How to Troubleshoot Apps for the Modern Connected Worker
Learning groovy -EU workshop
1. Beginning Groovy 3.0
Adam L. Davis
The Solution Design Group, Inc.
Author of “Learning Groovy”
(& Reactive Streams in Java & others)
16 years Java Dev.
github.com/adamldavis
/2019-gr8conf
thesdg.com
5. groovy-lang.org
sdkman.io
Flat learning curve
Smooth Java integration
Vibrant and rich ecosystem
Powerful features
Domain-Specific Languages (DSLs)
Scripting and testing glue
Inspired by Python, Ruby,
Smalltalk, ...
6. ●
Dynamic or Static
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(@CompileStatic @TypeChecked)
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As fast as Java (with static & indy)
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Meta-programming
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Optional semi-colons
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Optional parentheses (command chains)
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Short-hand for Lists and Maps
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Automatic getters and setters
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A better switch
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Groovy GDK…
Groovy pre-2.5 Features
7. ●
Closures
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Currying
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Method references
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Map/Filter/Reduce as collect, findAll, inject
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Internal iterating using each
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Operator Overloading (+ - * % / …)
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methodMissing and propertyMissing
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AST Transformations
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Traits
…
Groovy pre-2.5 Features (cont.)
8. Groovy 2.5
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Groovy 2.5 added support for JDK9+
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11 new AST transformations
– @AutoFinal, @AutoImplement, @ImmutableBase,
@ImmutableOptions, @MapConstructor,
@NamedDelegate, @NamedParam,
@NamedParams, @NamedVariant,
@PropertyOptions, and @VisibilityOptions
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Macro feature - makes writing AST
transformations much easier!
9. Starting Out
Option 1: Using sdkman.io
– sdk install groovy
Option 2: Download from groovy-lang.org
– Alter your PATH
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Export PATH=$PATH:/usr/lib/groovy/bin
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Option 3: Mac – see http://groovy-lang.org/install.html
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Option π: Windows – see https://github.com/groovy/groovy-windows-installer
Then: $ groovyConsole
IntelliJ IDEA or NetBeans
10. Dynamic typing
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def keyword
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Parameters’ typing optional
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Possible to mock using a map
– def dog = [bark: { println ‘woof’ }]
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Using @TypeChecked or @CompileStatic you
can make Groovy statically typed in some
classes or methodsz
11. Groovy Strings
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‘normal string’
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“groovy string can contain $variables”
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“can also do expressions ${x + 1}”
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Use triple quote to start/end multi-line strings
‘’’
This is a
Multi-line
String
‘’’
12. Math, Groovy Truth, and Equals
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Numbers are BigDecimal by default not Double
– 3.14 is a BigDecimal
– 3.14d is a Double
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Groovy truth: null, “”, [], 0 are false
– if (!thing) println “thing was null”
– if (!str) println “str was empty”
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Groovy == means .equals
– For identity use a.is(b)
– Groovy 3: a === b
13. Property Access
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Everything is public
by default
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Every field has a
getter and setter by
default
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Gotcha’s
– Map access
– String.class->String
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Property access
automatically uses getters
and setters
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foo.bar == foo.getBar()
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foo.bar = 2 == foo.setBar(2)
15. Maps Continued...
def map = [cars: 1, boats: 2, planes: 3]
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String key access: map.cars
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OR map[‘cars’]
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Also works for modifying:
– map.cars = 42
– map[‘cars’] = 42
16. Groovy 3
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Groovy 3 sports a completely rewritten parser
(Parrot) that brings Groovy up to parity with the
latest Java 11 syntax along with new Groovy-only
features. It runs on JDK 8 minimum and has better
support for JDK 9/10/11.
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Java-style: lambda expressions and method
references, array initialization, and do/while loops
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Support for try-with-resources and “var”
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New operators: !in !instanceof
18. A better switch
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Switch can use types, lists, ranges, patterns…
Switch (x) {
case Map: println “was a map”; break
case [4,5,6]: println “was 4, 5 or 6”; break
case 0..20: println “was 0 to 20”; break
case ~/w+/: println “ was a word”; break
case “hello”: println x; break
case BigDecimal: println “was a BigDecimal”
19. Groovy GDK
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Adds methods to everything! Adds its own classes...
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Collections: sort, findAll, collect, inject, each,…
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IO: toFile(), text, bytes, withReader, URL.content
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Ranges: x..y, x..<y
– GetAt syntax for Strings and Lists:
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text[0..4] == text.substring(0,5)
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Utilities: ConfigSlurper, Expando,
ObservableList/Map/Set, JsonSlurper, JsonBuilder, ...
20. in keyword
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Use the “in” keyword to test inclusion or loops:
– assert 'Groovy' in ['Java', 'Groovy']
– assert 7 in 0..10
– for (i in 0..10) {}
– for (str in strArray) {}
21. Safe dereference & Elvis operator
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Safe dereference ?.
– String name = person?.name
– Java: person == null ? null : person.getName()
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Elvis operator ?:
– String name = person?.name ?: “Bob”
– Java: if (name == null) name = “Bob”
22. Closures
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Closure: “a self-containing method” (like Lambda exp.)
– def say = { x -> println x }
– say(‘hello gr8conf’)
– def say = { println it }
– def adder = { x, y -> x + y }
●
Closures have several implicit variables:
– it - If the closure has one argument
– this - Refers to the enclosing class
– owner - The same as this unless it is enclosed in another closure.
– delegate - Usually the same as owner but you can change it (this
allows the methods of delegate to be in scope).
23. Closures Continued...
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When used as last parameter, closure can go
outside parentheses
– methodCalled(param1, param2) { closureHere() }
– methodWithOnlyClosure { closureHere() }
24. Regex Pattern Matching
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Regex = regular expressions
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Within forward slashes / is a regex
– You don’t need to use double
– Example: /d+/ matches any number
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=~ for matching anywhere within a string
– if (text =~ /d+/) println “there was a number in it”
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==~ for matching the whole string
– if (email ==~ /[w.]+@[w.]+/) println “it’s an email”
25. Meta-programming
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Every class and instance has a metaClass
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String.metaClass.upper =
{ delegate.toUpperCase() }
– “foo”.upper() == “FOO”
● ●
Extension Modules!
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Traits can be used as
mixins
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Maps can be cast to
actual types using as
[bark: {println “Woof!”}]
as Dog
33. Spock
Built on JUnit
Somewhat enhanced groovy
“test names can be any string”
given: when: then: expect:
Built-in mocking
Table-syntax for provided test data
Pretty assert output
34. Thanks!
Adam L. Davis
“Learning Groovy”
github.com/adamldavis
/2019-gr8conf
adamldavis.com
@adamldavis
http://bit.ly/Gr8-2019BG
How? Gedit + https://github.com/aeischeid/gedit-grails-bundle
