DEPENDENCY INJECTION ANDAOP

Proxy

Limits of object-oriented programming

•问题Code scattering

•Blocks of duplicated code •Blocks of complementary code, and different modules implementing complementary parts of the concern

Code tangling •Code tangling occurs when a module has to manage several concerns at the same time such as logging, exception handling, security, caching, and more or when a module has elements of the implementation of other concerns inside.

AOP 面向对象Aspect ClassJoinpoint This is the application point of the aspect. It

is a point of the execution of a program such as the invocation of a constructor or the execution of a method or the management of an exception (WHEN).

Advice This is the action an aspect performs at a certain joinpoint. Advices can be "around", "before", and "after".

Pointcut This is the expression for the joinpoint's selection, for instance a method's execution with a certain signature (WHERE)

AOP

AOPAOP 面向对象Introduction

This is the declaration of methods or additional fields on the object to which the aspect will be applied. It allows the introduction of new interfaces and implementations on the objects.

Target object

This is the module (Object) to which the aspect will be applied.

Weaving This is the linking action between the aspect and the objects to which advices must be applied

AdviceAOP 面向对象Before advice

After returning advice Throws advice

After (finally) advice Around advice

the crosscutting concerns should be analysed as a third dimension of the design. In these situations, aspect-oriented programming provides support to object-oriented programming for uncoupling modules that implement crosscutting concerns.

AOP定义方式 Spring XML 方式 AspectJ annotation方式 Schema-based 配置方式

AOP in Spring Spring permits only method execution to be used

as a joinpoint. So we can't use with Spring AOP all the features of AOP, but we can do so with AspectJcalled by Spring. For example, we must use the support of AspectJif we want to use as a joinpoint: The invocations of constructors Access to the domains of objects with the setter and

getter The initialization of an object The initialization of an object with a calling super() The execution inside a class with this() The calling of a method

JoinPoint A pointcut is an expression for the selection of

joinpoints. It can be a collection of joinpoints used to define an advice that has to be executed.

Methods starting with a certain prefix (such as, getter and setter)

Methods with a particular package (such as org.springaop.domain.*)

Methods that return a certain kind of output (such as public MyClass get*(...))

A pointcut is the composition of a ClassFilter and a MethodMatcher.

1. NameMatchMethodPointcut 2. RegexpMethodPointcut 3. StaticMethodMatcherPointcut 4. DynamicMethodMatcherPointcut ComposablePointcut ControlFlowPointcut

public class NameMethodMatcherExample { public static void main(String[] args) { NameMethodTargetExample target = new NameMethodTargetExample(); NameMatchMethodPointcut pc = new NameMatchMethodPointcut(); pc.addMethodName("printSpot"); pc.addMethodName("printAction"); Advisor advisor = new DefaultPointcutAdvisor(pc, new AdviceExample()); ProxyFactory pf = new ProxyFactory(); pf.setTarget(target); pf.addAdvisor(advisor); NameMethodTargetExample proxy =

(NameMethodTargetExample)pf.getProxy(); proxy.printName(); proxy.printAction(); proxy.printSpot(); } }

Joinpoint A joinpoint is a well-defined point during

the execution of your application. Typical examples of joinpoints include a method call, method execution, class initialization, and object instantiation. Joinpoints are a core concept of AOP and define the points in your application at which you can insert additional logic using AOP.

Spring AOP only supports one joinpoint type—method invocation.

Advice An advice specifies what must be done at

a joinpoint. Spring uses a chain of interceptors to

wrap the invocation of the method and apply to it the advices contained into this chain. As said before, Spring is consistent with the specifications of the AOP Alliance, but provides a slightly different programming model

Advice

Advice Before Advice After Returning Advice After throwing Advice

Advisor The advisor isn't a concept from AOP in

general, but is specific to Spring AOP. The advisor links together pointcuts and

advice.So it contains both the action to be

executed (defined in the advice) and the point where it is to be executed (defined in the pointcut). The advisor's role is to decouple pointcuts and advice, in order to reuse them independently from each other.

Introduction Introductions are a very strong component of

the Spring AOP. They permit us to dynamically introduce new one-object functionalities as the implementation of interfaces on existing objects:

To create a mixin, adding to the state held in the object. This is probably the most important use.

To expose additional states associated with a special TargetSource. This is used within Spring, for example, with scripting support.

To expose an object or object graph in a different way—for example, making an object graph implement the XML DOM interfaces.

a normal advice can be applied to any object since it has a per-class lifecycle,

an introduction has a per-instance lifecycle.

ProxyFactoryBeanThis allows us to focus our attention and development

on crosscutting concerns to apply through the proxy, rather than focus on the proxy.

setTarget: Specify the target object you want to proxy.setProxyTargetClass: The default behavior is the

following: If an interface is available, it's used as a JDK proxy. If an interface is not available, it's used as a CGLIB

proxy. If we set the value to true, it's used as a CGLIB

proxy.

参考 http://www.cnblogs.com/leoo2sk/archive/

2010/11/30/aop-postsharp.html