Groovy

External

• API: https://groovy-lang.org/gdk.html

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

Working with Closures

http://groovy-lang.org/closures.html

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.

https://mrhaki.blogspot.com/2009/11/groovy-goodness-passing-closures-to.html

Template Engines

Groovy 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 = [:]

@Field

https://docs.groovy-lang.org/latest/html/gapi/groovy/transform/Field.html

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.