@AspectJ refers to a style of declaring aspects as regular Java classes annotated with Java 5 annotations. The @AspectJ support is enabled by including the following element inside your XML Schema-based configuration file.
<aop:aspectj-autoproxy/>
You will also need the 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
- aopalliance.jar
Declaring an aspect
Aspects classes are like any other normal bean and may have methods and fields just like any other class, except that they will be annotated with @Aspect as follows −
package org.xyz; import org.aspectj.lang.annotation.Aspect; @Aspect public class AspectModule { }
They will be configured in XML like any other bean as follows −
<bean id = "myAspect" class = "org.xyz.AspectModule"> <!-- configure properties of aspect here as normal --> </bean>
Declaring a pointcut
A pointcut helps in determining the join points (ie methods) of interest to be executed with different advices. While working with @AspectJ-based configuration, pointcut declaration has two parts −
- A pointcut expression that determines exactly which method executions we are interested in.
- A pointcut signature comprising a name and any number of parameters. The actual body of the method is irrelevant and in fact should be empty.
The following example defines a pointcut named 'businessService' that will match the execution of every method available in the classes under the package com.xyz.myapp.service −
import org.aspectj.lang.annotation.Pointcut; @Pointcut("execution(* com.xyz.myapp.service.*.*(..))") // expression private void businessService() {} // signature
The following example defines a pointcut named 'getname' that will match the execution of getName() method available in the Student class under the package com.tutorialspoint −
import org.aspectj.lang.annotation.Pointcut; @Pointcut("execution(* com.tutorialspoint.Student.getName(..))") private void getname() {}
Declaring advices
You can declare any of the five advices using @{ADVICE-NAME} annotations as given in the code snippet. This assumes that you already have defined a pointcut signature method 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(){ ... }
You can define a pointcut inline for any of the advices. Following is an example to define inline pointcut for before advice −
@Before("execution(* com.xyz.myapp.service.*.*(..))") public doBeforeTask(){ ... }
@AspectJ Based AOP Example
To understand the above-mentioned concepts related to @AspectJ based AOP, let us write an example which will implement few of the advices. To write our example with few advices, let us have a working Eclipse IDE in place and take the following steps to create a Spring application −
Steps | Description |
---|---|
1 | Create a project with a name SpringExample and create a package com.tutorialspoint 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.tutorialspoint 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. |
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; 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()); } }
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: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>
Once you are done creating the source and bean configuration files, let us run the application. If everything is fine with your application, it 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
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