Monday, 12 November 2018

Spring AOP ThrowsAdvice Example | Spring Tutorial

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Mastering Spring AOP ThrowsAdvice

In the world of Spring AOP (Aspect-Oriented Programming), handling errors gracefully is a superpower. Today, we are exploring ThrowsAdvice—a specific type of advice that triggers only when your code runs into an exception.

1. What is ThrowsAdvice?

Imagine you have a method that might fail (like a database connection). Instead of cluttering your main logic with try-catch blocks, ThrowsAdvice lets you write "error-handling logic" separately. It automatically catches exceptions thrown by your target methods and performs actions like logging or sending alerts.

2. How to Implement It

To use this, your class must implement the ThrowsAdvice interface. Interestingly, this interface doesn't have any methods you must override. Instead, Spring looks for a specifically named method called afterThrowing using reflection.

3. The Example Scenario

In our video example, we create a simple Validator class. If a user enters an invalid value, the class throws an exception. Our ThrowsAdvice then steps in to catch that specific error and print a helpful message, keeping our original code clean and focused.

4. Why Beginners Love It

It helps you follow the DRY (Don't Repeat Yourself) principle. You don't need to write the same error-handling code over and over again. You write it once in your Advice class, and Spring handles the rest!

Check Out These Other Tutorials:

Click here to watch on Youtube:
https://www.youtube.com/watch?v=xtm0kCyfbFo&list=UUhwKlOVR041tngjerWxVccw

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Spring AOP ThrowsAdvice 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>

    </dependencies>

</project>

EmployeeService.java

package com.ram.service;

public class EmployeeService

{

    public String getEmployeeName(int age)

    {

        System.out.println("Get Employee Information");

        if(age != 28)

        {

             throw new ArithmeticException("Not a valid age"); 

        }

        return "Dave";

    }

}

LoggingAdvice.java

package com.ram.Advice;

import org.springframework.aop.ThrowsAdvice;

public class LoggingAdvice implements ThrowsAdvice

{

    public void afterThrowing(Exception ex)

    {

        System.out.println(

                "LoggingAdvice applied if exception occurs, exe message = "

                        + ex.getMessage());

    }

}

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"

    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">

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

    <bean id="loggingAdvice" class="com.ram.Advice.LoggingAdvice"></bean>

    <bean id="employeeServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="employeeService"></property>

        <property name="interceptorNames">

            <list>

                <value>loggingAdvice</value>

            </list>

        </property>

    </bean>

</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("employeeServiceProxy",

                EmployeeService.class);

        employeeService.getEmployeeName(50);

    }

}

Output

Oct 15, 2018 9:34:53 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@6ebc05a6: startup date [Mon Oct 15 09:34:53 IST 2018]; root of context hierarchy

Oct 15, 2018 9:34:53 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

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

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

Get Employee Information

LoggingAdvice applied if exception occurs, exe message = Not a valid age