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Spring基於XML模式的AOP

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要使用本節所述的AOP命名空間的標簽，需要如下所述導入Spring AOP架構：

<?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 ">

   <!-- bean definition & AOP specific configuration -->

</beans>

還需要在以下應用程序CLASSPATH中的AspectJ庫。這些庫可以在AspectJ的安裝'lib'目錄可用，可以從互聯網上下載它們。

  • aspectjrt.jar

  • aspectjweaver.jar

  • aspectj.jar

聲明一個切麵

一個方麵是使用<aop:aspect>元素中聲明，並且支持bean是使用ref屬性如下參考：

<aop:config>
   <aop:aspect id="myAspect" ref="aBean">
   ...
   </aop:aspect>
</aop:config>

<bean id="aBean" class="...">
...
</bean>

這裡的“aBean”將配置和依賴注入，就像任何其他的Spring bean，我們已經在前麵的章節看到。

聲明一個切入點

一個切入點有助於確定與不同要執行的連接點的利息（即方法）。同時與XML架構基礎的配置工作，切入點將被定義如下：

<aop:config>
   <aop:aspect id="myAspect" ref="aBean">

   <aop:pointcut id="businessService"
      expression="execution(* com.xyz.myapp.service.*.*(..))"/>
   ...
   </aop:aspect>
</aop:config>

<bean id="aBean" class="...">
...
</bean>

下麵的示例定義一個名為'的businessService“切入點將匹配可用的軟件包com.yiibai下執行getName()方法在Student類： 

<aop:config>
   <aop:aspect id="myAspect" ref="aBean">

   <aop:pointcut id="businessService"
      expression="execution(* com.yiibai.Student.getName(..))"/>
   ...
   </aop:aspect>
</aop:config>

<bean id="aBean" class="...">
...
</bean>

聲明建議

可以聲明任意五個建議的使用<aop:{ADVICE NAME}>元素下麵給出一個<aop:aspect>內：

<aop:config>
   <aop:aspect id="myAspect" ref="aBean">
      <aop:pointcut id="businessService"
         expression="execution(* com.xyz.myapp.service.*.*(..))"/>

      <!-- a before advice definition -->
      <aop:before pointcut-ref="businessService" 
         method="doRequiredTask"/>

      <!-- an after advice definition -->
      <aop:after pointcut-ref="businessService" 
         method="doRequiredTask"/>

      <!-- an after-returning advice definition -->
      <!--The doRequiredTask method must have parameter named retVal -->
      <aop:after-returning pointcut-ref="businessService"
         returning="retVal"
         method="doRequiredTask"/>

      <!-- an after-throwing advice definition -->
      <!--The doRequiredTask method must have parameter named ex -->
      <aop:after-throwing pointcut-ref="businessService"
         throwing="ex"
         method="doRequiredTask"/>

      <!-- an around advice definition -->
      <aop:around pointcut-ref="businessService" 
         method="doRequiredTask"/>
   ...
   </aop:aspect>
</aop:config>

<bean id="aBean" class="...">
...
</bean>

可以使用相同的doRequiredTask或不同的方法針對不同的建議。這些方法將被定義為縱橫模塊的一部分。

基於XML模式的AOP例

要理解上述關係到XML模式的AOP提到的概念，讓我們寫這將實現幾個建議的一個例子。寫我們的例子中有一些建議，讓我們使用Eclipse IDE，並按照下麵的步驟來創建一個Spring應用程序：

步驟 描述
1 Create a project with a name SpringExample and create a package com.yiibai under the src folder in the created project.
2 Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter.
3 Add Spring AOP specific libraries aspectjrt.jar, aspectjweaver.jar and aspectj.jar in the project.
4 Create Java classes Logging, Student and MainApp under the com.yiibai package.
5 Create Beans configuration file Beans.xml under the src folder.
6 The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below.

這裡是Logging.java文件的內容。這實際上是縱橫模塊的一個示例，它定義的方法被調用的各個點。

package com.yiibai;

public class Logging {

   /** 
    * This is the method which I would like to execute
    * before a selected method execution.
    */
   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.
    */
   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.
    */
   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.
    */
   public void AfterThrowingAdvice(IllegalArgumentException ex){
      System.out.println("There has been an exception: " + ex.toString());   
   }
   
}

以下是Student.java文件的內容：

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文件的內容：

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

以下是配置文件beans.xml文件：

<?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:config>
      <aop:aspect id="log" ref="logging">
         <aop:pointcut id="selectAll" 
         expression="execution(* com.yiibai.*.*(..))"/>
         <aop:before pointcut-ref="selectAll" method="beforeAdvice"/>
         <aop:after pointcut-ref="selectAll" method="afterAdvice"/>
         <aop:after-returning pointcut-ref="selectAll" 
                              returning="retVal"
                              method="afterReturningAdvice"/>
         <aop:after-throwing pointcut-ref="selectAll" 
                             throwing="ex"
                             method="AfterThrowingAdvice"/>
      </aop:aspect>
   </aop:config>

   <!-- Definition for student bean -->
   <bean id="student" class="com.yiibai.Student">
      <property name="name"  value="Zara" />
      <property name="age"  value="11"/>      
   </bean>

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

創建源代碼和bean配置文件完成後，讓我們運行應用程序。如果一切順利，這將打印以下信息：

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

解釋一下，上麵定義<aop:pointcut>選擇所有的包com.yiibai下定義的方法。讓我們假設，想有一個特定的方法之前或之後執行意見，可以定義切入點與實際的類和方法的名稱取代星號（*）的切入點定義來縮小執行。下麵是修改後的XML配置文件，以顯示概念：

<?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:config>
   <aop:aspect id="log" ref="logging">
      <aop:pointcut id="selectAll" 
      expression="execution(* com.yiibai.Student.getName(..))"/>
      <aop:before pointcut-ref="selectAll" method="beforeAdvice"/>
      <aop:after pointcut-ref="selectAll" method="afterAdvice"/>
   </aop:aspect>
   </aop:config>

   <!-- Definition for student bean -->
   <bean id="student" class="com.yiibai.Student">
      <property name="name"  value="Zara" />
      <property name="age"  value="11"/>      
   </bean>

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

如果執行這些配置更改的示例應用程序，這將打印以下信息：

Going to setup student profile.
Name : Zara
Student profile has been setup.
Age : 11
Exception raised
.....
other exception content


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