<chapter id="annotations" xreflabel="Annotations">
<title>Annotations</title>
<sect1 id="annotations-inJava5">
<title>Annotations in Java 5</title>
<para>
This section provides the essential information about annotations in
Java 5 needed to understand how annotations are treated in AspectJ 5.
For a full introduction to annotations in Java, please see the
documentation for the Java 5 SDK.
</para>
<sect2 id="using-annotations" xreflabel="using-annotations">
<title>Using Annotations</title>
<para>
Java 5 introduces <emphasis>annotation types</emphasis> which can
be used to express metadata relating to program members in the
form of <emphasis>annotations</emphasis>. Annotations in Java 5
can be applied to package and type declarations (classes,
interfaces, enums, and annotations), constructors, methods,
fields, parameters, and variables. Annotations are specified in the
program source by using the <literal>@</literal> symbol. For example,
the following piece of code uses the <literal>@Deprecated</literal>
annotation to indicate that the <literal>obsoleteMethod()</literal>
has been deprecated:
</para>
<programlisting><![CDATA[
@Deprecated
public void obsoleteMethod() { ... }
]]></programlisting>
<para>
Annotations may be <emphasis>marker annotations</emphasis>,
<emphasis>single-valued annotations</emphasis>, or
<emphasis>multi-valued annotations</emphasis>.
Annotation types with no members or that provide default values
for all members may be used simply as marker annotations, as in
the deprecation example above. Single-value annotation types have
a single member, and the annotation may be written in one of
two equivalent forms:
</para>
<programlisting><![CDATA[
@SuppressWarnings({"unchecked"})
public void someMethod() {...}
]]></programlisting>
<para>
or
</para>
<programlisting><![CDATA[
@SuppressWarnings(value={"unchecked"})
public void someMethod() {...}
]]></programlisting>
<para>
Multi-value annotations must use the <literal>member-name=value
</literal> syntax to specify annotation values. For example:
</para>
<programlisting><![CDATA[
@Authenticated(role="supervisor",clearanceLevel=5)
public void someMethod() {...}
]]></programlisting>
</sect2>
<sect2 id="retention-policies" xreflabel="retention-policies">
<title>Retention Policies</title>
<para>
Annotations can have one of three retention policies:
</para>
<variablelist>
<varlistentry>
<term>Source-file retention</term>
<listitem>
<para>
Annotations with source-file retention are read by the
compiler during the compilation process, but are not
rendered in the generated <literal>.class</literal> files.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Class-file retention</term>
<listitem>
<para>
This is the default retention policy. Annotations
with class-file retention are read by the compiler
and also retained in the generated <literal>
.class</literal> files.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Runtime retention</term>
<listitem>
<para>
Annotations with runtime retention are read by the
compiler, retained in the generated <literal>
.class</literal> files, and also made available
at runtime.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>Local variable annotations are not retained in class files (or at runtime)
regardless of the retention policy set on the annotation type. See JLS 9.6.1.2.</para>
</sect2>
<sect2 id="accessing-annotations-at-runtime" xreflabel="accessing-annotations-at-runtime">
<title>Accessing Annotations at Runtime</title>
<para>
Java 5 supports a new interface,
<literal>java.lang.reflect.AnnotatedElement</literal>, that is
implemented by the reflection classes in Java (<literal>Class</literal>,
<literal>Constructor</literal>,
<literal>Field</literal>, <literal>Method</literal>, and
<literal>Package</literal>). This interface gives you access
to annotations <emphasis>that have runtime retention</emphasis> via
the <literal>getAnnotation</literal>, <literal>getAnnotations</literal>,
and <literal>isAnnotationPresent</literal>. Because annotation types are
just regular Java classes, the annotations returned by these methods
can be queried just like any regular Java object.
</para>
</sect2>
<sect2 id="annotation-inheritance" xreflabel="annotation-inheritance">
<title>Annotation Inheritance</title>
<para>
It is important to understand the rules relating to inheritance of
annotations, as these have a bearing on join point matching
based on the presence or absence of annotations.
</para>
<para>
By default annotations are <emphasis>not</emphasis> inherited. Given
the following program
</para>
<programlisting><![CDATA[
@MyAnnotation
class Super {
@Oneway public void foo() {}
}
class Sub extends Super {
public void foo() {}
}
]]></programlisting>
<para>
Then <literal>Sub</literal> <emphasis>does not</emphasis> have
the <literal>MyAnnotation</literal> annotation, and
<literal>Sub.foo()</literal> is not an <literal>@Oneway</literal>
method, despite the fact that it overrides
<literal>Super.foo()</literal> which is.
</para>
<para>
If an annotation type has the meta-annotation <literal>@Inherited</literal>
then an annotation of that type on a <emphasis>class</emphasis> will cause
the annotation to be inherited by sub-classes. So, in the example
above, if the <literal>MyAnnotation</literal> type had the
<literal>@Inherited</literal> attribute, then <literal>Sub</literal>
would have the <literal>MyAnnotation</literal> annotation.
</para>
<para>
<literal>@Inherited</literal> annotations are not inherited when used to
annotate anything other than a type. A type
that implements one or more interfaces never inherits any annotations from
the interfaces it implements.
</para>
</sect2>
</sect1>
<!-- ============================== -->
<sect1 id="annotations-aspectmembers">
<title>Annotating Aspects</title>
<para>
AspectJ 5 supports annotations on aspects, and on method, field,
constructor, advice, and inter-type declarations within aspects.
Method and advice parameters may also be annotated.
Annotations are not permitted on pointcut declarations or on
<literal>declare</literal> statements.
</para>
<para>
The following example illustrates the use of annotations in aspects:
</para>
<programlisting><![CDATA[
@AspectAnnotation
public abstract aspect ObserverProtocol {
@InterfaceAnnotation
interface Observer {}
@InterfaceAnnotation
interface Subject {}
@ITDFieldAnnotation
private List<Observer> Subject.observers;
@ITDMethodAnnotation
public void Subject.addObserver(Observer o) {
observers.add(o);
}
@ITDMethodAnnotation
public void Subject.removeObserver(Observer o) {
observers.remove(o);
}
@MethodAnnotation
private void notifyObservers(Subject subject) {
for(Observer o : subject.observers)
notifyObserver(o,subject);
}
/**
* Delegate to concrete sub-aspect the actual form of
* notification for a given type of Observer.
*/
@MethodAnnotation
protected abstract void notifyObserver(Observer o, Subject s);
/* no annotations on pointcuts */
protected abstract pointcut observedEvent(Subject subject);
@AdviceAnnotation
after(Subject subject) returning : observedEvent(subject) {
notifyObservers(subject);
}
}
]]></programlisting>
<para>
An annotation on an aspect will be inherited by sub-aspects, iff it has
the <literal>@Inherited</literal> meta-annotation.
</para>
<para>
AspectJ 5 supports a new XLint warning, "the pointcut associated with this
advice does not match any join points". The warning is enabled by default and
will be emitted by the compiler if the pointcut expression associated with an
advice statement can be statically determined to not match any join points. The
warning can be suppressed for an individual advice statement by using the
<literal>@SuppressAjWarnings({"adviceDidNotMatch"})</literal> annotation. This works in
the same way as the Java 5 SuppressWarnings annotation (See JLS 9.6.1.5), but has class file
retention.
</para>
<programlisting><![CDATA[
import org.aspectj.lang.annotation.SuppressAjWarnings;
public aspect AnAspect {
pointcut anInterfaceOperation() : execution(* AnInterface.*(..));
@SuppressAjWarnings // may not match if there are no implementers of the interface...
before() : anInterfaceOperation() {
// do something...
}
@SuppressAjWarnings("adviceDidNotMatch") // alternate form
after() returning : anInterfaceOperation() {
// do something...
}
}
]]></programlisting>
</sect1>
<!-- ============================== -->
<sect1 id="annotations-pointcuts-and-advice">
<title>Join Point Matching based on Annotations</title>
<para>
This section discusses changes to type pattern and signature pattern matching in
AspectJ 5 that support matching join points based on the presence or absence of
annotations. We then discuss means of exposing annotation values within the body
of advice.
</para>
<sect2 id="annotation-patterns" xreflabel="annotation-patterns">
<title>Annotation Patterns</title>
<para>
For any kind of annotated element (type, method, constructor, package, etc.),
an annotation pattern can be used to match against the set of annotations
on the annotated element.An annotation pattern element has one of two basic
forms:
</para>
<itemizedlist>
<listitem>@<qualified-name>, for example, @Foo, or
@org.xyz.Foo.</listitem>
<listitem>@(<type-pattern>), for example, @(org.xyz..*), or
@(Foo || Boo)</listitem>
</itemizedlist>
<para>These simple elements may be negated using <literal>!</literal>, and
combined by simple concatentation. The pattern <literal>@Foo @Boo</literal>
matches an annotated element that has both an annotation of type <literal>Foo</literal>
and an annotation of type <literal>Boo</literal>.</para>
<para>Some examples of annotation patterns follow:</para>
<variablelist>
<varlistentry>
<term>@Immutable</term>
<listitem>
<para>
Matches any annotated element which has an annotation of
type <literal>Immutable</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>!@Persistent</term>
<listitem>
<para>
Matches any annotated element which does not have an annotation of
type <literal>Persistent</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>@Foo @Goo</term>
<listitem>
<para>
Matches any annotated element which has both an annotation of type <literal>Foo</literal> and
an annotation of type <literal>Goo</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>@(Foo || Goo)</term>
<listitem>
<para>
Matches any annotated element which has either an annotation of a type matching
the type pattern <literal>(Foo || Goo)</literal>.
In other words, an annotated element with either an
annotation of type <literal>Foo</literal> or
an annotation of type <literal>Goo</literal> (or both). (The parenthesis are required in this example).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>@(org.xyz..*)</term>
<listitem>
<para>
Matches any annotated element which has either an annotation of a type matching
the type pattern <literal>(org.xyz..*)</literal>.
In other words, an annotated element with an annotation that is declared in the
org.xyz package or a sub-package. (The parenthesis are required in this example).
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2 id="type-patterns" xreflabel="type-patterns">
<title>Type Patterns</title>
<para>AspectJ 1.5 extends type patterns to allow an optional <literal>AnnotationPattern</literal>
prefix.</para>
<programlisting><![CDATA[
TypePattern := SimpleTypePattern |
'!' TypePattern |
'(' AnnotationPattern? TypePattern ')'
TypePattern '&&' TypePattern |
TypePattern '||' TypePattern
SimpleTypePattern := DottedNamePattern '+'? '[]'*
DottedNamePattern := FullyQualifiedName RestOfNamePattern? |
'*' NotStarNamePattern?
RestOfNamePattern := '..' DottedNamePattern |
'*' NotStarNamePattern?
NotStarNamePattern := FullyQualifiedName RestOfNamePattern? |
'..' DottedNamePattern
FullyQualifiedName := JavaIdentifierCharacter+ ('.' JavaIdentifierCharacter+)*
]]></programlisting>
<para>Note that in most cases when annotations are used as part of a type pattern,
the parenthesis are required (as in <literal>(@Foo Hello+)</literal>). In
some cases (such as a type pattern used within a <literal>within</literal> or
<literal>handler</literal>
pointcut expression), the parenthesis are optional:</para>
<programlisting><![CDATA[
OptionalParensTypePattern := AnnotationPattern? TypePattern
]]></programlisting>
<para>
The following examples illustrate the use of annotations in type
patterns:
</para>
<variablelist>
<varlistentry>
<term>(@Immutable *)</term>
<listitem>
<para>
Matches any type with an <literal>@Immutable</literal> annotation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>(!@Immutable *)</term>
<listitem>
<para>
Matches any type which does not have an <literal>@Immutable</literal> annotation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term> (@Immutable (org.xyz.* || org.abc.*))</term>
<listitem>
<para>
Matches any type in the <literal>org.xyz</literal> or <literal>org.abc</literal>
packages with the <literal>@Immutable</literal> annotation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>((@Immutable Foo+) || Goo)</term>
<listitem>
<para>
Matches a type <literal>Foo</literal> or any of its subtypes, which have the <literal>@Immutable</literal>
annotation, or a type <literal>Goo</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>((@(Immutable || NonPersistent) org.xyz..*)</term>
<listitem>
<para>
Matches any type in a package beginning with the prefix <literal>org.xyz</literal>,
which has either the <literal>@Immutable</literal> annotation or the
<literal>@NonPersistent</literal> annotation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>(@Immutable @NonPersistent org.xyz..*)</term>
<listitem>
<para>
Matches any type in a package beginning with the prefix <literal>org.xyz</literal>,
which has both an <literal>@Immutable</literal> annotation and an
<literal>@NonPersistent</literal> annotation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term> (@(@Inherited *) org.xyz..*)</term>
<listitem>
<para>
Matches any type in a package beginning with the prefix <literal>org.xyz</literal>,
which has an inheritable annotation. The annotation pattern
<literal>@(@Inherited *)</literal> matches any annotation of a type matching the
type pattern <literal>@Inherited *</literal>, which in turn matches any type with the
<literal>@Inherited</literal> annotation.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2 id="signaturePatterns" xreflabel="Signature Patterns">
<title>Signature Patterns</title>
<sect3 id="fieldPatterns" xreflabel="Field Patterns">
<title>Field Patterns</title>
<para>A <literal>FieldPattern</literal> can optionally specify an annotation-matching
pattern as the first element:</para>
<programlisting><![CDATA[
FieldPattern :=
AnnotationPattern? FieldModifiersPattern?
TypePattern (TypePattern DotOrDotDot)? SimpleNamePattern
FieldModifiersPattern := '!'? FieldModifier FieldModifiersPattern*
FieldModifier := 'public' | 'private' | 'protected' | 'static' |
'transient' | 'final'
DotOrDotDot := '.' | '..'
SimpleNamePattern := JavaIdentifierChar+ ('*' SimpleNamePattern)?
]]></programlisting>
<para>
If present, the <literal>AnnotationPattern</literal> restricts matches to fields with
annotations that match the pattern. For example:
</para>
<variablelist>
<varlistentry>
<term>@SensitiveData * *</term>
<listitem>
<para>
Matches a field of any type and any name, that has an annotation of
type <literal>@SensitiveData</literal>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>@SensitiveData List org.xyz..*.*</term>
<listitem>
<para>
Matches a member field of a type in a package with prefix <literal>org.xzy</literal>,
where the field is of type <literal>List</literal>, and has an annotation of type
<literal>@SensitiveData</literal>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>(@SensitiveData *) org.xyz..*.*</term>
<listitem>
<para>
Matches a member field of a type in a package with prefix <literal>org.xzy</literal>,
where the field is of a type which has a <literal>@SensitiveData</literal> annotation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>@Foo (@Goo *) (@Hoo *).*</term>
<listitem>
<para>
Matches a field with an annotation <literal>@Foo</literal>, of a type with an
annotation <literal>@Goo</literal>, declared in a type with annotation
<literal>@Hoo</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>@Persisted @Classified * *</term>
<listitem>
<para>
Matches a field with an annotation <literal>@Persisted</literal> and
an annotation <literal>@Classified</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="methodPatterns" xreflabel="Method Patterns">
<title>Method and Constructor Patterns</title>
<para>A <literal>MethodPattern</literal> can optionally specify an annotation-matching
pattern as the first element.</para>
<programlisting><![CDATA[
MethodPattern :=
AnnotationPattern? MethodModifiersPattern? TypePattern
(TypePattern DotOrDotDot)? SimpleNamePattern
'(' FormalsPattern ')'ThrowsPattern?
MethodModifiersPattern := '!'? MethodModifier MethodModifiersPattern*
MethodModifier := 'public' | 'private' | 'protected' | 'static' |
'synchronized' | 'final'
FormalsPattern := '..' (',' FormalsPatternAfterDotDot)* |
OptionalParensTypePattern (',' FormalsPattern)* |
TypePattern '...'
FormalsPatternAfterDotDot :=
OptionalParensTypePattern (',' FormalsPatternAfterDotDot)* |
TypePattern '...'
ThrowsPattern := 'throws' TypePatternList
TypePatternList := TypePattern (',' TypePattern)*
]]></programlisting>
<para>A <literal>ConstructorPattern</literal> has the form</para>
<programlisting><![CDATA[
ConstructorPattern :=
AnnotationPattern? ConstructorModifiersPattern?
(TypePattern DotOrDotDot)? 'new' '(' FormalsPattern ')'
ThrowsPattern?
ConstructorModifiersPattern := '!'? ConstructorModifier ConstructorModifiersPattern*
ConstructorModifier := 'public' | 'private' | 'protected'
]]></programlisting>
<para>
The optional <literal>AnnotationPattern</literal> at the beginning of a
method or constructor pattern restricts matches to methods/constructors with
annotations that match the pattern. For example:
</para>
<variablelist>
<varlistentry>
<term>@Oneway * *(..)</term>
<listitem>
<para>
Matches a method with any return type and any name, that has an annotation of
type <literal>@Oneway</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>@Transaction * (@Persistent org.xyz..*).*(..)</term>
<listitem>
<para>
Matches a method with the <literal>@Transaction</literal> annotation,
declared in a type with the <literal>@Persistent</literal> annotation, and
in a package beginning with the <literal>org.xyz</literal> prefix.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>* *.*(@Immutable *,..)</term>
<listitem>
<para>
Matches any method taking at least one parameter, where the parameter
type has an annotation <literal>@Immutable</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
</sect2>
<sect2 id="example-pointcuts" xreflabel="example-pointcuts">
<title>Example Pointcuts</title>
<variablelist>
<varlistentry>
<term>within(@Secure *)</term>
<listitem>
<para>
Matches any join point where the code executing is declared in a
type with an <literal>@Secure</literal>
annotation. The format of the <literal>within</literal> pointcut designator
in AspectJ 5 is <literal>'within' '(' OptionalParensTypePattern ')'</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>staticinitialization(@Persistent *)</term>
<listitem>
<para>
Matches the staticinitialization join point of any type with the
<literal>@Persistent</literal> annotation. The format of the
<literal>staticinitialization</literal> pointcut designator
in AspectJ 5 is <literal>'staticinitialization' '(' OptionalParensTypePattern ')'</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>call(@Oneway * *(..))</term>
<listitem>
<para>
Matches a call to a method with a <literal>@Oneway</literal> annotation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>execution(public (@Immutable *) org.xyz..*.*(..))</term>
<listitem>
<para>
The execution of any public method in a package with prefix
<literal>org.xyz</literal>, where the method returns an
immutable result.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>set(@Cachable * *)</term>
<listitem>
<para>
Matches the set of any cachable field.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>handler(!@Catastrophic *)</term>
<listitem>
<para>
Matches the handler join point for the handling of any exception that is
not <literal>Catastrophic</literal>. The format of the <literal>handler</literal>
pointcut designator in AspectJ 5 is <literal>'handler' '(' OptionalParensTypePattern ')'</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2 id="runtime-type-matching-and-context-exposure" xreflabel="runtime-type-matching-and-context-exposure">
<title>Runtime type matching and context exposure</title>
<para>AspectJ 5 supports a set of "@" pointcut designators which
can be used both to match based on the presence of an annotation at
runtime, and to expose the annotation value as context in a pointcut or
advice definition. These designators are <literal>@args, @this, @target,
@within, @withincode</literal>, and <literal>@annotation</literal>
</para>
<para>It is a compilation error to attempt to match on an annotation type
that does not have runtime retention using <literal>@this, @target</literal>
or <literal>@args</literal>. It is a compilation error to attempt to use
any of these designators to expose an annotation value that does not
have runtime retention.</para>
<para>
The <literal>this()</literal>, <literal>target()</literal>, and
<literal>args()</literal> pointcut designators allow matching based
on the runtime type of an object, as opposed to the statically
declared type. In AspectJ 5, these designators are supplemented
with three new designators : <literal>@this()</literal> (read, "this
annotation"), <literal>@target()</literal>, and <literal>@args()</literal>.
</para>
<para>
Like their counterparts, these pointcut designators can be used
both for join point matching, and to expose context. The format of
these new designators is:
</para>
<programlisting><![CDATA[
AtThis := '@this' '(' AnnotationOrIdentifer ')'
AtTarget := '@target' '(' AnnotationOrIdentifier ')'
AnnotationOrIdentifier := FullyQualifiedName | Identifier
AtArgs := '@args' '(' AnnotationsOrIdentifiersPattern ')'
AnnotationsOrIdentifiersPattern :=
'..' (',' AnnotationsOrIdentifiersPatternAfterDotDot)? |
AnnotationOrIdentifier (',' AnnotationsOrIdentifiersPattern)* |
'*' (',' AnnotationsOrIdentifiersPattern)*
AnnotationsOrIdentifiersPatternAfterDotDot :=
AnnotationOrIdentifier (',' AnnotationsOrIdentifiersPatternAfterDotDot)* |
'*' (',' AnnotationsOrIdentifiersPatternAfterDotDot)*
]]></programlisting>
<para>
The forms of <literal>@this()</literal> and <literal>@target()</literal> that
take a single annotation name are analogous to their counterparts that take
a single type name. They match at join points where the object bound to
<literal>this</literal> (or <literal>target</literal>, respectively) has an
annotation of the specified type. For example:
</para>
<variablelist>
<varlistentry>
<term>@this(Foo)</term>
<listitem>
<para>
Matches any join point where the object currently bound to 'this'
has an annotation of type <literal>Foo</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>call(* *(..)) && @target(Classified)</term>
<listitem>
<para>
Matches a call to any object where the target of the call has
a <literal>@Classified</literal> annotation.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
Annotations can be exposed as context in the body of advice by
using the forms of <literal>@this(), @target()</literal> and
<literal>@args()</literal> that use bound variables in the place
of annotation names. For example:
</para>
<programlisting><![CDATA[
pointcut callToClassifiedObject(Classified classificationInfo) :
call(* *(..)) && @target(classificationInfo);
pointcut txRequiredMethod(Tx transactionAnnotation) :
execution(* *(..)) && @this(transactionAnnotation)
&& if(transactionAnnotation.policy() == TxPolicy.REQUIRED);
]]></programlisting>
<para>
The <literal>@args</literal> pointcut designator behaves as its <literal>args</literal>
counterpart, matching join points based on number and position of arguments, and
supporting the <literal>*</literal> wildcard and at most one <literal>..</literal>
wildcard. An annotation at a given position in an <literal>@args</literal> expression
indicates that the runtime type of the argument in that position at a join point must
have an annotation of the indicated type. For example:
</para>
<programlisting><![CDATA[
/**
* matches any join point with at least one argument, and where the
* type of the first argument has the @Classified annotation
*/
pointcut classifiedArgument() : @args(Classified,..);
/**
* matches any join point with three arguments, where the third
* argument has an annotation of type @Untrusted.
*/
pointcut untrustedData(Untrusted untrustedDataSource) :
@args(*,*,untrustedDataSource);
]]></programlisting>
<para>In addition to accessing annotation information at runtime through context binding,
access to <literal>AnnotatedElement</literal> information is also available
reflectively with the body of advice through the <literal>thisJoinPoint</literal>,
<literal>thisJoinPointStaticPart</literal>, and
<literal>thisEnclosingJoinPointStaticPart</literal> variables. To access
annotations on the arguments, or object bound to this or target at a join
point you can use the following code fragments:</para>
<programlisting><![CDATA[
Annotation[] thisAnnotations = thisJoinPoint.getThis().getClass().getAnnotations();
Annotation[] targetAnnotations = thisJoinPoint.getTarget().getClass().getAnnotations();
Annotation[] firstParamAnnotations = thisJoinPoint.getArgs()[0].getClass().getAnnotations();
]]></programlisting>
<para>
The <literal>@within</literal> and <literal>@withincode</literal> pointcut designators
match any join point where the executing code is defined within a type (<literal>@within</literal>),
or a method/constructor (<literal>@withincode</literal>) that has an annotation of the specified
type. The form of these designators is:
</para>
<programlisting><![CDATA[
AtWithin := '@within' '(' AnnotationOrIdentifier ')'
AtWithinCode := '@withincode' '(' AnnotationOrIdentifier ')'
]]></programlisting>
<para>Some examples of using these designators follow:</para>
<variablelist>
<varlistentry>
<term>@within(Foo)</term>
<listitem>
<para>
Matches any join point where the executing code is defined
within a type which has an annotation of type <literal>Foo</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>pointcut insideCriticalMethod(Critical c) :
@withincode(c);</term>
<listitem>
<para>
Matches any join point where the executing code is defined
in a method or constructor which has an annotation of type <literal>@Critical</literal>,
and exposes the value of the annotation in the parameter
<literal>c</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>The <literal>@annotation</literal> pointcut designator matches any
join point where the <emphasis>subject</emphasis> of the join point has
an annotation of the given type. Like the other @pcds, it can also be
used for context exposure.</para>
<programlisting><![CDATA[
AtAnnotation := '@annotation' '(' AnnotationOrIdentifier ')'
]]></programlisting>
<para>The subject of a join point is defined in the table in chapter one of
this guide.</para>
<para>
Access to annotation information on members at a matched join point is also available
through the <literal>getSignature</literal> method of the <literal>JoinPoint</literal>
and <literal>JoinPoint.StaticPart</literal> interfaces. The <literal>Signature</literal>
interfaces are extended with additional operations that provide access to the
<literal>java.lang.reflect</literal> <literal>Method, Field</literal> and
<literal>Constructor</literal> objects on which annnotations can be queried. The following fragment
illustrates an example use of this interface to access annotation information.
</para>
<programlisting><![CDATA[
Signature sig = thisJoinPointStaticPart.getSignature();
AnnotatedElement declaringTypeAnnotationInfo = sig.getDeclaringType();
if (sig instanceof MethodSignature) {
// this must be a call or execution join point
Method method = ((MethodSignature)sig).getMethod();
}
]]></programlisting>
<para>
<emphasis>Note again that it would be nicer to add the method getAnnotationInfo
directly to MemberSignature, but this would once more couple the runtime library
to Java 5.</emphasis>
</para>
<para>
The <literal>@this,@target</literal> and <literal>@args</literal>
pointcut designators can only be used to match against annotations
that have runtime retention. The <literal>@within, @withincode</literal>
and <literal>@annotation</literal> pointcut designators can only be used
to match against annotations that have at least class-file retention, and
if used in the binding form the annotation must have runtime retention.
</para>
</sect2>
<sect2 id="package-and-parameter-annotations" xreflabel="package-and-parameter-annotations">
<title>Package and Parameter Annotations</title>
<para>
<emphasis>Matching on package and parameter annotations is not supported
in AspectJ 1.5.0. Support for this capability may be considered in a future
release.</emphasis>
</para>
<!-- @withinpackage ??? -->
<!--
<para>
Java 5 allows both packages and parameters to be annotated. To allow matching on package and parameter annotations,
AspectJ 5 introduces the <literal>@package</literal> and <literal>@parameters</literal> pointcut designators.
</para>
<programlisting><![CDATA[
PackageAnnotationPointcut := '@package' '(' AnnotationPattern ')'
]]></programlisting>
<para>The <literal>@package</literal> pointcut matches any join point
occuring within the scope of a package with
annotations matching the giving <literal>AnnotationPattern</literal>. For
example:
</para>
<programlisting><![CDATA[
@package(@Model)
]]></programlisting>
<para>
Matches any join point occuring within the scope of a package with the
<literal>@Model</literal> annotation.
</para>
<para>
<emphasis>
Note: we added @package as a result of a conscious decision not to allow the
specification of package annotation patterns within a general TypePattern. A
consequence of this decision is that we lose the ability to say the following
things: "a call to a method defined in a type in a package with annotations
matching..." ; "the set of a field defined in a type in a package with annotations
matching..." ; "the get of a field defined in a type in a package with annotations
matching...". As well as the package of the target at these join points, there is
also the package of the runtime type of the target (call/target difference). So
there are at least three possible sets of package annotations you could theoretically
want to match on at a call, get, or set join point. We have chosen to provide the
means to express the simplest of these, and could consider extending the language
to allow for the others in the future when we better understanding how users will
really use both package annotations and these features.
</emphasis>
</para>
<para>
The <literal>@parameter</literal> pointcut designator acts in a similar manner to
<literal>args</literal> in that it matches based on number and position of arguments
at a join point (and supports the same wildcard options of <literal>*</literal> and
<literal>..</literal>.
</para>
<programlisting><![CDATA[
ParamsAnnotationPointcut := '@parameters' '(' ParamsAnnotationPattern ')'
ParamsAnnotationPattern := AnnotationPattern (',' ParamsAnnotationPattern)? |
'*' (',' ParamsAnnotationPattern)? |
'..' (',' SingleParamsAnnotationPattern)*
SingleParamsAnnotationPattern := AnnotationPattern (',' SingleParamsAnnotationPattern)? |
'*' (',' SingleParamsAnnotationPattern)?
]]></programlisting>
<para>The <literal>*</literal> wildcard matches a single parameter regardless of its annotations.
The <literal>..</literal> wildcard matches zero or more parameters with any annotations. An
annotation pattern in a given parameter position matches a parameter in that position with annotations
matching the given annotation pattern. For example, the method signature</para>
<programlisting><![CDATA[
public void foo(@Immutable int i, String s, @Cached Object o);
]]></programlisting>
<para>
Is matched by:
</para>
<programlisting><![CDATA[
@parameters(@Immutable, *, @Cached);
and,
@parameters(..,@Cached);
and,
@parameters(@Immutable, *, *);
]]></programlisting>
<para>
It is not matched by:
</para>
<programlisting><![CDATA[
@parameters(@Immutable, *);
or,
@parameters(*,@Immutable);
or,
@parameters(*, int, @Cached);
]]></programlisting>
<para>
This last example will result in a compilation error since <literal>int</literal> is not a
valid annotation pattern.
</para>
-->
</sect2>
<sect2 id="annotation-inheritance-and-pointcut-matching" xreflabel="annotation-inheritance-and-pointcut-matching">
<title>Annotation Inheritance and pointcut matching</title>
<para>
According to the Java 5 specification, non-type annotations are not
inherited, and annotations on types are only inherited if they have the
<literal>@Inherited</literal> meta-annotation.
Given the following program:
</para>
<programlisting><![CDATA[
class C1 {
@SomeAnnotation
public void aMethod() {...}
}
class C2 extends C1 {
public void aMethod() {...}
}
class Main {
public static void main(String[] args) {
C1 c1 = new C1();
C2 c2 = new C2();
c1.aMethod();
c2.aMethod();
}
}
aspect X {
pointcut annotatedC2MethodCall() :
call(@SomeAnnotation * C2.aMethod());
pointcut annotatedMethodCall() :
call(@SomeAnnotation * aMethod());
}
]]></programlisting>
<para>
The pointcut <literal>annotatedC2MethodCall</literal> will not match anything
since the definition of <literal>aMethod</literal> in <literal>C2</literal>
does not have the annotation.
</para>
<para>
The pointcut <literal>annotatedMethodCall</literal> matches
<literal>c1.aMethod()</literal> but not <literal>c2.aMethod()</literal>. The call
to <literal>c2.aMethod</literal> is not matched because join point matching for
modifiers (the visibility modifiers, annotations, and throws clause) is based on
the subject of the join point (the method actually being called).
</para>
</sect2>
<sect2 id="matchingOnAnnotationValues" xreflabel="matchingOnAnnotationValues">
<title>Matching based on annotation values</title>
<para>
The <literal>if</literal> pointcut designator can be used to write pointcuts
that match based on the values annotation members. For example:
</para>
<programlisting><![CDATA[
pointcut txRequiredMethod(Tx transactionAnnotation) :
execution(* *(..)) && @this(transactionAnnotation)
&& if(transactionAnnotation.policy() == TxPolicy.REQUIRED);
]]></programlisting>
</sect2>
</sect1>
<!-- ============================== -->
<sect1 id="annotations-decp">
<title>Using Annotations with declare statements</title>
<sect2 id="declare-error-and-declare-warning" xreflabel="declare-error-and-declare-warning">
<title>Declare error and declare warning</title>
<para>
Since pointcut expressions in AspectJ 5 support join point matching based
on annotations, this facility can be exploited when writing
<literal>declare warning</literal> and <literal>declare error</literal>
statements. For example:
</para>
<programlisting><![CDATA[
declare warning : withincode(@PerformanceCritical * *(..)) &&
call(@ExpensiveOperation * *(..))
: "Expensive operation called from within performance critical section";
]]></programlisting>
<programlisting><![CDATA[
declare error : call(* org.xyz.model.*.*(..)) &&
!@within(Trusted)
: "Untrusted code should not call the model classes directly";
]]></programlisting>
</sect2>
<sect2 id="declare-parents" xreflabel="declare-parents">
<title>declare parents</title>
<para>
The general form of a <literal>declare parents</literal> statement is:
</para>
<programlisting><![CDATA[
declare parents : TypePattern extends Type;
declare parents : TypePattern implements TypeList;
]]></programlisting>
<para>
Since AspectJ 5 supports annotations as part of a type pattern
specification, it is now possible to match types based on the presence
of annotations <emphasis>with either class-file or runtime retention</emphasis>.
For example:
</para>
<variablelist>
<varlistentry>
<term>declare parents : (@Secured *) implements SecuredObject;</term>
<listitem>
<para>
All types with the <literal>@Secured</literal> annotation
implement the <literal>SecuredObject</literal> inteface.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>declare parents : (@Secured BankAccount+) implements SecuredObject;</term>
<listitem>
<para>
The subset of types drawn from the <literal>BankAccount</literal> type and any subtype of
<literal>BankAccount</literal>, where the
<literal>@Secured</literal> annotation is present, implement the
<literal>SecuredObject</literal> interface.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>An annotation type may not be used as the target of a declare parents
statement. If an annotation type is named explicitly as the target of a
declare parents statement, a compilation error will result. If an annotation
type is matched by a non-explicit type pattern used in a declare parents
statement it will be ignored (and an XLint warning issued).</para>
</sect2>
<sect2 id="declare-precedence" xreflabel="declare-precedence">
<title>declare precedence</title>
<para>
The general form of a declare precedence statement is:
</para>
<programlisting><![CDATA[
declare precedence : TypePatList;
]]></programlisting>
<para>
AspectJ 5 allows the type patterns in the list to include annotation information
as part of the pattern specification. For example:
</para>
<variablelist>
<varlistentry>
<term>declare precedence : (@Security *),*;</term>
<listitem>
<para>
All aspects with the <literal>@Security</literal> annotation
take precedence over any other aspects in the system. (Or, more
informally, all security-related aspects take precedence).
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
</sect1>
<!-- ============================== -->
<sect1 id="annotations-declare">
<title>Declare Annotation</title>
<para>AspectJ 5 supports a new kind of declare statement, <literal>declare annotation</literal>.
This takes different forms according to the recipient of the annotation:
<literal>declare @type</literal> for types, <literal>declare @method</literal> for methods,
<literal>declare @constructor</literal> for constructors, and <literal>declare @field</literal>
for fields. <literal>declare @package</literal> may be supported in a future release.
</para>
<para>The general form is:</para>
<programlisting><![CDATA[
declare @<kind> : ElementPattern : Annotation ;
]]></programlisting>
<para>Where annotation is a regular annotation expression as defined in the Java 5 language. If the annotation has
the <literal>@Target</literal> meta-annotation, then the elements matched by <literal>ElementPattern</literal>
must be of the kind specified by the <literal>@Target</literal> annotation.</para>
<para><literal>ElementPattern</literal> is defined as follows:</para>
<programlisting><![CDATA[
ElementPattern := TypePattern |
MethodPattern |
ConstructorPattern |
FieldPattern
]]></programlisting>
<para>The following examples illustrate the use of <literal>declare annotation</literal>.</para>
<variablelist>
<varlistentry>
<term>declare @type : org.xyz.model..* : @BusinessDomain ;</term>
<listitem>
<para>
All types defined in a package with the prefix <literal>org.xyz.model</literal>
have the <literal>@BusinessDomain</literal> annotation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>declare @method : public * BankAccount+.*(..) : @Secured(role="supervisor")</term>
<listitem>
<para>
All public methods in <literal>BankAccount</literal> and its subtypes have the
annotation <literal>@Secured(role="supervisor")</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>declare @constructor : BankAccount+.new(..) : @Secured(role="supervisor")</term>
<listitem>
<para>
All constructors in <literal>BankAccount</literal> and its subtypes have the
annotation <literal>@Secured(role="supervisor")</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>declare @field : * DAO+.* : @Persisted;</term>
<listitem>
<para>
All fields defined in <literal>DAO</literal> or its subtypes have the
<literal>@Persisted</literal> annotation.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect1>
<sect1 id="annotations-itds">
<title>Inter-type Declarations</title>
<para>An annotation type may not be the target of an inter-type declaration.</para>
</sect1>
</chapter>