1. Aspect Oriented Programming Adlux Consultancy Services Pvt Ltd
Presentation By
ANUSHA N
Aspect Oriented Programming
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AGENDA
Introduction To AOP
AOP Concepts
Aspect
Joinpoint
Advice
Pointcuts
Target Object
Weaving
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What Is AOP
Aspect-oriented programming, or AOP, is a programming technique that allows programmers to modularize crosscutting concerns
It is often defined as a programming technique that promotes separation of crosscutting concerns with in a software system.
concerns :
A concern is a particular issue, concept, or area of interest for an application: typically, a goal the application must meet.
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4. Cross-cutting concerns
The systems or concerns that tend to cut across multiple components in a system are referred as Cross-cutting concerns
System wide concerns that span multiple modules.
Cuts across the typical division of responsibility.
Examples such as
Transaction Management
Security
Logging
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5. Cross Cutting Concerns in OOP Approach
OOP creates a coupling between core and crosscutting concerns. This causes
Leads to duplicated code.
Hard to maintain code.
Hard to use code.
Cross cutting concerns
Withdraw method
Deposit method
Transaction Management
Logging
Checking for the Privileged User
Actual Withdraw Logic
comes here
Transaction Management
Logging
Checking for the Privileged User
Actual Deposit Logic
comes here
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Public class Account { public void deposit() { // Transaction Management // Logging // Checking for the Privileged User // Actual Deposit Logic comes here } public void withdraw() { // Actual Withdraw Logic comes here AOP calls this kind of logic that cross-cuts the existing business logic as Cross-Cutting Concerns .
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7. Could we not write these cross cutting concerns as functions and call?
Results in code permeating though the system at various places – hard to maintain
Harder to express concerns this way
You have to modify your code to invoke these concerns
requires understanding at each level
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If we use AOP
Spring AOP will take care of calling concerns, we just need to declare about concerns once in configuration file.
You can focus on the concerns at one place
Easier to add and remove concerns
Easier to modify or fine tune concerns
Easier to understand
Efficient to implement
More efficient
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AOP Terminology
Joinpoint
A point during the execution of a program, such as the execution
of a method or the handling of an exception.
We can insert additional logic at Joinpoint's.
In Spring AOP, a join point always represents a method execution.
Advice
Action taken at a particular joinpoint is called Advice.
PointCut
A declarative condition that identifies for which joinpoint, the advices should fire.
Aspect:
An aspect is a modularization of a crosscutting concern; the gathering together of code that might otherwise have been scattered. It is termed as the combination of the point-cut and the advice.
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AOP vs OOP
Object Oriented
Aspect Oriented
Class – code unit that encapsulates methods and attributes.
Aspect – code unit that encapsulates pointcuts, advice, and attributes.
Method signatures – define the entry points for the execution of method bodies.
Pointcut – define the set of entry points (triggers) in which advice is executed.
Method bodies – implementations of the primary concerns.
Advice – implementations of the cross cutting concerns.
Compiler – converts source code into object code.
Weaver – instruments code (source or object) with advice.
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AOP History
Spring implements the AOP Alliance interception interfaces .
Emerged about 10 years ago from different research efforts studying the separation of concerns in software
Supported in industry today by IBM, BEA,
AOP support is available for Java, C++, C, PHP,
AspectJ, AspectC++, AspectC, AOPHP,
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Advice
Action taken at a particular joinpoint is called Advice.
The following are the different types of advices available in Spring.
Before Advice
After Advice
Throws Advice
Around Advice
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Advice
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Advice
Before Advice :
It is used to intercept before the method execution starts.
public class Authentication extends BeforeAdvice {
public void before(Method method, Object[] args, Object target) throws Throwable
if (args[0] instanceof User)
User user = (User)args[0];
// Authenticate if he/she is the right user }  }
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Advice
From the above code
before() method will be called before the execution of method call.
method object represents target method to be invoked.
Object[] args refers to the various arguments that are passed on to the method.
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Advice
After Advice
It will be useful if some logic has to be executed before Returning the Control within a method execution.
public class CleanUpOperation implements AfterReturningAdvice { 
public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
// Clean up session and user information. }
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Advice
From the above code
afterReturning() will be called once the method returns normal execution.
If some exception happens in the method execution the afterReturning() method will never be called.
Throws Advice :
some kind of exception happens during the execution of a method, then to handle the exception properly.
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Advice
public class DeleteFile implements ThrowsAdvice {
public void afterThrowing(Method method, Object[] args, Object target, IOException exception)
String targetFileName = (String)args[2];
// Code to delete the target file. }
From the above code
afterThrowing() method will be called when an Exception, that too of type IOException is thrown
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Advice
Around Advice :
Advice that surrounds a joinpoint such as a method invocation.
They are responsible for choosing whether to proceed to the joinpoint executing by returning their own return value or throwing an exception.
Intercepts the calls to the target method.
this Advice provides finer control whether the target method has to be called or not.
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Advice
public class ValidateArguments implements MethodInterceptor { public Object invoke(MethodInvocation invocation) throws Throwable Object arguments [] = invocation.getArguments(); if ((arguments[0] instanceof Parent) && (arguments[1] instanceof Child) ) { Object returnValue = invocation.proceed(); return returnValue; } throw new Exception ("Arguments are of wrong type");
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Advice
From the above code
It is important to make a call to MethodInvocation.proceed(), if we are happy with the arguments validation, else the target method will never gets invoked.
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POINTCUTS
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Pointcuts
Point Cuts define where exactly the Advices have to be applied in various Join Points i.e Set of Joinpoints specifying when an advice should fire.
Generally they act as Filters for the application of various Advices into the real implementation.
Each built-in Pointcuts has an advisor
PointcutAdvisor=Pointcut + Advice
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Pointcuts
public interface Pointcut { ClassFilter getClassFilter(); MethodMatcher getMethodMatcher(); } public interface ClassFilter boolean matches(Class clazz); public interface MethodMatcher boolean matches(Method m,Class targetClass); boolean isRuntime(); boolean matches(Method m,Class targetClass,Object[] args);
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Pointcuts
Spring defines two types of Point Cuts namely the
Static and Dynamic Point Cuts.
Static Pointcuts
NameMatchMethod Pointcut
Regular Expression Pointcut
NameMatchMethod Pointcut :
Here the name of the methods that are to be given advices can be directly mentioned in the Configuration File.
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Pointcuts
MyInterface.java public interface MyInterface { public void setMessage(String msg); public void method1(); public void method2(); public void getMethod1(); public void getMethod2(); } MyClass.java public class MyClass implements MyInterface { private String message; public void setMessage(String msg) { this.message=msg; public void method1(){} public void method2(){} public void getMethod1() {} public void getMethod2(){}
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Pointcuts
ApplicationContext.xml <beans> <bean id=“getMethodsAdvisor" class="org.springframework. aop. support.NameMatchMethodPointcutAdvisor"> <property name="mappedName"> <value>get*</value> </property> (OR) <property name=“mappedNames”> <list> <value>get*</value> <value>set*</value> <value>method1</value> </list> <property name="advice"> <ref bean=“sampleAdvice "/> </bean>
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Pointcuts
<bean id=“myTargetClass" class=“MyClass“/>
<bean id=“sampleAdvice" class=“MySampleAdvice“/>
<bean id=“proxy“ class=“org.springframework.aop.framework.ProxyFactoryBean“>
<property name="proxyInterfaces“>
<value>MyInterface</value>
</property>
<property name="target">
<ref bean=“myTargetClass "/>
<property name="interceptorNames">
<value>getMethodsAdvisor </value>
</bean>
</beans>
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Pointcuts
get* tells that all method names starting with the method name get will be given Advices.
If we want all the methods in the MyClass to be adviced, then the 'value' tag should be given '*' meaning all the methods in the Class.
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Pointcuts
Regular Expression Pointcut
It is used if you want to match the name of the methods in the Class based on Regular Expression.
Spring distribution already comes with two supported flavors of Regular Expression namely Perl Regular Expression and Jdk Regular Expression .
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Pointcuts
MyInterface.java public interface MyInterface { public void method1(); public void method11(); public void method2(); public void getMethod1(); public void getMethod2(); } MyClass.java public class MyClass implements MyInterface { public void method1(){} public void method11(){} public void method2(){} public void getMethod1(){} public void getMethod2(){}
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Pointcuts
ApplicationContext.xml <bean id="regExpAdvisor“ class="org.springframework.aop. support.RegexpMethodPointcutAdvisor "> <property name=“advice"> <ref bean="sampleAdvice"/> </property> <property name=“patterns”> <list> <value>m.*1</value> <value>.*method.*</value> </list> </bean>
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Pointcuts
<bean id=“myTargetClass" class=“MyClass“/>
<bean id=“sampleAdvice" class=“MySampleAdvice“/>
<bean id="person" class=“org.springframework.aop. framework.ProxyFactoryBean“>
<property name=“proxyInterfaces” >
<value>MyInterface</value>
</property>
<property name=“target”>
<ref bean=“myTargetClass”/>
<property name=“interceptorNames”>
<value> regExpAdvisor </value>
</bean>
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Pointcuts
Symbol
Description .
Matches Any Single Character +
Mathches the Preceding Character one or more times *
Mathches the Preceding Character Zero or more times /
Escapes any Regular Expression Symbols
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Pointcuts
Dynamic Pointcuts :
However, there may be some cases where your pointcuts will need to evaluate runtime attributes.
Spring provides one built-in dynamic pointcut: ControlFlowPointcut.
This pointcut matches based on information about the current thread’s call stack.
That is, it can be configured to return true only if a particular method or class is found in the current thread’s stack of execution.
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Pointcuts
Dynamic Pointcut Configuration
<bean id="dynamicPointcut“ class="org.springframework. aop support.ControlFlowPointcut">
<constructor-arg>
<value>javax.servlet.http.HttpServlet</value>
</constructor-arg>
</bean>
<bean id="dynamicAdvisor" class="org.springframework. aop.support.DefaultPointcutAdvisor">
<property name="advice">
<ref bean=" sampleAdvice "/>
</property>
<property name="pointcut">
<ref bean="dynamicPointcut"/>
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Pointcuts
<bean id=“myTargetClass" class=“MyClass“/>
<bean id=“sampleAdvice" class=“MySampleAdvice“/>
<bean id="person" class=“org.springframework.aop. framework.ProxyFactoryBean“>
<property name=“proxyInterfaces” >
<value>MyInterface</value>
</property>
<property name=“target”>
<ref bean=“myTargetClass”/>
<property name=“interceptorNames”>
<value>dynamicAdvisor</value>
</bean>
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Target
Object containing the joinpoint .
Also referred to as the advised or proxied object .
Example
<bean id=“myTargetClass” class=“sample.MyClass”>
<property name=“message”>
<value>Welcome to Adlux</value>
</property>
</bean>
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Weaving
It is the process of applying aspects to a target object to create a new proxied object.
The aspects are woven into the target object at the specified joinpoints.
different points where weaving can be applied ·  Compile Time
·   Class load Time
·   Runtime
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AOP Proxy
A proxy is the object created after applying advice to the target object.
The target object (pre-AOP) & the proxy object
(post-AOP) are the same.
The object created by the AOP framework that includes the advise.
The three properties you will probably use most often are
1. target
2. proxyInterfaces
3. interceptorNames
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AOP Proxy
Sample ProxyFactoryBean Configuration
<bean id=“sampleProxy" class=“org.springframework.aop. framework.ProxyFactoryBean“>
<property name="proxyInterfaces“>
<value>SampleInterface</value>
</property>
<property name="target">
<ref bean="sampleTarget"/>
<property name="interceptorNames">
<value>sampleAdvice</value>
</bean>
<bean id=“sampleTarget" class=“MySampleTarget“/>
<bean id=“sampleAdvice" class=“MySampleAdvice“/>
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AOP Proxy
Spring will create a proxy using a JDK dynamic proxy or a CGLIB proxy.
First providing the ProxyFactory with all the aspects that you want to be woven into the proxy.
You typically use ProxyFactoryBean class to provide declarative proxy creation.
Different types of AutoProxying
·    DefaultAdvisorAutoProxyCreator
·    BeanNameAutoProxyCreator
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AOP Proxy
BeanNameAutoProxyCreator
<bean id=“beanNameAutoProxy” class="org.springframework.aop framework.autoproxy.BeanNameAutoProxyCreator">
<property name="beanNames">
<list><value>*Service</value></list>
</property>
<property name="interceptorNames">
<value>performanceThresholdInterceptor</value>
</bean>
<bean id=“performanceThresholdInterceptor” class=“student.performanceThresholdInterceptor”/>
<bean id=“studentService” class=“student.StudentService”/>
<bean id=“courseService” class=“student.CourseService”/>
<bean id=“sampleService” class=“sample.SampleService”/>
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AOP Proxy
2. DefaultAdvisorAutoProxyCreator
<bean id="advisor" class="org.springframework.aop.support.
RegexpMethodPointcutAdvisor">
<property name="advice">
<bean class="performanceThresholdInterceptor"/>
</property>
<property name="pattern">
<value>.+Service\..+</value>
</bean>
<bean id="autoProxyCreator” class="org.springframework.aop. framework.autoproxy.DefaultAdvisorAutoProxyCreator"/>
<bean id=“studentService” class=“student.StudentService”/>
<bean id=“courseService” class=“student.CourseService”/>
<bean id=“sampleService” class=“sample.SampleService”/>
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46. Spring AOP Capabilities
Implemented in pure Java
Suitable for use in J2EE container since does not need to control the class loader hierarchy
Spring supports interception of methods
Does not support field interception
Provides classes to represent pointcuts and different advise types
Spring advises object at instance, rather than class loader level
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THANK YOU
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