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《AspectJ Cookbook》讀書筆記十五: 定義方面的關(guān)系

一.繼承切入點(diǎn)定義
創(chuàng)建一個(gè)抽象類。使用合適的public、protected或default訪問修飾符在抽象方面內(nèi)定義可重用的切入點(diǎn)邏輯。最后，把抽象方面繼承進(jìn)子方面中，以重用聲明的切入點(diǎn)。

package com.aspectj;

public abstract aspect BasePointcutDefinitionsAspect {

public pointcut callPointcut() : call(void MyClass.foo(int,String));

}

package com.aspectj;

public aspect ReusePointcutsRecipe extends BasePointcutDefinitionsAspect {

//Advice declaration

before():callPointcut()&&!within(ReusePointcutsRecipe+) {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice attached to the call point cut");

System.out.println("Target: " + thisJoinPoint.getTarget());

System.out.println("This: " + thisJoinPoint.getThis());

System.out.println("-----------------------------------------");

}

二.實(shí)現(xiàn)抽象切入點(diǎn)
在聲明切入點(diǎn)和周圍的方面時(shí)，使用abstract關(guān)鍵字，并且不要提供任何切入點(diǎn)邏輯。

package com.aspectj;

public abstract aspect BaseAbstractAspect {

/**

* Specifies an abstract pointcut placeholder

* for derived aspects to specify

*/

public abstract pointcut abstractBasepointcut();

/**

* Specifies calling advice whenever a join point

* picked by the abstractBasePointcut (specified

* by specialized aspects) is encountered, and not within

* this aspect or any inheriting aspects.

*/

pointcut runAdvicePointcut() : abstractBasepointcut() && !within(BaseAbstractAspect+);

}

package com.aspectj;

public aspect AbstractImplementationAspect extends BaseAbstractAspect {

/**

* Specifies calling advice whenever a method

* matching the following rules gets called:

*

* Class Name: MyClass

* Method Name:foo

* Method Return:void

* Method Parameters:an int followed by a string

*/

public pointcut abstractBasepointcut():call(void MyClass.foo(int,String));

//Advice declaration

before():runAdvicePointcut(){

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());

System.out.println("Source Location: " + thisJoinPoint.getStaticPart().getSourceLocation());

System.out.println("-----------------------------------------");

}

三.把類繼承進(jìn)方面中
使用extends關(guān)鍵字來(lái)聲明方面擴(kuò)展類。示例為一個(gè)偽日志記錄類，它代表一種現(xiàn)有的日志記錄機(jī)制。其目標(biāo)是：重構(gòu)對(duì)應(yīng)用程序中日志記錄類的所有現(xiàn)有的調(diào)用，并把日志記錄模塊化進(jìn)一個(gè)方面中，它可以更靈活地織入進(jìn)應(yīng)用程序中。

package com.aspectj;

public class OOLogging {

public void logEntry(String entry) {

System.out.println("Entry logged: " + entry);

}

package com.aspectj;

public aspect AOLogging extends OOLogging{

/**

* Specifies calling advice whenever a method

* matching the following rules gets called:

*

* Class Name: MyClass

* Method Name:foo

* Method Return:void

* Method Parameters:an int followed by a string

*/

pointcut callPointcut() : call(void MyClass.foo(int,String));

//Advice declaration

before():callPointcut()&&!within(AOLogging+)&&!within(AOLogging) {

this.logEntry(thisJoinPoint.toShortString());

}

posted @ 2008-08-26 15:34 Brian 閱讀(286) | 評(píng)論 (0) | 編輯收藏

《AspectJ Cookbook》讀書筆記十四: 定義方面實(shí)例化

一. 定義單件(singleton)方面
通過把issingleton()語(yǔ)句顯示添加到方面聲明中，來(lái)顯示建立單件方面實(shí)例化策略。

package com.aspectj;

public aspect Singleton issingleton() {

/**

* Specifies calling advice whenever a method

* matching the following rules gets called:

*

* Class Name: MyClass

* Method Name:foo

* Method Return Type:void

* Method Parameters:an int followed by a String

*/

pointcut callPointCut() : call(void MyClass.foo(int,String));

//Advice declartion

before():callPointCut() && !within(Singleton+) {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice attached to the call point cut");

System.out.println("Target: " + thisJoinPoint.getTarget());

System.out.println("This: " + thisJoinPoint.getThis());

System.out.println("Aspect Instance: " + Singleton.aspectOf());

System.out.println("-----------------------------------------");

}

傳統(tǒng)的面向?qū)ο髥渭闹饕秉c(diǎn)是：使用單件的每個(gè)類都與單件的公共接口緊密耦合。而面向方面的單件沒有這個(gè)缺點(diǎn)。

二.在每個(gè)實(shí)例上定義一個(gè)方面
AspectJ提供了perthis(Pointcut)和pertarget(Pointcut)方面實(shí)例化策略，他們依據(jù)Pointcut定義選擇的類，來(lái)聲明應(yīng)該為每個(gè)新的對(duì)象實(shí)例所實(shí)例化的方面。
perthis(Pointcut)聲明和pertarget(Poinitcut)聲明之間的區(qū)別必須涉及：在到達(dá)通知的連接點(diǎn)時(shí)，將會(huì)檢查什么對(duì)象。perthis(Pointcut)聲明指定：將為通知觸發(fā)連接點(diǎn)處的this說引用的每個(gè)新對(duì)象而實(shí)例化一個(gè)新的方面。pertarget(Pointcut)實(shí)例化策略指定：如果新對(duì)象是通知觸發(fā)連接點(diǎn)的目標(biāo)，則為每個(gè)這樣的新對(duì)象實(shí)例化一個(gè)新的方面。

package com.aspectj;

public aspect PerThis perthis(callPointCut()) {

/**

* Specifies calling advice whenever a method matching the following rules

* gets called:

*

* Class Name: MyClass Method Name:foo Method Return Type:void Method

* Parameters:an int followed by a String

*/

pointcut callPointCut() : call(void MyClass.foo(int,String));

// Advice declaration

before():callPointCut()&&!within(PerThis+){

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice attached to the call point cut");

System.out.println("Target: " + thisJoinPoint.getTarget());

System.out.println("This: " + thisJoinPoint.getThis());

System.out.println("Aspect Instance: " + PerThis.aspectOf(thisJoinPoint.getThis()));

System.out.println("-----------------------------------------");

}

在考慮可以通過單個(gè)方面通知多個(gè)類時(shí)，perthis(Pointcut)和pertarget(Pointcut)方面實(shí)例化策略聲明上的Pointcut參數(shù)提供了一些有趣的問題。以下示例中perthis(Pointcut)方面實(shí)例化策略只與executeMyClass()切入點(diǎn)指定的MyClass類的對(duì)象相關(guān)。

package com.aspectj;

public aspect AdviseMultipleClasses perthis(executeMyClassFoo()){

public pointcut executeMyClassFoo() : execution(void MyClass.foo());

public pointcut executeAnotherClassFoo() : execution(void AnotherClass.foo());

before():executeMyClassFoo() {

System.out.println("Advising foo");

System.out.println("Aspect is: " + this);

}

before():executeAnotherClassFoo() {

System.out.println("Advising foo");

System.out.println("Aspect is: " + this);

}

聲明只為executeMyClassFoo()切入點(diǎn)指定的每個(gè)新對(duì)象實(shí)例化AdviseMultipleClasses方面，這隱式排除了其他類的對(duì)象。即使聲明了executeAnotherClassFoo()切入點(diǎn)，并且他具有相應(yīng)的通知，也不會(huì)導(dǎo)致把任何方面應(yīng)用于除了它與executeMyClassFoo()共享的那些類之外的任何類。在示例中，兩個(gè)切入點(diǎn)之間沒有共享任何公共類，因此,executeMyClassFoo()切入點(diǎn)及關(guān)聯(lián)的通知會(huì)被忽略，因?yàn)檫@個(gè)切入點(diǎn)參與了perthis(Pointcut)實(shí)例化策略的定義。

一個(gè)方面不能具有針對(duì)兩類不同對(duì)象的兩種實(shí)例化策。為了確保方面的實(shí)例化策略與它通知的類的素有對(duì)象相關(guān)，一種有用的技術(shù)是：純粹為了使用方面的實(shí)例化策略，聲明一個(gè)切入點(diǎn)來(lái)結(jié)合方面中的所有其他的切入點(diǎn)聲明，如:

package com.aspectj;

public aspect AdviseMultipleClasses perthis(executeMyClassFoo()){

public pointcut executeMyClassFoo() : execution(void MyClass.foo());

public pointcut executeAnotherClassFoo() : execution(void AnotherClass.foo());

public pointcut applyLifecyclePolicy() : executeMyClassFoo()||executeAnotherClassFoo();

before():executeMyClassFoo() {

System.out.println("Advising foo");

System.out.println("Aspect is: " + this);

}

before():executeAnotherClassFoo() {

System.out.println("Advising foo");

System.out.println("Aspect is: " + this);

}

三.在每個(gè)控制流程上定義一個(gè)方面
使用percflow(Pointcut)方面實(shí)例化聲明。percflow(Pointcut)語(yǔ)句指示編譯器，它應(yīng)該為從Pointcut參數(shù)指定的連接點(diǎn)集合內(nèi)進(jìn)入的每個(gè)新控制流程創(chuàng)建方面的一個(gè)新實(shí)例。

package com.aspectj;

public aspect PerControlFlow percflow(callPointCut()){

/**

* Specifies calling advice whenever a method matching the following rules

* gets called:

*

* Class Name: MyClass Method Name:foo Method Return Type:void Method

* Parameters:an int followed by a String

*/

pointcut callPointCut() : call(void MyClass.foo(int,String));

// Advice declaration

before():callPointCut()&&!within(PerControlFlow+){

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice attached to the call point cut");

System.out.println("Target: " + thisJoinPoint.getTarget());

System.out.println("This: " + thisJoinPoint.getThis());

System.out.println("Aspect Instance: " + PerControlFlow.aspectOf());

System.out.println("-----------------------------------------");

}

percflow(Pointcut)語(yǔ)句代表最細(xì)粒度的方面實(shí)例化策略，并且會(huì)為特定的代碼段創(chuàng)建最大蘇聯(lián)高的不同方面實(shí)例。

posted @ 2008-08-26 14:37 Brian 閱讀(463) | 評(píng)論 (0) | 編輯收藏

《AspectJ Cookbook》讀書筆記十三: 定義通知

摘要: 一.訪問類成員 package com.aspectj; public privileged aspect MemberAccessRecipe { /** *//** * Specifies&nb... 閱讀全文

posted @ 2008-08-26 13:45 Brian 閱讀(1562) | 評(píng)論 (1) | 編輯收藏

《AspectJ Cookbook》讀書筆記十二: 捕獲基于布爾或復(fù)合表達(dá)式的連接點(diǎn)

摘要: 一.捕獲何時(shí)連接點(diǎn)上的運(yùn)行時(shí)條件評(píng)估為true 使用if(Expression)語(yǔ)句來(lái)評(píng)估包含要比較的運(yùn)行時(shí)變量的布爾表達(dá)式。if(Expression)語(yǔ)句的語(yǔ)法如下： pointcut <pointcut name>(<any values to be picked up>... 閱讀全文

posted @ 2008-08-25 20:40 Brian 閱讀(420) | 評(píng)論 (0) | 編輯收藏

《AspectJ Cookbook》讀書筆記十一: 捕獲基于對(duì)象的連接點(diǎn)

摘要: this([Type | Identifier])研究的是在捕捉的連接點(diǎn)處由this引用的對(duì)象的類型。連接點(diǎn)的目標(biāo)(通過target([Type | Identifier])切入點(diǎn)指定)依賴于連接點(diǎn)類型而有所不同，但它常常是在其上調(diào)用方法的對(duì)象，或者是以某種方式訪問的在其中遇到連接點(diǎn)的屬性。... 閱讀全文

posted @ 2008-08-25 15:11 Brian 閱讀(293) | 評(píng)論 (0) | 編輯收藏

《AspectJ Cookbook》讀書筆記十: 捕獲基于控制流程的連接點(diǎn)

    本章中描述的切入點(diǎn)支持捕獲另一個(gè)初始連接點(diǎn)作用域或環(huán)境內(nèi)的所有連接點(diǎn)。每個(gè)連接點(diǎn)在程序的控制流程中都有一個(gè)具體位置，這為通過這里描述的切入點(diǎn)聲明捕獲的連接點(diǎn)提供了環(huán)境。
    一. 捕獲通過初始連接點(diǎn)開始的程序控制流程內(nèi)的所有連接點(diǎn)
    使用cflow(Pointcut)切入點(diǎn)。cflow(Pointcut)切入點(diǎn)的語(yǔ)法如下：
    pointcut <pointcut name>(<any values to be picked up>) : cflow(<pointcut>);

    cflow(Pointcut)切入點(diǎn)具有3個(gè)關(guān)鍵特征:
        1.cflow(Pointcut)切入點(diǎn)捕獲在初始特定的連接點(diǎn)環(huán)境內(nèi)遇到的所有連接點(diǎn)，這個(gè)初始連接點(diǎn)是通過另一個(gè)切入點(diǎn)選擇的。
        2.捕獲的連接點(diǎn)包括初始連接點(diǎn)。
        3.作用域是cflow(pointcut)切入點(diǎn)中重要的鑒別器。這個(gè)切入點(diǎn)將捕獲通過切入點(diǎn)參數(shù)捕獲的連接點(diǎn)的控制流程內(nèi)的所有連接點(diǎn)。

package com.aspectj;

public aspect CFlowRecipe {

/**

* Specifies calling advice whenever a method

* matching the following rules gets called:

*

* Class Name:MyClass

* Method Name:foo

* Method Return Type:void

* Method Parameters: an int followed by a String

*/

pointcut callInitialPointcut():call(void MyClass.foo(int,String));

/**

* Specifies calling advice whenever a join point is encountered

* including and after the initial join point triggers the pointcut

* that is specified in the parameter:

*

* Pointcut Name:callInitialPointcut

*/

pointcut cflowPointcut():cflow(callInitialPointcut());

//Advice declaration

before() : cflowPointcut() && !within(CFlowRecipe+) {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by CFlowRecipe()");

System.out.println("Join Point Kind: " + thisJoinPoint.getKind());

System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());

System.out.println("Source Line: " + thisJoinPoint.getStaticPart().getSourceLocation());

System.out.println("-----------------------------------------");

}

值得更詳細(xì)研究cflow(Pointcut)做什么。這個(gè)特殊的切入點(diǎn)引入了連接點(diǎn)環(huán)境的概念。它是指每個(gè)連接點(diǎn)具有一個(gè)作用域，在這個(gè)用途域內(nèi)，它被看成是執(zhí)行程序的控制流程的一部分。
在這個(gè)控制流程內(nèi)，任何遇到的連接點(diǎn)都會(huì)觸發(fā)cflow(Pointcut)切入點(diǎn)，并調(diào)用任何關(guān)聯(lián)的通知。當(dāng)初始連接點(diǎn)觸發(fā)指定的切入點(diǎn)參數(shù)時(shí)，cflow(Pointcut)切入點(diǎn)會(huì)起作用，并觸發(fā)其關(guān)聯(lián)的通知。然后，將為在初始連接點(diǎn)環(huán)境內(nèi)的控制流程中遇到的每個(gè)連接點(diǎn)調(diào)用與cflow(Pointcut)關(guān)聯(lián)的通知。最后，捕獲的連接點(diǎn)集合包括初始連接點(diǎn)本身，這就是這個(gè)切入點(diǎn)與cflowbelow(Pointcut)切入點(diǎn)之間的主要區(qū)別。

在cflow(Pointcut)的當(dāng)前實(shí)現(xiàn)中，在使用它時(shí)，其實(shí)現(xiàn)方式會(huì)引入大量的系統(tǒng)開銷。在可能的地方，并且連接點(diǎn)重用不受影響時(shí)，可以考慮優(yōu)先使用withincode(Signature)切入點(diǎn)。

    二.捕獲程序控制流程內(nèi)的所有連接點(diǎn)，不包括初始連接點(diǎn)
    使用cflowbelow(Pointcut)切入點(diǎn)。cflowbelow(Pointcut)切入點(diǎn)的語(yǔ)法如下：
    pointcut <pointcut name>(<any values to be picked up>) : cflowbelow(<pointcut>);

package com.aspectj;

public aspect CFlowBelowRecipe {

/**

* Specifies calling advice whenever a method

* matching the following rules gets called:

*

* Class Name:MyClass

* Method Name:foo

* Method Return Type:void

* Method Parameters: an int followed by a String

*/

pointcut callInitialPointcut():call(void MyClass.foo(int,String));

/**

* Specifies calling advice whenever a join point is encountered

* after the initial join point triggers the pointcut

* that is specified in the parameter:

*

* Pointcut Name:callInitialPointcut

*/

pointcut cflowPointcut():cflowbelow(callInitialPointcut());

//Advice declaration

before() : cflowPointcut() && !within(CFlowBelowRecipe+) {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by CFlowBelowRecipe()");

System.out.println("Join Point Kind: " + thisJoinPoint.getKind());

System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());

System.out.println("Source Line: " + thisJoinPoint.getStaticPart().getSourceLocation());

System.out.println("-----------------------------------------");

}

這里和第一部分介紹的內(nèi)容有點(diǎn)區(qū)別；其區(qū)別是實(shí)際捕獲的連接點(diǎn)數(shù)量。cflow(Pointcut)切入點(diǎn)會(huì)觸發(fā)在初始連接點(diǎn)環(huán)境內(nèi)遇到的所有連接點(diǎn)(包括初始連接點(diǎn))上的通知，而cflowbelow(Pointcut)切入點(diǎn)則不包括那個(gè)初始連接點(diǎn)。

posted @ 2008-08-25 10:36 Brian 閱讀(427) | 評(píng)論 (0) | 編輯收藏

《AspectJ Cookbook》讀書筆記九: 捕獲程序作用域內(nèi)的連接點(diǎn)

    切入點(diǎn)定義設(shè)計(jì)中的常用方式是：基于關(guān)注的程序作用域，限制捕獲連接點(diǎn)的范圍。這可以讓你即使控制在進(jìn)一步的切入點(diǎn)定義中將會(huì)涉及哪些連接點(diǎn)。
    本章中的切入點(diǎn)相當(dāng)容易理解，并且他們是AspectJ中一些常用的元素。例如，廣泛使用的within(TypePattern)切入點(diǎn)將以!within(%THIS_ASPECT%)形式使用它。這個(gè)AspectJ術(shù)語(yǔ)限制了當(dāng)前方面之外的每個(gè)連接點(diǎn)的作用域，從而可以防止通知觸發(fā)對(duì)相同通知塊的遞歸調(diào)用，并導(dǎo)致一個(gè)無(wú)限循環(huán)。
    一. 捕獲特定類中的所有連接點(diǎn)
    使用within(TypePattern)切入點(diǎn)，利用TypePattern指定特定類類型模式，within(TypePattern)切入點(diǎn)的語(yǔ)法如下：
    pointcut <pointcut name>(<any values to be picked up>) : within(<class>);

    within(TypePattern)切入點(diǎn)具有3個(gè)關(guān)鍵特征：
        1.within(TypePattern)切入點(diǎn)捕獲指定類作用域中的所有連接點(diǎn)。
        2.within(TypePattern)切入點(diǎn)極少孤立使用。相反，它通常與切入點(diǎn)結(jié)合使用，用于減少將觸發(fā)附帶通知的連接點(diǎn)。
        3.TypePattern可以包含通配符，用于選擇不同類上的一系列連接點(diǎn)。

package com.aspectj;

public aspect WithinClassRecipe {

/**

* Specifies calling advice on any join point encountered within

* the defined scope:

*

* Scope:MyClass

*/

pointcut withinMyClass() : within(MyClass);

//Advice declaration

before() : withinMyClass() && !within(WithinClassRecipe+) {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by withinMyClass()");

System.out.println("Join Point Kind: " + thisJoinPoint.getKind());

System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());

System.out.println("Source Line: " + thisJoinPoint.getStaticPart().getSourceLocation());

System.out.println("-----------------------------------------");

}

二. 捕獲特定包中的所有連接點(diǎn)
within(TypePattern)切入點(diǎn)提供一種有用的手段，它使用通配符在出現(xiàn)在每個(gè)類中的連接點(diǎn)中指定一個(gè)關(guān)注?？梢栽赥ypePattern中使用合適的通配符，從切入點(diǎn)邏輯的余下部分中包含或排除連接點(diǎn)的整個(gè)包。

package com.aspectj;

public aspect WithinPackageRecipe {

/**

* Specifies calling advice on any join point encountered within

* the defined scope:

*

* Scope:packageA

*/

pointcut withinPackageA() : within(packageA.*);

//Advice declaration

before() : withinPackageA() && !within(WithinPackageRecipe+) {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by WitinPackageRecipe()");

System.out.println("Join Point Kind: " + thisJoinPoint.getKind());

System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());

System.out.println("Source Line: " + thisJoinPoint.getStaticPart().getSourceLocation());

System.out.println("-----------------------------------------");

}

三. 捕獲特定方法內(nèi)的所有連接點(diǎn)
使用withincode(Signature)切入點(diǎn)。withincode(Signature)切入點(diǎn)的語(yǔ)法如下：
pointcut <pointcut name>(<any values to be picked up>) : withincode(<modifier> <class>.<method>(<paramter types>));

    withincode(Signature)切入點(diǎn)有3個(gè)關(guān)鍵特征：
        1. withincode(Signature)切入點(diǎn)指定了特定方法的本地作用域內(nèi)的所有連接點(diǎn)。
        2. withincode(Signature)切入點(diǎn)極少孤立使用。相反，他通常與其他切入點(diǎn)結(jié)合使用，用于減少將觸發(fā)附帶通知的連接點(diǎn)。
        3. Signaure可以包含通配符，用于選擇不同類的不同方法上的一系列連接點(diǎn)。

package com.aspectj;

public aspect WithinMethodRecipe {

/**

* Specifies calling advice whenever a method

* matching the following rules gets called:

*

* Class Name：MyClass

* Method Name:foo

* Method Return Type: * (any return type)

* Method Parameters: an int followed by a String

*/

pointcut withinFooIntStringAnyReturnPointcut() : withincode(* MyClass.foo(int,String));

//Advice declaration

before() : withinFooIntStringAnyReturnPointcut() && !within(WithinMethodRecipe+) {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by withinMyClass()");

System.out.println("Join Point Kind: " + thisJoinPoint.getKind());

System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());

System.out.println("Source Line: " + thisJoinPoint.getStaticPart().getSourceLocation());

System.out.println("-----------------------------------------");

}

posted @ 2008-08-25 10:32 Brian 閱讀(340) | 評(píng)論 (0) | 編輯收藏

《AspectJ Cookbook》讀書筆記八: 捕獲屬性上的連接點(diǎn)

一. 捕獲何時(shí)訪問對(duì)象的屬性
    使用get(Signature)切入點(diǎn)。get(Signature)切入點(diǎn)的語(yǔ)法如下：
    pointcut <pointcut name>(<any values to be picked up>) : get(<optional modifier> <type> <class>.<field>);
    get(Signature)具有4個(gè)關(guān)鍵特征：
    1.get(Signature)切入點(diǎn)會(huì)觸發(fā)直接在其中(而不僅僅是在訪問器方法的調(diào)用上)訪問屬性的通知。
    2.get(Signature)切入點(diǎn)不能捕獲對(duì)靜態(tài)屬性的訪問，盡管從AspectJ的語(yǔ)法角度講以這種方式定義切入點(diǎn)是完全合法的。
    3.Signature必須解析成特定類的屬性。
    4.Signature可以包含通配符，用于選擇不同屬性上的一系列連接點(diǎn)。

package com.aspectj;

public aspect GetRecipe {

/**

* Specifies calling advice whenever an attribute matching the following rules

* is accessed:

*

* Type:String

* Class Name:MyClass

* Attribute Name:name

*/

pointcut getNamePointcut(): get(String MyClass.name);

// Advice declaration

before():getNamePointcut() {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by getNamePointcut()");

System.out.println("Signature: " + thisJoinPoint.getSignature());

System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());

System.out.println("-----------------------------------------");

}

你可能期待類使用static和final關(guān)鍵字定義一個(gè)常量屬性，這樣，在訪問這個(gè)常量時(shí)你就可能使用get(Signature)切入點(diǎn)來(lái)捕獲。

package com.aspectj;

public aspect GetConstant {

/**

* Specifies calling advice whenever an attribute matching the following rules

* is accessed:

*

* Type:String

* Class Name:MyClass

* Attribute Name:CONSTANT

*/

pointcut getConstantPointcut():get(public static final String MyClass.CONSTANT);

//Advice declaration

before():getConstantPointcut() {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by getConstantPointcut()");

System.out.println("Signature: " + thisJoinPoint.getSignature());

System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());

System.out.println("-----------------------------------------");

}

二. 捕獲訪問的字段值
使用after returning(<ReturnValue>)形式的通知。它在聲明的returning()部分中帶有一個(gè)標(biāo)識(shí)符，用于包含訪問過的值。

package com.aspectj;

public aspect CaptureAccessedFieldValue {

pointcut getNamePointcut() : get(String MyClass.name);

//Advice declaration

after() returning(String value) : getNamePointcut() {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by getNamePointcut()");

System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());

System.out.println("Source Line: " + thisJoinPoint.getStaticPart().getSourceLocation());

System.out.println("-----------------------------------------");

}

三. 捕獲何時(shí)修改對(duì)象的字段
    使用set(Signature)切入點(diǎn)。set(Signature)切入點(diǎn)的語(yǔ)法如下：
    pointcut <pointcut name>(<any values to be picked up>) : set(<optional modifier> <type> <class>.<field>);

    set(Signature)具有4個(gè)關(guān)鍵特征：
    1.set(Signature)切入點(diǎn)在修改字段時(shí)觸發(fā)。
    2.set(Signature)切入點(diǎn)不能捕獲對(duì)靜態(tài)字段的修改，盡管從AspectJ的語(yǔ)法角度講以這種方式定義切入點(diǎn)是完全合法的。
    3.Signature必須解析成特定類的屬性。
    4.Signature可以包含通配符，用于選擇不同屬性上的一系列連接點(diǎn)。

package com.aspectj;

public aspect SetRecipe {

/*

* Specifies calling advice whenever an attribute

* matching the following rules is modified:

*

* Type: String

* Class Name: MyClass

* Attribute: name

*/

pointcut setNamePointcut() :set(String MyClass.name);

//Advice declaration

before():setNamePointcut() && !within(SetRecipe+) {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by setNamePointcut()");

System.out.println("Signature: " + thisJoinPoint.getSignature());

System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());

System.out.println("-----------------------------------------");

}

四. 在修改字段時(shí)捕獲它的值
結(jié)合使用args([Types | Identifiers])切入點(diǎn)和set(Signature)切入點(diǎn)，展示字段的新值，該字段被設(shè)置成切入點(diǎn)上的標(biāo)識(shí)符，可將其傳遞給相應(yīng)的通知。

package com.aspectj;

public aspect CaptureModifiedFieldValue {

pointcut setNamePointcut(String newValue):set(String MyClass.name) && args(newValue);

//Advice declaration

before(String newValue) : setNamePointcut(newValue) {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by setNamePointcut()");

System.out.println("Signature: " + thisJoinPoint.getSignature());

System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());

System.out.println("-----------------------------------------");

}

posted @ 2008-08-22 10:43 Brian 閱讀(1186) | 評(píng)論 (0) | 編輯收藏

《AspectJ Cookbook》讀書筆記七: 捕獲類和對(duì)象構(gòu)造上的連接點(diǎn)

一. 捕獲對(duì)構(gòu)造函數(shù)的調(diào)用
使用Call(Signature)寫入點(diǎn)，它帶有額外的new關(guān)鍵字作為簽名的一部分。使用與構(gòu)造函數(shù)有關(guān)的call(Signature)切入點(diǎn)的語(yǔ)法如下：
pointcut <pointcut name>(<any values to be picked up>): call(<optional modifier> <class>.new(<parameter types>));

    在用于捕獲對(duì)構(gòu)造函數(shù)的調(diào)用時(shí)，call(Signature)切入點(diǎn)具有3個(gè)關(guān)鍵特征：
    1.在把一個(gè)類實(shí)例化成一個(gè)對(duì)象時(shí)，具有new關(guān)鍵字的call(Signature)切入點(diǎn)會(huì)捕獲連接點(diǎn)。
    2.通過使用around()形式的通知，call(Signature)寫入點(diǎn)可以在Java的正常繼承規(guī)則的限制下重寫返回對(duì)象的類型。
    3.編譯器不會(huì)檢查指定的Signature是否對(duì)應(yīng)于實(shí)際的構(gòu)造函數(shù)。

package com.aspectj;

public aspect CallNewRecipe {

/*

* Specifies calling advice when any constructor is called

* that meets the following signature rules:

*

* Class Name:MyClass

* Method Name:new (This is a keyword indicating the constructor call)

* Method Parameters: int , String

*/

pointcut myClassConstructorWithIntAndStringPointcut() : call(MyClass.new(int , String));

//Advice declaration

before() : myClassConstructorWithIntAndStringPointcut() {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by myClassConstructorWithIntAndOthersPointcut()");

System.out.println("The current type of object under construction is:");

System.out.println(thisJoinPoint.getThis());

System.out.println("Signature: " + thisJoinPoint.getSignature());

System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());

System.out.println("-----------------------------------------");

}

二. 在執(zhí)行構(gòu)造函數(shù)時(shí)捕獲它
使用execution(Signature)切入點(diǎn)，它帶有額外的new關(guān)鍵字作為簽名的一部分。使用與構(gòu)造函數(shù)有關(guān)的execution(Signature)切入點(diǎn)的語(yǔ)法如下：
pointcut <pointcut name>(<any values to be picked up>):execution(<optional modifier> <class>.new<parameter types>));

    在用于捕獲構(gòu)造函數(shù)的執(zhí)行時(shí)，execution(Signature)切入點(diǎn)具有3個(gè)關(guān)鍵特征：
    1.在執(zhí)行類的構(gòu)造函數(shù)時(shí)，具有new關(guān)鍵字的execution(Signature)切入點(diǎn)會(huì)觸發(fā)連接點(diǎn)。
    2.不能在調(diào)用類的構(gòu)造函數(shù)之前那一刻觸發(fā)連接點(diǎn)。這會(huì)阻止重寫返回的對(duì)象。
    3.可以使用around()通知來(lái)重寫構(gòu)造函數(shù)方法的實(shí)現(xiàn)，當(dāng)不能重寫正在構(gòu)造的對(duì)象的類型。

package com.aspectj;

public aspect ExecutionNewRecipe {

/*

* Specifies calling advice when any constructor executes

* that meets the following signature rules:

*

* Class Name:MyClass

* Method Name:new (This is a keyword indicating the constructor call)

* Method Parameters: int , String

*/

pointcut myClassConstructorWithIntAndStringPointcut() : execution(MyClass.new(int,String));

//Advice declaration

before() : myClassConstructorWithIntAndStringPointcut() {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by myClassConstructorWithIntAndOthersPointcut()");

System.out.println("The current type of object under construction is:");

System.out.println(thisJoinPoint.getThis().getClass());

System.out.println("Signature: " + thisJoinPoint.getSignature());

System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());

System.out.println("-----------------------------------------");

}

三. 捕獲何時(shí)初始化對(duì)象
使用initialization(Signature)切入點(diǎn)。initialization(Signature)切入點(diǎn)的語(yǔ)法如下：
pointcut <pointcut name>(<any values to be picked up>):initialization(<optional modifier> <class>.new<parameter types>));

    initialization(Signature)切入點(diǎn)具有5個(gè)關(guān)鍵特征：
    1.initialization(Signature)切入點(diǎn)必須包含new關(guān)鍵字。
    2.initialization(Signature)切入點(diǎn)捕獲連接點(diǎn)發(fā)生在任何超類的初始化之后，以及從構(gòu)造函數(shù)方法返回之前。
    3.Signature必須解析成特定類的構(gòu)造函數(shù)，而不是一個(gè)簡(jiǎn)單的方法。
    4.initialization(Signature)切入點(diǎn)提供了編譯時(shí)的檢查，用于檢查構(gòu)造函數(shù)是否正在被引用。
    5.由于AspectJ編譯器中的編譯器限制，當(dāng)與around()通知關(guān)聯(lián)時(shí)，不能使用initialization(Signature)切入點(diǎn)。

package com.aspectj;

public aspect InitializationRecipe {

/*

* Specifies calling advice when any object

* initializes using a constructor

* that meets the following signature rules:

*

* Class Name:MyClass

* Method Name:new (This is a keyword indicating the constructor call)

* Method Parameters: int and any others

*/

pointcut myClassObjectInitializationWithIntAndStringPointcut() : execution(MyClass.new(int,*));

//Advice declaration

before() : myClassObjectInitializationWithIntAndStringPointcut() {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by myClassObjectInitializationWithIntAndStringPointcut()");

System.out.println("The current type of object under construction is:");

System.out.println(thisJoinPoint.getThis().getClass());

System.out.println("Signature: " + thisJoinPoint.getSignature());

System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());

System.out.println("-----------------------------------------");

}

四. 捕獲何時(shí)將要初始化一個(gè)對(duì)象
    使用preinitialization(Signature)切入點(diǎn)。preinitialization(Signature)切入點(diǎn)的語(yǔ)法如下：
    pointcut <pointcut name>(<any values to be picked up>):preinitialization(<optional modifier> <class>.new<parameter types>));

    preinitialization(Signature)切入點(diǎn)具有5個(gè)關(guān)鍵特征：
    1.preinitialization(Signature)切入點(diǎn)必須包含new關(guān)鍵字。
    2.preinitialization(Signature)切入點(diǎn)捕獲連接點(diǎn)發(fā)生在進(jìn)入捕獲構(gòu)造函數(shù)之后，以及調(diào)用任何超類構(gòu)造函數(shù)之前。
    3.Signature必須解析成一個(gè)構(gòu)造函數(shù)。
    4.preinitialization(Signature)切入點(diǎn)提供了編譯時(shí)的檢查，用于檢查構(gòu)造函數(shù)是否正在被引用。
    5.由于AspectJ編譯器中的編譯器限制，當(dāng)與around()通知關(guān)聯(lián)時(shí)，不能使用preinitialization(Signature)切入點(diǎn)。

package com.aspectj;

public aspect PreInitializationRecipe {

/*

* Specifies calling advice just before an object initializes

* using a constructor that meets the following signature rules:

*

* Class Name:MyClass

* Method Name:new (This is a keyword indicating the constructor call)

* Method Parameters: an int followed by a String

*/

pointcut myClassIntStringObjectPreInitializationPointcut() : preinitialization(MyClass.new(int,String));

//Advice declaration

before(int number , String name) : myClassIntStringObjectPreInitializationPointcut() && args(number , name) {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by anyMyClassObjectInitializationPointcut()");

System.out.println("The current type of object under construction is:");

System.out.println(thisJoinPoint.getThis());

System.out.println("The values passed in where: " + number + " , " + name);

System.out.println("Signature: " + thisJoinPoint.getSignature());

System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());

System.out.println("-----------------------------------------");

}

五. 捕獲何時(shí)初始化類
使用staticinitialization(TypePattern)寫入點(diǎn)。staticinitialization(TypePattern)寫入點(diǎn)的語(yǔ)法如下：
pointcut <pointcout name>(<any values to be picked up>) : staticinitialization(<class>);

    staticinitialization(TypePattern)切入點(diǎn)具有兩個(gè)關(guān)鍵特征：
    1.對(duì)可供staticinitialization(TypePattern)切入點(diǎn)所選通知使用的環(huán)境有一些限制。沒有父對(duì)象觸發(fā)靜態(tài)初始化；因此，沒有this引用。也不涉及實(shí)例對(duì)象，因此，沒有目標(biāo)引用。
    2.TypePattern可以包含通配符，用于選擇一系列不同的類。

package com.aspectj;

public aspect StaticinitializationRecipe {

/*

* Specifies calling advice when a class is initialized

* that meets the following type pattern rules:

*

* Class Name:MyClass

*/

pointcut myClassStaticInitializationPointcut() : staticinitialization(MyClass);

//Advice declaration

before() : myClassStaticInitializationPointcut() {

System.out.println("---------- Aspect Advice Logic ----------");

System.out.println("In the advice picked by myClassStaticInitializationPointcut()");

System.out.println("Join Point Kind: ");

System.out.println(thisJoinPoint.getStaticPart().getKind());

System.out.println("Signature: " + thisJoinPoint.getSignature());

System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());

System.out.println("-----------------------------------------");

}

posted @ 2008-08-22 10:32 Brian 閱讀(1239) | 評(píng)論 (0) | 編輯收藏

《AspectJ Cookbook》讀書筆記五: 捕獲異常處理上的連接點(diǎn)

    在Java中拋出異常時(shí)，會(huì)將其向上傳遞給調(diào)用者，直到它被作為try/catch塊一部分的catch語(yǔ)句處理或者到達(dá)Java運(yùn)行庫(kù)并在控制臺(tái)引發(fā)一條混亂的消息。如果捕獲到異常，就應(yīng)該將異常作為一個(gè)對(duì)象傳遞給catch塊做合適的處理。同時(shí)，還有一種可能需要方面作為橫切行為做一部分事情，或者替代catch塊的正常行為。
一. 捕獲何時(shí)捕捉異常
    使用handler(TypePattern)切入點(diǎn)。其語(yǔ)法如下:
    pointcut <pointcut name>(<any values to be picked up>) : handler(<class>):

   handler(TypePattern)切入點(diǎn)具有5個(gè)關(guān)鍵特征：
   1. handler(TypePattern)在捕獲異常的作用域內(nèi)選擇連接點(diǎn)。
   2. handler(TypePattern)切入點(diǎn)的通知僅用于類型模式指定Throwable或其子類的地方。
   3. TypePattern聲明無(wú)論何時(shí)捕捉到異常或其子類的匹配模式，都會(huì)應(yīng)用相應(yīng)的通知。
   4. handler(TypePattern)切入點(diǎn)只支持before()形式的通知。這意味著不能使用像around()這樣的通知來(lái)重寫catch塊的正常行為。
   5. TypePattern可以包含通配符，用于選擇不同類上的一系列連接點(diǎn)。

帶有通配符的TypePattern 描述

mypackage..* 捕獲mypackage包及其子包中的連接點(diǎn)類

MyClass+ 捕獲MyClass類及其任何子類中的連接點(diǎn)

    下面的例子展示了捕獲任何類拋出MyException類異常：

package com.aspectj;

public aspect HandlerRecipe {

/**

* Specifies calling advice when any exception object

* is caught that matches the following rules for its

* type pattern;

*

* Type:MyException

*/

pointcut myExceptionHandlerPointcut() : handler(MyException);

//Advice declaration

before() : myExceptionHandlerPointcut() {

System.out.println("------------------- Aspect Advice Logic -------------------");

System.out.println("In the advice picked by " + "myExceptionHandlerPointcut()");

System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());

System.out.println("Source Line: " + thisJoinPoint.getStaticPart().getSourceLocation());

System.out.println("------------------------------------------");

}

二. 捕獲拋出的異常
結(jié)合使用args([Types | Identifiers])切入點(diǎn) 與handler(TypePattern)切入點(diǎn)，將捕獲的異常展示為切入點(diǎn)上的標(biāo)識(shí)符，可將其傳遞給相應(yīng)的通知。

package com.aspectj;

public aspect AccessThrownException {

pointcut myExceptionHandlerPointout(MyException exception) : handler(MyException) && args(exception);

//Advice declaration

before(MyException exception) : myExceptionHandlerPointout(exception) {

System.out.println("------------------- Aspect Advice Logic -------------------");

System.out.println("In the advice picked by " + "myExceptionHandlerPointcut()");

System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());

System.out.println("Source Line: " + thisJoinPoint.getStaticPart().getSourceLocation());

System.out.println("Exception caught:");

exception.printStackTrace();

System.out.println("------------------------------------------");

}

posted @ 2008-07-11 09:28 Brian 閱讀(1617) | 評(píng)論 (1) | 編輯收藏

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帶有通配符的TypePattern	描述
mypackage..*	捕獲mypackage包及其子包中的連接點(diǎn)類
MyClass+	捕獲MyClass類及其任何子類中的連接點(diǎn)