XML Schema Based AOP with Spring

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To use the aop namespace tags described in this section, you need to import the spring-aop schema as described below:

<?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>

You will also need following AspectJ libraries on the CLASSPATH of your application. These libraries are available in the 'lib' directory of an AspectJ installation, otherwise you can download them from the internet.

  • aspectjrt.jar

  • aspectjweaver.jar

  • aspectj.jar

Declaring an aspect

An aspect is declared using the <aop:aspect> element, and the backing bean is referenced using the ref attribute as follows:

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

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

Here "aBean" will be configured and dependency injected just like any other Spring bean as you have seen in previous chapters.

Declaring a pointcut

A pointcut helps in determining the join points (ie methods) of interest to be executed with different advices. While working with XML Schema based configuration, pointcut will be defined as follows:

<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>

The following example defines a pointcut named 'businessService' that will match the execution of getName() method available in Student class under the package com.tutorialspoint:

<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>

Declaring advices

You can declare any of the five advices inside an <aop:aspect> using the <aop:{ADVICE NAME}> element as given below:

<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>

You can use same doRequiredTask or different methods for different advices. These methods will be defined as a part of aspect module.

XML Schema Based AOP Example

To understand above mentioned concepts related to XML Schema Based AOP, let us write an example which will implement few of the advices. To write our example with few advices, let us have working Eclipse IDE in place and follow the following steps to create a Spring application:

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

Here is the content of Logging.java file. This is actually a sample of aspect module which defines methods to be called at various points.

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());   
   }
   
}

Following is the content of the Student.java file:

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();
   }
}

Following is the content of the MainApp.java file:

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();
   }
}

Following is the configuration file 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>

Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will print the following message:

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

Let me explain that above defined <aop:pointcut> selects all the methods defined under the package com.tutorialspoint. Let us suppose, you want to execute your advice before or after a particular method, you can define your pointcut to narrow down your execution by replacing stars (*) in pointcut definition with actual class and method names. Below is a modified XML configuration file to show the concept:

<?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>

If you will execute sample application with these configuration changes, this will print the following message:

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


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