一.捕獲何時連接點上的運行時條件評估為true
使用if(Expression)語句來評估包含要比較的運行時變量的布爾表達式。if(Expression)語句的語法如下：
pointcut <pointcut name>(<any values to be picked up>) : if(<Boolean expression>);
if(Expression)語句有兩個關鍵特征：
1.if(Expression)切入點評估在運行時提供的變量，得到關于連接點是否應該觸發相應通知的true或false結果。
2.Expression可以由多個邏輯元素組成，包括展示的連接點環境，靜態變以及其他切入點聲明。
package com.aspectj;
public aspect IfRecipe 
{
// Define some variables for comparison
private static final long realisticSalary=300001;
/** *//**
* Specifies calling advice if this is referencing an object of class MyClass
* and the object has a realistic salary:
*/
pointcut ifJoinPointThishasRealisticSalaryPointcut():if(
(thisJoinPoint.getThis() instanceof MyClass)
&& ((MyClass) thisJoinPoint.getThis()).getSalary() < realisticSalary
&& ((MyClass) thisJoinPoint.getThis()).getSalary() > 0)
&& !withincode(* MyClass.get*())
&& !execution(* MyClass.get*());
//Advice declaration
//This advice will be executed before the pointcut that picks it
after() : ifJoinPointThishasRealisticSalaryPointcut() && !within(IfRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by ifJoinPointThishasRealisticSalaryPointcut()");
System.out.println("Join Point Kind" + thisJoinPoint.getKind());
System.out.println("Executing object: " + thisJoinPoint.getThis());
System.out.println("MyClass instance: " + ((MyClass) thisJoinPoint.getThis()).getName() + ":" + ((MyClass) thisJoinPoint.getThis()).getSalary());
System.out.println("Signature: " + thisJoinPoint.getStaticPart().getSignature());
System.out.println("Source Line: " + thisJoinPoint.getStaticPart().getSourceLocation());
System.out.println("-----------------------------------------");
}
}
if(Expression)語句允許定義是否應該把一份通知應用于特定連接點的條件邏輯。這個條件邏輯在運行時執行，并且在到達連接點那一刻必須工作在有效的類型上。
例子中ifJoinPointThisHasRealisticSalaryPointcut()切入點中包含的條件邏輯指定在發生以下事件時，應該觸發相應的after通知：
1.執行對象是MyClass類型
2.對象的salary屬性小于realisticSalary常量
3.對象的salary屬性小于0
4.當前連接點不在getSalary()方法內。通過使用通配符，連接點絕對不能出現在開始到達的MyClass類的任何方法中。
可以使用AND(&&)運算符來邏輯地結合每個條件。前3個條件可以相當容易地理解成切入點布爾邏輯的一部分，但是最后一個條件更有趣一點。必須包含!withincode(* MyClass.get*())條件，以防止從通知內調用getSalary(),這反過來又會觸發對通知的遞歸調用，并導致一個死循環。
二.使用邏輯AND(&&)結合切入點
使用&&運算符。&& operator運算符的語法如下：
pointcut <pointcut name>(<any values to be picked up>) : <pointcut declaation> && <pointcut declaration>
package com.aspectj;
public aspect LogicalAndRecipe {
/** *//**
* Specifies calling advice whenever a method
* matching the following rules gets called:
*
* Class Name: MyClass
* Method Name:Any Method
* Method Return Type:Any Return Type
* Method Parameters:Any Parameters
*/
pointcut callAnyMethodOnMyClass():call(* MyClass.* (..));
/** *//**
* Specifies calling advice whenever a method
* matching the following rules gets called:
*
* Class Name: MyClass
* Method Name:bar
* Method Return Type:void
* Method Parameters:None
*/
pointcut callBarPointcut() : call(void MyClass.bar());
/** *//**
* Specifies calling advice whenever a join points is
* encountered that would be picked by both pointcuts
* specified:
*
* Pointcut Name: callAyMethodOnMyClass
* Pointcut Name:callBarPointcut
* Method Return Type:void
* Method Parameters:None
*/
pointcut callIntersectionAnyAndBar():callAnyMethodOnMyClass() && callBarPointcut();
//Advice declaration
before():callAnyMethodOnMyClass()&&!within(LogicalAndRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by callAnyMethodOnMyClass()");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
//Advice declaration
before():callBarPointcut()&&!within(LogicalAndRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by callBarPointcut()");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
//Advice declaration
before():callIntersectionAnyAndBar()&&!within(LogicalAndRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by callIntersectionAnyAndBar()");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
}
在AspectJ環境中，當用&&運算符吧兩個或多個簡單的切入點結合進一步復合切入點時，被兩個獨立的切入點選擇的連接點將觸發復合切入點的關聯通知。更簡單地說，如果任一個簡單切入點選擇了任何一個連接點，那么整個復合切入點就不會選擇這個連接點。
使用&&運算符結合切入點的次序還會影響復合切入點的解釋方式。&&運算符的運行時分析是從左到右執行的。這意味著在檢查候選連接點時，指示它不包含連接點的第一個切入點就是停止比較的地方。這對于Java中的&&運算符是成立的，并且當復合中的比較之一必須通過前一個條件加以保護時特別有用。
三. 使用邏輯OR(||)結合切入點
使用||運算符。|| operator運算符的語法如下：
pointcut <pointcut name>(<any values to be picked up>) : <pointcut declaation> || <pointcut declaration>
package com.aspectj;
public aspect LogicalOrRecipe {
/** *//**
* Specifies calling advice whenever a method
* matching the following rules gets called:
*
* Class Name: MyClass
* Method Name:foo
* Method Return Type:void
* Method Parameters:int and a String
*/
pointcut callFooIntStringPointcut():call(void MyClass.foo(int,String));
/** *//**
* Specifies calling advice whenever a method
* matching the following rules gets called:
*
* Class Name: MyClass
* Method Name:bar
* Method Return Type:void
* Method Parameters:None
*/
pointcut callBarPointcut() : call(void MyClass.bar());
/** *//**
* Specifies calling advice whenever a join points is
* encountered that would be picked by both pointcuts
* specified:
*
* Pointcut Name: callFooIntStringPointcut
* Pointcut Name:callBarPointcut
* Method Return Type:void
* Method Parameters:None
*/
pointcut callIntersectionFooOrBar():callFooIntStringPointcut() || callBarPointcut();
//Advice declaration
before():callFooIntStringPointcut()&&!within(LogicalOrRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by callFooIntStringPointcut()");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
//Advice declaration
before():callBarPointcut()&&!within(LogicalOrRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by callBarPointcut()");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
//Advice declaration
before():callIntersectionFooOrBar()&&!within(LogicalOrRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by callIntersectionFooOrBar()");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
}
在AspectJ語言中，如果連接點在使用邏輯OR結合進入復合切入點的任何成分切入點上啟動通知，連接點就會觸發那個通知。
AspectJ中的||運算符還顯示了短路行為，這個&&運算符相似且相反。
四.捕獲所有未通過切入點聲明指定的連接點
使用一元!運算符，指定忽略那些通常由特定切入點捕獲的連接點。!運算符的語法如下：
pointcut <pointcut name>(<any values to be picked up>): !<pointcut declaation>
package com.aspectj;
public aspect LogicalNotRecipe {
/** *//**
* Specifies calling advice whenever a method
* matching NOT match the following rules:
*
* Class Name: MyClass
* Method Name:foo
* Method Return Type:void
* Method Parameters:int and a String
*/
pointcut notCallPointcutFooIntString() : !call(void MyClass.foo(int,String));
//Advice declaration
before():notCallPointcutFooIntString()&&!within(LogicalNotRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by callFooIntStringPointcut()");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
}
五.聲明匿名切入點
匿名切入點是切入點聲明的構件。在所有基于切入點的章節中都會用它，但是我們在這里更細致地關注匿名切入點。
package com.aspectj;
public aspect AnonymousPointcutRecipe {
/** *//**
* A pointcut declaration that is built up from one
* anonymous pointcut:
*
* Anonymous Pointcuts:call(void MyClass.foo(int,String))
*/
pointcut singleAnonymousPointcut() : call(void MyClass.foo(int,String));
/** *//**
* A pointcut declaration that is built up from two
* anonymous pointcut:
*
* Anonymous Pointcuts:call(void MyClass.foo(int,String))
* call(void MyClass.foo(int,String))
* !within(AnonymousPointcutRecipe+)
*/
pointcut multipleAnonymousPointcut() : (
call(void MyClass.bar())
|| call(void MyClass.foo(int,String))
&& !within(AnonymousPointcutRecipe+));
/** *//**
* A pointcut declaration attached to the advice it will invoke,
* built up from anonymous pointcut:
*
* Anonymous Pointcuts：within(LogicalOrRecipe+)
*/
//Advice declaration
before():singleAnonymousPointcut()&&!within(LogicalNotRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by singleanonymousPointcut and !within(AnonymousPointcutRecipe+)");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
/** *//**
* A pointcut declaration attached to the advice it will invoke,
* built up from anonymous pointcut:
*
* Anonymous Pointcuts：None
*/
//Advice declaration
before():multipleAnonymousPointcut() {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by multipleAnonymousPointcut()");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
}
匿名切入點用于聲明切入點，而不是檢查特定的切入點類型。可以在命名切入點聲明內匿名地聲明切入點，或者通過把切入點直接附加到它們將調用的通知上來進行聲明。
六.重用切入點
聲明一個切入點，可以在需要重用它的地方通過名稱來引用它。
package com.aspectj;
public aspect PointcutReuseRecipe {
/** *//**
* A pointcut declaration that is to be used and reused:
* Anonymous Pointcuts: call(void MyClass.foo(int,String))
*/
pointcut foundationNamedPointcut():call(void MyClass.foo(int,String));
/** *//**
* A pointcut declaration that is built up from two
* pointcuts:
*
* Anonymous Pointcuts:!within(AnonymousPointcutRecipe+)
* Named Pointcuts:foundationNamedPointcut()
*/
pointcut reuseNamedPointcut():foundationNamedPointcut()&&!within(PointcutReuseRecipe+);
/** *//**
* A pointcut declaration attached to the advice it will invoke,
* built up from simple named and anonymous pointcuts:
* Anonymous Pointcut:!within(LogicOrRecipe+)
* Named Pointcuts:foundationNamedPointcut();
*/
before():foundationNamedPointcut()&&!within(PointcutReuseRecipe+) {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by foundationNamedPointcut and !within(PointcutReuseRecipe+)");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
/** *//**
* A pointcut declaration attached to the advice it will invoke,
* built up from complex pointcut built reusing other pointcut
* declarations:
*
* Named Pointcuts：reuseNamedPointcut();
*/
before():reuseNamedPointcut() {
System.out.println("---------- Aspect Advice Logic ----------");
System.out.println("In the advice picked by reuseNamedPointcut()");
System.out.println("Signature: " + thisJoinPoint.getSignature());
System.out.println("Source Line: " + thisJoinPoint.getSourceLocation());
System.out.println("-----------------------------------------");
}
}