Monday, 3 December 2018

Spring AOP AspectJ @AfterThrowing Annotation Example | Spring Tutorial

Mastering Spring AOP: @AfterThrowing AspectJ Annotation Explained

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What is @AfterThrowing Annotation?

In the world of Spring Aspect-Oriented Programming (AOP), the @AfterThrowing annotation is a specific type of "Advice." This advice is triggered only when a method in your application throws an exception. It’s the perfect way to handle errors, log stack traces, or notify developers without cluttering your core business logic with try-catch blocks.

Why use it?

Imagine you have dozens of methods in your service layer. Instead of writing manual error-handling code in every single one, you can define one central "Aspect" that watches for exceptions. This keeps your code clean, maintainable, and readable.

Key Implementation Steps

Define the Pointcut: You specify which methods the advice should watch (e.g., all methods in a specific package).
Create the Advice: Write a method inside your Aspect class and annotate it with @AfterThrowing.
Accessing the Exception: You can use the "throwing" attribute in the annotation to capture the specific exception object and log its message.

Example Scenario

If an EmployeeService method like addEmployee() fails due to a database error, the @AfterThrowing advice will automatically catch that exception, allowing you to log "An error occurred while adding an employee!" instantly.

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Spring AOP AspectJ @AfterThrowing Annotation Example | Spring Tutorial

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.ram.core</groupId>

    <artifactId>SpringDemo</artifactId>

    <packaging>jar</packaging>

    <version>1.0-SNAPSHOT</version>

    <name>SpringDemo</name>

    <url>http://maven.apache.org</url>

    <properties>

        <spring.version>5.0.5.RELEASE</spring.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>junit</groupId>

            <artifactId>junit</artifactId>

            <version>3.8.1</version>

            <scope>test</scope>

        </dependency>

        <!-- Spring 5 dependencies -->

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-core</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-context</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <!-- Spring AOP + AspectJ -->

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-aop</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.aspectj</groupId>

            <artifactId>aspectjrt</artifactId>

            <version>1.9.1</version>

        </dependency>

        <dependency>

            <groupId>org.aspectj</groupId>

            <artifactId>aspectjweaver</artifactId>

            <version>1.9.1</version>

        </dependency>

    </dependencies>

</project>

EmployeeService.java

package com.ram.service;

public class EmployeeService

{

    public String addEmployee()

    {

        System.out.println("Add Employee");

        String name = null;

        name.toLowerCase();

        return "Employee Peter information is added successfully";

    }

    public void modifyEmployee()

    {

        System.out.println("Modify Employee");

    }

    public void deleteEmployee()

    {

        System.out.println("Delete Employee");

    }

}

LoggingAspect.java

package com.ram.Aspect;

import org.aspectj.lang.JoinPoint;

import org.aspectj.lang.annotation.AfterThrowing;

import org.aspectj.lang.annotation.Aspect;

@Aspect

public class LoggingAspect

{

    @AfterThrowing(

            pointcut = "execution(* com.ram.service.EmployeeService.addEmployee())",

            throwing = "exception")

    public void logAfterThrowing(JoinPoint joinPoint,

            Throwable exception)

    {

        System.out.print("logAfterThrowing() is running!");

        System.out.println(

                ", after " + joinPoint.getSignature().getName()

                        + " method throwing exception");

        System.out.println("exception = " + exception);

        System.out.println("******");

    }

}

applicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

    xmlns:context="http://www.springframework.org/schema/context"

    xmlns:aop="http://www.springframework.org/schema/aop"

    xsi:schemaLocation="http://www.springframework.org/schema/beans

    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd

    http://www.springframework.org/schema/context

    http://www.springframework.org/schema/context/spring-context-4.3.xsd

    http://www.springframework.org/schema/aop 

    http://www.springframework.org/schema/aop/spring-aop-4.3.xsd">

    <aop:aspectj-autoproxy />

    <bean id="employeeService" class="com.ram.service.EmployeeService"></bean>

    <!-- Aspect -->

    <bean id="logAspect" class="com.ram.Aspect.LoggingAspect" />

</beans>

App.java

package com.ram.core;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.service.EmployeeService;

public class App

{

    public static void main(String[] args)

    {

        ApplicationContext context = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

        System.out.println("---------------------------------------");

        EmployeeService employeeService = context

                .getBean("employeeService", EmployeeService.class);

        try

        {

            employeeService.addEmployee();

        }

        catch(Exception exe)

        {

            System.out.println("exception message  = "+exe.getMessage());

        }

        employeeService.modifyEmployee();

        employeeService.deleteEmployee();

    }

}

Output

Nov 12, 2018 9:56:43 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@32709393: startup date [Mon Nov 12 09:56:43 IST 2018]; root of context hierarchy

Nov 12, 2018 9:56:43 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

INFO: Loading XML bean definitions from class path resource [applicationContext.xml]

---------------------------------------

Add Employee

logAfterThrowing() is running!, after addEmployee method throwing exception

exception = java.lang.NullPointerException

******

exception message  = null

Modify Employee

Delete Employee