Groovy is a great language with extremely powerful capabilities about compile time meta-programming. Do you know that provides more than 40 AST transformations out-of-the box just to make your life as a developer easier? In this talk you will learn the most important transformations provided by Groovy. I'll use a lot of code examples to explain all the concepts.

1. G3 Summit
Taking advantage of
Groovy Annotations
Iván López - @ilopmar

2. ➢ Iván López - @ilopmar
➢ Groovy & Grails developer
Member of Grails team at OCI
➢ @MadridGUG coordinator
http://www.madridgug.com
➢ Greach organizer (@greachconf)
http://greachconf.com
➢ Speaker: SpringOne 2GX, GR8Conf, Codemotion,
GeeCon, Spring IO, Greach, JavaCro, RigaDevDay,...
About me...

3. “
The best code is not code at all

4. 1.
A little bit of theory

5. AST and compilation
▷ Abstract Syntax Tree
▷ AST modified during compilation
▷ Hook into the compiler phases

6. AST Transformations
▷ Global ▷ Local

7. 2.
Out-of-the-box ASTs

8. AST transformations categories
▷ Code generation
▷ Class design
▷ Logging improvements
▷ Declarative concurrency
▷ Cloning and externalizing
▷ Safe scripting
▷ Compiler directives
▷ Dependencies handling

9. Code generation

10. @ToString
▷ Human readable toString
▷ Effective Java by Joshua Bloch (item 10)

11. class User {
String name
Integer age
}
def u = new User(name: 'Iván', age: 36)
println u // User@1d2a54b2

12. @groovy.transform.ToString
class User {
String name
Integer age
}
def u = new User(name: 'Iván', age: 36)
assert u.toString() == 'User(Iván, 36)'
class User {
String name
Integer age
}
def u = new User(name: 'Iván', age: 36)
println u // User@1d2a54b2

13. @groovy.transform.ToString
class User {
String name
Integer age
}
def u = new User(name: 'Iván', age: 36)
assert u.toString() == 'User(Iván, 36)'
String toString() {
def _result = new StringBuilder()
_result.append('User(')
_result.append(this.name)
_result.append(', ')
_result.append(this.age)
_result.append(')')
return _result.toString()
}
class User {
String name
Integer age
}
def u = new User(name: 'Iván', age: 36)
println u // User@1d2a54b2

14. @ToString
▷ includeNames, excludes, includes, includeSuper,
includeSuperProperties, includeFields, ignoreNulls,
includePackage, cache

15. @ToString
▷ includeNames, excludes, includes, includeSuper,
includeSuperProperties, includeFields, ignoreNulls,
includePackage, cache
@groovy.transform.ToString(includeNames = true, excludes = ['name'])
class User {
String name
Integer age
}
def u = new User(name: 'Iván', age: 36)
assert u.toString() == 'User(age:36)'

16. @EqualsAndHashCode
▷ Generate equals and hashCode implementations
▷ Effective Java items 8 & 9

17. @EqualsAndHashCode
▷ Generate equals and hashCode implementations
▷ Effective Java items 8 & 9
@groovy.transform.EqualsAndHashCode
class User {
String name
Integer age
}
def u1 = new User(name: 'Iván', age: 36)
def u2 = new User(name: 'Iván', age: 36)
assert u1 == u2
assert u1.hashCode() == u2.hashCode()

18. int hashCode() {
def _result = HashCodeHelper.initHash()
_result = HashCodeHelper.updateHash(_result, this.name)
_result = HashCodeHelper.updateHash(_result, this.age)
return _result
}
boolean canEqual(Object other) {
return other instanceof User
}
boolean equals(Object other) {
if (other == null) { return false }
if (this.is(other)) { return true }
if (!(other instanceof User)) { return false }
User otherTyped = ((other) as User)
if (!(otherTyped.canEqual(this))) { return false }
if (!(this.getName().is(otherTyped.getName()))) {
if (this.getName().is(this) && !(otherTyped.getName().is(otherTyped)) || !(this.getName().is(this)) && otherTyped.getName().is(otherTyped))
return false
} else {
if (!(this.getName().is(this) && otherTyped.getName().is(otherTyped))) {
if (!(this.getName() == otherTyped.getName())) {
return false
}
}
}
}
if (!(this.getAge().is(otherTyped.getAge()))) {
if (this.getAge().is(this) && !(otherTyped.getAge().is(otherTyped)) || !(this.getAge().is(this)) && otherTyped.getAge().is(otherTyped)) {
return false
} else {
if (!(this.getAge().is(this) && otherTyped.getAge().is(otherTyped))) {
if (!(this.getAge() == otherTyped.getAge())) {
return false
}
}
}
}
return true
}

20. @EqualsAndHashCode
▷ excludes, includes, callSuper, includeFields, cache,
useCanEqual

21. @EqualsAndHashCode
▷ excludes, includes, callSuper, includeFields, cache,
useCanEqual
@groovy.transform.EqualsAndHashCode(includes = 'name')
class User {
String name
Integer age
}
def u1 = new User(name: 'Iván', age: 36)
def u2 = new User(name: 'Iván', age: 42)
assert u1 == u2
assert u1.hashCode() == u2.hashCode()

22. @TupleConstructor
▷ Generate constructors

23. @TupleConstructor
▷ Generate constructors
@groovy.transform.TupleConstructor
class User {
String name
Integer age
}

24. @TupleConstructor
▷ Generate constructors
@groovy.transform.TupleConstructor
class User {
String name
Integer age
}
// Default map constructor
def u1 = new User(name: 'Iván', age: 36)

25. @TupleConstructor
▷ Generate constructors
@groovy.transform.TupleConstructor
class User {
String name
Integer age
}
// Default map constructor
def u1 = new User(name: 'Iván', age: 36)
// Generated tuple constructor
def u2 = new User('Iván', 36)
def u3 = new User('Iván')

26. @TupleConstructor
▷ Generate constructors
@groovy.transform.TupleConstructor
class User {
String name
Integer age
}
// Default map constructor
def u1 = new User(name: 'Iván', age: 35)
// Generated tuple constructor
def u2 = new User('Iván', 36)
def u3 = new User('Iván')
User(String name = null, Integer age = null) {
this.name = name
this.age = age
}

27. @TupleConstructor
▷ excludes, includes, includeFields, includeProperties,
includeSuperFields, includeSuperProperties,
callSuper, force

28. @Canonical
▷ @ToString + @EqualsAndHashCode +
@TupleConstructor

29. @Canonical
▷ @ToString + @EqualsAndHashCode +
@TupleConstructor
@groovy.transform.Canonical
class User {
String name
Integer age
}

30. @Canonical
▷ @ToString + @EqualsAndHashCode +
@TupleConstructor
def u1 = new User(name: 'Iván', age: 36)
assert u1.toString() == 'User(Iván, 36)' // @ToString
@groovy.transform.Canonical
class User {
String name
Integer age
}

31. @Canonical
▷ @ToString + @EqualsAndHashCode +
@TupleConstructor
def u2 = new User('Iván', 36) // @TupleConstructor
assert u2.toString() == 'User(Iván, 36)'
def u1 = new User(name: 'Iván', age: 36)
assert u1.toString() == 'User(Iván, 36)' // @ToString
@groovy.transform.Canonical
class User {
String name
Integer age
}

32. @Canonical
▷ @ToString + @EqualsAndHashCode +
@TupleConstructor
assert u1 == u2 // @EqualsAndHashCode
assert u1.hashCode() == u2.hashCode() // @EqualsAndHashCode
def u2 = new User('Iván', 36) // @TupleConstructor
assert u2.toString() == 'User(Iván, 36)'
def u1 = new User(name: 'Iván', age: 36)
assert u1.toString() == 'User(Iván, 36)' // @ToString
@groovy.transform.Canonical
class User {
String name
Integer age
}

33. @InheritConstructors
▷ Reduce boilerplate code when parent classes
have multiple constructors
▷ Useful when overriding exception classes

34. @groovy.transform.InheritConstructors
class MyException extends Exception {
}

35. protected MyException(String param0, Throwable param1, boolean param2, boolean param3) {
super(param0, param1, param2, param3)
}
public MyException(Throwable param0) { super(param0) }
public MyException(String param0, Throwable param1) { super(param0, param1) }
public MyException(String param0) { super(param0) }
public MyException() { super() }
@groovy.transform.InheritConstructors
class MyException extends Exception {
}

36. @Lazy
▷ Lazy initialization of fields
▷ Useful when creating expensive resources
▷ Effective Java item 71

37. class SomeBean {
@Lazy
LinkedList myField
}

38. class SomeBean {
@Lazy
LinkedList myField
}
public LinkedList getMyField() {
if ($myField != null) {
$myField
} else {
$myField = new LinkedList()
}
}

39. @Sortable
▷ Comparable interface
▷ compareTo method natural order
▷ N methods returning comparators
▷ Effective Java item 12

40. @groovy.transform.Sortable
class User {
String name
Integer age
Integer born
}

41. public int compareTo(User other) {
if (this.is(other)) return 0
Integer value = 0
value = this.name <=> other.name
if (value != 0) return value
value = this.age <=> other.age
if (value != 0) return value
value = this.born <=> other.born
if (value != 0) return value
return 0
}
private static class User$NameComparator extends AbstractComparator<User> {
public int compare(User arg0, User arg1) {
if (arg0 == arg1) return 0
if (arg0 != null && arg1 == null) return -1
if (arg0 == null && arg1 != null) return 1
return arg0.name <=> arg1.name
}
}
private static class User$AgeComparator extends AbstractComparator<User> {
...
}
@groovy.transform.Sortable
class User {
String name
Integer age
Integer born
}

42. @groovy.transform.Sortable
class User {
String name
Integer age
Integer born
}

43. def users = [
new User(name: 'Mary', age: 15, born: 2000),
new User(name: 'Peter', age: 44, born: 1970),
new User(name: 'John', age: 35, born: 1979),
]
@groovy.transform.Sortable
class User {
String name
Integer age
Integer born
}

44. assert users.sort(false, User.comparatorByName())*.name == ['John', 'Mary', 'Peter']
assert users.sort(false, User.comparatorByAge())*.born == [2000, 1979, 1970]
def users = [
new User(name: 'Mary', age: 15, born: 2000),
new User(name: 'Peter', age: 44, born: 1970),
new User(name: 'John', age: 35, born: 1979),
]
@groovy.transform.Sortable
class User {
String name
Integer age
Integer born
}

45. @Sortable
▷ includes, excludes
@groovy.transform.Sortable(excludes = 'age')
class User {
String name
Integer age
Integer born
}
def users = [
new User(name: 'Mary', age: 15, born: 2000),
new User(name: 'Peter', age: 44, born: 1970),
new User(name: 'John', age: 35, born: 1979),
]
assert users.sort(false, User.comparatorByName())*.name == ['John', 'Mary', 'Peter']
assert users.sort(false, User.comparatorByAge())*.born == [2000, 1979, 1970]

46. @Builder
▷ Create fluent API calls
▷ Multiple building strategies
▷ Multiple configuration options: builder name,
prefix, excludes, includes,...
▷ Effective Java item 2

47. @groovy.transform.builder.Builder
class User {
String name
Integer age
Integer born
}

48. @groovy.transform.builder.Builder
class User {
String name
Integer age
Integer born
}
def u = User.builder()
.name('Iván')
.age(36)
.born(1979)
.build()
assert u.name == 'Iván'
assert u.age == 36
assert u.born == 1979

49. public static class User$UserBuilder extends Object {
private String name
private Integer age
private Integer born
public User$UserBuilder() {
}
public User$UserBuilder name(String name) {
this.name = name
return this
}
public User$UserBuilder age(Integer age) {
this.age = age
return this
}
public User$UserBuilder born(Integer born) {
this.born = born
return this
}
public User build() {
User _theUser = new User()
_theUser.name = name
_theUser.age = age
_theUser.born = born
return _theUser
}
}
@groovy.transform.builder.Builder
class User {
String name
Integer age
Integer born
}
def u = User.builder()
.name('Iván')
.age(36)
.born(1979)
.build()
assert u.name == 'Iván'
assert u.age == 36
assert u.born == 1979

50. Class design

51. @Delegate
▷ Implements delegation design pattern
▷ Delegate calls on object to method on delegated
properties
▷ All public methods are delegated

52. import java.time.LocalDate
class Conference {
@groovy.lang.Delegate
LocalDate when
String name
}

53. import java.time.LocalDate
class Conference {
@groovy.lang.Delegate
LocalDate when
String name
}
def greach = new Conference(name: 'Greach', when: LocalDate.of(2017, 03, 31))
def gr8conf = new Conference(name: 'GR8Conf' when: LocalDate.of(2017, 05, 31))

54. def greach = new Conference(name: 'Greach', when: LocalDate.of(2017, 03, 31))
def gr8conf = new Conference(name: 'GR8Conf' when: LocalDate.of(2017, 05, 31))
assert greach.isBefore(gr8conf)
import java.time.LocalDate
class Conference {
@groovy.lang.Delegate
LocalDate when
String name
}

55. class Conference {
...
public boolean isAfter(ChronoLocalDate param0) {
when.isAfter(param0)
}
public boolean isBefore(ChronoLocalDate param0) {
when.isBefore(param0)
}
...
}
def greach = new Conference(name: 'Greach', when: LocalDate.of(2017, 03, 31))
def gr8conf = new Conference(name: 'GR8Conf' when: LocalDate.of(2017, 05, 31))
assert greach.isBefore(gr8conf)
import java.time.LocalDate
class Conference {
@groovy.lang.Delegate
LocalDate when
String name
}

56. @Immutable
▷ Create immutable classes
▷ Effective Java item 15
▷ Rules for immutability

57. @groovy.transform.Immutable
class User {
String name
Integer age
}
def u = new User(name: 'Iván', age: 36)

58. // This does not compile
// You are not allowed to overwrite
// the final class 'User'.
class Admin extends User {
}
@groovy.transform.Immutable
class User {
String name
Integer age
}
def u = new User(name: 'Iván', age: 36)

59. @groovy.transform.Immutable
class User {
String name
Integer age
}
def u = new User(name: 'Iván', age: 36)
try {
u.name = 'John'
} catch (ReadOnlyPropertyException e) {
println e
}
// This does not compile
// You are not allowed to overwrite
// the final class 'User'.
class Admin extends User {
}

60. @Memoized
▷ Cache the result of a method

61. @Memoized
▷ Cache the result of a method
@groovy.transform.Memoized
Long fibonacci(Integer n) {
if (n < 2) return 1
else return fibonacci(n-1) + fibonacci(n-2)
}
fibonacci(300)

62. @Memoized
▷ Cache the result of a method
@groovy.transform.Memoized
Long fibonacci(Integer n) {
if (n < 2) return 1
else return fibonacci(n-1) + fibonacci(n-2)
}
fibonacci(300)
@groovy.transform.Memoized
User getUserInfo(Long userId) {
// Expensive repetitive
// network operation
}

63. Logging
improvements

64. @Log, @Log4j, @Log4j2, @Slf4j
▷ Static final field for the logger

65. @Log, @Log4j, @Log4j2, @Slf4j
@groovy.util.logging.Log4j
class MyClass {
void method() {
log.debug "My debug message"
}
}
▷ Static final field for the logger

66. @Log, @Log4j, @Log4j2, @Slf4j
@groovy.util.logging.Log4j
class MyClass {
void method() {
log.debug "My debug message"
}
}
▷ Static final field for the logger
class MyClass {
private static final Logger log = Logger.getLogger(Saludador.name)
void method() {
if (log.isLoggable(Level.DEBUG)) {
log.debug "My debug message"
}
}
}

67. Declarative concurrency

68. Declarative concurrency
▷ @Synchronized
▷ @WithReadLock
▷ @WithWriteLock

69. Cloning and externalizing

70. Cloning and externalizing
▷ @AutoClone
▷ @AutoExternalize

71. Safe scripting

72. Safe scripting
▷ @ThreadInterrupt
▷ @TimedInterrupt
▷ @ConditionalInterrupt

73. Compiler directives

74. Compiler directives
▷ @TypeChecked
▷ @CompileStatic
▷ @CompileDynamic

75. Dependencies
handling

76. @Grab
▷ Grape dependency manager

77. @Grab
▷ Grape dependency manager
@Grab(group='org.springframework', module='spring-orm', version='3.2.5.RELEASE')
import org.springframework.jdbc.core.JdbcTemplate
// or
@Grab('org.springframework:spring-orm:3.2.5.RELEASE')
import org.springframework.jdbc.core.JdbcTemplate

78. @GrabResolver
▷ Grape dependency manager
@Grab(group='org.springframework', module='spring-orm', version='3.2.5.RELEASE')
import org.springframework.jdbc.core.JdbcTemplate
// or
@Grab('org.springframework:spring-orm:3.2.5.RELEASE')
import org.springframework.jdbc.core.JdbcTemplate
@GrabResolver(name='restlet', root='http://maven.restlet.org/')
@Grab(group='org.restlet', module='org.restlet', version='1.1.6')

79. @GrabExclude
▷ Grape dependency manager
@Grab(group='org.springframework', module='spring-orm', version='3.2.5.RELEASE')
import org.springframework.jdbc.core.JdbcTemplate
// or
@Grab('org.springframework:spring-orm:3.2.5.RELEASE')
import org.springframework.jdbc.core.JdbcTemplate
@GrabResolver(name='restlet', root='http://maven.restlet.org/')
@Grab(group='org.restlet', module='org.restlet', version='1.1.6')
@Grab('net.sourceforge.htmlunit:htmlunit:2.8')
@GrabExclude('xml-apis:xml-apis')

80. Bonus

81. @Pokemon
class Foo {
void doStuff() {
try {
// Some code that can throws
// different exceptions
} catch (e) {
// Gotta catch’em all
}
}
}

82. @Pokemon
class Foo {
void doStuff() {
try {
// Some code that can throws
// different exceptions
} catch (e) {
// Gotta catch’em all
}
}
}
class Foo {
@com.github.danveloper.ast.Pokemon
void doStuff() {
// code
}
}

83. 3.
Demo

84. 4.
Summary

85. “
The best code is not code at all

86. Thanks!
Any questions?
@ilopmar
lopez.ivan@gmail.com
https://github.com/ilopmar
Iván López
http://bit.ly/g3summit-groovy