Spring AOP

Spring AOP
ASPECT ORIENTED PROGRAMMING

Spring AOP - Introduction

Aspect – Unit of Modularity

Entails breaking down program logic into distinct parts called so-
called concerns. The functions that span multiple points of an
application are called cross-cutting concerns

Cross-cutting concerns are conceptually separate from the
application's business logic.

AOP in Business

Logging

Transaction Management – Declarative

Caching

Security

AOP Terminologies

Aspect

Advice

Join Point

Pointcut

Introduction

Target Object

Weaving

AOP Advice

This is the actual action to be taken either before or after
the method execution.

This is actual piece of code that is invoked during program
execution by Spring AOP framework.

Types of Advices

Before - Run advice before the a method execution.

After - Run advice after the a method execution regardless
of its outcome.

After Returning - Run advice after the a method execution
only if method completes successfully.

After throwing - Run advice after the a method execution
only if method exits by throwing an exception.

Around- Run advice before and after the advised method
is invoked.

Advices - Examples

@Before("execution(* *.*(..))")

@After("execution(* *.*(..))")

@AfterReturning("execution(* *.*(..))")

@AfterThrowing("execution(* *.*(..))")

@Around("execution(* *.*(..))")

Aspects Implementation

XML Schema Based

Annotaion Based

Join Point

An Advice is applied to different program execution points,
which are called join points.

An Advice to take the correct action, it often requires
detailed information about join points.

Accessing Join Point
Information

Kind

Method signature

Argument values

Target Object

Proxy Object

AspectJ Precedence

More than one Aspect classes – need Precedence

How to implement?

Ordered Interface

Order Annotation

Point Cut Expressions

It is a powerful expression language that can match
various kinds of join points.

Indicate which method should be intercept, by method
name or regular expression pattern.

expression(<method scope> <return type> <fully qualified
class name>.*(parametes))

Continue..,

method scope: Advice will be applied to all the methods
having this scope. For e.g., public, private, etc. Please note
that Spring AOP only supports advising public methods.

return type: Advice will be applied to all the methods
having this return type.

Continue..,

fully qualified class name: 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

parameters: You can also filter the method names based
on the types. Two dots(..) means any number and type of
parameters.

Pointcut Examples

execution(* com.aspects.pointcut.DemoClass.*(..)) : This
advice will be applied to all the methods of DemoClass.

execution(* DemoClass.*(..)): You can omit the package if
the DemoClass and the advice is in the same package.

execution(public * DemoClass.*(..)): This advice will be
applied to the public methods of DemoClass.

Pointcut Examples

execution(public int DemoClass.*(..)): This advice will be
applied to the public methods of DemoClass and returning
an int.

execution(public int DemoClass.*(int, ..)): This advice will be
applied to the public methods of DemoClass and returning
an int and having first parameter as int.

execution(public int DemoClass.*(int, int)): This advice will
be applied to the public methods of DemoClass and
returning an int and having both parameters as int.

Reusing Pointcut Expression
@Pointcut("execution(* *.*(..))")
private void loggingOperation()
{}
@Before("loggingOperation()")
public void logBefore(JoinPoint joinPoint)
{}

PointCut Class Aspect
@Aspect
Class PointCut
{
@Pointcut("execution(* *.*(..))")
private void loggingOperation()
{}
}

@AfterReturning(
pointcut = "PointCut.loggingOperation()",
returning = "result")
public void logAfterReturning(JoinPoint joinPoint, Object result) {
}

Type Signature Pattern

Within - pointcut expressions matches all join points within
certain types.

pointcut matches all the method execution join points
within the com.msoftgp.spring package
within(com.msoftgp.spring.*)

To match the join points within a package and its
subpackage, you have to add one more dot before the
wildcard.
within(com.msoftgp.spring..*)


The pointcut expression matches the method execution
join points within a particular class:
within(com.msoftgp.spring.ArithmeticCalculatorImpl)

Again, if the target class is located in the same package
as this aspect, the package name can be omitted.
within(ArithmeticCalculatorImpl)


You can match the method execution join points within all
classes that implement the ArithmeticCalculator interface
by adding a plus symbol.
within(ArithmeticCalculator+)

Combining Pointcuts
@Aspect
public class CalculatorPointcuts {
@Pointcut("within(ArithmeticCalculator+)")
public void arithmeticOperation() {}
@Pointcut("within(UnitCalculator+)")
public void unitOperation() {}
@Pointcut("arithmeticOperation()|| unitOperation()")
public void loggingOperation() {}
}

Pointcut Parameters

execution(* *.*(..)) && target(target) && args(a,b)

Public void logBefore(Object target,int a,int b)

AOP Introduction

Special type of Advice

Same effect as multiple inheritance

Mechanism used – Dynamic Proxy

@DeclareParents

Load Time Weaving AspectJ

Purpose – Additional Pointcuts ,apply aspects
to objects created outside the Spring IoC container

Weaving is the process of applying aspects to your target
objects.

Weaving happens at runtime through dynamic proxies.

Supports compile time and load time weaving.

Types of AspectJ Weaving

Complie time weaving

Load time weaving

By AspectJ Weaver

Spring Load time Weaver

Application Used : Caching

Configuring AspectJ Aspects in
Spring

Factory-method is aspectof()

Injecting Spring Beans into
Domain Beans

Wiring Spring objects and Domain Objects

Injection of Spring beans is a cross cutting concern

Annotate the Domain class with @Configurable

Spring AOP

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