Groovy with Style — GR8Conf Europe 2015

Groovy
with Style
Guillaume Laforge
@glaforge
Restlet — the Web API platform
Groovy project team

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We know
about
APIs!

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GR8Conf Promo Code: cfgr8eu39
http://www.manning.com/koenig2/
GROOVY
IN ACTION
2ND EDITION

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11+ years of
Groovy experience

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Quick intro to REST

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What style?

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<=>

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12
http://www.groovy-lang.org/style-guide.html

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15
No semicolons!
class Hello { 
private String message = 'Hello!'; 
String greet(String name) { 
"$message, $name speaking"; 
}  
} 
 
print new Hello().greet('Guillaume');

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16
No semicolons!
class Hello { 
private String message = 'Hello' 
String greet(String name) { 
"$message, $name speaking" 
}  
} 
 
print new Hello().greet('Guillaume')

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18
Public by default
public class Hello { 
private static String message = 'Hello' 
private String name 
 
public Hello(String name) { 
this.name = name 
} 
public String greet() { 
return "$message, $name speaking" 
}  
}

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19
Public by default
class Hello { 
 
Hello(String name) { 
this.name = name 
} 
String greet() { 
}  
}
Methods and classes are
public by default

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20
class Hello { 
static String message = 'Hello’ 
String name 
 
this.name = name 
} 
String greet() { 
}  
}
Fields and static fields require visibility

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20
class Hello { 
static String message = 'Hello’ 
String name 
 
this.name = name 
} 
String greet() { 
}  
}
Fields and static fields require visibility
You created both an
instance property and a
static property!

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22
Get rid of the useless ‘def’
class Hello { 
private def String name 
def Hello(def String name) { 
this.name = name 
} 
public def String greet() { 
def String result = "$message, $name speaking" 
return result 
}  
} 

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23
class Hello { 
this.name = name 
} 
String greet() { 
String result = "$message, $name speaking" 
return result 
}  
} 

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24
class Hello { 
private String message = 'Hello' 
this.name = name 
} 
String greet() { 
def result = "$message, $name speaking" 
return result 
}  
} 
But it’s fine to use ‘def’
for local variables

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26
Return is optional too
String greet() {  
}

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27
}

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27
}
But return is fine for
early returns, or for
clarity of intent

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28
Optional return for if / else
int color(String name) { 
if (name == 'red') 
1 
else if (name == 'green') 
2 
else 
-1 
}

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29
Optional return for switch / case
switch (name) { 
case 'red': 1; break 
case 'green': 2; break 
default: -1 
} 
}

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29
Optional return for switch / case
switch (name) { 
case 'red': 1; break 
case 'green': 2; break 
default: -1 
} 
}
Yeah, yeah, ugly
semicolon and break…

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30
Optional return for try / catch
boolean isInt(String s) { 
try { 
Integer.parseInt(s) 
true 
} catch (NumberFormatException nfe) { 
false 
} finally { 
println 'done' 
} 
} 
 
assert isInt('123') && assert !isInt('abc')

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30
Optional return for try / catch
boolean isInt(String s) { 
try { 
Integer.parseInt(s) 
true 
} catch (NumberFormatException nfe) { 
false 
} finally { 
println 'done' 
} 
} 
 
assert isInt('123') && assert !isInt('abc')
‘finally’ blocks don’t
return a value

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32
Omit parentheses
println('Hello, World')

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33
Omit parentheses
println 'Hello, World'

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34
Command chains
move forward at 3.km/h

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34
Command chains
move forward at 3.km/h
Parsed as:
move(forward).at(3.getKm().div(h))

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35
Command chains & named arguments
check that: wine tastes good

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35
Command chains & named arguments
check that: wine tastes good
Parsed as:
check(that: wine).tastes(good)

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36
Trailing closure argument gets out
void unless(boolean b, Closure c) { 
if (!b) c() 
} 
 
def (speed, limit) = [80, 90] 
 
unless(speed > limit) { 
println "speed up a notch" 
}

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36
Trailing closure argument gets out
void unless(boolean b, Closure c) { 
if (!b) c() 
} 
 
def (speed, limit) = [80, 90] 
 
unless(speed > limit) { 
println "speed up a notch" 
}
Parsed as:
unless(speed > limit, {…})

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38
Class as first-class citizen
connection.doPost("${BASE_URI}/submit", params,
ResourcesResponse.class)

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39
Class as first-class citizen
connection.doPost("${BASE_URI}/submit", params,
ResourcesResponse)

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41
No need for dumb getters and setters
class Person { 
private int age 
 
void setName(String name) { 
this.name = name 
} 
String getName() { 
this.name 
} 
void setAge(int age) { 
this.age = age 
} 
int getAge() { 
this.age 
} 
}

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42
class Person { 
String name 
int age 
}

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42
class Person { 
String name 
int age 
}
Icing on the cake:
add @Immutable
or @Canonical

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43
Use the property notation
class Person { 
String name 
int age 
} 
 
def p = new Person(name: 'Guillaume',  
age: 36) 
assert p.name == 'Guillaume' 
 
p.age = 37 
assert p.age == 37

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45
Use the named-argument constructor
def p = new Person(name: 'Guillaume',  
age: 37)

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46
The @Builder transformation
import groovy.transform.builder.* 
 
@Builder 
class Person { 
String name 
int age 
} 
 
Person.builder()
.name('Guillaume')
.age(37)
.build()

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46
The @Builder transformation
import groovy.transform.builder.* 
 
@Builder 
class Person { 
String name 
int age 
} 
 
Person.builder()
.name('Guillaume')
.age(37)
.build()
Different strategies available:
chained setters, external builder
class, type-safe initializer

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48
Equals and ==
status != null &&
status.equals(Control.STATUS_COMPLETED)

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49
Equals and ==
status == Control.STATUS_COMPLETED

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51
Use single quotes for String constants
def msg = 'Groovy Rocks!'

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53
Native syntax for data structures
def list = [1, 2, 3] 
def range = 'a'..'b' 
def map = [a: 1, b: 2, c: 3] 
def regex = ~/.*foo.*/

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55
The Groovy Development Kit

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55
The Groovy Development Kit
Know your GDK!
So much groovy-ness in there!

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57
Switch / case on steroids
switch(obj) { 
case 123: "number 123"; break 
case "abc": "string abc"; break 
case String: "is a string"; break 
case [1, 2, 3]: "in list"; break 
case ~/.*o+.*/: "regex match"; break 
case { it < 3 }: "closure criteria"; break 
default: "unknown" 
}

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59
Import aliasing
import java.util.List as juList 
import java.awt.List as aList 
 
import javax.swing.WindowConstants as WC

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60
Import aliasing with static imports too
import static java.lang.Integer.parseInt as atoi 
 
assert atoi('123') == 123

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62
Groovy Truth
assert !( null ) 
assert !( "" ) 
assert !( [] ) 
assert !( 0 )
assert new Object() 
assert "string" 
assert [1, 2, 3] 
assert 1234

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62
Groovy Truth
assert !( null ) 
assert !( "" ) 
assert !( [] ) 
assert !( 0 )
assert "string" 
assert [1, 2, 3] 
assert 1234
False

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62
Groovy Truth
assert !( null ) 
assert !( "" ) 
assert !( [] ) 
assert !( 0 )
assert "string" 
assert [1, 2, 3] 
assert 1234
False
True

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63
Customize the truth with asBoolean()
class Account { 
String name 
boolean disabled = false 
 
boolean asBoolean() { !disabled } 
} 
 
assert new Account(name: 'current') 
assert !new Account(name: 'old', disabled: true)

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65
Safe navigation
// Java
if (order != null) { 
if (order.getCustomer() != null) { 
if (order.getCustomer().getAddress() != null) { 
System.out.println(order.getCustomer().getAddress()); 
} 
} 
} 
// Groovy
println order?.customer?.address

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65
Safe navigation
// Java
if (order != null) { 
if (order.getCustomer() != null) { 
if (order.getCustomer().getAddress() != null) { 
System.out.println(order.getCustomer().getAddress()); 
} 
} 
} 
// Groovy
println order?.customer?.address
Also give more
meaningful NPEs!

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67
Power Assert
def (a, b, c, d) = [10, 20, 30, 610] 
assert a + b * c == d - 40

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67
Power Assert
def (a, b, c, d) = [10, 20, 30, 610] 
assert a + b * c == d - 40
Assertion failed: 
 
assert a + b * c == d - 40 
| | | | | | | | 
10| 20| 30| | 570 
610 600 | 610 
false

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69
Calling Elvis for default values
def result = name != null &&
name.length() > 0 ?
name : "Unknown" 
 
def result = name ?: "Unknown"

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69
Calling Elvis for default values
def result = name != null &&
name.length() > 0 ?
name : "Unknown" 
 
def result = name ?: "Unknown"
Groovy Truth  
at play here

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71
Catch ‘any’ exception
try { 
something() 
} catch (any) { 
// ... 
}

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71
Catch ‘any’ exception
try { 
something() 
} catch (any) { 
// ... 
}
Someone suggested me:
catch(emAll)

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73
Of the importance of contracts
• Use explicit typing for
• method signatures
• properties & fields
• Nice for
• Java interoperability
• documenting your APIs
• IDE auto-completion and refactoring

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Thanks for your attention!

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Q & A

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76
Picture credits
Style: http://1hdwallpapers.com/wallpapers/my_style.jpg
Eurostar: http://www.whatsupwhatson.com/wp-content/uploads/2014/04/Eurostar_3012_Waterloo.jpg
Puzzle: http://joyinthecause.org/wp-content/uploads/2014/03/missing-puzzle-piece_00449088.jpg
Gems: http://www.freewhd.com/blue-gems-wallpaper/
Wise: http://fc00.deviantart.net/fs70/i/2012/044/f/6/three_wise_men_color_by_csoro-d4pmlv2.jpg
Ready: http://nameshapers.com/wp-content/uploads/2013/12/Social-Media-Coaching-for-CEOs-Getting-started.jpg
Semicolon: http://www.freeimageslive.co.uk/image/view/3944/_original
Till death to us part: https://mypencillines.files.wordpress.com/2013/04/img_0171.jpg
Public: http://www.levelupliving.com/wp-content/uploads/2012/05/Fear-of-Public-Speaking-image.jpg
Contract: https://www.icts.uiowa.edu/sites/default/files/contract.jpg
Exception: http://www.quotescover.com/wp-content/uploads/Its-the-exception-that-proves__quotes-by-French-Proverb-77.png
Banana: http://texturetaddka.com/wp-content/uploads/2011/10/DSC2008.jpg
Elvis: http://natedsanders.com/blog/wp-content/uploads/2013/10/Elvis-Presley-Wallpaper-1280-x-960.jpeg
Assert: http://www.itshouldjustworktm.com/wp-content/uploads/2012/03/assert-sign-photoshopped.jpg
Compass: https://lh4.ggpht.com/WtY8QL0re9kMssF6q4RopDHC6QEpou7ybQo7qNRjn1X8Iu5uKUZv7huHA_PxPB8iGfs=h900
Safety vest: http://media.nautisports.com/catalog/product/image/gilet-de-sauvetage-gonflable-hydrostatique-hammar-pilot-275-n-avec-harnais-pro-rouge-
nav_17452_web_1_1.jpg
Class: http://upload.wikimedia.org/wikipedia/en/5/50/A_Class_in_Progress.jpg
Aliasing: http://i.imgur.com/JrFly.png
Light switch: http://www.hapihour.org/wp-content/uploads/2014/04/lighting-design-wall-light-winsome-designer-light-switches-australia-designer-light-
switchesdesigner-light-switches-and-platesdesigner-light-switches-coversdesigner-light-switches-graydesign.jpg
Steel structure: http://www.jingtabuilding.com/UploadFiles/sl6.jpg
Quotes: http://g.fastcompany.net/multisite_files/fastcompany/poster/2013/09/3018353-poster-1280-quotess3.jpg
Setter: http://upload.wikimedia.org/wikipedia/commons/b/b4/Rzesz%C3%B3w_Irish_Red_and_White_Setter_1pl.jpg
Argument: http://www.familytreecounseling.com/kathysblog/wp-content/uploads/2014/01/arguing_couple.jpg
Equal cupcake: http://static.communitytable.com/wp-content/uploads/2013/04/marriage-equality-cupcakes-ftr.jpg
Obama truth: http://upload.wikimedia.org/wikipedia/commons/7/7c/Obama_swearing_in.JPG
Quiz: http://a622.phobos.apple.com/us/r30/Purple/v4/df/a9/6e/dfa96e6c-ea9b-ee4c-4d6c-f9edf2775e1d/mzl.exfkkuro.png
return: http://legacyofshadow.com/wp-content/uploads/2012/04/no-return-sign.jpg
spock: http://trekcore.com/gallery/albums/spock09/spock_pb04.jpg
London: http://www.100percentoptical.com/images/2014/10/london.jpg
Tie fighter: http://img3.wikia.nocookie.net/__cb20090419001710/uncyclopedia/images/f/fe/Darthvader_tie_fighter.jpg

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Groovy with Style — GR8Conf Europe 2015

Groovy with Style — GR8Conf Europe 2015

Guillaume Laforge

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