?? 默認(rèn)的情況下，Aspect類只有一個(gè)實(shí)例存在于虛擬機(jī)中，也就是作為單例存在的，對(duì)于每個(gè)對(duì)象來(lái)說(shuō)，方面是共享的。一般這樣的方面，不能用來(lái)保存相應(yīng)對(duì)象的狀態(tài)。
?? 對(duì)于AspectJ 來(lái)說(shuō)，Aspect方面類，包括以下的實(shí)例化方式。

• 每虛擬機(jī)(默認(rèn)），只有一個(gè)實(shí)例，其生命周期從虛擬機(jī)啟動(dòng)開始，一直到虛擬機(jī)停止。
• 每對(duì)象，對(duì)于每一個(gè)對(duì)象都有一個(gè)方面實(shí)例，其生命周期跟隨相關(guān)聯(lián)的對(duì)象。
• 每控制流，對(duì)于每個(gè)controlFlow點(diǎn)，都會(huì)創(chuàng)建相應(yīng)的方面實(shí)例，可以參考事務(wù)管理（對(duì)于事務(wù)，每個(gè)原子操作，都是一個(gè)控制流，方面的生命周期，從控制流開始，一直到控制流結(jié)束）。

1)?? 每虛擬機(jī)關(guān)聯(lián)

默認(rèn)方面，它的狀態(tài)是共享的。

2)每對(duì)象關(guān)聯(lián)

通常，重用基礎(chǔ)方面需要保持每個(gè)對(duì)象的狀態(tài)，也就是對(duì)象的數(shù)據(jù)。對(duì)于每個(gè)對(duì)象都會(huì)創(chuàng)建一個(gè)方面實(shí)例。

對(duì)于每對(duì)象關(guān)聯(lián)可以指定兩種類型：

perthis()-與當(dāng)前所匹配的連接點(diǎn)的執(zhí)行對(duì)象，所關(guān)聯(lián)

pertarget()—與當(dāng)前所匹配的連接點(diǎn)的目標(biāo)執(zhí)行對(duì)象，所關(guān)聯(lián)

3)每控制流關(guān)聯(lián)

可以指定兩種類型的每控制流對(duì)象關(guān)聯(lián)：

percflow()--對(duì)于在percflow()指定的pointcut所匹配的連接點(diǎn)，關(guān)聯(lián)每一個(gè)獨(dú)立的方面實(shí)例和控制流執(zhí)行。

percflowbelow()，對(duì)于在prcflowbelow ()指定的pointcut所匹配的連接點(diǎn)，關(guān)聯(lián)每一個(gè)獨(dú)立的方面實(shí)例和控制流下的執(zhí)行。

下面來(lái)看一個(gè)實(shí)例：來(lái)區(qū)別不同點(diǎn)：

聲明必要的測(cè)試類

public class TestBean { ??? private String name; ??? public TestBean(String name) { ??????? this.name = name; ??? } ??? public void method1() { ??? } ??? public void method2() { ??? } ??? @Override ??? public String toString() { ??????? return name; ??? } } 測(cè)試類： public class LogAspectTest { ??? @Test ??? public void testAssociation() { ??????? TestBean bean1 = new TestBean("bean1"); ??????? TestBean bean2 = new TestBean("bean2"); ??????? bean1.method1(); ??????? bean1.method2(); ??????? bean2.method1(); ??????? bean2.method2(); ??? } } 方面類： public aspect LogAspect { ??? private static Log log = LogFactory.getLog(LogAspect.class); ??? public LogAspect() { ??????? log.info("create LogAspect instance"); ??? } ??? pointcut logMethod(TestBean bean) ??????? :execution(* TestBean.method*(..))&&this(bean)&&!within(LogAspect+); ??? before(TestBean bean):logMethod( bean){ ??????? log.info("JoinPoint: " ???????????????? + thisJoinPointStaticPart ???????????????? + "\n\taspect: " ???????????????? + this ???????????????? + "\n\tobject: " ???????????????? + bean); ??? } }

默認(rèn)的輸出為：
2006-10-21 20:42:02,275 [demo.chap4.log.LogAspect] - create LogAspect instance
2006-10-21 20:42:02,275 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method1())
??? aspect: demo.chap4.log.LogAspect@15601ea
??? object: bean1
2006-10-21 20:42:02,275 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method2())
??? aspect: demo.chap4.log.LogAspect@15601ea
??? object: bean1
2006-10-21 20:42:02,275 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method1())
??? aspect: demo.chap4.log.LogAspect@15601ea
??? object: bean2
2006-10-21 20:42:02,275 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method2())
??? aspect: demo.chap4.log.LogAspect@15601ea
??? object: bean2

可以看到只是實(shí)例化了一次

現(xiàn)在更改相應(yīng)的aspect，

public aspect LogAspect perthis(logMethod(TestBean)){

??? ....

??? }
}

只是增加了perthis(logMethod(TestBean))

輸出時(shí)，可以看到創(chuàng)建了兩個(gè)實(shí)例

2006-10-21 20:45:21,306 [demo.chap4.log.LogAspect] - create LogAspect instance
2006-10-21 20:45:21,306 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method1())
??? aspect: demo.chap4.log.LogAspect@197d257
??? object: bean1
2006-10-21 20:45:21,306 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method2())
??? aspect: demo.chap4.log.LogAspect@197d257
??? object: bean1
2006-10-21 20:45:21,306 [demo.chap4.log.LogAspect] - create LogAspect instance
2006-10-21 20:45:21,306 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method1())
??? aspect: demo.chap4.log.LogAspect@7259da
??? object: bean2
2006-10-21 20:45:21,306 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method2())
??? aspect: demo.chap4.log.LogAspect@7259da
??? object: bean2

繼續(xù)更改aspect，把perthis改為percflow

輸出改為：

2006-10-21 20:46:58,009 [demo.chap4.log.LogAspect] - create LogAspect instance
2006-10-21 20:46:58,009 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method1())
??? aspect: demo.chap4.log.LogAspect@eee36c
??? object: bean1
2006-10-21 20:46:58,009 [demo.chap4.log.LogAspect] - create LogAspect instance
2006-10-21 20:46:58,009 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method2())
??? aspect: demo.chap4.log.LogAspect@194df86
??? object: bean1
2006-10-21 20:46:58,009 [demo.chap4.log.LogAspect] - create LogAspect instance
2006-10-21 20:46:58,009 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method1())
??? aspect: demo.chap4.log.LogAspect@defa1a
??? object: bean2
2006-10-21 20:46:58,009 [demo.chap4.log.LogAspect] - create LogAspect instance
2006-10-21 20:46:58,009 [demo.chap4.log.LogAspect] - JoinPoint: execution(void demo.chap4.log.TestBean.method2())
??? aspect: demo.chap4.log.LogAspect@f5da06
??? object: bean2

每個(gè)方法都創(chuàng)建相應(yīng)的實(shí)例。