Groovy
External
TODO
- Tutorial: www.tutorialspoint.com/groovy/index.htm
TODO Groovy basics: https://docs.gradle.org/current/userguide/writing_build_scripts.html#groovy-dsl-basics
Strings
TODO next time I need it.
Single-Quoted vs. Double-Quoted Strings
Groovy has both double-quoted and single-quoted String literals. The main difference is that double-quoted String literals support String interpolation:
def x = 10
println "result is $x" // prints: result is 10
Rules for String Interpolation
Groovy supports declaring a string with either single quotes or double quotes.
If the string is single-quoted, the variable interpolation behavior is turned off, similarly to how bash handles single-quoted strings.
def user="Elemental"
echo 'Hello ${user}'
will output:
Hello ${user}
Double-quoted string support dollar-sign based interpolation:
def user="Elemental"
echo "Hello ${user}"
will output:
Hello Elemental
Variables
Variables can be defined using either their type (String) or with the keywords def, which is equivalent with var
String a
def b
var c
def/var act as a replacement for the type name when the actual type is not provided (either because you don't care about it or you're relying on type inference). You can think about them as an alias to Object.
For scripts, undeclared variables are assumed to come from the Script binding.
Working with Closures
Defining a Closure
def myClosure = { e -> println "Clicked on $e.source" }
Implicit Paramenter
When a closure does not explicitly define a parameter using the '->' syntax, the closure 'always defines an implicit parameter named "it".
Passing Closures to Methods
If the closure is the last argument for a method, it can be passed outside the argument list.
Template Engines
Files
filename = 'example.txt'
File f = new File(filename)
def lines = f.readLines()
for (line in lines) {
// ...
}
filename = 'example.txt'
File f = new File(filename)
f.eachLine({
if (!it.startsWith("#") && !it.trim().isEmpty()) {
...
}
})
Data Structures
Map
def artifacts = [
"chart-A": [
"watchFor": ["src/charts/chart-A"],
"chartName": "a",
],
"chart-B": [
"watchFor": ["src/charts/chart-B"],
"chartName": "b",
],
"script": [
"watchFor": ["src/bin/run", "src/ansible", "script/bin/lib/a.shlib"],
]
]
Empty map:
Map testingBranches = [:]
Dynamic Keywords
@Field
Variable annotation used for changing the scope of a variable within a script from being within the run method of the script to being at the class level for the script. The annotated variable will become a private field of the script class.
Script
Groovy is automatically wrapping every program in a class called Script.
Method Parameters with Default Values
Default values can be assigned to a parameter in a method:
def say(msg = 'Hello', name = 'world') {
"$msg $name!"
}