Using Annotations with declare statements
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Using Annotations with declare statements

Declare error and declare warning

Since pointcut expressions in AspectJ 5 support join point matching based on annotations, this facility can be exploited when writing declare warning and declare error statements. For example: 

  	declare warning : withincode(@PerformanceCritical * *(..)) &&
  	                  call(@ExpensiveOperation * *(..))
  	                : "Expensive operation called from within performance critical section";
	
  	declare error : call(* org.xyz.model.*.*(..)) &&
  	                !@within(Trusted)
  	                : "Untrusted code should not call the model classes directly";

declare parents

The general form of a declare parents statement is: 

  	declare parents : TypePattern extends Type;
  	declare parents : TypePattern implements TypeList;

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 with either class-file or runtime retention. For example:

declare parents : (@Secured *) implements SecuredObject;

All types with the @Secured annotation implement the SecuredObject inteface.

declare parents : (@Secured BankAccount+) implements SecuredObject;

The subset of types drawn from the BankAccount type and any subtype of BankAccount, where the @Secured annotation is present, implement the SecuredObject interface.

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).

declare precedence

The general form of a declare precedence statement is: 

  	declare precedence : TypePatList;

AspectJ 5 allows the type patterns in the list to include annotation information as part of the pattern specification. For example:

declare precedence : (@Security *),*;

All aspects with the @Security annotation take precedence over any other aspects in the system. (Or, more informally, all security-related aspects take precedence).

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