Field annotation to automatically delegate part of the functionality of an owner class to the annotated field.
All public instance methods present in the type of the annotated field and not present in the owner class will be added to owner class at compile time. The implementation of such automatically added methods is code which calls through to the delegate as per the normal delegate pattern.
As an example, consider this code:
class Event {
@Delegate Date when
String title, url
}
def gr8conf = new Event(title: "GR8 Conference",
url: "http://www.gr8conf.org",
when: Date.parse("yyyy/MM/dd", "2009/05/18"))
def javaOne = new Event(title: "JavaOne",
url: "http://java.sun.com/javaone/",
when: Date.parse("yyyy/MM/dd", "2009/06/02"))
assert gr8conf.before(javaOne.when)
In this example, the Event class will have a method called
before(Date otherDate) as well as other public methods of the
Date class.
The implementation of the before() method will look like this:
public boolean before(Date otherDate) {
return when.before(otherDate);
}
By default, the owner class will also be modified to implement any interfaces
implemented by the field. So, in the example above, because Date
implements Cloneable the following will be true:
assert gr8conf instanceof CloneableThis behavior can be disabled by setting the annotation's
interfaces element to false,
i.e. @Delegate(interfaces = false), e.g. in the above
example, the delegate definition would become:
@Delegate(interfaces = false) Date when
and the following would be true:
assert !(gr8conf instanceof Cloneable)If multiple delegate fields are used and the same method signature occurs in more than one of the respective field types, then the delegate will be made to the first defined field having that signature. If this does occur, it might be regarded as a smell (or at least poor style) and it might be clearer to do the delegation by long hand.
By default, methods of the delegate type marked as @Deprecated are
not automatically added to the owner class (but see the technical note
about interfaces below). You can force these methods to
be added by setting the annotation's deprecated element to true,
i.e. @Delegate(deprecated = true).
For example, in the example above if we change the delegate definition to:
@Delegate(deprecated = true) Date when
then the following additional lines will execute successfully (during 2009):
assert gr8conf.year + 1900 == 2009
assert gr8conf.toGMTString().contains(" 2009 ")
Otherwise these lines produce a groovy.lang.MissingPropertyException
or groovy.lang.MissingMethodException respectively as those two methods are
@Deprecated in Date.
Technical notes:
GroovyObject interface
are not candidates for delegation@Delegate field@Delegate field@Delegate with default method arguments is known not to work in some cases.
We recommend not using these features together.deprecated attribute will be
ignored if the owner class implements that interface (i.e. you must set interfaces=false
if you want the deprecated attribute to be used). Otherwise, the resulting class would
not compile anyway without manually adding in any deprecated methods in the interface.| Type | Name and Description |
|---|---|
boolean |
deprecatedWhether to apply the delegate pattern to deprecated methods; to avoid compilation errors, this is ignored if the type of the delegate field is an interface and interfaces=true. |
Class[] |
excludeTypesList of interfaces containing method signatures to exclude when delegating. |
String[] |
excludesList of method and/or property names to exclude when delegating. |
Class[] |
includeTypesList of interfaces containing method signatures to exclude when delegating. |
String[] |
includesList of method and/or property names to include when delegating. |
boolean |
interfaces@default true
|
boolean |
methodAnnotationsWhether to carry over annotations from the methods of the delegate to your delegating method. |
boolean |
parameterAnnotationsWhether to carry over annotations from the parameters of delegate methods to your delegating method. |
Whether to apply the delegate pattern to deprecated methods; to avoid compilation
errors, this is ignored if the type of the delegate field is an interface and
interfaces=true.
List of interfaces containing method signatures to exclude when delegating. Only one of 'includes', 'includeTypes', 'excludes', 'excludeTypes' should be used. If interfaces is true (the default), you will need to manually supply any methods excluded from delegation that are required for the interface. @default {}
List of method and/or property names to exclude when delegating. Must not be used if 'includes' is used. For convenience, a String with comma separated names can be used in addition to an array (using Groovy's literal list notation) of String values. If interfaces is true (the default), you will need to manually supply any methods excluded from delegation that are required for the interface. @default {}
List of interfaces containing method signatures to exclude when delegating. Only one of 'includes', 'includeTypes', 'excludes', 'excludeTypes' should be used. If interfaces is true (the default), you will need to manually supply any methods excluded from delegation that are required for the interface. @default {}
List of method and/or property names to include when delegating. Must not be used if 'excludes' is used. For convenience, a String with comma separated names can be used in addition to an array (using Groovy's literal list notation) of String values. If interfaces is true (the default), you will need to manually supply any methods not included via delegation that are required for the interface. @default {}
@default true
Whether to carry over annotations from the methods of the delegate to your delegating method. Currently Closure annotation members are not supported. @default false
Whether to carry over annotations from the parameters of delegate methods to your delegating method. Currently Closure annotation members are not supported. @default false