This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Framework 6.0.26! |
Declaring Advice
Advice is associated with a pointcut expression and runs before, after, or around method executions matched by the pointcut. The pointcut expression may be either an inline pointcut or a reference to a named pointcut.
Before Advice
You can declare before advice in an aspect by using the @Before
annotation.
The following example uses an inline pointcut expression.
-
Java
-
Kotlin
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
@Aspect
public class BeforeExample {
@Before("execution(* com.xyz.dao.*.*(..))")
public void doAccessCheck() {
// ...
}
}
import org.aspectj.lang.annotation.Aspect
import org.aspectj.lang.annotation.Before
@Aspect
class BeforeExample {
@Before("execution(* com.xyz.dao.*.*(..))")
fun doAccessCheck() {
// ...
}
}
If we use a named pointcut, we can rewrite the preceding example as follows:
-
Java
-
Kotlin
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
@Aspect
public class BeforeExample {
@Before("com.xyz.CommonPointcuts.dataAccessOperation()")
public void doAccessCheck() {
// ...
}
}
import org.aspectj.lang.annotation.Aspect
import org.aspectj.lang.annotation.Before
@Aspect
class BeforeExample {
@Before("com.xyz.CommonPointcuts.dataAccessOperation()")
fun doAccessCheck() {
// ...
}
}
After Returning Advice
After returning advice runs when a matched method execution returns normally.
You can declare it by using the @AfterReturning
annotation.
-
Java
-
Kotlin
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterReturning;
@Aspect
public class AfterReturningExample {
@AfterReturning("execution(* com.xyz.dao.*.*(..))")
public void doAccessCheck() {
// ...
}
}
import org.aspectj.lang.annotation.Aspect
import org.aspectj.lang.annotation.AfterReturning
@Aspect
class AfterReturningExample {
@AfterReturning("execution(* com.xyz.dao.*.*(..))")
fun doAccessCheck() {
// ...
}
}
You can have multiple advice declarations (and other members as well), all inside the same aspect. We show only a single advice declaration in these examples to focus the effect of each one. |
Sometimes, you need access in the advice body to the actual value that was returned.
You can use the form of @AfterReturning
that binds the return value to get that
access, as the following example shows:
-
Java
-
Kotlin
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterReturning;
@Aspect
public class AfterReturningExample {
@AfterReturning(
pointcut="execution(* com.xyz.dao.*.*(..))",
returning="retVal")
public void doAccessCheck(Object retVal) {
// ...
}
}
import org.aspectj.lang.annotation.Aspect
import org.aspectj.lang.annotation.AfterReturning
@Aspect
class AfterReturningExample {
@AfterReturning(
pointcut = "execution(* com.xyz.dao.*.*(..))",
returning = "retVal")
fun doAccessCheck(retVal: Any?) {
// ...
}
}
The name used in the returning
attribute must correspond to the name of a parameter
in the advice method. When a method execution returns, the return value is passed to
the advice method as the corresponding argument value. A returning
clause also
restricts matching to only those method executions that return a value of the
specified type (in this case, Object
, which matches any return value).
Please note that it is not possible to return a totally different reference when using after returning advice.
After Throwing Advice
After throwing advice runs when a matched method execution exits by throwing an
exception. You can declare it by using the @AfterThrowing
annotation, as the
following example shows:
-
Java
-
Kotlin
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterThrowing;
@Aspect
public class AfterThrowingExample {
@AfterThrowing("execution(* com.xyz.dao.*.*(..))")
public void doRecoveryActions() {
// ...
}
}
import org.aspectj.lang.annotation.Aspect
import org.aspectj.lang.annotation.AfterThrowing
@Aspect
class AfterThrowingExample {
@AfterThrowing("execution(* com.xyz.dao.*.*(..))")
fun doRecoveryActions() {
// ...
}
}
Often, you want the advice to run only when exceptions of a given type are thrown,
and you also often need access to the thrown exception in the advice body. You can
use the throwing
attribute to both restrict matching (if desired — use Throwable
as the exception type otherwise) and bind the thrown exception to an advice parameter.
The following example shows how to do so:
-
Java
-
Kotlin
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterThrowing;
@Aspect
public class AfterThrowingExample {
@AfterThrowing(
pointcut="execution(* com.xyz.dao.*.*(..))",
throwing="ex")
public void doRecoveryActions(DataAccessException ex) {
// ...
}
}
import org.aspectj.lang.annotation.Aspect
import org.aspectj.lang.annotation.AfterThrowing
@Aspect
class AfterThrowingExample {
@AfterThrowing(
pointcut = "execution(* com.xyz.dao.*.*(..))",
throwing = "ex")
fun doRecoveryActions(ex: DataAccessException) {
// ...
}
}
The name used in the throwing
attribute must correspond to the name of a parameter in
the advice method. When a method execution exits by throwing an exception, the exception
is passed to the advice method as the corresponding argument value. A throwing
clause
also restricts matching to only those method executions that throw an exception of the
specified type (DataAccessException
, in this case).
Note that |
After (Finally) Advice
After (finally) advice runs when a matched method execution exits. It is declared by
using the @After
annotation. After advice must be prepared to handle both normal and
exception return conditions. It is typically used for releasing resources and similar
purposes. The following example shows how to use after finally advice:
-
Java
-
Kotlin
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.After;
@Aspect
public class AfterFinallyExample {
@After("execution(* com.xyz.dao.*.*(..))")
public void doReleaseLock() {
// ...
}
}
import org.aspectj.lang.annotation.Aspect
import org.aspectj.lang.annotation.After
@Aspect
class AfterFinallyExample {
@After("execution(* com.xyz.dao.*.*(..))")
fun doReleaseLock() {
// ...
}
}
Note that |
Around Advice
The last kind of advice is around advice. Around advice runs "around" a matched method’s execution. It has the opportunity to do work both before and after the method runs and to determine when, how, and even if the method actually gets to run at all. Around advice is often used if you need to share state before and after a method execution in a thread-safe manner – for example, starting and stopping a timer.
Always use the least powerful form of advice that meets your requirements. For example, do not use around advice if before advice is sufficient for your needs. |
Around advice is declared by annotating a method with the @Around
annotation. The
method should declare Object
as its return type, and the first parameter of the method
must be of type ProceedingJoinPoint
. Within the body of the advice method, you must
invoke proceed()
on the ProceedingJoinPoint
in order for the underlying method to
run. Invoking proceed()
without arguments will result in the caller’s original
arguments being supplied to the underlying method when it is invoked. For advanced use
cases, there is an overloaded variant of the proceed()
method which accepts an array of
arguments (Object[]
). The values in the array will be used as the arguments to the
underlying method when it is invoked.
The behavior of The approach taken by Spring is simpler and a better match to its proxy-based,
execution-only semantics. You only need to be aware of this difference if you compile
|
The value returned by the around advice is the return value seen by the caller of the
method. For example, a simple caching aspect could return a value from a cache if it has
one or invoke proceed()
(and return that value) if it does not. Note that proceed
may be invoked once, many times, or not at all within the body of the around advice. All
of these are legal.
If you declare the return type of your around advice method as void , null
will always be returned to the caller, effectively ignoring the result of any invocation
of proceed() . It is therefore recommended that an around advice method declare a return
type of Object . The advice method should typically return the value returned from an
invocation of proceed() , even if the underlying method has a void return type.
However, the advice may optionally return a cached value, a wrapped value, or some other
value depending on the use case.
|
The following example shows how to use around advice:
-
Java
-
Kotlin
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.ProceedingJoinPoint;
@Aspect
public class AroundExample {
@Around("execution(* com.xyz..service.*.*(..))")
public Object doBasicProfiling(ProceedingJoinPoint pjp) throws Throwable {
// start stopwatch
Object retVal = pjp.proceed();
// stop stopwatch
return retVal;
}
}
import org.aspectj.lang.annotation.Aspect
import org.aspectj.lang.annotation.Around
import org.aspectj.lang.ProceedingJoinPoint
@Aspect
class AroundExample {
@Around("execution(* com.xyz..service.*.*(..))")
fun doBasicProfiling(pjp: ProceedingJoinPoint): Any? {
// start stopwatch
val retVal = pjp.proceed()
// stop stopwatch
return retVal
}
}
Advice Parameters
Spring offers fully typed advice, meaning that you declare the parameters you need in the
advice signature (as we saw earlier for the returning and throwing examples) rather than
work with Object[]
arrays all the time. We see how to make argument and other contextual
values available to the advice body later in this section. First, we take a look at how to
write generic advice that can find out about the method the advice is currently advising.
Access to the Current JoinPoint
Any advice method may declare, as its first parameter, a parameter of type
org.aspectj.lang.JoinPoint
. Note that around advice is required to declare a first
parameter of type ProceedingJoinPoint
, which is a subclass of JoinPoint
.
The JoinPoint
interface provides a number of useful methods:
-
getArgs()
: Returns the method arguments. -
getThis()
: Returns the proxy object. -
getTarget()
: Returns the target object. -
getSignature()
: Returns a description of the method that is being advised. -
toString()
: Prints a useful description of the method being advised.
See the javadoc for more detail.
Passing Parameters to Advice
We have already seen how to bind the returned value or exception value (using after
returning and after throwing advice). To make argument values available to the advice
body, you can use the binding form of args
. If you use a parameter name in place of a
type name in an args
expression, the value of the corresponding argument is passed as
the parameter value when the advice is invoked. An example should make this clearer.
Suppose you want to advise the execution of DAO operations that take an Account
object as the first parameter, and you need access to the account in the advice body.
You could write the following:
-
Java
-
Kotlin
@Before("execution(* com.xyz.dao.*.*(..)) && args(account,..)")
public void validateAccount(Account account) {
// ...
}
@Before("execution(* com.xyz.dao.*.*(..)) && args(account,..)")
fun validateAccount(account: Account) {
// ...
}
The args(account,..)
part of the pointcut expression serves two purposes. First, it
restricts matching to only those method executions where the method takes at least one
parameter, and the argument passed to that parameter is an instance of Account
.
Second, it makes the actual Account
object available to the advice through the account
parameter.
Another way of writing this is to declare a pointcut that "provides" the Account
object value when it matches a join point, and then refer to the named pointcut
from the advice. This would look as follows:
-
Java
-
Kotlin
@Pointcut("execution(* com.xyz.dao.*.*(..)) && args(account,..)")
private void accountDataAccessOperation(Account account) {}
@Before("accountDataAccessOperation(account)")
public void validateAccount(Account account) {
// ...
}
@Pointcut("execution(* com.xyz.dao.*.*(..)) && args(account,..)")
private fun accountDataAccessOperation(account: Account) {
}
@Before("accountDataAccessOperation(account)")
fun validateAccount(account: Account) {
// ...
}
See the AspectJ programming guide for more details.
The proxy object (this
), target object (target
), and annotations (@within
,
@target
, @annotation
, and @args
) can all be bound in a similar fashion. The next
set of examples shows how to match the execution of methods annotated with an
@Auditable
annotation and extract the audit code:
The following shows the definition of the @Auditable
annotation:
-
Java
-
Kotlin
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Auditable {
AuditCode value();
}
@Retention(AnnotationRetention.RUNTIME)
@Target(AnnotationTarget.FUNCTION)
annotation class Auditable(val value: AuditCode)
The following shows the advice that matches the execution of @Auditable
methods:
-
Java
-
Kotlin
@Before("com.xyz.Pointcuts.publicMethod() && @annotation(auditable)") (1)
public void audit(Auditable auditable) {
AuditCode code = auditable.value();
// ...
}
1 | References the publicMethod named pointcut defined in Combining Pointcut Expressions. |
@Before("com.xyz.Pointcuts.publicMethod() && @annotation(auditable)") (1)
fun audit(auditable: Auditable) {
val code = auditable.value()
// ...
}
1 | References the publicMethod named pointcut defined in Combining Pointcut Expressions. |
Advice Parameters and Generics
Spring AOP can handle generics used in class declarations and method parameters. Suppose you have a generic type like the following:
-
Java
-
Kotlin
public interface Sample<T> {
void sampleGenericMethod(T param);
void sampleGenericCollectionMethod(Collection<T> param);
}
interface Sample<T> {
fun sampleGenericMethod(param: T)
fun sampleGenericCollectionMethod(param: Collection<T>)
}
You can restrict interception of method types to certain parameter types by tying the advice parameter to the parameter type for which you want to intercept the method:
-
Java
-
Kotlin
@Before("execution(* ..Sample+.sampleGenericMethod(*)) && args(param)")
public void beforeSampleMethod(MyType param) {
// Advice implementation
}
@Before("execution(* ..Sample+.sampleGenericMethod(*)) && args(param)")
fun beforeSampleMethod(param: MyType) {
// Advice implementation
}
This approach does not work for generic collections. So you cannot define a pointcut as follows:
-
Java
-
Kotlin
@Before("execution(* ..Sample+.sampleGenericCollectionMethod(*)) && args(param)")
public void beforeSampleMethod(Collection<MyType> param) {
// Advice implementation
}
@Before("execution(* ..Sample+.sampleGenericCollectionMethod(*)) && args(param)")
fun beforeSampleMethod(param: Collection<MyType>) {
// Advice implementation
}
To make this work, we would have to inspect every element of the collection, which is not
reasonable, as we also cannot decide how to treat null
values in general. To achieve
something similar to this, you have to type the parameter to Collection<?>
and manually
check the type of the elements.
Determining Argument Names
Parameter binding in advice invocations relies on matching the names used in pointcut expressions to the parameter names declared in advice and pointcut method signatures.
This section uses the terms argument and parameter interchangeably, since AspectJ APIs refer to parameter names as argument names. |
Spring AOP uses the following ParameterNameDiscoverer
implementations to determine
parameter names. Each discoverer will be given a chance to discover parameter names, and
the first successful discoverer wins. If none of the registered discoverers is capable
of determining parameter names, an exception will be thrown.
AspectJAnnotationParameterNameDiscoverer
-
Uses parameter names that have been explicitly specified by the user via the
argNames
attribute in the corresponding advice or pointcut annotation. See Explicit Argument Names for details. KotlinReflectionParameterNameDiscoverer
-
Uses Kotlin reflection APIs to determine parameter names. This discoverer is only used if such APIs are present on the classpath.
StandardReflectionParameterNameDiscoverer
-
Uses the standard
java.lang.reflect.Parameter
API to determine parameter names. Requires that code be compiled with the-parameters
flag forjavac
. Recommended approach on Java 8+. LocalVariableTableParameterNameDiscoverer
-
Analyzes the local variable table available in the byte code of the advice class to determine parameter names from debug information. Requires that code be compiled with debug symbols (
-g:vars
at a minimum). Deprecated as of Spring Framework 6.0 for removal in Spring Framework 6.1 in favor of compiling code with-parameters
. Not supported in a GraalVM native image. AspectJAdviceParameterNameDiscoverer
-
Deduces parameter names from the pointcut expression,
returning
, andthrowing
clauses. See the javadoc for details on the algorithm used.
Explicit Argument Names
@AspectJ advice and pointcut annotations have an optional argNames
attribute that you
can use to specify the argument names of the annotated method.
If an @AspectJ aspect has been compiled by the AspectJ compiler ( Similarly, if an @AspectJ aspect has been compiled with |
The following example shows how to use the argNames
attribute:
-
Java
-
Kotlin
@Before(
value = "com.xyz.Pointcuts.publicMethod() && target(bean) && @annotation(auditable)", (1)
argNames = "bean,auditable") (2)
public void audit(Object bean, Auditable auditable) {
AuditCode code = auditable.value();
// ... use code and bean
}
1 | References the publicMethod named pointcut defined in Combining Pointcut Expressions. |
2 | Declares bean and auditable as the argument names. |
@Before(
value = "com.xyz.Pointcuts.publicMethod() && target(bean) && @annotation(auditable)", (1)
argNames = "bean,auditable") (2)
fun audit(bean: Any, auditable: Auditable) {
val code = auditable.value()
// ... use code and bean
}
1 | References the publicMethod named pointcut defined in Combining Pointcut Expressions. |
2 | Declares bean and auditable as the argument names. |
If the first parameter is of type JoinPoint
, ProceedingJoinPoint
, or
JoinPoint.StaticPart
, you can omit the name of the parameter from the value of the
argNames
attribute. For example, if you modify the preceding advice to receive the join
point object, the argNames
attribute does not need to include it:
-
Java
-
Kotlin
@Before(
value = "com.xyz.Pointcuts.publicMethod() && target(bean) && @annotation(auditable)", (1)
argNames = "bean,auditable") (2)
public void audit(JoinPoint jp, Object bean, Auditable auditable) {
AuditCode code = auditable.value();
// ... use code, bean, and jp
}
1 | References the publicMethod named pointcut defined in Combining Pointcut Expressions. |
2 | Declares bean and auditable as the argument names. |
@Before(
value = "com.xyz.Pointcuts.publicMethod() && target(bean) && @annotation(auditable)", (1)
argNames = "bean,auditable") (2)
fun audit(jp: JoinPoint, bean: Any, auditable: Auditable) {
val code = auditable.value()
// ... use code, bean, and jp
}
1 | References the publicMethod named pointcut defined in Combining Pointcut Expressions. |
2 | Declares bean and auditable as the argument names. |
The special treatment given to the first parameter of type JoinPoint
,
ProceedingJoinPoint
, or JoinPoint.StaticPart
is particularly convenient for advice
methods that do not collect any other join point context. In such situations, you may
omit the argNames
attribute. For example, the following advice does not need to declare
the argNames
attribute:
-
Java
-
Kotlin
@Before("com.xyz.Pointcuts.publicMethod()") (1)
public void audit(JoinPoint jp) {
// ... use jp
}
1 | References the publicMethod named pointcut defined in Combining Pointcut Expressions. |
@Before("com.xyz.Pointcuts.publicMethod()") (1)
fun audit(jp: JoinPoint) {
// ... use jp
}
1 | References the publicMethod named pointcut defined in Combining Pointcut Expressions. |
Proceeding with Arguments
We remarked earlier that we would describe how to write a proceed
call with
arguments that works consistently across Spring AOP and AspectJ. The solution is
to ensure that the advice signature binds each of the method parameters in order.
The following example shows how to do so:
-
Java
-
Kotlin
@Around("execution(List<Account> find*(..)) && " +
"com.xyz.CommonPointcuts.inDataAccessLayer() && " +
"args(accountHolderNamePattern)") (1)
public Object preProcessQueryPattern(ProceedingJoinPoint pjp,
String accountHolderNamePattern) throws Throwable {
String newPattern = preProcess(accountHolderNamePattern);
return pjp.proceed(new Object[] {newPattern});
}
1 | References the inDataAccessLayer named pointcut defined in Sharing Named Pointcut Definitions. |
@Around("execution(List<Account> find*(..)) && " +
"com.xyz.CommonPointcuts.inDataAccessLayer() && " +
"args(accountHolderNamePattern)") (1)
fun preProcessQueryPattern(pjp: ProceedingJoinPoint,
accountHolderNamePattern: String): Any? {
val newPattern = preProcess(accountHolderNamePattern)
return pjp.proceed(arrayOf<Any>(newPattern))
}
1 | References the inDataAccessLayer named pointcut defined in Sharing Named Pointcut Definitions. |
In many cases, you do this binding anyway (as in the preceding example).
Advice Ordering
What happens when multiple pieces of advice all want to run at the same join point? Spring AOP follows the same precedence rules as AspectJ to determine the order of advice execution. The highest precedence advice runs first "on the way in" (so, given two pieces of before advice, the one with highest precedence runs first). "On the way out" from a join point, the highest precedence advice runs last (so, given two pieces of after advice, the one with the highest precedence will run second).
When two pieces of advice defined in different aspects both need to run at the same
join point, unless you specify otherwise, the order of execution is undefined. You can
control the order of execution by specifying precedence. This is done in the normal
Spring way by either implementing the org.springframework.core.Ordered
interface in
the aspect class or annotating it with the @Order
annotation. Given two aspects, the
aspect returning the lower value from Ordered.getOrder()
(or the annotation value) has
the higher precedence.
Each of the distinct advice types of a particular aspect is conceptually meant to apply
to the join point directly. As a consequence, an As of Spring Framework 5.2.7, advice methods defined in the same When two pieces of the same type of advice (for example, two |