切面編程(環繞通知與前後置通知區別)
本文系作者原創,轉載請註明出處:http://www.cnblogs.com/further-further-further/p/7867034.html
解決問題
1、擁有前置通知和後置通知的功能,並能解決前置通知和後置通知在共享信息方面的不足(例如:統計切點方法執行時間);
2、在多線程併發條件下,能保證線程安全(因爲在一個方法內定義的局部變量);
3、解決代碼重複性,降低代碼複雜程度;
內容說明
1、以下會給出前置通知、後置通知與環繞通知實例(觀衆觀看錶演),通過對比更能理解彼此之間的區別;
2、兩者都通過@Component註解,掃描(Audience,Juggler)bean並註冊到spring容器中時,需在XML配置文件中引入component-scan(前後置通知:<context:component-scan base-package="com.spring.example.aspectAspectJNoArgs"/> 環繞通知:<context:component-scan base-package="com.spring.example.aspectAround"/>)
3、切面是觀衆(Audience),切點是節目表演(Performance.perform())
前置通知:在節目表演之前,觀衆就坐(調用Audience的takeSeats方法),並關掉手機(調用Audience的turnOffCellPhones方法);
後置通知:在節目表演結束,觀衆鼓掌(調用Audience的applaud方法);
異常通知:節目表演出現異常,觀衆要求退票(調用Audience的demandRefund方法);
環繞通知:其他與上面相同,只是在節目表演開始與結束時打印時間,統計節目表演時長;
4、通過執行Juggler的perform方法,從而執行切面Audience中相應的方法,達到通知的效果;
應用實例:觀衆觀看錶演所做出的相應行爲
先列出相關接口以及類代碼
節目表演接口(切點方法)
1 package com.spring.example.aspectAround; 2 3 /** 4 * Created by weixw on 2017/11/16. 5 */ 6 public interface Performer { 7 8 void perform(); 9 }
切點類實現接口Juggler
1 package com.spring.example.aspectAround; 2 3 import org.springframework.stereotype.Component; 4 5 /** 6 * Created by weixw on 2017/11/16. 7 */ 8 @Component 9 public class Juggler implements Performer { 10 private int beanBags = 3; 11 public Juggler(){ 12 13 } 14 public Juggler(int beanBags){ 15 this.beanBags = beanBags ; 16 } 17 @Override 18 public void perform() { 19 System.out.println("JUGGLING "+ beanBags + " BEANBAGS"); 20 try { 21 Thread.sleep(1); 22 }catch (InterruptedException e){ 23 e.printStackTrace(); 24 } 25 } 26 27 28 }
上述代碼都能共用,下面分別列舉前後置通知與環繞通知區別代碼
前後置通知(通過AspectJ註解實現,注意:<aop:aspectj-autoproxy/>不能少,它實現了切面相關方法綁定在切點上,切點方法執行就能觸發相應通知)
XML配置文件:spring/aspect-aspectJnoArgs.xml(放在spring文件夾下)
1 <?xml version="1.0" encoding="UTF-8"?> 2 <beans xmlns="http://www.springframework.org/schema/beans" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xmlns:aop="http://www.springframework.org/schema/aop" 5 xmlns:context="http://www.springframework.org/schema/context" 6 xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> 7 8 <!--使用前置通知和後置通知唯一方式:在前置通知中記錄開始時間,並在後置通知中報告表演耗費的時長,必須保存開始時間。因爲Audience是單例,如果像這樣保--> 9 <!--存狀態,會存在線程安全問題;--> 10 <context:component-scan base-package="com.spring.example.aspectAspectJNoArgs"/> 11 <aop:aspectj-autoproxy/> 12 </beans>
前後置通知切面實現類
1 package com.spring.example.aspectAspectJNoArgs; 2 3 import org.aspectj.lang.annotation.*; 4 import org.springframework.stereotype.Component; 5 6 /** 7 * Created by weixw on 2017/11/16. 8 * 通過AspectJ註解實現切面編程 9 * 切點方法 id 默認是所依賴方法(public void performance(){})的小寫方法名performance 10 */ 11 12 @Component 13 @Aspect 14 public class Audience { 15 @Pointcut("execution(* com.spring.example.aspectAspectJNoArgs.Performer.perform(..))") //定義切點 16 public void performance(){} 17 @Before("performance()")//表演之前 18 public void takeSeats(){ 19 System.out.println("The audience is taking their seats."); 20 } 21 @Before("performance()")//表演之前 22 public void turnOffCellPhones(){ 23 System.out.println("The audience is turning off their cellphones."); 24 } 25 @AfterReturning("performance()")//表演之後 26 public void applaud(){ 27 System.out.println("CLAP CLAP CLAP CLAP CLAP "); 28 } 29 @AfterThrowing("performance()") //表演失敗之後 30 public void demandRefund(){ 31 System.out.println("Boo! We want our money back!"); 32 } 33 }
環繞通知
XML配置文件:spring/aspect-around.xml(放在spring文件夾下)
1 <?xml version="1.0" encoding="UTF-8"?> 2 <beans xmlns="http://www.springframework.org/schema/beans" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xmlns:aop="http://www.springframework.org/schema/aop" 5 xmlns:context="http://www.springframework.org/schema/context" 6 xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> 7 8 <!--前置通知和後置通知是在一個方法中實現,所以不需要保存變量值,自然是線程安全的;--> 9 10 <context:component-scan base-package="com.spring.example.aspectAround"/> 11 <!--通過component-scan自動掃描,@Component註解將Magician註冊到spring容器--> 12 <aop:config> 13 <!--audience :切面 watchPerformance:切面方法 performance:切點--> 14 <aop:aspect ref="audience"> 15 <aop:pointcut id="performance" expression="execution(* com.spring.example.aspectAround.Performer.perform(..))"/> 16 <aop:around pointcut-ref="performance" method="watchPerformance" /> 17 </aop:aspect> 18 </aop:config> 19 </beans>
環繞通知切面實現類
1 package com.spring.example.aspectAround; 2 3 import org.aspectj.lang.ProceedingJoinPoint; 4 import org.springframework.stereotype.Component; 5 6 /** 7 * Created by weixw on 2017/11/16. 8 */ 9 @Component 10 public class Audience { 11 public void takeSeats(){ 12 System.out.println("The audience is taking their seats."); 13 } 14 public void turnOffCellPhones(){ 15 System.out.println("The audience is turning off their cellphones."); 16 } 17 public void applaud(){ 18 System.out.println("CLAP CLAP CLAP CLAP CLAP"); 19 } 20 public void demandRefund(){ 21 System.out.println("Boo! We want our money back!"); 22 } 23 24 public void watchPerformance(ProceedingJoinPoint joinPoint){ 25 try{ 26 takeSeats(); //表演之前 27 turnOffCellPhones(); //表演之前 28 long start = System.currentTimeMillis(); 29 System.out.println("The performance start ......");//節目開始 30 joinPoint.proceed(); //執行被通知的方法 31 System.out.println("The performance end ......");//節目結束 32 long end = System.currentTimeMillis(); //表演之後 33 applaud();//表演之後 34 System.out.println("The performance took milliseconds:"+ (end - start) );//表演時長 35 }catch (Throwable t){ 36 demandRefund(); //表演失敗之後 37 } 38 } 39 }
測試代碼
環繞通知測試代碼如下,前後置通知測試代碼只需將配置文件名稱改成spring/aspect-aspectJnoArgs.xml即可
1 package com.spring.example.aspectAround;/** 2 * Created by weixw on 2017/11/16. 3 */ 4 5 import javafx.application.Application; 6 import javafx.stage.Stage; 7 import org.springframework.context.ApplicationContext; 8 import org.springframework.context.support.ClassPathXmlApplicationContext; 9 10 public class Driver extends Application { 11 12 public static void main(String[] args) { 13 launch(args); 14 } 15 16 @Override 17 public void start(Stage primaryStage) { 18 try { 19 20 21 ApplicationContext ctx = new ClassPathXmlApplicationContext("spring/aspect-around.xml"); 22 Performer performer = (Performer) ctx.getBean("juggler"); 23 performer.perform(); 24 25 }catch (Exception e){ 26 e.printStackTrace(); 27 } 28 } 29 }
運行結果
環繞通知結果:
前後置通知結果:
總結
上述列出前後置通知和環繞通知樣例。對於有變量緩存需求,線程安全的應用場景,前後置通知實現比較困難,而環繞通知實現就非常容易;
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