AspectJ is an aspect oriented framework that extends the Java language. AspectJ defines AOP syntax and has a special compiler to generate Class files that comply with Java byte coding specifications.

AspetJ is an open source project of Eclipse. The official website is as follows:

• A seamless aspect oriented extension to the Java TM programming language
• Java platform compatible (compatible with Java platform and can be extended seamlessly)
• easy to learn and use

There are five types of notifications commonly used in AspectJ:

Pre notification, post notification, surround notification, exception notification and final notification

<properties>
  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  <maven.compiler.source>1.8</maven.compiler.source>
  <maven.compiler.target>1.8</maven.compiler.target>
</properties>
<dependencies>
  <!--unit testing -->
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
  </dependency>
  <!--Spring rely on-->
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>5.2.5.RELEASE</version>
  </dependency>
  <!--aspectJ rely on-->
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aspects</artifactId>
    <version>5.2.5.RELEASE</version>
  </dependency>
</dependencies>

Maven on the right to view the added dependencies

Com. The following classes and interfaces of hik package:

SomeService interface

package com.hik;
 
public interface SomeSeivece {
    void doSome(String name, Integer age);
}

Implementation class of SomeService interface SomeServiceImpl

package com.hik;
 
public class SomeSeiveceImpl implements SomeSeivece {
    @Override
    public void doSome(String name, Integer age) {
        //to doSome()Method adds a function in doSome The execution time of the output method before execution
        System.out.println("Target method doSome()implement");
    }
}

MyAspect class

package com.hik;
 
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
 
import java.util.Date;
 
/*
* @Aspect: Is an annotation in the framework of aspectJ.
* Function: to indicate that the current class is a faceted class. A faceted class is a class that adds functions to business methods. In this class, there are faceted function codes
* Where annotations are used: above the definition of the section class
* */
@Aspect
public class MyAspect {
    /*
    * Definition method: the method is to realize the section function.
    * Method definition requirements:
    * 1.Public method public
    * 2.Method has no return value
    * 3.The method name is custom
    * 4.Methods can have parameters or no parameters. If there are parameters, and the parameters are not user-defined, there are several parameter types available
    * */
 
    /*
    * @Before: Pre notification annotation
    * This annotation has an attribute value. The attribute value is value: it is the pointcut expression execution (), indicating the execution position of the function in the aspect
    *@Befor Annotation location: add annotation on the method
    * characteristic:
    * 1.Execute before target method
    * 2.The execution result of the target method will not be changed
    * 3.Does not affect the operation of the target method
    * */
    /*execution(Access modifier package name Class name Method name (parameter type 1, parameter type 2...)*/
    @Before(value = "execution(public void com.hik.SomeSeiveceImpl.doSome(String,Integer))")
    public void myBefore(){
        //Is the function code to be executed
        System.out.println("Pre notification, aspect function: output the execution time before the target method:" + new Date());
    }
}

Set the configuration file in the resource under the main directory: ApplicationContext 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.xsd
       http://www.springframework.org/schema/aop
       https://www.springframework.org/schema/aop/spring-aop.xsd">
 
    <!--Give the object to Spring Container, by Spring Containers create and manage objects uniformly-->
    <!--Declare target object-->
    <bean id="someService" class="com.hik.SomeSeiveceImpl"></bean>
 
    <!--Declare slice object-->
    <bean id="myAspect" class="com.hik.MyAspect"></bean>
 
    <!--Declaring automatic proxy generators: Using aspectJ Functions within the framework to create proxy objects for target objects.
        Creating a proxy object is implemented in memory and modifying the in memory structure of the target object.
        As a proxy object, the target object is the modified proxy object-->
    <!--This tag will find all the objects in the container, and then find the target and generate the proxy of the target according to the declaration information of the pointcut expression,
        Will put Spring The target object in generates a proxy object at once-->
    <aop:aspectj-autoproxy>
 
    </aop:aspectj-autoproxy>

Test class

package com.hik;
 
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
 
public class MyTest {
    @Test
    public void Test01(){
        String config = "applicationcontext.xml";
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext(config);
        //Get target object from container
        SomeSeivece proxy = (SomeSeivece) applicationContext.getBean("someService");
        //Through the proxy object execution method, the function is enhanced when the target method is executed
        proxy.doSome("Rita", 18);
    }
}

Execution results:

Pre notification, aspect function: output execution time before the target method: Thu Jan 13 16:30:16 CST 2022

The target method doSome() executes

Process finished with exit code 0