus.groovy.runtime.ExtensionModule”

8. Closures, with, delegate, owner
●
Closures { }
●
object.with { * all methods, properties of object
available here * }
●
Closure.delegate = myThing
●
Closure.owner = myThing
●
method(@DelegatesTo(Foo) Closure param)
– Tells the compiler/IDE the class of the delegate
– Allows for auto-completion (in IntelliJ IDEA)

9. Demo 1

10. propertyMissing, methodMissing
●
def propertyMissing(String name): called
whenever something could be a property
reference.
– with/delegate/script-base: allows on the fly reference
of anything.
– propertyMissing(String name, value): assignment.
●
def methodMissing(String name, args):
– Name = name of method
– Args = array of arguments to method (0..n)

11. Groovy Scripts
●
No class or main(args) needed
●
GroovyShell
●
Ability to customize
– ImportCustomizer
– CompilerConfiguration
– Binding
– Change the script base-class
– Supply a class-loader

12. Demo 2

13. Groovy 3.0
●
Lambda expressions and :: supported
●
New operators:
– !in
– !instanceof
– ?=
– ?[x]

14. Groovy DSLs: JSONBuilder
def json = new groovy.json.JsonBuilder()
def root = json { // call(Closure)
person { // methodMissing( “person”, [Closure] )
firstName 'Adam' //methodMissing( “firstName”, [Adam] )
lastName 'Davis'
address( //methodMissing( “address”, [Map] )
city: 'Orlando',
country: 'USA',
zip: 32765
)
married true
// a list of values
conferences 'JavaOne', 'Gr8conf'
}
}

15. Groovy DSLs: Gradle
//def task(object)
task myTask //propertyMissing(“myTask”)
task myTask { configure closure }
//methodMissing(“myTask”, [closure])
task myTask(type: SomeType)
//methodMissing(“myTask”, [map])
task myTask(type: SomeType) { configure closure }
//methodMissing(“myTask”, [map,closure])

16. Groovy DSLs: GrooCSS
‘.myclass’.$ {} // Extension module: String
width 10.em // Extension module: Number
{ width 400.px height 200.px color black }
//Command chains
keyframes ‘flash’ {
10 % { color white }
50 % { color black }
100% { color white }
} // operator overloading

17. Thanks! Any ?’s
Adam L. Davis
The Solution Design Group, Inc.
@adamldavis.com
github.com/adamldavis/2019-gr8conf
or http://bit.ly/Gr8-2019BG
thesdg.com

18. This work is licensed under a Creative Commons
Attribution-ShareAlike 3.0 Unported License.
It makes use of the works of Mateus Machado Luna.
Thanks!