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Declaring a Pointcut

Pointcuts determine join points of interest and thus enable us to control when advice runs. Spring AOP only supports method execution join points for Spring beans, so you can think of a pointcut as matching the execution of methods on Spring beans. A pointcut declaration has two parts: a signature comprising a name and any parameters and a pointcut expression that determines exactly which method executions we are interested in. In the @AspectJ annotation-style of AOP, a pointcut signature is provided by a regular method definition, and the pointcut expression is indicated by using the @Pointcut annotation (the method serving as the pointcut signature must have a void return type).

An example may help make this distinction between a pointcut signature and a pointcut expression clear. The following example defines a pointcut named anyOldTransfer that matches the execution of any method named transfer:

Java
Kotlin

@Pointcut("execution(* transfer(..))") // the pointcut expression
private void anyOldTransfer() {} // the pointcut signature

@Pointcut("execution(* transfer(..))") // the pointcut expression
private fun anyOldTransfer() {} // the pointcut signature

The pointcut expression that forms the value of the @Pointcut annotation is a regular AspectJ pointcut expression. For a full discussion of AspectJ’s pointcut language, see the AspectJ Programming Guide (and, for extensions, the AspectJ 5 Developer’s Notebook) or one of the books on AspectJ (such as Eclipse AspectJ, by Colyer et al., or AspectJ in Action, by Ramnivas Laddad).

Supported Pointcut Designators

Spring AOP supports the following AspectJ pointcut designators (PCD) for use in pointcut expressions:

execution: For matching method execution join points. This is the primary pointcut designator to use when working with Spring AOP.
within: Limits matching to join points within certain types (the execution of a method declared within a matching type when using Spring AOP).
this: Limits matching to join points (the execution of methods when using Spring AOP) where the bean reference (Spring AOP proxy) is an instance of the given type.
target: Limits matching to join points (the execution of methods when using Spring AOP) where the target object (application object being proxied) is an instance of the given type.
args: Limits matching to join points (the execution of methods when using Spring AOP) where the arguments are instances of the given types.
@target: Limits matching to join points (the execution of methods when using Spring AOP) where the class of the executing object has an annotation of the given type.
@args: Limits matching to join points (the execution of methods when using Spring AOP) where the runtime type of the actual arguments passed have annotations of the given types.
@within: Limits matching to join points within types that have the given annotation (the execution of methods declared in types with the given annotation when using Spring AOP).
@annotation: Limits matching to join points where the subject of the join point (the method being run in Spring AOP) has the given annotation.

Other pointcut types

The full AspectJ pointcut language supports additional pointcut designators that are not supported in Spring: call, get, set, preinitialization, staticinitialization, initialization, handler, adviceexecution, withincode, cflow, cflowbelow, if, @this, and @withincode. Use of these pointcut designators in pointcut expressions interpreted by Spring AOP results in an IllegalArgumentException being thrown.

The set of pointcut designators supported by Spring AOP may be extended in future releases to support more of the AspectJ pointcut designators.

Because Spring AOP limits matching to only method execution join points, the preceding discussion of the pointcut designators gives a narrower definition than you can find in the AspectJ programming guide. In addition, AspectJ itself has type-based semantics and, at an execution join point, both this and target refer to the same object: the object executing the method. Spring AOP is a proxy-based system and differentiates between the proxy object itself (which is bound to this) and the target object behind the proxy (which is bound to target).

Due to the proxy-based nature of Spring’s AOP framework, calls within the target object are, by definition, not intercepted. For JDK proxies, only public interface method calls on the proxy can be intercepted. With CGLIB, public and protected method calls on the proxy are intercepted (and even package-visible methods, if necessary). However, common interactions through proxies should always be designed through public signatures.

Note that pointcut definitions are generally matched against any intercepted method. If a pointcut is strictly meant to be public-only, even in a CGLIB proxy scenario with potential non-public interactions through proxies, it needs to be defined accordingly.

If your interception needs include method calls or even constructors within the target class, consider the use of Spring-driven native AspectJ weaving instead of Spring’s proxy-based AOP framework. This constitutes a different mode of AOP usage with different characteristics, so be sure to make yourself familiar with weaving before making a decision.

Spring AOP also supports an additional PCD named bean. This PCD lets you limit the matching of join points to a particular named Spring bean or to a set of named Spring beans (when using wildcards). The bean PCD has the following form:

bean(idOrNameOfBean)

The idOrNameOfBean token can be the name of any Spring bean. Limited wildcard support that uses the * character is provided, so, if you establish some naming conventions for your Spring beans, you can write a bean PCD expression to select them. As is the case with other pointcut designators, the bean PCD can be used with the && (and), || (or), and ! (negation) operators, too.

The bean PCD is supported only in Spring AOP and not in native AspectJ weaving. It is a Spring-specific extension to the standard PCDs that AspectJ defines and is, therefore, not available for aspects declared in the @Aspect model.

The bean PCD operates at the instance level (building on the Spring bean name concept) rather than at the type level only (to which weaving-based AOP is limited). Instance-based pointcut designators are a special capability of Spring’s proxy-based AOP framework and its close integration with the Spring bean factory, where it is natural and straightforward to identify specific beans by name.

Combining Pointcut Expressions

You can combine pointcut expressions by using &&, || and !. You can also refer to pointcut expressions by name. The following example shows three pointcut expressions:

Java
Kotlin

package com.xyz;

public class Pointcuts {

	@Pointcut("execution(public * *(..))")
	public void publicMethod() {} (1)

	@Pointcut("within(com.xyz.trading..*)")
	public void inTrading() {} (2)

	@Pointcut("publicMethod() && inTrading()")
	public void tradingOperation() {} (3)
}

1	`publicMethod` matches if a method execution join point represents the execution of any public method.
2	`inTrading` matches if a method execution is in the trading module.
3	`tradingOperation` matches if a method execution represents any public method in the trading module.

package com.xyz

class Pointcuts {

	@Pointcut("execution(public * *(..))")
	fun publicMethod() {} (1)

	@Pointcut("within(com.xyz.trading..*)")
	fun inTrading() {} (2)

	@Pointcut("publicMethod() && inTrading()")
	fun tradingOperation() {} (3)
}

1	`publicMethod` matches if a method execution join point represents the execution of any public method.
2	`inTrading` matches if a method execution is in the trading module.
3	`tradingOperation` matches if a method execution represents any public method in the trading module.

It is a best practice to build more complex pointcut expressions out of smaller named pointcuts, as shown above. When referring to pointcuts by name, normal Java visibility rules apply (you can see private pointcuts in the same type, protected pointcuts in the hierarchy, public pointcuts anywhere, and so on). Visibility does not affect pointcut matching.

Sharing Named Pointcut Definitions

When working with enterprise applications, developers often have the need to refer to modules of the application and particular sets of operations from within several aspects. We recommend defining a dedicated class that captures commonly used named pointcut expressions for this purpose. Such a class typically resembles the following CommonPointcuts example (though what you name the class is up to you):

Java
Kotlin

package com.xyz;

import org.aspectj.lang.annotation.Pointcut;

public class CommonPointcuts {

	/**
	 * A join point is in the web layer if the method is defined
	 * in a type in the com.xyz.web package or any sub-package
	 * under that.
	 */
	@Pointcut("within(com.xyz.web..*)")
	public void inWebLayer() {}

	/**
	 * A join point is in the service layer if the method is defined
	 * in a type in the com.xyz.service package or any sub-package
	 * under that.
	 */
	@Pointcut("within(com.xyz.service..*)")
	public void inServiceLayer() {}

	/**
	 * A join point is in the data access layer if the method is defined
	 * in a type in the com.xyz.dao package or any sub-package
	 * under that.
	 */
	@Pointcut("within(com.xyz.dao..*)")
	public void inDataAccessLayer() {}

	/**
	 * A business service is the execution of any method defined on a service
	 * interface. This definition assumes that interfaces are placed in the
	 * "service" package, and that implementation types are in sub-packages.
	 *
	 * If you group service interfaces by functional area (for example,
	 * in packages com.xyz.abc.service and com.xyz.def.service) then
	 * the pointcut expression "execution(* com.xyz..service.*.*(..))"
	 * could be used instead.
	 *
	 * Alternatively, you can write the expression using the 'bean'
	 * PCD, like so "bean(*Service)". (This assumes that you have
	 * named your Spring service beans in a consistent fashion.)
	 */
	@Pointcut("execution(* com.xyz..service.*.*(..))")
	public void businessService() {}

	/**
	 * A data access operation is the execution of any method defined on a
	 * DAO interface. This definition assumes that interfaces are placed in the
	 * "dao" package, and that implementation types are in sub-packages.
	 */
	@Pointcut("execution(* com.xyz.dao.*.*(..))")
	public void dataAccessOperation() {}

}

package com.xyz

import org.aspectj.lang.annotation.Pointcut

class CommonPointcuts {

	/**
	 * A join point is in the web layer if the method is defined
	 * in a type in the com.xyz.web package or any sub-package
	 * under that.
	 */
	@Pointcut("within(com.xyz.web..*)")
	fun inWebLayer() {}

	/**
	 * A join point is in the service layer if the method is defined
	 * in a type in the com.xyz.service package or any sub-package
	 * under that.
	 */
	@Pointcut("within(com.xyz.service..*)")
	fun inServiceLayer() {}

	/**
	 * A join point is in the data access layer if the method is defined
	 * in a type in the com.xyz.dao package or any sub-package
	 * under that.
	 */
	@Pointcut("within(com.xyz.dao..*)")
	fun inDataAccessLayer() {}

	/**
	 * A business service is the execution of any method defined on a service
	 * interface. This definition assumes that interfaces are placed in the
	 * "service" package, and that implementation types are in sub-packages.
	 *
	 * If you group service interfaces by functional area (for example,
	 * in packages com.xyz.abc.service and com.xyz.def.service) then
	 * the pointcut expression "execution(* com.xyz..service.*.*(..))"
	 * could be used instead.
	 *
	 * Alternatively, you can write the expression using the 'bean'
	 * PCD, like so "bean(*Service)". (This assumes that you have
	 * named your Spring service beans in a consistent fashion.)
	 */
	@Pointcut("execution(* com.xyz..service.*.*(..))")
	fun businessService() {}

	/**
	 * A data access operation is the execution of any method defined on a
	 * DAO interface. This definition assumes that interfaces are placed in the
	 * "dao" package, and that implementation types are in sub-packages.
	 */
	@Pointcut("execution(* com.xyz.dao.*.*(..))")
	fun dataAccessOperation() {}

}

You can refer to the pointcuts defined in such a class anywhere you need a pointcut expression by referencing the fully-qualified name of the class combined with the @Pointcut method’s name. For example, to make the service layer transactional, you could write the following which references the com.xyz.CommonPointcuts.businessService() named pointcut:

<aop:config>
	<aop:advisor
		pointcut="com.xyz.CommonPointcuts.businessService()"
		advice-ref="tx-advice"/>
</aop:config>

<tx:advice id="tx-advice">
	<tx:attributes>
		<tx:method name="*" propagation="REQUIRED"/>
	</tx:attributes>
</tx:advice>

The <aop:config> and <aop:advisor> elements are discussed in Schema-based AOP Support. The transaction elements are discussed in Transaction Management.

Examples

Spring AOP users are likely to use the execution pointcut designator the most often. The format of an execution expression follows:

execution(modifiers-pattern?
			ret-type-pattern
			declaring-type-pattern?name-pattern(param-pattern)
			throws-pattern?)

All parts except the returning type pattern (ret-type-pattern in the preceding snippet), the name pattern, and the parameters pattern are optional. The returning type pattern determines what the return type of the method must be in order for a join point to be matched. * is most frequently used as the returning type pattern. It matches any return type. A fully-qualified type name matches only when the method returns the given type. The name pattern matches the method name. You can use the * wildcard as all or part of a name pattern. If you specify a declaring type pattern, include a trailing . to join it to the name pattern component. The parameters pattern is slightly more complex: () matches a method that takes no parameters, whereas (..) matches any number (zero or more) of parameters. The (*) pattern matches a method that takes one parameter of any type. (*,String) matches a method that takes two parameters. The first can be of any type, while the second must be a String. Consult the Language Semantics section of the AspectJ Programming Guide for more information.

The following examples show some common pointcut expressions:

The execution of any public method:
```
execution(public * *(..))
```
The execution of any method with a name that begins with set:
```
execution(* set*(..))
```
The execution of any method defined by the AccountService interface:
```
execution(* com.xyz.service.AccountService.*(..))
```
The execution of any method defined in the service package:
```
execution(* com.xyz.service.*.*(..))
```
The execution of any method defined in the service package or one of its sub-packages:
```
execution(* com.xyz.service..*.*(..))
```
Any join point (method execution only in Spring AOP) within the service package:
```
within(com.xyz.service.*)
```
Any join point (method execution only in Spring AOP) within the service package or one of its sub-packages:
```
within(com.xyz.service..*)
```
Any join point (method execution only in Spring AOP) where the proxy implements the AccountService interface:
```
this(com.xyz.service.AccountService)
```
this is more commonly used in a binding form. See the section on Declaring Advice for how to make the proxy object available in the advice body.
Any join point (method execution only in Spring AOP) where the target object implements the AccountService interface:
```
target(com.xyz.service.AccountService)
```
target is more commonly used in a binding form. See the Declaring Advice section for how to make the target object available in the advice body.
Any join point (method execution only in Spring AOP) that takes a single parameter and where the argument passed at runtime is Serializable:
```
args(java.io.Serializable)
```
args is more commonly used in a binding form. See the Declaring Advice section for how to make the method arguments available in the advice body.

Note that the pointcut given in this example is different from execution(* *(java.io.Serializable)). The args version matches if the argument passed at runtime is Serializable, and the execution version matches if the method signature declares a single parameter of type Serializable.
Any join point (method execution only in Spring AOP) where the target object has a @Transactional annotation:
```
@target(org.springframework.transaction.annotation.Transactional)
```
You can also use @target in a binding form. See the Declaring Advice section for how to make the annotation object available in the advice body.
Any join point (method execution only in Spring AOP) where the declared type of the target object has an @Transactional annotation:
```
@within(org.springframework.transaction.annotation.Transactional)
```
You can also use @within in a binding form. See the Declaring Advice section for how to make the annotation object available in the advice body.
Any join point (method execution only in Spring AOP) where the executing method has an @Transactional annotation:
```
@annotation(org.springframework.transaction.annotation.Transactional)
```
You can also use @annotation in a binding form. See the Declaring Advice section for how to make the annotation object available in the advice body.
Any join point (method execution only in Spring AOP) which takes a single parameter, and where the runtime type of the argument passed has the @Classified annotation:
```
@args(com.xyz.security.Classified)
```
You can also use @args in a binding form. See the Declaring Advice section how to make the annotation object(s) available in the advice body.
Any join point (method execution only in Spring AOP) on a Spring bean named tradeService:
```
bean(tradeService)
```
Any join point (method execution only in Spring AOP) on Spring beans having names that match the wildcard expression *Service:
```
bean(*Service)
```

Writing Good Pointcuts

During compilation, AspectJ processes pointcuts in order to optimize matching performance. Examining code and determining if each join point matches (statically or dynamically) a given pointcut is a costly process. (A dynamic match means the match cannot be fully determined from static analysis and that a test is placed in the code to determine if there is an actual match when the code is running). On first encountering a pointcut declaration, AspectJ rewrites it into an optimal form for the matching process. What does this mean? Basically, pointcuts are rewritten in DNF (Disjunctive Normal Form) and the components of the pointcut are sorted such that those components that are cheaper to evaluate are checked first. This means you do not have to worry about understanding the performance of various pointcut designators and may supply them in any order in a pointcut declaration.

However, AspectJ can work only with what it is told. For optimal performance of matching, you should think about what you are trying to achieve and narrow the search space for matches as much as possible in the definition. The existing designators naturally fall into one of three groups: kinded, scoping, and contextual:

Kinded designators select a particular kind of join point: execution, get, set, call, and handler.
Scoping designators select a group of join points of interest (probably of many kinds): within and withincode
Contextual designators match (and optionally bind) based on context: this, target, and @annotation

A well written pointcut should include at least the first two types (kinded and scoping). You can include the contextual designators to match based on join point context or bind that context for use in the advice. Supplying only a kinded designator or only a contextual designator works but could affect weaving performance (time and memory used), due to extra processing and analysis. Scoping designators are very fast to match, and using them means AspectJ can very quickly dismiss groups of join points that should not be further processed. A good pointcut should always include one if possible.