1. SPRING AOP
INTRODUCTION Boris Trofimov @ Sigma Ukraine
@b0ris_1

2. One example
AOP introduction
Spring AOP basics
Examples and Use Cases
Best practices
Weaknesses
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AGENDA

3. Convert exceptions crossing layers, respecting layer rules (UI
alerts, shaping exceptions etc.)
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ONE EXAMPLE

4. Exception handling – with handlers, typical approach
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ONE EXAMPLE

5. Exception handling – with handlers, typical approach
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ONE EXAMPLE

6. There is cross-cutting functionality that does not belong to
specific module or object. Often it should be supported by many
objects from different places (logging, exception handling, audit,
auth, …). Spreading it throughout the project is not a option.
It would be good to handle specific cross-cutting concern in one
place. However pure major paradigms (OOP, procedural,
component-driven) cannot encapsulate and express this logic
efficiently.
Functional Scala-like approach might help through closures-
decorators, however it has own weaknesses.
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THE PROBLEM

7. Crosscutting concern is decomposed into several notions:
Aspect – crosscutting implementation, regular bean with
method (examples: exception handling)
Join point – usually it represents a method execution.
Pointcut – expression that matches join point.
Advice – join-point and aspect integration, types "around,"
"before" and "after“.
Target Object – object to be advised by one or more aspects.
AOP proxy (or Advised Object ) – proxy with advice calls
Weaving – linking advice with other target objects to create an
advised object (compile or creation stage)
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AOP BASIC CONCEPTS

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HELLO, IT’S SPRING AOP

9. Spring AOP is implemented in pure Java
Aspect is an ordinary bean with own injection rules
Weaving with Spring AOP is performed during instantiation
time: injection/creation or direct
ApplicationContext.getBean (through Spring DI)
Only Proxy Approach (JDK dynamic proxies or CGLIB)
Spring AOP is based on AspectJ framework interfaces.
Two ways of aspect integration: XML and Annotations
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SPRING AOP

10. Add Spring references into maven pom file:
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STEPS TO ADD ASPECT – 1 (3)
( FOR AROUND ADVICE)
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-aop</artifactId>
<version>3.2.2.RELEASE</version>
</dependency>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjrt</artifactId>
<version>1.7.2</version>
</dependency>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjweaver</artifactId>
<version>1.6.12</version>
</dependency>

11. Create bean-aspect into project, register it as Spring bean:
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STEPS TO ADD ASPECT – 1 (3)
( FOR AROUND ADVICE)
package com.xyz.services.aspect;
public class ServiceAspect {
public Object run(ProceedingJoinPoint call) throws Throwable {
// do something, part 1
Object ret = call.proceed();
// do something, part 2
return ret;
}
}
<bean id="AspectBeanReference"
class="com.xyz.services.aspect.ServiceAspect"/>

12. Register Advice and Pointcut:
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STEPS TO ADD ASPECT – 2 (3)
( FOR AROUND ADVICE)
<aop:config>
<aop:aspect id="MyAspect" ref="AspectBeanReference" order="250">
<aop:pointcut id="MyNameOfPointcut"
expression=
"execution(* com.xyz.services.impl.*ServiceImpl.*(..))"/>
<aop:around pointcut-ref="MyNameOfPointcut" method="run"/>
</aop:aspect>
</aop:config>
<!-- <aop:aspectj-autoproxy/> -->

13.  Spring AOP uses AspectJ subset language to express
pointcuts.
 Pointcuts might define classes as well as interfaces
Examples
execution(* *.*(..)) – expresses aspect call after execution of any
public method;
execution(* *.set*(..)) – expresses aspect call after execution of any
method which name starts with “set”;
execution(* com.xyz.service.AccountService.*(..)) – expresses
aspect call after execution of any method for class
com.xyz.service.AccountService;
execution(* com.xyz.service.*.*(..)) – expresses aspect call for any
method of objects from package service;
annotation(com.xyz.service.MyAnnotation) - expresses aspect
call for method, whose object support annotation.
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A FEW WORDS ON POINTCUTS

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ADVICES
BEFORE ADVICE
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
@Aspect
public class BeforeExample {
@Before("execution(* com.xyz.myapp.dao.*.*(..))")
public void doAccessCheck() {
// ...
}
}

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ADVICES
AFTER RETURNING
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterReturning;
@Aspect
public class AfterReturningExample {
@AfterReturning(
pointcut="execution(* com.xyz.myapp.dao.*.*(..))",
returning="retVal")
public void doAccessCheck(Object retVal) {
// ...
}
}

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ADVICES
AFTER THROWING ADVICE
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterThrowing;
@Aspect
public class AfterThrowingExample {
@AfterThrowing(
pointcut="execution(* com.xyz.myapp.dao.*.*(..))",
throwing="ex")
public void doRecoveryActions(Exception ex) {
// ...
}
}

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ADVICES
AFTER (FINALLY) ADVICE
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.After;
@Aspect
public class AfterFinallyExample {
@After("execution(* com.xyz.myapp.dao.*.*(..))")
public void doReleaseLock() {
// ...
}
}

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ADVICES
AROUND ADVICE
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.myapp.dao.*.*(..))")
public Object doBasicProfiling(ProceedingJoinPoint pjp)
throws Throwable {
// start stopwatch
Object retVal = pjp.proceed();
// stop stopwatch
return retVal;
}
}

19. Task is to convert exceptions crossing layers.
Define pointcut covering edge components for specific layer.
Define aspect
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TRANSPARENT EXCEPTION HANDLING
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.ProceedingJoinPoint;
@Aspect
public class ExceptionTranslatorExample {
@Around("execution(* com.xyz.domain.*Repository.*(..)) ")
public Object doBasicProfiling(ProceedingJoinPoint pjp)
throws Throwable {
try{
Object retVal = pjp.proceed();
return retVal;
}
catch (SQLException ex){
throw new DomainException(ex);
}
}
}

20. Define pointcut to cover beans with @Transactional
annotations. Usually it is top edge of application service layer.
Take into account aspect order – transactions should have
bigger value.
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RE-LAUNCHING BROKEN TRANSACTIONS
@Aspect
public class ExceptionTranslatorExample {
@Around("execution(* com.xyz.applicationServices.*Service.*(..)) ")
public Object doBasicProfiling(ProceedingJoinPoint pjp)
throws Throwable {
int counter = 0;
do{
try{
return pjp.proceed();
}
catch (DeadLockException ex)
if((++counter)==2)
throw ex;
}
while(true);
}
}

21. Audit
Perform authentication rules
Hidden Logging
Measure method execution
Aligning to transaction result
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MORE APPLICATIONS

22. Any pointcut should be expressed by single
expression.
Any pointcut should be “linearized”.
Do not invent a wheel: use customized Spring
AOP technics like exception handling for Spring
MVC or Spring declarative transactions.
One cross-cutting concern should be matched
to one aspect implementation.
In case of layered architecture and XML
approach treat all aspects from one layer in
one place [like board room].
AOP might be integrated into legacy project, it
should have clear architecture and DI (is it
possible?!).
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BEST PRACTICES

23. AOP is not silver bullet. Do not use it
everywhere. Excessive AOP usage makes
application even more difficult to
understand than without it.
Take into account overhead (creation&
execution time ). In many cases it might
matter. Use AspectJ bytecode weaving
approach.
Be aware of Spring’s proxy approach.
Spring AOP is based on Spring DI.
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AOP CONCERNS

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AOP OVERHEAD
5000 (in ms) 50000 (in ms) 500.000 (in ms) 5.000.000 (in ms)
Calling pure math object (Series 1) 46,008952 131,986317 1194,716932 13661,97206
Calling weaved object with empty aspect (Series 2) 55,736513 225,285998 1897,525577 20110,53607
Calling weaved object with math aspect (Series 3) 65,556692 343,241082 3141,977656 32587,01187
0
5000
10000
15000
20000
25000
30000
35000
5000 (in ms) 50000 (in ms) 500.000 (in ms) 5.000.000 (in ms)
Series1
Series2
Series3
Experiment details:
AMD Athlon X4, 3 GHz

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AOP BENCHMARKS
AWBench
(relative %)
aspectwerkz aspectj spring dynaop
before, args()
target()
1 x 1 x 35.5 x 39 x
around x 2, args()
target()
1 x 0.6 x 5.4 x 5.6 x
before, rtti info
access
1 x 1 x 5.5 x 6.7 x
after returning 1 x 1 x 28.5 x 31.5 x
before + after 1 x 1 x 22.2 x 17.2 x
before, args()
primitives
1 x 1 x 35 x 37.5 x
before, args()
objects
1 x 2 x 65 x 69 x
around, rtti info
access
1 x 0.7 x 3.5 x 4.8 x
around, static
info access
1 x 0.3 x 3 x 4.1 x
Source: http://docs.codehaus.org/display/AW/AOP+Benchmark

26. Thank you for your attention!