Package groovy.lang

Class ExpandoMetaClass

java.lang.Object
groovy.lang.MetaClassImpl
groovy.lang.ExpandoMetaClass
All Implemented Interfaces:
GroovyObject, MetaClass, MetaObjectProtocol, MutableMetaClass
public class ExpandoMetaClass extends MetaClassImpl implements GroovyObject
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) }
You can also now do this: 
 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!"
As another example, consider the following class definitions: 
 class Student {
     List schedule = []
     def addLecture(String lecture) { schedule << lecture }
 }

 class Worker {
     List schedule = []
     def addMeeting(String meeting) { schedule << meeting }
 }
We can mimic a form of multiple inheritance as follows: 
 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
 }
Which outputs these lines when run: 
 [Performance review with Boss]
 [Learn about Groovy Mixins]
 [Performance review with Boss]
Perhaps some explanation is required here. The methods and properties of Student and Worker are added to CollegeStudent. Worker is added last, so for overlapping methods, its methods will be used, e.g. when calling schedule, it will be the schedule property (getSchedule method) from Worker that is used. The schedule property from Student will be shadowed but the mixedIn notation allows us to get to that too if we need as the last two lines show.

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
 }
Which outputs this line when run: 
 [Learn about Groovy Mixins, Performance review with Boss]
As another example, we can also define a no dup queue by mixing in some Queue and Set functionality as follows: 
 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
As a final example, we sometimes need to pass such mixed in classes or objects into Java methods which require a given static type but the ExpandoMetaClass mixin approach uses a very dynamic approach based on duck typing rather than static interface definitions, so doesn't by default produce objects matching the required static type. Luckily, there is a mixins capability within ExpandoMetaClass which supports the use of Groovy's common 'as StaticType' notation to produce an object having the correct static type so that it can be passed to the Java method call in question. A slightly contrived example illustrating this feature: 
 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 multithreaded 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 metaclass 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.

Since:
1.5

  • Field Details

  • Constructor Details

    • 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 affect 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 affect all instances if changed
      allowChangesAfterInit - Should the metaclass be modifiable after initialization. Default is false.

  • Method Details

    • getExpandoSubclassMethods

      public Collection getExpandoSubclassMethods()

    • findMixinMethod

      public MetaMethod findMixinMethod(String methodName, Class[] arguments)
      Overrides:
      findMixinMethod in class MetaClassImpl

    • onInvokeMethodFoundInHierarchy

      protected void onInvokeMethodFoundInHierarchy(MetaMethod method)
      Overrides:
      onInvokeMethodFoundInHierarchy in class MetaClassImpl

    • onSuperMethodFoundInHierarchy

      protected void onSuperMethodFoundInHierarchy(MetaMethod method)
      Overrides:
      onSuperMethodFoundInHierarchy in class MetaClassImpl

    • onSuperPropertyFoundInHierarchy

      protected void onSuperPropertyFoundInHierarchy(MetaBeanProperty property)
      Overrides:
      onSuperPropertyFoundInHierarchy in class MetaClassImpl

    • onSetPropertyFoundInHierarchy

      protected void onSetPropertyFoundInHierarchy(MetaMethod method)
      Overrides:
      onSetPropertyFoundInHierarchy in class MetaClassImpl

    • onGetPropertyFoundInHierarchy

      protected void onGetPropertyFoundInHierarchy(MetaMethod method)
      Overrides:
      onGetPropertyFoundInHierarchy in class MetaClassImpl

    • isModified

      public boolean isModified()
      Description copied from class: MetaClassImpl
      Returns whether this MetaClassImpl has been modified. Since MetaClassImpl is not designed for modification this method always returns false
      Specified by:
      isModified in interface MutableMetaClass
      Overrides:
      isModified in class MetaClassImpl
      Returns:
      false

    • registerSubclassInstanceMethod

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

    • registerSubclassInstanceMethod

      public void registerSubclassInstanceMethod(MetaMethod metaMethod)

    • addMixinClass

      public void addMixinClass(MixinInMetaClass mixin)

    • castToMixedType

      public Object castToMixedType(Object obj, Class type)

    • enableGlobally

      public static void enableGlobally()
      Call to enable global use of ExpandoMetaClass within the registry. This has the advantage that inheritance will function correctly and metaclass modifications will also apply to existing objects, but has a higher memory usage on the JVM than normal Groovy

    • disableGlobally

      public static void disableGlobally()
      Call to disable the global use of ExpandoMetaClass

    • initialize

      public void initialize()
      Complete the initialisation process. After this method is called no methods should be added to the metaclass. Invocation of methods or access to fields/properties is forbidden unless this method is called. This method should contain any initialisation code, taking a longer time to complete. An example is the creation of the Reflector. It is suggested to synchronize this method.
      Specified by:
      initialize in interface MetaClass
      Overrides:
      initialize in class MetaClassImpl

    • isInitialized

      protected boolean isInitialized()
      Checks if the metaclass is initialized.
      Overrides:
      isInitialized in class MetaClassImpl
      See Also:

    • setInitialized

      protected void setInitialized(boolean b)
      Overrides:
      setInitialized in class MetaClassImpl

    • invokeConstructor

      public Object invokeConstructor(Object[] arguments)
      Description copied from interface: MetaObjectProtocol
      Invokes a constructor for the given arguments. The MetaClass will attempt to pick the best argument which matches the types of the objects passed within the arguments array
      Specified by:
      invokeConstructor in interface MetaObjectProtocol
      Overrides:
      invokeConstructor in class MetaClassImpl
      Parameters:
      arguments - The arguments to the constructor
      Returns:
      An instance of the java.lang.Class that this MetaObjectProtocol object applies to

    • getMetaClass

      public MetaClass getMetaClass()
      Description copied from interface: GroovyObject
      Returns the metaclass for a given class.
      Specified by:
      getMetaClass in interface GroovyObject
      Returns:
      the metaClass of this instance

    • getProperty

      public Object getProperty(String property)
      Description copied from interface: GroovyObject
      Retrieves a property value.
      Specified by:
      getProperty in interface GroovyObject
      Parameters:
      property - the name of the property of interest
      Returns:
      the given property

    • isValidExpandoProperty

      public static boolean isValidExpandoProperty(String property)

    • invokeMethod

      public Object invokeMethod(String name, Object args)
      Description copied from interface: GroovyObject
      Invokes the given method.
      Specified by:
      invokeMethod in interface GroovyObject
      Parameters:
      name - the name of the method to call
      args - the arguments to use for the method call
      Returns:
      the result of invoking the method

    • setMetaClass

      public void setMetaClass(MetaClass metaClass)
      Description copied from interface: GroovyObject
      Allows the MetaClass to be replaced with a derived implementation.
      Specified by:
      setMetaClass in interface GroovyObject
      Parameters:
      metaClass - the new metaclass

    • setProperty

      public void setProperty(String property, Object newValue)
      Description copied from interface: GroovyObject
      Sets the given property to the new value.
      Specified by:
      setProperty in interface GroovyObject
      Parameters:
      property - the name of the property of interest
      newValue - the new value for the property

    • define

      public ExpandoMetaClass define(@DelegatesTo(value=groovy.lang.ExpandoMetaClass.DefiningClosure.class,strategy=3) Closure closure)

    • performOperationOnMetaClass

      protected void performOperationOnMetaClass(groovy.lang.ExpandoMetaClass.Callable c)

    • checkInitalised

      protected void checkInitalised()
      Description copied from class: MetaClassImpl
      checks if the initialisation of the class id complete. This method should be called as a form of assert, it is no way to test if there is still initialisation work to be done. Such logic must be implemented in a different way.
      Overrides:
      checkInitalised in class MetaClassImpl

    • registerBeanProperty

      public void registerBeanProperty(String property, Object newValue)
      Registers a new bean property
      Parameters:
      property - The property name
      newValue - The properties initial value

    • 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)

    • getMethods

      public List<MetaMethod> getMethods()
      Overrides the behavior of parent getMethods() method to make MetaClass aware of added Expando methods
      Specified by:
      getMethods in interface MetaClass
      Specified by:
      getMethods in interface MetaObjectProtocol
      Overrides:
      getMethods in class MetaClassImpl
      Returns:
      A list of MetaMethods
      See Also:

    • getProperties

      public List<MetaProperty> getProperties()
      Description copied from class: MetaClassImpl
      Get all the properties defined for this type
      Specified by:
      getProperties in interface MetaClass
      Specified by:
      getProperties in interface MetaObjectProtocol
      Overrides:
      getProperties in class MetaClassImpl
      Returns:
      a list of MetaProperty objects
      See Also:

    • registerStaticMethod

      protected void registerStaticMethod(String name, Closure callable)

    • registerStaticMethod

      protected void registerStaticMethod(String name, Closure callable, Class[] paramTypes)
      Registers a new static method for the given method name and closure on this MetaClass
      Parameters:
      name - The method name
      callable - The callable Closure

    • getSubclassMetaMethods

      protected Object getSubclassMetaMethods(String methodName)
      Overrides:
      getSubclassMetaMethods in class MetaClassImpl

    • getJavaClass

      public Class getJavaClass()
      Returns:
      The Java class enhanced by this MetaClass

    • refreshInheritedMethods

      public void refreshInheritedMethods(Set modifiedSuperExpandos)
      Called from ExpandoMetaClassCreationHandle in the registry if it exists to set up inheritance handling
      Parameters:
      modifiedSuperExpandos - A list of modified super ExpandoMetaClass

    • getExpandoMethods

      public List<MetaMethod> getExpandoMethods()
      Returns a list of expando MetaMethod instances added to this ExpandoMetaClass
      Returns:
      the expandoMethods

    • getExpandoProperties

      public Collection<MetaProperty> getExpandoProperties()
      Returns a list of MetaBeanProperty instances added to this ExpandoMetaClass
      Returns:
      the expandoProperties

    • invokeMethod

      public Object invokeMethod(Class sender, Object object, String methodName, Object[] originalArguments, boolean isCallToSuper, boolean fromInsideClass)
      Overrides default implementation just in case invokeMethod has been overridden by ExpandoMetaClass
      Specified by:
      invokeMethod in interface MetaClass
      Overrides:
      invokeMethod in class MetaClassImpl
      Parameters:
      sender - The java.lang.Class instance that invoked the method
      object - The object which the method was invoked on
      methodName - The name of the method
      originalArguments - The arguments to the method
      isCallToSuper - Whether the method is a call to a super class method
      fromInsideClass - Whether the call was invoked from the inside or the outside of the class
      Returns:
      The return value of the method
      See Also:

    • invokeStaticMethod

      public Object invokeStaticMethod(Object object, String methodName, Object[] arguments)
      Overrides default implementation just in case a static invoke method has been set on ExpandoMetaClass
      Specified by:
      invokeStaticMethod in interface MetaObjectProtocol
      Overrides:
      invokeStaticMethod in class MetaClassImpl
      Parameters:
      object - An instance of the class returned by the getTheClass() method or the class itself
      methodName - The name of the method
      arguments - The arguments to the method
      Returns:
      The return value of the method which is null if the return type is void
      See Also:

    • 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
      Specified by:
      getProperty in interface MetaClass
      Overrides:
      getProperty in class MetaClassImpl
      Parameters:
      sender - The java.lang.Class instance that requested the property
      object - The Object which the property is being retrieved from
      name - The name of the property
      useSuper - Whether the call is to a super class property
      fromInsideClass - ??
      Returns:
      the given property's value on the object
      See Also:

    • getProperty

      public Object getProperty(Object object, String name)
      Overrides default implementation just in case getProperty method has been overridden by ExpandoMetaClass
      Specified by:
      getProperty in interface MetaObjectProtocol
      Overrides:
      getProperty in class MetaClassImpl
      Parameters:
      object - The Object which the property is being retrieved from
      name - The name of the property
      Returns:
      The properties value
      See Also:

    • setProperty

      public void setProperty(Class sender, Object object, String name, Object newValue, boolean useSuper, boolean fromInsideClass)
      Overrides default implementation just in case setProperty method has been overridden by ExpandoMetaClass
      Specified by:
      setProperty in interface MetaClass
      Overrides:
      setProperty in class MetaClassImpl
      Parameters:
      sender - The java.lang.Class instance that is mutating the property
      object - The Object which the property is being set on
      name - The name of the property
      newValue - The new value of the property to set
      useSuper - Whether the call is to a super class property
      fromInsideClass - Whether the call was invoked from the inside or the outside of the class.
      See Also:

    • getMetaProperty

      public MetaProperty getMetaProperty(String name)
      Looks up an existing MetaProperty by name
      Specified by:
      getMetaProperty in interface MetaObjectProtocol
      Overrides:
      getMetaProperty in class MetaClassImpl
      Parameters:
      name - The name of the MetaProperty
      Returns:
      The MetaProperty or null if it doesn't exist
      See Also:

    • hasMetaProperty

      public boolean hasMetaProperty(String name)
      Returns true if the MetaClass has the given property
      Parameters:
      name - The name of the MetaProperty
      Returns:
      True it exists as a MetaProperty

    • hasMetaMethod

      public boolean hasMetaMethod(String name, Class[] args)
      Checks whether a MetaMethod for the given name and arguments exists
      Parameters:
      name - The name of the MetaMethod
      args - The arguments to the meta method
      Returns:
      True if the method exists otherwise null

    • getPropertyForSetter

      public String getPropertyForSetter(String setterName)
      Returns a property name equivalent for the given setter name or null if it is not a getter
      Parameters:
      setterName - The setter name
      Returns:
      The property name equivalent

    • isSetter

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

    • createPojoCallSite

      public CallSite createPojoCallSite(CallSite site, Object receiver, Object[] args)
      Description copied from class: MetaClassImpl
      Create a CallSite
      Overrides:
      createPojoCallSite in class MetaClassImpl

    • createStaticSite

      public CallSite createStaticSite(CallSite site, Object[] args)
      Description copied from class: MetaClassImpl
      Create a CallSite
      Overrides:
      createStaticSite in class MetaClassImpl

    • hasCustomStaticInvokeMethod

      public boolean hasCustomStaticInvokeMethod()
      Description copied from class: MetaClassImpl
      indicates is the metaclass method invocation for static methods is done through a custom invoker object.
      Overrides:
      hasCustomStaticInvokeMethod in class MetaClassImpl
      Returns:
      true - if the method invocation is not done by the metaclass itself

    • createPogoCallSite

      public CallSite createPogoCallSite(CallSite site, Object[] args)
      Description copied from class: MetaClassImpl
      Create a CallSite
      Overrides:
      createPogoCallSite in class MetaClassImpl

    • createPogoCallCurrentSite

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

    • retrieveConstructor

      public MetaMethod retrieveConstructor(Object[] args)
      Description copied from class: MetaClassImpl
      This is a helper method added in Groovy 2.1.0, which is used only by indy. This method is for internal use only.
      Overrides:
      retrieveConstructor in class MetaClassImpl

    • createConstructorSite

      public CallSite createConstructorSite(CallSite site, Object[] args)
      Description copied from class: MetaClassImpl
      Create a CallSite
      Overrides:
      createConstructorSite in class MetaClassImpl