groovy.lang
[Java] Class ExpandoMetaClass

java.lang.Object
  groovy.lang.MetaClassImpl
      groovy.lang.ExpandoMetaClass

All Implemented Interfaces:

GroovyObject

public class ExpandoMetaClass
extends MetaClassImpl

ExpandoMetaClass is a MetaClass that behaves like an Expando, allowing the addition or replacement of methods, properties and constructors on the fly.

Some examples of usage:

 // defines or replaces instance method:
 metaClass.myMethod = { args -> }

 // defines a new instance method
 metaClass.myMethod << { args -> }

 // creates multiple overloaded methods of the same name
 metaClass.myMethod << { String s -> } << { Integer i -> }

 // defines or replaces a static method with the 'static' qualifier
 metaClass.'static'.myMethod = { args ->  }

 // defines a new static method with the 'static' qualifier
 metaClass.'static'.myMethod << { args ->  }

 // defines a new constructor
 metaClass.constructor << { String arg -> }

 // defines or replaces a constructor
 metaClass.constructor = { String arg -> }

 // defines a new property with an initial value of "blah"
 metaClass.myProperty = "blah"
 

ExpandoMetaClass also supports a DSL/builder like notation to combine multiple definitions together. So instead of this:

 Number.metaClass.multiply = { Amount amount -> amount.times(delegate) }
 Number.metaClass.div =      { Amount amount -> amount.inverse().times(delegate) }
 

 Number.metaClass {
     multiply { Amount amount -> amount.times(delegate) }
     div      { Amount amount -> amount.inverse().times(delegate) }
 }
 

ExpandoMetaClass also supports runtime mixins. While @Mixin allows you to mix in new behavior to classes you own and are designing, you can not easily mixin anything to types you didn't own, e.g. from third party libraries or from JDK library classes. Runtime mixins let you add a mixin on any type at runtime.

 interface Vehicle {
     String getName()
 }

 // Category annotation style
 @Category(Vehicle) class FlyingAbility {
     def fly() { "I'm the ${name} and I fly!" }
 }

 // traditional category style
 class DivingAbility {
     static dive(Vehicle self) { "I'm the ${self.name} and I dive!" }
 }

 // provided by a third-party, so can't augment using Mixin annotation
 class JamesBondVehicle implements Vehicle {
     String getName() { "James Bond's vehicle" }
 }

 // Can be added via metaClass, e.g.:
 // JamesBondVehicle.metaClass.mixin DivingAbility, FlyingAbility
 // Or using shorthand through DGM method on Class
 JamesBondVehicle.mixin DivingAbility, FlyingAbility

 assert new JamesBondVehicle().fly() ==
        "I'm the James Bond's vehicle and I fly!"
 assert new JamesBondVehicle().dive() ==
        "I'm the James Bond's vehicle and I dive!"
 

 class Student {
     List schedule = []
     def addLecture(String lecture) { schedule << lecture }
 }

 class Worker {
     List schedule = []
     def addMeeting(String meeting) { schedule << meeting }
 }
 

 class CollegeStudent {
     static { mixin Student, Worker }
 }
 new CollegeStudent().with {
     addMeeting('Performance review with Boss')
     addLecture('Learn about Groovy Mixins')
     println schedule
     println mixedIn[Student].schedule
     println mixedIn[Worker].schedule
 }
 

 [Performance review with Boss]
 [Learn about Groovy Mixins]
 [Performance review with Boss]
 

We can also be a little more dynamic and not require the CollegeStudent class to be defined at all, e.g.:

 def cs = new Object()
 cs.metaClass {
     mixin Student, Worker
     getSchedule {
         mixedIn[Student].schedule + mixedIn[Worker].schedule
     }
 }
 cs.with {
     addMeeting('Performance review with Boss')
     addLecture('Learn about Groovy Mixins')
     println schedule
 }
 

 [Learn about Groovy Mixins, Performance review with Boss]
 

 def ndq = new Object()
 ndq.metaClass {
     mixin ArrayDeque
     mixin HashSet
     leftShift = { Object o ->
         if (!mixedIn[Set].contains(o)) {
             mixedIn[Queue].push(o)
             mixedIn[Set].add(o)
         }
     }
 }
 ndq << 1
 ndq << 2
 ndq << 1
 assert ndq.size() == 2
 

 class CustomComparator implements Comparator {
     int compare(Object a, b) { return a.size() - b.size() }
 }

 class CustomCloseable implements Closeable {
     void close() { println 'Lights out - I am closing' }
 }

 import static mypackage.IOUtils.closeQuietly
 import static java.util.Collections.sort
 def o = new Object()
 o.metaClass.mixin CustomComparator, CustomCloseable
 def items = ['a', 'bbb', 'cc']
 sort(items, o as Comparator)
 println items                // => [a, cc, bbb]
 closeQuietly(o as Closeable) // => Lights out - I am closing
 

Further details

When using the default implementations of MetaClass, methods are only allowed to be added before initialize() is called. In other words you create a new MetaClass, add some methods and then call initialize(). If you attempt to add new methods after initialize() has been called, an error will be thrown. This is to ensure that the MetaClass can operate appropriately in multi-threaded environments as it forces you to do all method additions at the beginning, before using the MetaClass.

ExpandoMetaClass differs here from the default in that it allows you to add methods after initialize has been called. This is done by setting the initialize flag internally to false and then add the methods. Since this is not thread safe it has to be done in a synchronized block. The methods to check for modification and initialization are therefore synchronized as well. Any method call done through this meta class will first check if the it is synchronized. Should this happen during a modification, then the method cannot be selected or called unless the modification is completed.

Authors:

Graeme Rocher

Since:

1.5

CONSTRUCTOR

public static final String CONSTRUCTOR

STATIC_QUALIFIER

public static final String STATIC_QUALIFIER

inRegistry

public boolean inRegistry

ExpandoMetaClass

public ExpandoMetaClass(Class theClass, boolean register, boolean allowChangesAfterInit, MetaMethod[] add)

ExpandoMetaClass

public ExpandoMetaClass(MetaClassRegistry registry, Class theClass, boolean register, boolean allowChangesAfterInit, MetaMethod[] add)

ExpandoMetaClass

public ExpandoMetaClass(Class theClass)

Constructs a new ExpandoMetaClass instance for the given class

Parameters:

theClass - The class that the MetaClass applies to

ExpandoMetaClass

public ExpandoMetaClass(Class theClass, MetaMethod[] add)

ExpandoMetaClass

public ExpandoMetaClass(Class theClass, boolean register)

Constructs a new ExpandoMetaClass instance for the given class optionally placing the MetaClass in the MetaClassRegistry automatically

Parameters:

theClass - The class that the MetaClass applies to

register - True if the MetaClass should be registered inside the MetaClassRegistry. This defaults to true and ExpandoMetaClass will effect all instances if changed

ExpandoMetaClass

public ExpandoMetaClass(Class theClass, boolean register, MetaMethod[] add)

ExpandoMetaClass

public ExpandoMetaClass(Class theClass, boolean register, boolean allowChangesAfterInit)

Constructs a new ExpandoMetaClass instance for the given class optionally placing the MetaClass in the MetaClassRegistry automatically

Parameters:

theClass - The class that the MetaClass applies to

register - True if the MetaClass should be registered inside the MetaClassRegistry. This defaults to true and ExpandoMetaClass will effect all instances if changed

allowChangesAfterInit - Should the meta class be modifiable after initialization. Default is false.

addMixinClass

public void addMixinClass(MixinInMetaClass mixin)

castToMixedType

public Object castToMixedType(Object obj, Class type)

checkInitalised

protected void checkInitalised()

Registers a new bean property

Parameters:

property - The property name

newValue - The properties initial value

createConstructorSite

public CallSite createConstructorSite(CallSite site, Object[] args)

createPogoCallCurrentSite

public CallSite createPogoCallCurrentSite(CallSite site, Class sender, String name, Object[] args)

createPogoCallSite

public CallSite createPogoCallSite(CallSite site, Object[] args)

createPojoCallSite

public CallSite createPojoCallSite(CallSite site, Object receiver, Object[] args)

createStaticSite

public CallSite createStaticSite(CallSite site, Object[] args)

define

public ExpandoMetaClass define(Closure closure)

disableGlobally

public static void disableGlobally()

Call to disable the global use of ExpandoMetaClass

enableGlobally

public static void enableGlobally()

Call to enable global use of global use of ExpandoMetaClass within the registry. This has the advantage that inheritance will function correctly, but has a higher memory usage on the JVM than normal Groovy

findMixinMethod

public MetaMethod findMixinMethod(String methodName, Class[] arguments)

getExpandoMethods

public List getExpandoMethods()

Returns a list of MetaBeanProperty instances added to this ExpandoMetaClass

Returns:

the expandoProperties

getExpandoProperties

public Collection getExpandoProperties()

Overrides default implementation just in case a static invoke method has been set on ExpandoMetaClass

See Also:

MetaClassImpl.invokeStaticMethod

getExpandoSubclassMethods

public Collection getExpandoSubclassMethods()

getJavaClass

public Class getJavaClass()

getMetaClass

public MetaClass getMetaClass()

getMetaProperty

public MetaProperty getMetaProperty(String name)

getMethods

public List getMethods()

getProperties

public List getProperties()

getProperty

public Object getProperty(String property)

getProperty

public Object getProperty(Class sender, Object object, String name, boolean useSuper, boolean fromInsideClass)

Overrides default implementation just in case getProperty method has been overridden by ExpandoMetaClass

See Also:

MetaClassImpl.getProperty

getProperty

public Object getProperty(Object object, String name)

Overrides default implementation just in case setProperty method has been overridden by ExpandoMetaClass

See Also:

MetaClassImpl.setProperty

getPropertyForSetter

public String getPropertyForSetter(String setterName)

getSubclassMetaMethods

protected Object getSubclassMetaMethods(String methodName)

Returns:

The Java class enhanced by this MetaClass

hasMetaMethod

public boolean hasMetaMethod(String name, Class[] args)

Returns true if the name of the method specified and the number of arguments make it a javabean property

Parameters:

name - True if its a Javabean property

args - The arguments

Returns:

True if it is a javabean property method

hasMetaProperty

public boolean hasMetaProperty(String name)

Determine if this method name suffix is a legitimate bean property name. Either the first or second letter must be upperCase for that to be true.

initialize

public void initialize()

invokeConstructor

public Object invokeConstructor(Object[] arguments)

invokeMethod

public Object invokeMethod(String name, Object args)

invokeMethod

public Object invokeMethod(Class sender, Object object, String methodName, Object[] originalArguments, boolean isCallToSuper, boolean fromInsideClass)

invokeStaticMethod

public Object invokeStaticMethod(Object object, String methodName, Object[] arguments)

isInitialized

protected boolean isInitialized()

Checks if the meta class is initialized.

See Also:

MetaClassImpl.isInitialized

isModified

public boolean isModified()

isSetter

public boolean isSetter(String name, CachedClass[] args)

isValidExpandoProperty

public static boolean isValidExpandoProperty(String property)

onGetPropertyFoundInHierarchy

protected void onGetPropertyFoundInHierarchy(MetaMethod method)

onInvokeMethodFoundInHierarchy

protected void onInvokeMethodFoundInHierarchy(MetaMethod method)

onSetPropertyFoundInHierarchy

protected void onSetPropertyFoundInHierarchy(MetaMethod method)

onSuperMethodFoundInHierarchy

protected void onSuperMethodFoundInHierarchy(MetaMethod method)

onSuperPropertyFoundInHierarchy

protected void onSuperPropertyFoundInHierarchy(MetaBeanProperty property)

performOperationOnMetaClass

protected void performOperationOnMetaClass(ExpandoMetaClass.Callable c)

refreshInheritedMethods

public void refreshInheritedMethods(Set modifiedSuperExpandos)

registerBeanProperty

public void registerBeanProperty(String property, Object newValue)

registerInstanceMethod

public void registerInstanceMethod(MetaMethod metaMethod)

Registers a new instance method for the given method name and closure on this MetaClass

Parameters:

metaMethod

registerInstanceMethod

public void registerInstanceMethod(String name, Closure closure)

Overrides the behavior of parent getMethods() method to make MetaClass aware of added Expando methods

Returns:

A list of MetaMethods

See Also:

MetaObjectProtocol.getMethods

registerStaticMethod

protected void registerStaticMethod(String name, Closure callable)

Registers a new static method for the given method name and closure on this MetaClass

Parameters:

name - The method name

callable - The callable Closure

registerStaticMethod

protected void registerStaticMethod(String name, Closure callable, Class[] paramTypes)

registerSubclassInstanceMethod

public void registerSubclassInstanceMethod(String name, Class klazz, Closure closure)

registerSubclassInstanceMethod

public void registerSubclassInstanceMethod(MetaMethod metaMethod)

retrieveConstructor

@Override
public MetaMethod retrieveConstructor(Object[] args)

setInitialized

protected void setInitialized(boolean b)

setMetaClass

public void setMetaClass(MetaClass metaClass)

setProperty

public void setProperty(String property, Object newValue)

setProperty

public void setProperty(Class sender, Object object, String name, Object newValue, boolean useSuper, boolean fromInsideClass)

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