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Spring Framework
AOP
2st WEEK
30 Jun
GEEKY ACADEMY 2013

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2 | GEEK ACADEMY 2013
INSTRUCTOR TEAM
SALAHPIYA
Salah (Dean) Chalermthai
Siam Chamnan Kit
SChalermthai@sprint3r.com
Piya (Tae) Lumyong
-
piya.tae@gmail.com

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Topic
• Intro to AOP
• Basic AOP Concepts
• Getting Started with Spring AOP

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Introduction to AOP
GEEK ACADEMY 2013

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Intro to AOP
• Why worrying about Crosscutting Concerns?
• What AOP Does?
• Crosscutting Concerns
• Example

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Why worrying about Crosscutting Concerns?
public void withdraw(long accId, int amount) {
Account account = (Account)session.get(Account.class, accId);
double balance = account.getBalance();
balance = balance - amount;
account.setBalance(balance);
session.save(balance);
}
Business

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Why worrying about Crosscutting Concerns?
public void withdraw(long accId, int amount) {
if (hasPermission(accId)) {
Account account = (Account)session.get(Account.class, accId);
double balance = account.getBalance();
balance = balance - amount;
account.setBalance(balance);
session.save(balance);
} else {
throw new SecurityException("Access Denied");
}
}
Business
Permission

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Why worrying about Crosscutting Concerns?
public void withdraw(long accId, int amount) {
if (hasPermission(accId)) {
bankLogger.info(accId + " withdrow amount " + amount);
Account account = (Account)session.get(Account.class, accId);
double balance = account.getBalance();
balance = balance - amount;
account.setBalance(balance);
session.save(balance);
} else {
throw new SecurityException("Access Denied");
}
}
Business
Permission
Logger

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Why worrying about Crosscutting Concerns?
public void withdraw(long accId, int amount) {
if (hasPermission(accId)) {
bankLogger.info(accId + " withdrow amount " + amount);
Transaction tx = null;
try {
Transaction tx = session.beginTransaction();
Account account = (Account)session.get(Account.class, accId);
double balance = account.getBalance();
balance = balance - amount;
account.setBalance(balance);
session.save(balance);
tx.commit();
} catch(RuntimeException ex) {
if (tx!=null) tx.rollback;
}
} else {
throw new SecurityException("Access Denied");
}
}
Business
Permission
Logger
Transaction

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Why worrying about Crosscutting Concerns?
Business
Permission
Logger
Transaction
Service A
Service B
Service C

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Why worrying about Crosscutting Concerns?
• Too many relationship to the crosscutting objects
• Code is still required in all methods
• Cannot all be changed at one

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What AOP Does?
• AOP will separate the Crosscutting concerns from the
System

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Crosscutting Concerns
public void withdraw(int amount) {
balance = balance - amount;
}
public void deposit(int amount) {
balance = balance + amount;
}
Logger
bankLogger.info("Withdraw " + amount); bankLogger.info("Withdraw " + amount);
Transaction
tx.commit(); tx.commit();
tx.begin(); tx.begin();
Ref AOP Spring

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Cross-Cutting Concerns Examples
• Logging and Tracing
• Transaction Management
• Security
• Caching
• Error Handling
• Performance Monitoring
• Custom Business Rules

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Basic AOP Concepts
GEEK ACADEMY 2013

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Basic AOP Concepts
• What is AOP?
• AOP Terminology
• Advice
• How Spring AOP Works
• AOP and OOP
• Leading AOP Technologies

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What is AOP?
• is a programming paradigm
• extends OOP
• enables modularization of crosscutting concerns
• is second heart of
Spring Framework

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AOP Terminology

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AOP Terminology
• Joinpoint – Defines A Point During the Execution of a
program. We can insert Additional logics at Joinpoints
• Advice – Action taken(Functionality) at a Joinpoint.
• Pointcut – Combination of Joinpoints where the Advice
need to be Applied.

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AOP Terminology
• Aspect – a modularization of a Crosscutting concern.
• Target object - object being advised by one or more aspects.
• AOP proxy – Will manage the way of Applying Aspects at
particular Pointcuts.
PointCut
Advice
PointCut
Advice
PointCut
Advice
Aspect
Target Object
Proxy
Call

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AOP Weaving
• Process of applying aspects to a target object
• Will create a proxied object

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How AOP Works
• Write your mainline application logic (Solve core problem)
• Write aspects to implement cross-cutting concerns (Write aspects)
• Bind it all together (Weave at runtime)

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AOP and OOP
• Aspect – code unit that encapsulates
pointcuts, advice, and attributes
• Pointcut – define the set of entry points
(triggers) in which advice is executed
• Advice – implementation of cross
cutting concern
• Weaver – construct code (source or
object) with advice
• Class – code unit that encapsulates
methods and attributes
• Method signature – define the entry
points for the execution of method bodies
• Method bodies – implementation of the
business logic concerns
• Compiler – convert source code to object
code
AOP OOP

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Leading AOP Technologies
• AspectJ
– 1995, original AOP technology
– Offers a full Aspect Oriented Programming language
– Modifies byte code to add aspects into your application!
• Spring AOP
– Uses dynamic proxies to add aspects into your application
– Only spring beans can be advised
– Uses some of AspectJ expression syntax

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Getting Started with
Spring AOP
GEEK ACADEMY 2013

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Getting Started with Spring AOP
• Spring AOP
• Aspect
• Pointcut
• Advice
• Bean in Spring container
• How it really works
• Additional
• Spring AOP vs AspectJ
• @AspectJ vs XML

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Spring AOP
• Implemented in pure java
• No need for a special compilation process
• Supports only method execution join points
• Only runtime weaving is available
• AOP proxy
– JDK dynamic proxy
– CGLIB proxy
• Configuration
– @AspectJ annotation-style
– Spring XML configuration-style

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@Aspect
@Aspect
public class LoggingAspect {
...
}
<aop:aspectj-autoproxy />
<bean class="mypackage.LoggingAspect" />

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Pointcut

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Pointcut
• @Pointcut
• Pointcut expression
• Pointcut designators
• Example

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@Pointcut
@Aspect
public class LoggingAspect {
@Pointcut("execution(* mypackage.service..*.*(..))")
public void ifService() {}
@Pointcut("execution(* mypackage.repository..*.*(..))")
public void ifRepository() {}
...
}

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Pointcut expression
• PCD - Pointcut designators.
• method scope
– Advice will be applied to all the methods having this scope.
For e.g., public, private, etc. Spring AOP only supports
advising public methods.
• return type
– Advice will be applied to all the methods having this return
type.
PCD(<method scope> <return type> <declaring type>.<name(param)> <throw>)

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Pointcut expression(2)
• declaring type
– Advice will be applied to all the methods of this type. If the class
and advice are in the same package then package name is not
required
• name(param)
– Filter the method names and the argument types.
Two dots(..) means any number(0-more) and type of parameters.
• throw
PCD(<method scope> <return type> <declaring type>.<name(param)> <throw>)

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Pointcut designators
• Code based
– execution (Method Patterns)
• the primary pointcut designator you will use when working with Spring AOP
– within (Type Patterns)
• within certain types (simply the execution of a method declared within a
matching type when using Spring AOP)
– target
• where the target object (application object being proxied) is an instance of
the given type

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Pointcut designators(2)
• Code based(2)
– this
• where the bean reference (Spring AOP proxy) is an instance of the given
type
– args
• where the arguments are instances of the given types
– bean (Bean Name Patterns)
• to a particular named Spring bean, or to a set of named Spring beans (when
using wildcards)

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Pointcut designators(3)
• Annotation based
– @annotation
• where the subject of the join point (method being executed in Spring AOP)
has the given annotation
– @within
• within types that have the given annotation (the execution of methods
declared in types with the given annotation when using Spring AOP)

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Pointcut designators(4)
• Annotation based(2)
– @target
• where the class of the executing object has an annotation of the given type
– @args
• where the runtime type of the actual arguments passed have annotations of
the given type(s)

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Pointcut example
• the execution of any public method:
execution(public * *(..))
• the execution of any method with a name beginning with “set”:
execution(* set*(..))
• the execution of any method defined by the MyService interface
execution(* com.xyz.service.MyService.*(..))
• 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 a
sub-package:
execution(* com.xyz.service..*.*(..))

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Pointcut example(2)
• 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 a sub-package:
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)

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Pointcut example(3)
• Other example
– Pointcut example - Spring Framework Reference

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Advice

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Advice
• Advice types
• @Before
• @After
• @AfterReturning
• @AfterThrowing
• @Around

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Advice
• Action teken at particular Joinpoint is called as an Advice
• Defines What needs to be Applied and When
– What – Functionality
– When – Advice Type

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Advice types
• Before
• After
• After Returning
• After Throwing
• Around
Method
Return Throw
Success call
Call

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@Before
@Aspect
public class LoggingAspect {
@Pointcut("execution(* *(..))")
public void ifService() {}
@Before("ifService()")
public void logBefore(JoinPoint joinPoint) {
...
}
...
}

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@After
@Aspect
public class LoggingAspect {
@Pointcut("execution(* *(..))")
public void ifService() {}
@After("ifService()")
public void logAfter(JoinPoint joinPoint) {
...
}
...
}

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@AfterReturning
@Aspect
public class LoggingAspect {
@Pointcut("execution(* *(..))")
public void ifService() {}
@AfterReturning(pointcut = "ifService()", returning = "result")
public void logAfterReturning(JoinPoint joinPoint, Object result) {
...
}
...
}

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@AfterThrowing
@Aspect
public class LoggingAspect {
@Pointcut("execution(* *(..))")
public void ifService() {}
@AfterThrowing(pointcut = "ifService()", throwing = "error")
public void logAfterThrowing(JoinPoint joinPoint, Throwable error) {
...
}
...
}

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@Around
@Aspect
public class LoggingAspect {
@Pointcut("execution(* *(..))")
public void ifService() {}
@Around("ifService()")
public Object logAround(ProceedingJoinPoint joinPoint) throws Throwable {
...
Object result = joinPoint.proceed();
...
return result;
}
...
}

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Security
Bean in Spring container
Logging
Caching
Target
Object

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How it really works (TX example)

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LAB1 Basic Spring AOP

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LAB1 Basic Spring AOP
Target
Object
Logging

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Links
• SpringSource
• Spring Reference 3.2
• Thank for
– Dmitry Noskov
– chamilavt
– Java Brains

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Books

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GEEK ACADEMY 2013

57.
THANK YOU FOR
YOUR TIME
GEEK ACADEMY 2013