基於 AspectJ 的 Spring AOP

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@AspectJ 指的是一種將方面宣告為使用 Java 5 註解進行註解的常規 Java 類的方法。透過在基於 XML Schema 的配置檔案中包含以下元素，可以啟用 @AspectJ 支援。

<aop:aspectj-autoproxy/>

你還需要在應用程式的類路徑中包含以下 AspectJ 庫。這些庫可在 AspectJ 安裝的“lib”目錄中找到，或者你可以從網際網路上下載它們。

• aspectjrt.jar
• aspectjweaver.jar
• aspectj.jar
• aopalliance.jar

宣告一個方面

方面類就像任何其他普通 Bean 一樣，可以像任何其他類一樣擁有方法和欄位，只不過它們將使用 @Aspect 註解，如下所示：

package org.xyz;

import org.aspectj.lang.annotation.Aspect;

@Aspect
public class AspectModule {
}

它們將像任何其他 Bean 一樣在 XML 中進行配置，如下所示：

<bean id = "myAspect" class = "org.xyz.AspectModule">
   <!-- configure properties of aspect here as normal -->
</bean>

宣告切點

一個切點有助於確定要與不同通知一起執行的感興趣的連線點（即方法）。在使用基於 @AspectJ 的配置時，切點宣告包含兩個部分：

• 一個切點表示式，用於精確確定我們感興趣的方法執行。

• 一個切點簽名，包含一個名稱和任意數量的引數。方法的實際主體無關緊要，實際上應該為空。

以下示例定義了一個名為“businessService”的切點，該切點將匹配 com.xyz.myapp.service 包下類中每個方法的執行：

import org.aspectj.lang.annotation.Pointcut;

@Pointcut("execution(* com.xyz.myapp.service.*.*(..))") // expression 
private void businessService() {}  // signature

以下示例定義了一個名為“getname”的切點，該切點將匹配 com.tutorialspoint 包下 Student 類中 getName() 方法的執行：

import org.aspectj.lang.annotation.Pointcut;

@Pointcut("execution(* com.tutorialspoint.Student.getName(..))") 
private void getname() {}

宣告通知

你可以使用 @{ADVICE-NAME} 註解宣告任何五種通知，如程式碼片段所示。這假設你已經定義了一個切點簽名方法 businessService()：

@Before("businessService()")
public void doBeforeTask(){
   ...
}

@After("businessService()")
public void doAfterTask(){
   ...
}

@AfterReturning(pointcut = "businessService()", returning = "retVal")
public void doAfterReturnningTask(Object retVal) {
   // you can intercept retVal here.
   ...
}

@AfterThrowing(pointcut = "businessService()", throwing = "ex")
public void doAfterThrowingTask(Exception ex) {
  // you can intercept thrown exception here.
  ...
}

@Around("businessService()")
public void doAroundTask(){
   ...
}

你可以為任何通知內聯定義切點。以下是如何為 before 通知定義內聯切點的示例：

@Before("execution(* com.xyz.myapp.service.*.*(..))")
public doBeforeTask(){
   ...
}

基於 @AspectJ 的 AOP 示例

為了理解上述與基於 @AspectJ 的 AOP 相關的概念，讓我們編寫一個示例，該示例將實現一些通知。為了使用一些通知編寫我們的示例，讓我們準備一個可用的 Eclipse IDE，並採取以下步驟建立一個 Spring 應用程式：

以下是Logging.java檔案的內容。這實際上是一個方面模組的示例，它定義了要在各個點呼叫的方法。

package com.tutorialspoint;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.Around;

@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.tutorialspoint.*.*(..))")
   private void selectAll(){}

   /** 
      * This is the method which I would like to execute
      * before a selected method execution.
   */
   @Before("selectAll()")
   public void beforeAdvice(){
      System.out.println("Going to setup student profile.");
   }

   /** 
      * This is the method which I would like to execute
      * after a selected method execution.
   */
   @After("selectAll()")
   public void afterAdvice(){
      System.out.println("Student profile has been setup.");
   }

   /** 
      * This is the method which I would like to execute
      * when any method returns.
   */
   @AfterReturning(pointcut = "selectAll()", returning = "retVal")
   public void afterReturningAdvice(Object retVal){
      System.out.println("Returning:" + retVal.toString() );
   }

   /**
      * This is the method which I would like to execute
      * if there is an exception raised by any method.
   */
   @AfterThrowing(pointcut = "selectAll()", throwing = "ex")
   public void AfterThrowingAdvice(IllegalArgumentException ex){
      System.out.println("There has been an exception: " + ex.toString());   
   }
}

以下是Student.java檔案的內容

package com.tutorialspoint;

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.tutorialspoint;

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.getName();
      student.getAge();
      
      student.printThrowException();
   }
}

以下是配置檔案Beans.xml

<?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.tutorialspoint.Student">
      <property name = "name" value = "Zara" />
      <property name = "age"  value = "11"/>      
   </bean>

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

建立原始檔和 Bean 配置檔案後，讓我們執行應用程式。如果你的應用程式一切正常，它將列印以下訊息：

Going to setup student profile.
Name : Zara
Student profile has been setup.
Returning:Zara
Going to setup student profile.
Age : 11
Student profile has been setup.
Returning:11
Going to setup student profile.
Exception raised
Student profile has been setup.
There has been an exception: java.lang.IllegalArgumentException
.....
other exception content