Andrey Hihlovskiy

Professional blog on groovy, gradle, Java, Javascript and other stuff.

Monthly Archives: August 2013

Groovy language, spaceship operator

x <=> y

Useful in comparisons:

  • returns -1 if x is smaller than y
  • return 0 if x equals to y
  • returns 1 if x is greater than y.

Isn’t it sweet?

Groovy DSL == thermonuclear way of writing XML

import groovy.xml.MarkupBuilder

String createEAD(Closure closure) {
  def writer = new StringWriter()
  def xml = new MarkupBuilder(writer)
  xml.mkp.xmlDeclaration(version: '1.0', encoding: 'UTF-8')
  xml.'ead:ead'('xmlns:ead': 'urn:isbn:1-931666-22-9') {
    closure.delegate = new Object() {
      def text(Map attrs, content) {
        def a = attrs.keySet().find { it in ['bold', 'italic', 'underline'] }
        if(a && attrs[a]) {
          xml.'ead:emph' render: a, {
            text attrs.findAll({ it.key != a }), content
        } else
          text content
      def text(content) {
        if(content instanceof String)
          xml.mkp.yield content
        else if(content instanceof Closure)
  return writer.toString()

println createEAD {
  text bold: true, italic: true, {
    text 'Hello, '
    text underline: true, 'world!'

expected output:

<?xml version='1.0' encoding='UTF-8'?>
<ead:ead xmlns:ead='urn:isbn:1-931666-22-9'>
  <ead:emph render='bold'>
    <ead:emph render='italic'>Hello, 
      <ead:emph render='underline'>world!</ead:emph>

Firefox 23: Javascript is always ON

From Firefox 23 Release Notes:

“Enable JavaScript” preference checkbox has been removed and user-set values will be reset to the default

YESSS!!! javascript is now always ON, it is not even possible to turn it off! Other browsers, unite!
Bureaucrats will probably have to reconsider what they mean under Barrierefreiheit.

Partial interface implementation in groovy

interface X {
  void a()
  void b()

class XAdapter implements X {
  void a() { println 'default implementation of a' }
  void b() { println 'default implementation of b' }

def o = [
  a: { println 'overridden implementation of a' }
] as XAdapter


will output:

overridden implementation of a
default implementation of b

Fun with groovy files

The following one-liner can copy very large files without running out of memory:

new File("test").withInputStream { new File("test2") << it }

Just tested it in groovy console – 1 GB file is copied in 5 seconds, memory consumption stays low.
The copy is binary, i.e. it copies bytes, not chars.
One particularity: left-shift operator rather appends than overwrites. If you need to overwrite the file, first need to delete it.

Fun with groovy maps and function call syntax

A function having a Map as first parameter:

void doIt(Map attrs, Object content) {
  println attrs
  println content

supports equally valid call syntax variations:

// "classical" call syntax, known from java world
doIt([color: 'red', type: 'fruit'], 'hello!')

// parentheses can be omitted
doIt [color: 'red', type: 'fruit'], 'hello!'

// even square brackets for map can be omitted
doIt color: 'red', type: 'fruit', 'hello!'

// order of map properties does not matter,
// map properties can be intermixed with unnamed parameters.

doIt color: 'red', 'hello!', type: 'fruit'

doIt 'hello!', type: 'fruit', color: 'red'

this effectively allows to implement named parameters in groovy.