programming

• basic

  • Program structure

  • Customizable Operators

  • Special Operators

• elvis operator

  • if/elseif{if}/else

• execute shell commands in groovy

  • Get STDERR & STDERR

  • Show output during the process

  • with environment

• groovyConsole

  • environment

  • get console details

  • font

download

• apach software foundatin distribution directory

• groovy

  • 2.4.21

  • 2.5.19

  • 3.0.13

  • 4.0.6

reference:

• * Groovy Language Documentation

• * Groovy Scripting Reference

  • groovy basics

  • groovy tips and techniques

• * groovy cheatsheet

• * Groovy Cookbook

• * varargs in Groovy

• varargs : Variable Arguments (Varargs) in Java

• online compiler

• http://www.cheat-sheets.org/saved-copy/rc015-groovy_online.pdf

• Syntax

• Five Cool Things You Can Do With Groovy Scripts

• Java SE Specifications download

  • The Java Language Specification, Java SE 19 Edition : pdf | html

  • The Java Language Specification, Java SE 18 Edition : pdf | html

  • The Java Language Specification, Java SE 17 Edition : pdf | html

  • The Java Language Specification, Java SE 16 Edition : pdf | html

  • The Java Language Specification, Java SE 15 Edition : pdf | html

  • The Java Language Specification, Java SE 14 Edition : pdf | html

  • The Java Language Specification, Java SE 13 Edition : pdf | html

  • The Java Language Specification, Java SE 12 Edition : pdf | html

  • The Java Language Specification, Java SE 11 Edition : pdf | html

[!TIP] Java Tutorial :

• Java Exception Handling
• Java Tips, How-tos etc
• Java JSON Tutorial
• Java Logging
• Java Performance
• Java Regex - Java Regular Expressions
• Java Unit Testing
• 朝花夕拾——Groovy & Grails

basic

Program structure

Customizable Operators

Operator	Method
a + b	a.plus(b)
a - b	a.minus(b)
a * b	a.multiply(b)
a / b	a.div(b)
a % b	a.mod(b)
a++ or ++a	a.next()

assert [ a: true, b: false ]  +  [ a: false ] == [ a: false, b: false ]
assert [ a: true, b: false  ] << [ a: false ] == [ a: false, b: false ]

• difference +(plus) and <<(left shift) :

  • << is to add into left hand map
  • + it constructs a new Map based on the LHS`

Special Operators

Operator	Meaning	Name
a ? b : c	if(a) b else c	ternary if
a ?: b	a ? a : b	Elvis
a.?b	( a==null ) ? a : a.b	null safe
a(*list)	a(list[0], list[1], ...)	spread
list*.a()	[list[0].a, list[1].a, ...]	spread-out
a.&b	reference to method b in object a as closure	method closure
a.@field	direct field access	dot-at

• .& : Method pointer operator

  def str = 'example of method reference'
  def fun = str.&toUpperCase
  assert fun() == str.toUpperCase()
  println fun()
  
  // result
  EXAMPLE OF METHOD REFERENCE

  class Person {
    String name
    Integer age
  }
  def list = [
    new Person( name: 'Bob'   , age: 42 ) ,
    new Person( name: 'Julia' , age: 35 )
  ]
  String describe(Person p) { "$p.name is $p.age" }
  
  def action = this.&describe
  def transform( List<Person> elements, Closure action ) {
    elements.inject([]){ result, e ->
      result << action(e)
      result
    }
  }
  
  println transform( list, action )
  // result
  // [Bob is 42, Julia is 35]

elvis operator

if/elseif{if}/else

references:

• 5.3. Elvis operator
• Groovy Goodness: The Elvis Assignment Operator

usage

• ?: ( existing Elvis operator )

  displayName = user.name ? user.name : 'Anonymous'
  displayName = user.name ?: 'Anonymous'

• ?= ( new elvis assignment shorthand )

  name = name ?: 'Hydrogen'   // existing Elvis operator
  atomicNumber ?= 2           // new Elvis assignment shorthand

condition:

• if fruits is 'apple' or 'orange', get pre-defined number 5 ( number = 5 )

• if fruits is watermelon, get particular given numbers. number cannot be null

// by using if/elseif{if}/else
Map option = [:]
if ( [ 'apple', 'orange' ].contains(fruits) ) {
  option = [ "${fruits}" : '5' ]
} else if ( [ 'watermelon' ].contains(fruits) ) {
  if (number) {
    option = [ "${fruits}" : number ]
  }
} else {
  println( 'ERROR: number CANNOT be empty while fruits is watermelon. Exit ...' )
}

// by using elvis operator
Map option = ( [ 'apple', 'orange' ].contains(fruits) ) ? [ "${fruits}" : '5' ]
           : ( [ 'watermelon' ].contains(fruits) ) ? ( number )
              ? [ "${fruits}" : number ]
              : println( 'ERROR: number CANNOT be empty while fruits is watermelon. Exit ...' )
           : [:]

• example

  Closure option = { String fruits, String number = '' ->
      ( [ 'apple', 'orange' ].contains(fruits) ) ? [ (fruits) : '5' ]
      : ( [ 'watermelon' ].contains(fruits) ) ? ( number )
        ? [ (fruits) : number ]
        : println( 'ERROR: number CANNOT be empty while fruits is watermelon. Exit ...' )
      : [:]
  }
  
  assert option('apple') == ['apple' : '5']
  assert option('watermelon', '100') == [ 'watermelon' : '100' ]

• using [ "${fruits}" : '5' ], the class of key is class org.codehaus.groovy.runtime.GStringImpl

• using [ (fruits) : '5' ] , the class of key is class java.lang.String

execute shell commands in groovy

reference

• 101 groovy script - Execute commands
• Jenkins Groovy script to execute shell commands
• java.lang.Process
• gist: Run shell command in groovy

Get STDERR & STDERR

[!TIP] using new StringBuffer() or new StringBuilder()

i.e.:

def stdout = new StringBuffer(), stderr = new StringBuffer()
def proc = "cmd".execute()
proc.waitForProcessOutput( stdout, stderr )
int exitCode = proc.exitValue()
println( (exitCode == 0) ? stdout : "exit with ${exitCode}. error: ${stderr}" )

def stdout = new StringBuilder(), stderr = new StringBuilder()

def proc = "ls /tmp/NoFile".execute()
proc.consumeProcessOutput( stdout, stderr )
proc.waitForOrKill( 1000 )

int exitCode = proc.exitValue()
println( ( exitCode == 0 ) ? stdout : "error with exit code ${exitCode}.\nSTDERR: ${stderr}" )

or

def stdout = new StringBuilder(), stderr = new StringBuilder()
def proc = 'ls /tmp/NoFile'.execute()
proc.consumeProcesstdoutput( stdout, stderr )
proc.waitForOrKill(1000)
println( stdout ? "out> \n${stdout}" : '' + stderr ? "err> \n${stderr}" : '' )

Show output during the process

using System.out and System.err

def proc = "ls /tmp/NoFile".execute()
proc.waitForProcessOutput( System.out, System.err )
proc.waitForOrKill(1000)

int exitCode = proc.exitValue()
if ( exitCode != 0 ) {
  println "error with exit code ${exitCode}."
}

with environment

def envVars = ["GROOVY_HOME=/fake/path/groovy-3.0.7", "CLASSPATH=.:/fake/path/groovy-3.0.7/lib"]

def proc = './run.sh'.execute( envVars, new File(".") )
proc.waitForProcessOutput( System.out, System.err )
int exitCode = proc.exitValue()

println( (exitCode != 0) ? "exit with ${exitCode}" : '' )

• run.sh

  env
  echo ${GROOVY_HOME}

• result

with system environment

List envVars = System.getenv().collect { k, v -> "${k}=${v}" }

def proc = "./run.sh".execute( envVars, new File(".") )
proc.waitForProcessOutput( System.out, System.err )
int exitCode = proc.exitValue()

println( (exitCode != 0) ? "exit with ${exitCode}" : '' )

with partular path

reference:

• groovy execute shell with environment and working dir

def command = "git log -1"
def proc = command.execute( null, new File('/path/to/folder') )
proc.waitFor()

println """
  ${proc.err.text ?: ''}
  ${proc.in.text ?: ''}
  Process exit code: ${proc.exitValue()}
"""

groovyConsole

environment

[!NOTE]

• System.setProperty("file.encoding","UTF-8")
• font setup for groovyConsole
• Groovy console

> setx JAVA_OPT '-Dfile.encoding=UTF-8 -Dsun.jnu.encoding=UTF-8'
> setx GROOVY_OPT '-Dfile.encoding=UTF-8'
> setx JAVA_TOOL_OPTIONS '-Dfile.encoding=UTF-8'

get console details

• charset

  import java.nio.charset.Charset
  
  System.out.println( String.format("file.encoding: %s", System.getProperty("file.encoding")) );
  System.out.println( String.format("defaultCharset: %s", Charset.defaultCharset().name()) );

  • result

  file.encoding: UTF-8
  defaultCharset: UTF-8

font

[!NOTE|label:references:]

• GROOVY-6303: Add ability to use a different font for the input/output area of Groovy Console

  • windows : add font/Name into HKEY_CURRENT_USER\SOFTWARE\JavaSoft\Prefs\groovy\console\ui

    > REG ADD "HKCU\SOFTWARE\JavaSoft\Prefs\groovy\console\ui" /v "font/Name" /t REG_SZ /d "Monaco" /f

  • linux : add fontName into ~/.java/.userPrefs/groovy/ui/prefs.xml

  • macox : add fontName into ~/Library/Preferences/com.apple.java.JavaPreferences.plist

• Groovy Goodness: Customize Groovy Console Visual Output

• check font

  javax.swing.UIManager.getLookAndFeelDefaults()
  
  // or
  javax.swing.UIManager.getLookAndFeelDefaults().each {
    println "... ${it.key} : ${it.value}"
  }

• or

  import java.awt.Font
  for (Map.Entry<Object, Object> entry : javax.swing.UIManager.getDefaults().entrySet()) {
      Object key = entry.getKey();
      Object value = javax.swing.UIManager.get(key);
      if (value != null && value instanceof javax.swing.plaf.FontUIResource) {
        println ".. ${key} : ${value}"
      }
  }

  .. FormattedTextField.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. MenuItem.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. InternalFrame.titleFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. RadioButton.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. RadioButton.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. OptionPane.buttonFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ToolTip.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. FormattedTextField.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Panel.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. RadioButtonMenuItem.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. OptionPane.messageFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. PopupMenu.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. CheckBoxMenuItem.acceleratorFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. MenuItem.acceleratorFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. CheckBoxMenuItem.acceleratorFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. RadioButtonMenuItem.acceleratorFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. RadioButtonMenuItem.acceleratorFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TabbedPane.smallFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Panel.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. OptionPane.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. EditorPane.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Label.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ComboBox.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Button.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. MenuBar.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Tree.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Tree.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ToolBar.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Button.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ComboBox.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Label.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. EditorPane.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Menu.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TextArea.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TextField.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Spinner.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. CheckBoxMenuItem.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Spinner.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TextField.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. IconButton.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. InternalFrame.titleFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. OptionPane.messageFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Menu.acceleratorFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Menu.acceleratorFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ToolBar.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TitledBorder.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Menu.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. FileChooser.listFont : javax.swing.plaf.FontUIResource[family=Segoe UI,name=Segoe UI,style=plain,size=12]
  .. ToolTip.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TitledBorder.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. OptionPane.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. MenuBar.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TextArea.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. OptionPane.buttonFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. CheckBoxMenuItem.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. InternalFrame.optionDialogTitleFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. InternalFrame.paletteTitleFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Table.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. CheckBox.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. List.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ToggleButton.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ScrollPane.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ScrollPane.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ToggleButton.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. List.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ColorChooser.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. CheckBox.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ColorChooser.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Table.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. MenuItem.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TableHeader.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TextPane.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Viewport.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ProgressBar.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. PasswordField.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TabbedPane.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Slider.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Slider.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TabbedPane.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. RadioButtonMenuItem.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. PasswordField.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. ProgressBar.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TableHeader.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. TextPane.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. MenuItem.acceleratorFont : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. Viewport.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]
  .. PopupMenu.font : javax.swing.plaf.FontUIResource[family=Dialog,name=Monaco,style=plain,size=14]

• modify font

import javax.swing.plaf.FontUIResource
import javax.swing.UIManager
import java.awt.Font

UIManager.put("Panel.font", new FontUIResource(new Font ("Monaco", Font.PLAIN, 16)));

• other options

  [!NOTE|label:references:]

  • Swing UIManager Keys

  private void setFont(FontUIResource myFont) {
      UIManager.put("CheckBoxMenuItem.acceleratorFont", myFont);
      UIManager.put("Button.font", myFont);
      UIManager.put("ToggleButton.font", myFont);
      UIManager.put("RadioButton.font", myFont);
      UIManager.put("CheckBox.font", myFont);
      UIManager.put("ColorChooser.font", myFont);
      UIManager.put("ComboBox.font", myFont);
      UIManager.put("Label.font", myFont);
      UIManager.put("List.font", myFont);
      UIManager.put("MenuBar.font", myFont);
      UIManager.put("Menu.acceleratorFont", myFont);
      UIManager.put("RadioButtonMenuItem.acceleratorFont", myFont);
      UIManager.put("MenuItem.acceleratorFont", myFont);
      UIManager.put("MenuItem.font", myFont);
      UIManager.put("RadioButtonMenuItem.font", myFont);
      UIManager.put("CheckBoxMenuItem.font", myFont);
      UIManager.put("OptionPane.buttonFont", myFont);
      UIManager.put("OptionPane.messageFont", myFont);
      UIManager.put("Menu.font", myFont);
      UIManager.put("PopupMenu.font", myFont);
      UIManager.put("OptionPane.font", myFont);
      UIManager.put("Panel.font", myFont);
      UIManager.put("ProgressBar.font", myFont);
      UIManager.put("ScrollPane.font", myFont);
      UIManager.put("Viewport.font", myFont);
      UIManager.put("TabbedPane.font", myFont);
      UIManager.put("Slider.font", myFont);
      UIManager.put("Table.font", myFont);
      UIManager.put("TableHeader.font", myFont);
      UIManager.put("TextField.font", myFont);
      UIManager.put("Spinner.font", myFont);
      UIManager.put("PasswordField.font", myFont);
      UIManager.put("TextArea.font", myFont);
      UIManager.put("TextPane.font", myFont);
      UIManager.put("EditorPane.font", myFont);
      UIManager.put("TabbedPane.smallFont", myFont);
      UIManager.put("TitledBorder.font", myFont);
      UIManager.put("ToolBar.font", myFont);
      UIManager.put("ToolTip.font", myFont);
      UIManager.put("Tree.font", myFont);
      UIManager.put("FormattedTextField.font", myFont);
      UIManager.put("IconButton.font", myFont);
      UIManager.put("InternalFrame.optionDialogTitleFont", myFont);
      UIManager.put("InternalFrame.paletteTitleFont", myFont);
      UIManager.put("InternalFrame.titleFont", myFont);
  }
  setFont(new FontUIResource(new Font("Monaco", Font.PLAIN, 14)));