brief introduction on groovy and gradle

1. Groovy -> Gradle
GD Huang

2. Outline
• Groovy syntax
• Gradle DSL
• Groovy -> Gradle

3. Groovy
• Powerful features
• Smooth Java integration
• Domain-Specific Languages

4. Optional syntax
• Optional semincolon
• Optional parentheses for top-
level expressions
println “Hello" //println(“Hello”);
• Optional return
• Optional don in method chain
say "Hello" to “Fred" //say(“Hello”).to("Fred");
class Message {
String message
def to( String person) {
println "$message, $person!"
}
}
def say (String message) {
new Message(message:message)
}

5. Closure
• A snippet of code that
can be assigned to a
variable and executed
later
• We can put closure
outside the argument
list if it’s the last
argument
def p = {
println it
}
def work(input, cl) {
cl(input)
}
work ‘input’, p
work ‘input’, { println it}
work(‘input') { println it}

6. Java integration
In Java code, load and
compile groovy script with
groovy.lang.GroovyClassLo
ader
http://groovy-
lang.org/integrating.html#integ
-groovyshell
GroovyClassLoader gcl = new GroovyClassLoader();
Class aClass = gcl.parseClass(groovyScript);
Script script = (Script) aClass.newInstance();
script.run();

7. DSL
• deposit 100.00 currency GBP
to savings
=>deposit(100.00).currency(GBP
).to(savings)
enum Currency { USD, GBP, EUR }
class Account {
double balance
}
static def convert ( currency, amount) {
def result
switch (currency) {
case Currency.USD: result = amount
break
case Currency.GBP: result = amount * 1.3
break
case Currency.EUR: result = amount * 1.1
}
result
}
static def deposit (double amount) {
[
currency: { Currency currency ->
[to: { account ->
account.balance += convert( currency , amount )
}
]
}
]
}

8. AST transformations
• We can even hook AST transformers to customise
Groovy compilation process for building DSL

9. Gradle DSL
apply plugin: 'java'
task myTask {
setDescription 'this is myTask balabla'
}
call method apply on project with
a map argument [plugin: ‘java’]
call method task on project with
two arguments, a string and a closure

10. Groovy -> Gradle
https://github.com/gdhuang/MyGradle
• Launcher.java: load and compile groovy script with
groovy.lang.GroovyClassLoader
• TaskTransformer.java: TaskTransformer is hooked
to groovy to build task method call.
task myTask {…} => task (myTask, {…})

11. Summary
• We show gradle syntax and ast transformer.
Gradle dynamic semantic, e.g., invokeMethod and
metaclass is left to you
• Gradle is implemented in Java and is powered by
groovy to provide Gradle DSL