confess vienna 2015 - metaprogramming with groovy
TRANSCRIPT
METAPROGRAMMING WITH GROOVY
Iván López @ilopmar
Hello!I am Iván López
@ilopmar
http://greachconf.com@madridgug
Groovy is dynamic
▷ “Delay” to runtime some decisions
▷ Add properties/behaviours in runtime
▷ Wide range of applicability
What is metaprogramming?
“Metaprogramming is the writing of computer programs that write or manipulate other programs (or themselves) as their data.
- Wikipedia
1.Runtime metaprogramming
Runtime metaprogramming
▷ Groovy provides this through Meta-Object Protocol (MOP)
▷ Use MOP to:– Invoke methods dynamically– Synthesize classes and methods on
the fly
What is the Meta Object Protocol?
Groovy
Groovy
Java
Java
MOP
Intercepting methodsusing MOP
public interface GroovyObject { Object invokeMethod(String name, Object args) Object getProperty(String propertyName) void setProperty(String propertyName, Object newValue) MetaClass getMetaClass() void setMetaClass(MetaClass metaClass)}
Groovy Interceptable
▷ GroovyObject interface
▷ Implement GroovyInterceptable to hook into the execution
GroovyInterceptable exampleclass Person implements GroovyInterceptable {
String name Integer age
public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" }
public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue }}
def person = new Person()person.name = "Iván"person.age = 35
println "Hello ${person.name}, you're ${person.age}"
// ExecutionSetting property 'name' with value 'Iván'Setting property 'age' with value '35'Getting property 'name'Getting property 'age'Hello Iván, you're 35
GroovyInterceptable exampleclass Person implements GroovyInterceptable {
String name Integer age
public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" }
public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue }}
def person = new Person()person.name = "Iván"person.age = 35
println "Hello ${person.name}, you're ${person.age}"
// ExecutionSetting property 'name' with value 'Iván'Setting property 'age' with value '35'Getting property 'name'Getting property 'age'Hello Iván, you're 35
GroovyInterceptable exampleclass Person implements GroovyInterceptable {
String name Integer age
public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" }
public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue }}
def person = new Person()person.name = "Iván"person.age = 35
println "Hello ${person.name}, you're ${person.age}"
// ExecutionSetting property 'name' with value 'Iván'Setting property 'age' with value '35'Getting property 'name'Getting property 'age'Hello Iván, you're 35
GroovyInterceptable exampleclass Person implements GroovyInterceptable {
String name Integer age
public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" }
public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue }}
def person = new Person()person.name = "Iván"person.age = 35
println "Hello ${person.name}, you're ${person.age}"
// ExecutionSetting property 'name' with value 'Iván'Setting property 'age' with value '35'Getting property 'name'Getting property 'age'Hello Iván, you're 35
GroovyInterceptable exampleclass Person implements GroovyInterceptable {
String name Integer age
public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" }
public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue }}
def person = new Person()person.name = "Iván"person.age = 35
println "Hello ${person.name}, you're ${person.age}"
// ExecutionSetting property 'name' with value 'Iván'Setting property 'age' with value '35'Getting property 'name'Getting property 'age'Hello Iván, you're 35
class Hello implements GroovyInterceptable {
public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'"
def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) }
void sayHi(String name) { System.out.println "Hello ${name}" }}
def hello = new Hello()hello.sayHi("ConFess Vienna!")hello.anotherMethod()
GroovyInterceptable example (II)
// ExecutionInvoking method 'sayHi' with args '[ConFess Vienna!]'Hello ConFess Vienna!Invoking method 'anotherMethod' with args '[]'
class Hello implements GroovyInterceptable {
public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'"
def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) }
void sayHi(String name) { System.out.println "Hello ${name}" }}
def hello = new Hello()hello.sayHi("ConFess Vienna!")hello.anotherMethod()
GroovyInterceptable example (II)
// ExecutionInvoking method 'sayHi' with args '[ConFess Vienna!]'Hello ConFess Vienna!Invoking method 'anotherMethod' with args '[]'
class Hello implements GroovyInterceptable {
public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'"
def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) }
void sayHi(String name) { System.out.println "Hello ${name}" }}
def hello = new Hello()hello.sayHi("ConFess Vienna!")hello.anotherMethod()
GroovyInterceptable example (II)
// ExecutionInvoking method 'sayHi' with args '[ConFess Vienna!]'Hello ConFess Vienna!Invoking method 'anotherMethod' with args '[]'
class Hello implements GroovyInterceptable {
public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'"
def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) }
void sayHi(String name) { System.out.println "Hello ${name}" }}
def hello = new Hello()hello.sayHi("ConFess Vienna!")hello.anotherMethod()
GroovyInterceptable example (II)
// ExecutionInvoking method 'sayHi' with args '[ConFess Vienna!]'Hello ConFess Vienna!Invoking method 'anotherMethod' with args '[]'
MetaClass▷ MetaClass registry for each class
▷ Collection of methods/properties
▷ We can always modify the metaclass
▷ Intercept methods implementing invokeMethod on metaclass
class Hello { void sayHi(String name) { println "Hello ${name}" }}
Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'"
def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args)}
def hello = new Hello()
hello.sayHi("ConFess Vienna!")hello.anotherMethod()
// ExecutionInvoking method 'sayHi' with args '[ConFess Vienna!]'Hello ConFess Vienna!Invoking method 'anotherMethod' with args '[]'
MetaClass example
class Hello { void sayHi(String name) { println "Hello ${name}" }}
Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'"
def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args)}
def hello = new Hello()
hello.sayHi("ConFess Vienna!")hello.anotherMethod()
// ExecutionInvoking method 'sayHi' with args '[ConFess Vienna!]'Hello ConFess Vienna!Invoking method 'anotherMethod' with args '[]'
MetaClass example
class Hello { void sayHi(String name) { println "Hello ${name}" }}
Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'"
def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args)}
def hello = new Hello()
hello.sayHi("ConFess Vienna!")hello.anotherMethod()
// ExecutionInvoking method 'sayHi' with args '[ConFess Vienna!]'Hello ConFess Vienna!Invoking method 'anotherMethod' with args '[]'
MetaClass example
class Hello { void sayHi(String name) { println "Hello ${name}" }}
Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'"
def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args)}
def hello = new Hello()
hello.sayHi("ConFess Vienna!")hello.anotherMethod()
// ExecutionInvoking method 'sayHi' with args '[ConFess Vienna!]'Hello ConFess Vienna!Invoking method 'anotherMethod' with args '[]'
MetaClass example
class Hello { void sayHi(String name) { println "Hello ${name}" }}
Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'"
def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args)}
def hello = new Hello()
hello.sayHi("ConFess Vienna!")hello.anotherMethod()
// ExecutionInvoking method 'sayHi' with args '[ConFess Vienna!]'Hello ConFess Vienna!Invoking method 'anotherMethod' with args '[]'
MetaClass example
MOP method injection
MOP Method Injection▷ Injecting methods at code-writing time
▷ We can “open” a class any time
▷ Different techniques:– MetaClass– Categories– Extensions– Mixins vs Traits
class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') }}
String chuckIpsum = "If you can see Chuck Norris, he can see you.\If you can not see Chuck Norris you may be only seconds away from death"
println StringUtils.truncate(chuckIpsum, 72)println StringUtils.truncate(chuckIpsum, 72, true)
// ExecutionIf you can see Chuck Norris, he can see you. If you can not see Chuck NoIf you can see Chuck Norris, he can see you. If you can not see Chuck No...
String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '')}
assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass
class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') }}
String chuckIpsum = "If you can see Chuck Norris, he can see you.\If you can not see Chuck Norris you may be only seconds away from death"
println StringUtils.truncate(chuckIpsum, 72)println StringUtils.truncate(chuckIpsum, 72, true)
// ExecutionIf you can see Chuck Norris, he can see you. If you can not see Chuck NoIf you can see Chuck Norris, he can see you. If you can not see Chuck No...
String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '')}
assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass
class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') }}
String chuckIpsum = "If you can see Chuck Norris, he can see you.\If you can not see Chuck Norris you may be only seconds away from death"
println StringUtils.truncate(chuckIpsum, 72)println StringUtils.truncate(chuckIpsum, 72, true)
// ExecutionIf you can see Chuck Norris, he can see you. If you can not see Chuck NoIf you can see Chuck Norris, he can see you. If you can not see Chuck No...
String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '')}
assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass
class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') }}
String chuckIpsum = "If you can see Chuck Norris, he can see you.\If you can not see Chuck Norris you may be only seconds away from death"
println StringUtils.truncate(chuckIpsum, 72)println StringUtils.truncate(chuckIpsum, 72, true)
// ExecutionIf you can see Chuck Norris, he can see you. If you can not see Chuck NoIf you can see Chuck Norris, he can see you. If you can not see Chuck No...
String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '')}
assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass
class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') }}
String chuckIpsum = "If you can see Chuck Norris, he can see you.\If you can not see Chuck Norris you may be only seconds away from death"
println StringUtils.truncate(chuckIpsum, 72)println StringUtils.truncate(chuckIpsum, 72, true)
// ExecutionIf you can see Chuck Norris, he can see you. If you can not see Chuck NoIf you can see Chuck Norris, he can see you. If you can not see Chuck No...
String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '')}
assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass
class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') }}
String chuckIpsum = "If you can see Chuck Norris, he can see you.\If you can not see Chuck Norris you may be only seconds away from death"
println StringUtils.truncate(chuckIpsum, 72)println StringUtils.truncate(chuckIpsum, 72, true)
// ExecutionIf you can see Chuck Norris, he can see you. If you can not see Chuck NoIf you can see Chuck Norris, he can see you. If you can not see Chuck No...
String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '')}
assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass
class Utils {}
def utilsInstance = new Utils()
Utils.metaClass.version = "3.0"utilsInstance.metaClass.released = true
assert utilsInstance.version == "3.0"assert utilsInstance.released == true
Adding properties using MetaClass
Adding properties using MetaClass
class Utils {}
def utilsInstance = new Utils()
Utils.metaClass.version = "3.0"utilsInstance.metaClass.released = true
assert utilsInstance.version == "3.0"assert utilsInstance.released == true
class Utils {}
def utilsInstance = new Utils()
Utils.metaClass.version = "3.0"utilsInstance.metaClass.released = true
assert utilsInstance.version == "3.0"assert utilsInstance.released == true
Adding properties using MetaClass
class Utils {}
def utilsInstance = new Utils()
Utils.metaClass.version = "3.0"utilsInstance.metaClass.released = true
assert utilsInstance.version == "3.0"assert utilsInstance.released == true
Adding properties using MetaClass
// Integerassert '42' == 42.toString()
Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate)}
assert 42.toString() == 'The answer to life, the universe and everything'assert 100.toString() == '100'
// Booleanassert false.toBoolean() == false
Boolean.metaClass.toBoolean = { !delegate }assert false.toBoolean() == true
Overriding methods using MetaClass
// Integerassert '42' == 42.toString()
Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate)}
assert 42.toString() == 'The answer to life, the universe and everything'assert 100.toString() == '100'
// Booleanassert false.toBoolean() == false
Boolean.metaClass.toBoolean = { !delegate }assert false.toBoolean() == true
Overriding methods using MetaClass
// Integerassert '42' == 42.toString()
Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate)}
assert 42.toString() == 'The answer to life, the universe and everything'assert 100.toString() == '100'
// Booleanassert false.toBoolean() == false
Boolean.metaClass.toBoolean = { !delegate }assert false.toBoolean() == true
Overriding methods using MetaClass
// Integerassert '42' == 42.toString()
Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate)}
assert 42.toString() == 'The answer to life, the universe and everything'assert 100.toString() == '100'
// Booleanassert false.toBoolean() == false
Boolean.metaClass.toBoolean = { !delegate }assert false.toBoolean() == true
Overriding methods using MetaClass
// Integerassert '42' == 42.toString()
Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate)}
assert 42.toString() == 'The answer to life, the universe and everything'assert 100.toString() == '100'
// Booleanassert false.toBoolean() == false
Boolean.metaClass.toBoolean = { !delegate }assert false.toBoolean() == true
Overriding methods using MetaClass
// Integerassert '42' == 42.toString()
Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate)}
assert 42.toString() == 'The answer to life, the universe and everything'assert 100.toString() == '100'
// Booleanassert false.toBoolean() == false
Boolean.metaClass.toBoolean = { !delegate }assert false.toBoolean() == true
Overriding methods using MetaClass
Categories
▷ MetaClass changes are “persistent”
▷ Change metaclass in confined code
▷ MOP modified only in the closure
Categories exampleclass StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') }}
use (StringUtils) { println "Lorem ipsum".truncate(5)}
try { println "Lorem ipsum".truncate(5)} catch (MissingMethodException mme) { println mme}
// ExecutionLorem
groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5]Possible solutions: concat(java.lang.String), take(int)
Categories exampleclass StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') }}
use (StringUtils) { println "Lorem ipsum".truncate(5)}
try { println "Lorem ipsum".truncate(5)} catch (MissingMethodException mme) { println mme}
// ExecutionLorem
groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5]Possible solutions: concat(java.lang.String), take(int)
Categories exampleclass StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') }}
use (StringUtils) { println "Lorem ipsum".truncate(5)}
try { println "Lorem ipsum".truncate(5)} catch (MissingMethodException mme) { println mme}
// ExecutionLorem
groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5]Possible solutions: concat(java.lang.String), take(int)
Categories exampleclass StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') }}
use (StringUtils) { println "Lorem ipsum".truncate(5)}
try { println "Lorem ipsum".truncate(5)} catch (MissingMethodException mme) { println mme}
// ExecutionLorem
groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5]Possible solutions: concat(java.lang.String), take(int)
class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output
try { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file))
output << input } finally { input?.close() output?.close() } }}
Categories example (II)
class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output
try { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file))
output << input } finally { input?.close() output?.close() } }}
Categories example (II)
class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output
try { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file))
output << input } finally { input?.close() output?.close() } }}
Categories example (II)
File tmpFile = File.createTempFile('tmp_', '')
use (FileBinaryCategory) { tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL()}
println tmpFile
// Execution/tmp/tmp_7428855173238452155
class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output
try { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file))
output << input } finally { input?.close() output?.close() } }}
Categories example (II)
File tmpFile = File.createTempFile('tmp_', '')
use (FileBinaryCategory) { tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL()}
println tmpFile
// Execution/tmp/tmp_7428855173238452155
class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output
try { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file))
output << input } finally { input?.close() output?.close() } }}
Categories example (II)
File tmpFile = File.createTempFile('tmp_', '')
use (FileBinaryCategory) { tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL()}
println tmpFile
// Execution/tmp/tmp_7428855173238452155
class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output
try { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file))
output << input } finally { input?.close() output?.close() } }}
Categories example (II)
File tmpFile = File.createTempFile('tmp_', '')
use (FileBinaryCategory) { tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL()}
println tmpFile
// Execution/tmp/tmp_7428855173238452155
Extension modules
▷ JAR file that provides extra methods
▷ Meta-information file
▷ Put jar in classpath to enhance classes
// src/main/groovy/confess2015/StringUtilsExtension.groovypackage confess2015class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') }}
package confess2015import spock.lang.Specificationclass StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) }}
// Execute with:// gradle build// groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy
assert "Lorem..." == "Lorem ipsum". truncate(5, true)
# src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModulemoduleName = string-utils-modulemoduleVersion = 0.1extensionClasses = confess2015.StringUtilsExtension
Extension modules example
Extension modules example// src/main/groovy/confess2015/StringUtilsExtension.groovypackage confess2015class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') }}
# src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModulemoduleName = string-utils-modulemoduleVersion = 0.1extensionClasses = confess2015.StringUtilsExtension
package confess2015import spock.lang.Specificationclass StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) }}
// Execute with:// gradle build// groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy
assert "Lorem..." == "Lorem ipsum". truncate(5, true)
Extension modules example// src/main/groovy/confess2015/StringUtilsExtension.groovypackage confess2015class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') }}
package confess2015import spock.lang.Specificationclass StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) }}
// Execute with:// gradle build// groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy
assert "Lorem..." == "Lorem ipsum". truncate(5, true)
# src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModulemoduleName = string-utils-modulemoduleVersion = 0.1extensionClasses = confess2015.StringUtilsExtension
Extension modules example// src/main/groovy/confess2015/StringUtilsExtension.groovypackage confess2015class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') }}
package confess2015import spock.lang.Specificationclass StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) }}
// Execute with:// gradle build// groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy
assert "Lorem..." == "Lorem ipsum". truncate(5, true)
# src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModulemoduleName = string-utils-modulemoduleVersion = 0.1extensionClasses = confess2015.StringUtilsExtension
// src/main/groovy/confess2015/StringUtilsExtension.groovypackage confess2015class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') }}
package confess2015import spock.lang.Specificationclass StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) }}
// Execute with:// gradle build// groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy
assert "Lorem..." == "Lorem ipsum". truncate(5, true)
Extension modules example
# src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModulemoduleName = string-utils-modulemoduleVersion = 0.1extensionClasses = confess2015.StringUtilsExtension
Mixins
▷ “Bring in” or “mix in” implementations from multiple classes
▷ Calls first routed to mixed-in class
▷ Last mixin wins
▷ Not easily un-done
class SpidermanPower { String spiderSense() { "Using spider-sense..." }}
Mixins example
@Mixin([SpidermanPower])class Person {}
def person = new Person()assert person.spiderSense() == "Using spider-sense..."assert !(person instanceof SpidermanPower)
Person.mixin SupermanPowerassert person.fly() == "Flying..."assert !(person instanceof SupermanPower)
class SupermanPower { String fly() { "Flying..." }}
@Mixin([SpidermanPower])class Person {}
def person = new Person()assert person.spiderSense() == "Using spider-sense..."assert !(person instanceof SpidermanPower)
Person.mixin SupermanPowerassert person.fly() == "Flying..."assert !(person instanceof SupermanPower)
class SupermanPower { String fly() { "Flying..." }}
class SpidermanPower { String spiderSense() { "Using spider-sense..." }}
Mixins example
@Mixin([SpidermanPower])class Person {}
def person = new Person()assert person.spiderSense() == "Using spider-sense..."assert !(person instanceof SpidermanPower)
Person.mixin SupermanPowerassert person.fly() == "Flying..."assert !(person instanceof SupermanPower)
class SupermanPower { String fly() { "Flying..." }}
class SpidermanPower { String spiderSense() { "Using spider-sense..." }}
Mixins example
@Mixin([SpidermanPower])class Person {}
def person = new Person()assert person.spiderSense() == "Using spider-sense..."assert !(person instanceof SpidermanPower)
Person.mixin SupermanPowerassert person.fly() == "Flying..."assert !(person instanceof SupermanPower)
class SupermanPower { String fly() { "Flying..." }}
class SpidermanPower { String spiderSense() { "Using spider-sense..." }}
Mixins example
@Mixin([SpidermanPower])class Person {}
def person = new Person()assert person.spiderSense() == "Using spider-sense..."assert !(person instanceof SpidermanPower)
Person.mixin SupermanPowerassert person.fly() == "Flying..."assert !(person instanceof SupermanPower)
class SpidermanPower { String spiderSense() { "Using spider-sense..." }}
Mixins exampleclass SupermanPower { String fly() { "Flying..." }}
@Mixin([SpidermanPower])class Person {}
def person = new Person()assert person.spiderSense() == "Using spider-sense..."assert !(person instanceof SpidermanPower)
Person.mixin SupermanPowerassert person.fly() == "Flying..."assert !(person instanceof SupermanPower)
class SpidermanPower { String spiderSense() { "Using spider-sense..." }}
Mixins exampleclass SupermanPower { String fly() { "Flying..." }}
Traits▷ Groovy 2.3+
▷ Similar to Java 8 default methods
▷ Supported in JDK 6, 7 and 8
▷ Stateful
▷ Composition over inheritance
▷ Documentation
class Person implements SpidermanPower {}
def person = new Person()assert person.spiderSense() == "Using spider-sense..."assert person instanceof SpidermanPower
def person2 = person.withTraits SupermanPowerassert person2.fly() == "Flying..."assert person2 instanceof SupermanPower
Traits exampletrait SpidermanPower { String spiderSense() { "Using spider-sense..." }}
trait SupermanPower { String fly() { "Flying..." }}
class Person implements SpidermanPower {}
def person = new Person()assert person.spiderSense() == "Using spider-sense..."assert person instanceof SpidermanPower
def person2 = person.withTraits SupermanPowerassert person2.fly() == "Flying..."assert person2 instanceof SupermanPower
Traits exampletrait SpidermanPower { String spiderSense() { "Using spider-sense..." }}
trait SupermanPower { String fly() { "Flying..." }}
class Person implements SpidermanPower {}
def person = new Person()assert person.spiderSense() == "Using spider-sense..."assert person instanceof SpidermanPower
def person2 = person.withTraits SupermanPowerassert person2.fly() == "Flying..."assert person2 instanceof SupermanPower
Traits exampletrait SpidermanPower { String spiderSense() { "Using spider-sense..." }}
trait SupermanPower { String fly() { "Flying..." }}
class Person implements SpidermanPower {}
def person = new Person()assert person.spiderSense() == "Using spider-sense..."assert person instanceof SpidermanPower
def person2 = person.withTraits SupermanPowerassert person2.fly() == "Flying..."assert person2 instanceof SupermanPower
Traits exampletrait SpidermanPower { String spiderSense() { "Using spider-sense..." }}
trait SupermanPower { String fly() { "Flying..." }}
MOP method synthesis
MOP Method Synthesis
▷ Dynamically figure out behaviour upon invocation
▷ It may not exist until it's called/executed
▷ “Intercept, Cache, Invoke” pattern
def p = new Person(name: 'Iván', age: 34)
assert p.respondsTo('sayHi')assert p.respondsTo('sayHiTo', String)assert !p.respondsTo('goodbye')
assert p.hasProperty('name')assert !p.hasProperty('country')
Check for methods and properties
class Person { String name Integer age
String sayHi() { "Hi, my name is ${name} and I'm ${age}" }
String sayHiTo(String name) { "Hi ${name}, how are you?" }}
def p = new Person(name: 'Iván', age: 35)
assert p.respondsTo('sayHi')assert p.respondsTo('sayHiTo', String)assert !p.respondsTo('goodbye')
assert p.hasProperty('age')assert !p.hasProperty('country')
Check for methods and properties
class Person { String name Integer age
String sayHi() { "Hi, my name is ${name} and I'm ${age}" }
String sayHiTo(String name) { "Hi ${name}, how are you?" }}
Check for methods and properties
class Person { String name Integer age
String sayHi() { "Hi, my name is ${name} and I'm ${age}" }
String sayHiTo(String name) { "Hi ${name}, how are you?" }}
def p = new Person(name: 'Iván', age: 35)
assert p.respondsTo('sayHi')assert p.respondsTo('sayHiTo', String)assert !p.respondsTo('goodbye')
assert p.hasProperty('age')assert !p.hasProperty('country')
Check for methods and properties
class Person { String name Integer age
String sayHi() { "Hi, my name is ${name} and I'm ${age}" }
String sayHiTo(String name) { "Hi ${name}, how are you?" }}
def p = new Person(name: 'Iván', age: 35)
assert p.respondsTo('sayHi')assert p.respondsTo('sayHiTo', String)assert !p.respondsTo('goodbye')
assert p.hasProperty('age')assert !p.hasProperty('country')
MethodMissing example
▷ Requirements:– Send notifications to users by different
channels– +50 notifications– Not all notifications by all channels– Extensible and open to future
modifications
MethodMissing exampleabstract class Channel { void sendNewFollower(String username, String follower) { } void sendNewMessage(String username, String msg) { } ...}
class EmailChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending email notification to '${username}' for new follower '${follower}'" } void sendNewMessage(String username, String msg) { println "Sending email notification to '${username}' for new message '${msg}'" }}
class MobilePushChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending mobile push notification to '${username}' for new follower '${follower}'" }}
MethodMissing exampleabstract class Channel { void sendNewFollower(String username, String follower) { } void sendNewMessage(String username, String msg) { } ...}
class EmailChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending email notification to '${username}' for new follower '${follower}'" } void sendNewMessage(String username, String msg) { println "Sending email notification to '${username}' for new message '${msg}'" }}
class MobilePushChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending mobile push notification to '${username}' for new follower '${follower}'" }}
MethodMissing exampleabstract class Channel { void sendNewFollower(String username, String follower) { } void sendNewMessage(String username, String msg) { } ...}
class EmailChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending email notification to '${username}' for new follower '${follower}'" } void sendNewMessage(String username, String msg) { println "Sending email notification to '${username}' for new message '${msg}'" }}
class MobilePushChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending mobile push notification to '${username}' for new follower '${follower}'" }}
MethodMissing exampleclass NotificationService {
List channels = []
def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}"
// Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation
// Execute it! implementation(args) }}
MethodMissing exampleclass NotificationService {
List channels = []
def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}"
// Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation
// Execute it! implementation(args) }}
MethodMissing exampleclass NotificationService {
List channels = []
def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}"
// Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation
// Execute it! implementation(args) }}
notificationService.sendNewFollower(...)notificationService.sendNewMessage(...)
MethodMissing exampleclass NotificationService {
List channels = []
def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}"
// Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation
// Execute it! implementation(args) }}
MethodMissing exampleclass NotificationService {
List channels = []
def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}"
// Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation
// Execute it! implementation(args) }}
MethodMissing example
// Execution...methodMissing called for sendNewFollower with args [John, Peter]Sending email notification to 'John' for new follower 'Peter'Sending mobile push notification to 'John' for new follower 'Peter'
Sending email notification to 'Mary' for new follower 'Steve'Sending mobile push notification to 'Mary' for new follower 'Steve'
...methodMissing called for sendNewMessage with args [Iván, Hello!]Sending email notification to 'Iván' for new message 'Hello!'
def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()])
assert !notificationService.respondsTo('sendNewFollower', String, String)notificationService.sendNewFollower("John", "Peter")assert notificationService.respondsTo('sendNewFollower', String, String)
notificationService.sendNewFollower("Mary", "Steve")
notificationService.sendNewMessage("Iván", "Hello!")
MethodMissing example
// Execution...methodMissing called for sendNewFollower with args [John, Peter]Sending email notification to 'John' for new follower 'Peter'Sending mobile push notification to 'John' for new follower 'Peter'
Sending email notification to 'Mary' for new follower 'Steve'Sending mobile push notification to 'Mary' for new follower 'Steve'
...methodMissing called for sendNewMessage with args [Iván, Hello!]Sending email notification to 'Iván' for new message 'Hello!'
def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()])
assert !notificationService.respondsTo('sendNewFollower', String, String)notificationService.sendNewFollower("John", "Peter")assert notificationService.respondsTo('sendNewFollower', String, String)
notificationService.sendNewFollower("Mary", "Steve")
notificationService.sendNewMessage("Iván", "Hello!")
MethodMissing example
// Execution...methodMissing called for sendNewFollower with args [John, Peter]Sending email notification to 'John' for new follower 'Peter'Sending mobile push notification to 'John' for new follower 'Peter'
Sending email notification to 'Mary' for new follower 'Steve'Sending mobile push notification to 'Mary' for new follower 'Steve'
...methodMissing called for sendNewMessage with args [Iván, Hello!]Sending email notification to 'Iván' for new message 'Hello!'
def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()])
assert !notificationService.respondsTo('sendNewFollower', String, String)notificationService.sendNewFollower("John", "Peter")assert notificationService.respondsTo('sendNewFollower', String, String)
notificationService.sendNewFollower("Mary", "Steve")
notificationService.sendNewMessage("Iván", "Hello!")
MethodMissing example
// Execution...methodMissing called for sendNewFollower with args [John, Peter]Sending email notification to 'John' for new follower 'Peter'Sending mobile push notification to 'John' for new follower 'Peter'
Sending email notification to 'Mary' for new follower 'Steve'Sending mobile push notification to 'Mary' for new follower 'Steve'
...methodMissing called for sendNewMessage with args [Iván, Hello!]Sending email notification to 'Iván' for new message 'Hello!'
def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()])
assert !notificationService.respondsTo('sendNewFollower', String, String)notificationService.sendNewFollower("John", "Peter")assert notificationService.respondsTo('sendNewFollower', String, String)
notificationService.sendNewFollower("Mary", "Steve")
notificationService.sendNewMessage("Iván", "Hello!")
MethodMissing example
// Execution...methodMissing called for sendNewFollower with args [John, Peter]Sending email notification to 'John' for new follower 'Peter'Sending mobile push notification to 'John' for new follower 'Peter'
Sending email notification to 'Mary' for new follower 'Steve'Sending mobile push notification to 'Mary' for new follower 'Steve'
...methodMissing called for sendNewMessage with args [Iván, Hello!]Sending email notification to 'Iván' for new message 'Hello!'
def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()])
assert !notificationService.respondsTo('sendNewFollower', String, String)notificationService.sendNewFollower("John", "Peter")assert notificationService.respondsTo('sendNewFollower', String, String)
notificationService.sendNewFollower("Mary", "Steve")
notificationService.sendNewMessage("Iván", "Hello!")class EmailChannel extends Channel { void sendNewFollower(String username, String follower) {…} void sendNewMessage(String username, String msg) {…}}
class MobilePushChannel extends Channel { void sendNewFollower(String username, String follower) {…}}
MethodMissing example
// Execution...methodMissing called for sendNewFollower with args [John, Peter]Sending email notification to 'John' for new follower 'Peter'Sending mobile push notification to 'John' for new follower 'Peter'
Sending email notification to 'Mary' for new follower 'Steve'Sending mobile push notification to 'Mary' for new follower 'Steve'
...methodMissing called for sendNewMessage with args [Iván, Hello!]Sending email notification to 'Iván' for new message 'Hello!'
def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()])
assert !notificationService.respondsTo('sendNewFollower', String, String)notificationService.sendNewFollower("John", "Peter")assert notificationService.respondsTo('sendNewFollower', String, String)
notificationService.sendNewFollower("Mary", "Steve")
notificationService.sendNewMessage("Iván", "Hello!")
MethodMissing example
// Execution...methodMissing called for sendNewFollower with args [John, Peter]Sending email notification to 'John' for new follower 'Peter'Sending mobile push notification to 'John' for new follower 'Peter'
Sending email notification to 'Mary' for new follower 'Steve'Sending mobile push notification to 'Mary' for new follower 'Steve'
...methodMissing called for sendNewMessage with args [Iván, Hello!]Sending email notification to 'Iván' for new message 'Hello!'
def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()])
assert !notificationService.respondsTo('sendNewFollower', String, String)notificationService.sendNewFollower("John", "Peter")assert notificationService.respondsTo('sendNewFollower', String, String)
notificationService.sendNewFollower("Mary", "Steve")
notificationService.sendNewMessage("Iván", "Hello!")
MethodMissing exampledef notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()])
assert !notificationService.respondsTo('sendNewFollower', String, String)notificationService.sendNewFollower("John", "Peter")assert notificationService.respondsTo('sendNewFollower', String, String)
notificationService.sendNewFollower("Mary", "Steve")
notificationService.sendNewMessage("Iván", "Hello!")
// Execution...methodMissing called for sendNewFollower with args [John, Peter]Sending email notification to 'John' for new follower 'Peter'Sending mobile push notification to 'John' for new follower 'Peter'
Sending email notification to 'Mary' for new follower 'Steve'Sending mobile push notification to 'Mary' for new follower 'Steve'
...methodMissing called for sendNewMessage with args [Iván, Hello!]Sending email notification to 'Iván' for new message 'Hello!'
2.Compile-time metaprogramming
Compile-time metaprogramming
▷ Advance feature
▷ Analyze/modify program structure at compile time
▷ Cross-cutting features
▷ Write code that generates bytecode
AST and compilation
▷ AST: Abstract Syntax Tree
▷ AST modified during compilation
▷ Hook into the phases
▷ Initialization, Parsing, Conversion, Semantic analysis, Canonicalization, Instruction selection, Class generation, Output, Finalization
Global ASTtransformations
Global AST Transformations
▷ No annotation
▷ Meta-information file
▷ Applied to all code during compilation
▷ Any compilation phase
▷ Grails uses intensively in GORM
Local ASTtransformations
Local AST Transformations
▷ Annotate code
▷ No meta-information file
▷ Easy to debug
Steps to create local AST
Interface AST Enjoy!
Local AST example
package confess2015
import ...
@Retention(RetentionPolicy.SOURCE)@Target([ElementType.TYPE])@GroovyASTTransformationClass("confess2015.VersionASTTransformation")@interface Version { String value()}
class VersionedClass { public static final String VERSION = "1.0"}
import confess2015.Version
@Version('1.0')class VersionedClass {}
Local AST example
class VersionedClass { public static final String VERSION = "1.0"}
package confess2015
import ...
@Retention(RetentionPolicy.SOURCE)@Target([ElementType.TYPE])@GroovyASTTransformationClass("confess2015.VersionASTTransformation")@interface Version { String value()}
import confess2015.Version
@Version('1.0')class VersionedClass {}
Local AST example
class VersionedClass { public static final String VERSION = "1.0"}
package confess2015
import ...
@Retention(RetentionPolicy.SOURCE)@Target([ElementType.TYPE])@GroovyASTTransformationClass("confess2015.VersionASTTransformation")@interface Version { String value()}
import confess2015.Version
@Version('1.0')class VersionedClass {}
Local AST example@GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS)class VersionASTTransformation extends AbstractASTTransformation {
@Override public void visit(final ASTNode[] nodes, final SourceUnit source) { if (nodes.length != 2) { return }
if (nodes[0] instanceof AnnotationNode && nodes[1] instanceof ClassNode) { def annotation = nodes[0] def version = annotation.getMember('value')
if (version instanceof ConstantExpression) { nodes[1].addField('VERSION', ACC_PUBLIC | ACC_STATIC | ACC_FINAL, ClassHelper.STRING_TYPE, version) } else { source.addError(new SyntaxException("Invalid value for annotation", annotation.lineNumber, annotation.columnNumber)) } } }}
Local AST example@GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS)class VersionASTTransformation extends AbstractASTTransformation {
@Override public void visit(final ASTNode[] nodes, final SourceUnit source) { if (nodes.length != 2) { return }
if (nodes[0] instanceof AnnotationNode && nodes[1] instanceof ClassNode) { def annotation = nodes[0] def version = annotation.getMember('value')
if (version instanceof ConstantExpression) { nodes[1].addField('VERSION', ACC_PUBLIC | ACC_STATIC | ACC_FINAL, ClassHelper.STRING_TYPE, version) } else { source.addError(new SyntaxException("Invalid value for annotation", annotation.lineNumber, annotation.columnNumber)) } } }}
Local AST example// Execute with:// gradle build// groovy -cp build/libs/add-version-1.0.jar LocalASTExample.groovy
import confess.Version
@Version('1.0')class VersionedClass {}
println VersionedClass.VERSION
// Execution1.0
Local AST example// Execute with:// gradle build// groovy -cp build/libs/add-version-1.0.jar LocalASTExample.groovy
import confess.Version
@Version('1.0')class VersionedClass {}
println VersionedClass.VERSION
// Execution1.0
Local AST example// Execute with:// gradle build// groovy -cp build/libs/add-version-1.0.jar LocalASTExample.groovy
import confess.Version
@Version('1.0')class VersionedClass {}
println VersionedClass.VERSION
// Execution1.0
3.Why we should usemetaprogramming?
Let’s review some concepts
Metaprogramming out-of-the box
Easy and very powerful
Write better code
Add behaviour easily
Take advantage of this power
Because Groovy, it's groovy
With great powercomes great responsibility
Thanks!Any questions?
@ilopmar
https://github.com/lmivan
Iván López
http://kcy.me/208wq