一.訪問類成員
package com.aspectj;
public privileged aspect MemberAccessRecipe 
{
/** *//**
* Specifies calling advice whenever a method
* matching the following rules gets executed:
*
* Class Name: MyClass
* Method Name:foo
* Method Return Type:void
* Method Parameters:an int followed by a String
*/
pointcut executionOfFooPointCut() : execution(void MyClass.foo(int,String));
//Advice declaration
after(MyClass myClass):executionOfFooPointCut() && this(myClass){
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Accessing the set(float) member of the MyClass object");
System.out.println("Privileged access not required for this method call as it is public");
myClass.setF(2.0f);
System.out.println("Using the privileged aspect access to the private f member variable");
System.out.println("The current value of f is: ");
System.out.println(myClass.f);
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
}
通過使用this(Identifier)切入點定義，使得MyClass類的對象可供通知使用。this(Identifier)切入點定義有效地把通知展示給被觸發(fā)連接點處的this引用指向的對象。從通知內(nèi)調(diào)用setF(float)方法，并顯示對MyClass對象的公共方法的訪問。為了獲得對MyClass.f私有屬性的訪問，方面不得不對其結(jié)構(gòu)執(zhí)行一些額外的更改。方面嘗試通過直接訪問私有成員來破快封裝性，因此，必須把方面聲明為privileged，因為它正在提交潛在的侵入動作。
AspectJ提供了privieged關(guān)鍵字，它用在方面需要完全不受限制地訪問類的地方，包括那些未在類的公共接口上聲明的成員變量和方法。方面的privileged狀態(tài)應(yīng)該充當(dāng)一個警告，在對方面或者它所應(yīng)用的類執(zhí)行任何更改時，必須當(dāng)心這個警告，因為這些更改可能潛在地在整個應(yīng)用程序中引發(fā)其他問題。
二.訪問連接點環(huán)境
AspectJ提供了thisJoinPoint變量，用于展示this連接點環(huán)境。如果可以靜態(tài)地訪問正在訪問的環(huán)境，那么thisJoinPointStaticPart也是有用的。
package com.aspectj;
public aspect ThisJoinPointRecipe {
/** *//**
* Specifies calling advice whenever a method
* matching the following rules gets executed:
*
* 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(ThisJoinPointRecipe+){
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Exercising the static parts of AspectJ 1.1.1 thisJoinPoint");
System.out.println("Source Line: " + thisJoinPointStaticPart.getSourceLocation());
System.out.println("JoinPoint Kind: " + thisJoinPointStaticPart.getKind());
System.out.println("Simple toString: " + thisJoinPointStaticPart.toString());
System.out.println("Simple toShortString: " + thisJoinPointStaticPart.toShortString());
System.out.println("Simple toLongString: " + thisJoinPointStaticPart.toLongString());
System.out.println("Exercising the join point generic signature of AspectJ 1.1.1 thisJoinPoint");
System.out.println("Signature name:" + thisJoinPointStaticPart.getSignature().getName());
System.out.println("Signature declaring type:" + thisJoinPointStaticPart.getSignature().getDeclaringType());
System.out.println("-----------------------------------------");
}
before():callPointCut()&&!within(ThisJoinPointRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Exercising the dynamic parts of AspectJ 1.1.1 thisJoinPoint");
System.out.println("Get the this reference: " + thisJoinPoint.getThis());
System.out.println("Getting the Target: " + thisJoinPoint.getTarget());
System.out.println("Join Point Arguments:");
Object[] args = thisJoinPoint.getArgs();
for (int count = 0; count < args.length ; count++) {
System.out.println(args[count]);
}
System.out.println("-----------------------------------------");
}
}
thisJoinPoint變量包含關(guān)于觸發(fā)連接點的靜態(tài)和動態(tài)環(huán)境信息。靜態(tài)環(huán)境信息包含可以在編譯和織入時決定的任何信息。動態(tài)連接點環(huán)境信息則只能在運行時填充，因為它依賴于連接點環(huán)境實際的運行時狀態(tài)。
三.在連接點之前執(zhí)行通知
使用before()類型的通知
package com.aspectj;
public aspect BeforeAdviceRecipe {
/** *//**
* Specifies calling advice whenever a method
* matching the following rules gets executed:
*
* 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(BeforeAdviceRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Source Location: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("-----------------------------------------");
}
}
四.在連接點周圍執(zhí)行通知
使用around()類型的通知。
package com.aspectj;
public aspect AroundAdviceRecipe {
/** *//**
* 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 callFooPointCut() : call(int MyClass.foo());
/** *//**
* Specifies calling advice whenever a method
* matching the following rules gets called:
*
* Class Name: MyClass
* Method Name:bar2
* Method Return Type:int
* Method Parameters:an int
*/
pointcut callBarPointCut(int value) : call(int MyClass.bar(int)) && args(value);
/** *//**
* Specifies calling advice whenever a method
* matching the following rules gets called:
*
* Class Name: MyClass
* Method Name:baz
* Method Return Type:int
* Method Parameters:
*/
pointcut callBazPointCut() : call(int MyClass.baz());
//Advice declaration
//This advice will be executed before the pointcut that picks it
int around() : callFooPointCut()&& !within(AroundAdviceRecipe+){
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Location: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("-----------------------------------------");
return proceed();
}
//Advice declaration
//This advice will be executed before the pointcut that picks it
int around(int value):callBarPointCut(value)&&!within(AroundAdviceRecipe+){
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Location: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("-----------------------------------------");
return proceed(value);
}
//Advice declaration
//This advice will be executed before the pointcut that picks it
int around(int value):callBarPointCut(value)&&!within(AroundAdviceRecipe+){
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Location: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("-----------------------------------------");
return proceed(value);
}
//Advice declaration
//This advice will be executed before the pointcut that picks it
int around() : callBazPointCut() && !within(AroundAdviceRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Location: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("-----------------------------------------");
return 200;
}
}
around()通知是一種強大的構(gòu)造，它指示AspectJ應(yīng)該運行通知，而不是指示連接點觸發(fā)它。這允許重寫應(yīng)用程序中存在的原始邏輯。這說明了around()通知，可以依據(jù)是否從around()通知塊內(nèi)發(fā)起proceed()調(diào)用，來被動或主動地應(yīng)用這個通知。
proceed()調(diào)用指示around()通知應(yīng)該繼續(xù)執(zhí)行原始連接點邏輯，并傳遞原來可用的任何值。
在示例中，第一份通知沒有參數(shù)需要傳遞；第二份通知傳遞了一個與原始值完全不同的值；第三份通知則完全返回了一個不同的值。
around()通知必須具有指定的返回值，但是如果不需要值，那么可以是void。
五.在連接點之后無條件執(zhí)行通知
使用after()類型的通知
package com.aspectj;
public aspect AfterAdviceRecipe {
/** *//**
* 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
after():callPointCut()&&!within(AfterAdviceRecipe+){
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Source Location: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("-----------------------------------------");
}
}
六.僅在從連接點正常返回之后才執(zhí)行通知
使用after() returning或after() returning(<ReturnType> <Identifier>)類型的通知
package com.aspectj;
public aspect AfterReturningAdviceRecipe {
/** *//**
* 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));
//Advice declaration
after() returning:callPointCut()&&!within(AfterReturningAdviceRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Source Location: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("-----------------------------------------");
}
}
package com.aspectj;
public aspect AfterReturningValueAdviceRecipe {
/** *//**
* 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));
//Advice declaration
after() returning(Object value):callPointCut()&&!within(AfterReturningAdviceRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Source Location: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("Value being returned: " + value);
System.out.println("-----------------------------------------");
}
}
使用after() returning(<ReturnType> <Identifier>)通知訪問基本類型的一個有趣作用是：必須把基本的int值裝箱進Integer類的一個實例中，以傳遞給通知。當(dāng)通知期待的返回類型是Object類型時，并且如果返回值是基本類型，AspectJ將自動并且透明地把基本值裝箱進其對應(yīng)的Java類中。around()形式的通知也可以使用這種自動和透明的裝箱行為，其中會期待Object類型的值，并且將從通知傳遞基本值或?qū)⒒局祩鬟f給通知。
與正常的ater()相比，after() returning形式的通知提供了更精細(xì)的過濾器。
七.僅當(dāng)連接點中引發(fā)了一個異常之后才執(zhí)行通知
使用after() throwing或after() throwing(<ExceptionType> <Identifier>)類型的通知。
package com.aspectj;
public aspect AfterThrowingAdviceRecipe {
/** *//**
* 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));
//Advice declaration
after() throwing:callPointCut()&&!within(AfterThrowingAdviceRecipe+){
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("Source Location: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("-----------------------------------------");
}
}
八.控制通知優(yōu)先級
如果把位于不同方面中的相同類型的通知應(yīng)用同一連接點，則可以使用declare precedence通知。其語法如下：
declare precedence:TypePattern,TypePattern,...;
package com.aspectj;
public aspect AspectA {
// Declare precedence rules
declare precedence:AspectA,AspectB;
/** *//**
* 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(AspectA+){
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice of AspectA");
System.out.println("Target: " + thisJoinPoint.getTarget());
System.out.println("This: " + thisJoinPoint.getThis());
System.out.println("Aspect Instance: " + AspectA.aspectOf());
System.out.println("-----------------------------------------");
}
}
在declare precedence語句中使用TypePattern來指定不同的方面，以及他們的顯式次序。可以使用通配符來指定TypePatterns,以根據(jù)需要為特定的方面集合或方面的整個包指示優(yōu)先級。
當(dāng)把一個方面中的兩個相同類型的通知塊應(yīng)用于同一個連接點時，declare precedence語句就沒有意義了。為了處理這種情況，AspectJ基于方面聲明內(nèi)通知的類型和位置，來應(yīng)用隱式的優(yōu)先級次序：
- 按在方面中聲明before()和around()通知類型的次序，來應(yīng)用他們隱式優(yōu)先級規(guī)則。如果把同一方面的兩個before()通知塊應(yīng)用于同一個連接點，那么聲明第一個塊將具有最高的優(yōu)先級，而最后一個則最低。
- 而after()、aftr() returning和around() throwing通知類型的隱式優(yōu)先級則于before()相反。
九.通知方面
package com.aspectj;
public aspect AdviseAspectRecipe {
/** *//**
* 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(AdvisedAspect+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice attached to the call point cut");
System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());
System.out.println("Source Line: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("-----------------------------------------");
}
}