注释类型 AliasFor
@Retention(RUNTIME) @Target(METHOD) @Documented public @interface AliasFor
@AliasFor
is an annotation that is used to declare aliases for annotation attributes.Usage Scenarios
- Explicit aliases within an annotation: within a single annotation,
@AliasFor
can be declared on a pair of attributes to signal that they are interchangeable aliases for each other. - Explicit alias for attribute in meta-annotation: if the
annotation()
attribute of@AliasFor
is set to a different annotation than the one that declares it, theattribute()
is interpreted as an alias for an attribute in a meta-annotation (i.e., an explicit meta-annotation attribute override). This enables fine-grained control over exactly which attributes are overridden within an annotation hierarchy. In fact, with@AliasFor
it is even possible to declare an alias for thevalue
attribute of a meta-annotation. - Implicit aliases within an annotation: if one or more attributes within an annotation are declared as attribute overrides for the same meta-annotation attribute (either directly or transitively), those attributes will be treated as a set of implicit aliases for each other, resulting in behavior analogous to that for explicit aliases within an annotation.
Usage Requirements
Like with any annotation in Java, the mere presence of
@AliasFor
on its own will not enforce alias semantics. For alias semantics to be enforced, annotations must be loaded viaMergedAnnotations
.Implementation Requirements
- Explicit aliases within an annotation:
- Each attribute that makes up an aliased pair should be annotated with
@AliasFor
, and eitherattribute()
orvalue()
must reference the other attribute in the pair. Since Spring Framework 5.2.1 it is technically possible to annotate only one of the attributes in an aliased pair; however, it is recommended to annotate both attributes in an aliased pair for better documentation as well as compatibility with previous versions of the Spring Framework. - Aliased attributes must declare the same return type.
- Aliased attributes must declare a default value.
- Aliased attributes must declare the same default value.
annotation()
should not be declared.
- Each attribute that makes up an aliased pair should be annotated with
- Explicit alias for attribute in meta-annotation:
- The attribute that is an alias for an attribute in a meta-annotation must be annotated with
@AliasFor
, andattribute()
must reference the attribute in the meta-annotation. - Aliased attributes must declare the same return type.
annotation()
must reference the meta-annotation.- The referenced meta-annotation must be meta-present on the annotation class that declares
@AliasFor
.
- The attribute that is an alias for an attribute in a meta-annotation must be annotated with
- Implicit aliases within an annotation:
- Each attribute that belongs to a set of implicit aliases must be annotated with
@AliasFor
, andattribute()
must reference the same attribute in the same meta-annotation (either directly or transitively via other explicit meta-annotation attribute overrides within the annotation hierarchy). - Aliased attributes must declare the same return type.
- Aliased attributes must declare a default value.
- Aliased attributes must declare the same default value.
annotation()
must reference an appropriate meta-annotation.- The referenced meta-annotation must be meta-present on the annotation class that declares
@AliasFor
.
- Each attribute that belongs to a set of implicit aliases must be annotated with
Example: Explicit Aliases within an Annotation
In
@ContextConfiguration
,value
andlocations
are explicit aliases for each other.public @interface ContextConfiguration { @AliasFor("locations") String[] value() default {}; @AliasFor("value") String[] locations() default {}; // ... }
Example: Explicit Alias for Attribute in Meta-annotation
In
@XmlTestConfig
,xmlFiles
is an explicit alias forlocations
in@ContextConfiguration
. In other words,xmlFiles
overrides thelocations
attribute in@ContextConfiguration
.@ContextConfiguration public @interface XmlTestConfig { @AliasFor(annotation = ContextConfiguration.class, attribute = "locations") String[] xmlFiles(); }
Example: Implicit Aliases within an Annotation
In
@MyTestConfig
,value
,groovyScripts
, andxmlFiles
are all explicit meta-annotation attribute overrides for thelocations
attribute in@ContextConfiguration
. These three attributes are therefore also implicit aliases for each other.@ContextConfiguration public @interface MyTestConfig { @AliasFor(annotation = ContextConfiguration.class, attribute = "locations") String[] value() default {}; @AliasFor(annotation = ContextConfiguration.class, attribute = "locations") String[] groovyScripts() default {}; @AliasFor(annotation = ContextConfiguration.class, attribute = "locations") String[] xmlFiles() default {}; }
Example: Transitive Implicit Aliases within an Annotation
In
@GroovyOrXmlTestConfig
,groovy
is an explicit override for thegroovyScripts
attribute in@MyTestConfig
; whereas,xml
is an explicit override for thelocations
attribute in@ContextConfiguration
. Furthermore,groovy
andxml
are transitive implicit aliases for each other, since they both effectively override thelocations
attribute in@ContextConfiguration
.@MyTestConfig public @interface GroovyOrXmlTestConfig { @AliasFor(annotation = MyTestConfig.class, attribute = "groovyScripts") String[] groovy() default {}; @AliasFor(annotation = ContextConfiguration.class, attribute = "locations") String[] xml() default {}; }
Spring Annotations Supporting Attribute Aliases
As of Spring Framework 4.2, several annotations within core Spring have been updated to use
@AliasFor
to configure their internal attribute aliases. Consult the Javadoc for individual annotations as well as the reference manual for details.- 从以下版本开始:
- 4.2
- 作者:
- Sam Brannen
- 另请参阅:
MergedAnnotations
,SynthesizedAnnotation
- Explicit aliases within an annotation: within a single annotation,
可选元素概要
可选元素 修饰符和类型 可选元素 说明 Class<? extends Annotation>
annotation
The type of annotation in which the aliasedattribute()
is declared.String
attribute
The name of the attribute that this attribute is an alias for.String
value
Alias forattribute()
.
元素详细资料
value
@AliasFor("attribute") String value
Alias forattribute()
.Intended to be used instead of
attribute()
whenannotation()
is not declared — for example:@AliasFor("value")
instead of@AliasFor(attribute = "value")
.- 默认值:
- ""
annotation
Class<? extends Annotation> annotation
The type of annotation in which the aliasedattribute()
is declared.Defaults to
Annotation
, implying that the aliased attribute is declared in the same annotation as this attribute.- 默认值:
- java.lang.annotation.Annotation.class