使用 Spring 的基于 XML 模式的 AOP

要使用本节中描述的 AOP 命名空间标签，您需要按照描述导入 springAOP 模式 −

<?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>

您还需要在应用程序的 CLASSPATH 中包含以下 AspectJ 库。这些库位于 AspectJ 安装的"lib"目录中，否则您可以从 Internet 下载它们。

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

声明一个方面

aspect 使用 <aop:aspect> 元素声明，支持 bean 使用 ref 属性引用，如下所示 −

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

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

这里"aBean"将被配置和依赖注入，就像您在前面章节中看到的任何其他 Spring bean 一样。

声明切入点

切入点 有助于确定要使用不同建议执行的感兴趣的连接点（即方法）。在使用基于 XML Schema 的配置时，切入点将定义如下 −

<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>

以下示例定义了一个名为"businessService"的切入点，它将匹配 com.tutorialspoint 包下 Student 类中可用的 getName() 方法的执行 −

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

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

声明建议

您可以使用 <aop:{ADVICE NAME}> 元素在 <aop:aspect> 中声明五个建议中的任何一个，如下所示 −

<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>

您可以使用相同的 doRequiredTask 或不同的方法来获得不同的建议。这些方法将被定义为切面模块的一部分。

基于 XML 模式的 AOP 示例

为了理解上述与基于 XML Schema 的 AOP 相关的概念，让我们编写一个示例来实现一些建议。用一些建议来写我们的例子，让我们有一个可以工作的 Eclipse IDE，并按照以下步骤创建一个 Spring 应用程序 −

步骤	描述
1	创建一个名为 SpringExample 的项目，并在创建的项目中的 src 文件夹下创建一个包 com.tutorialspoint。
2	使用 Add External JARs 选项添加所需的 Spring 库，如 Spring Hello World 示例一章中所述。
3	在项目中添加 Spring AOP 特定库 aspectjrt.jar、aspectjweaver.jar 和 aspectj.jar。
4	在 com.tutorialspoint 包下创建 Java 类 Logging、Student 和 MainApp。
5	在 src 文件夹下创建 Beans 配置文件 Beans.xml。
6	最后一步是创建所有 Java 文件和 Bean 配置文件的内容，然后运行应用程序，如下所述。

这是 Logging.java 文件的内容。这实际上是一个切面模块的示例，它定义了要在各个点调用的方法。

package com.tutorialspoint;

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 文件的内容

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 文件的内容

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();
   }
}

以下是配置文件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:config>
      <aop:aspect id = "log" ref = "logging">
         <aop:pointcut id = "selectAll" 
            expression = "execution(* com.tutorialspoint.*.*(..))"/>
         
         <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.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>

完成创建源和 bean 配置文件后，让我们运行应用程序。如果您的应用程序一切正常，它将打印以下消息 −

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

上面定义的 <aop:pointcut> 选择了com.tutorialspoint包下定义的所有方法。让我们假设，您想在特定方法之前或之后执行您的建议，您可以定义您的切入点，通过将切入点定义中的星号 (*) 替换为实际的类和方法名称来缩小执行范围。下面是一个修改过的 XML 配置文件来展示这个概念 −

<?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.tutorialspoint.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.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>

如果您执行带有这些配置更改的示例应用程序，它将打印以下消息 −

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

❮ Spring 框架的 AOP

Spring 核心基础

Spring 其他资源

使用 Spring 的基于 XML 模式的 AOP

声明一个方面

声明切入点

声明建议

基于 XML 模式的 AOP 示例

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