Spring AOP基於註解的Around通知


@Around是一種建議型別,可確保方法執行前後的通知可以執行。 以下是@Around通知的語法:

語法

@Pointcut("execution(* com.yiibai.Student.getAge(..))")
private void selectGetName(){}

@Around("selectGetAge()")
public void aroundAdvice(ProceedingJoinPoint proceedingJoinPoint){
   System.out.println("[aroundAdvice] Around advice");
   Object[] args=jp.getArgs();
   if(args.length>0){
      System.out.print("[aroundAdvice] Arguments passed: " );
      for (int i = 0; i < args.length; i++) {
         System.out.print("[aroundAdvice] arg "+(i+1)+": "+args[i]);
      }
   }

   Object result=jp.proceed(args);
   System.out.println("[aroundAdvice] Returning " + result);
   return result.toString();   
}

在上面的語法範例中 -

  • @Pointcut - 將函式標記為切入點
  • execution( expression ) - 涵蓋應用通知的方法的表示式。
  • @Around - 將函式標記為在切入點覆蓋的方法之前執行的通知。

要了解上面提到的@Around通知相關的概念,我們寫一個Spring AOP基於註解的應用例子,它將使用基於註解組態實現通知。開啟並使用Eclipse IDE,並按照以下步驟建立一個Spring應用程式:

  1. 更新在Spring AOP應用範例中建立過的Student專案。
  2. 更新bean組態並執行應用程式,如下所述。

整個專案的目錄結構如下所示 -

下面是Logging.java檔案的內容。 這實際上是一個Aspect模組的樣本,它定義了在各個點被呼叫的方法。

package com.yiibai;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.ProceedingJoinPoint; 

@Aspect
public class Logging {

   /** Following is the definition for a pointcut to select
    *  all the methods available. So advice will be called
    *  for all the methods.
    */
   @Pointcut("execution(* com.yiibai.Student.getAge(..))")
   private void selectGetAge(){}

   /** 
    * This is the method which I would like to execute
    * around a selected method execution.
    */
   @Around("selectGetAge()")
   public void aroundAdvice(ProceedingJoinPoint proceedingJoinPoint) throws Throwable{
      System.out.println("Around advice");
      Object[] args=proceedingJoinPoint.getArgs();
      if(args.length>0){
         System.out.print("Arguments passed: " );
         for (int i = 0; i < args.length; i++) {
            System.out.print("arg "+(i+1)+": "+args[i]);
         }
      }

      Object result=proceedingJoinPoint.proceed(args);
      System.out.println("Returning " + result);
   }  
}

以下是Student.java檔案的內容:

package com.yiibai;

public class Student {
   private Integer age;
   private String name;

   public void setAge(Integer age) {
      this.age = age;
   }
   public Integer getAge() {
      System.out.println("Age : " + age );
      return age;
   }

   public void setName(String name) {
      this.name = name;
   }
   public String getName() {
      System.out.println("Name : " + name );
      return name;
   }

   public void printThrowException(){
       System.out.println("Exception raised");
       throw new IllegalArgumentException();
   }
}

以下是MainApp.java檔案的內容:

package com.yiibai;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = 
             new ClassPathXmlApplicationContext("Beans.xml");

      Student student = (Student) context.getBean("student");

      student.getAge();     
   }
}

以下是組態檔案Beans.xml檔案的內容:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
    http://www.springframework.org/schema/aop 
    http://www.springframework.org/schema/aop/spring-aop-3.0.xsd ">

   <aop:aspectj-autoproxy/>

   <!-- Definition for student bean -->
   <bean id="student" class="com.yiibai.Student">
      <property name="name"  value="minsu" />
      <property name="age"  value="24"/>      
   </bean>

   <!-- Definition for logging aspect -->
   <bean id="logging" class="com.yiibai.Logging"/> 

</beans>

執行專案

完成建立原始碼和組態檔案後,執行應用程式。右鍵單擊應用程式中的MainApp.java,並使用執行方式作為Java應用程式命令。 如果您的應用程式一切正常,這將列印以下訊息:

[aroundAdvice]Around advice
Age : 24
[aroundAdvice] Returning 24