In this post, I will show you how we can handle exceptions using Spring's aspect-oriented programming.

Prerequisites

To follow this article, you should have:

• JDK 8+  
• Gradle 2.3 + 
• Your favorite IDE (I use IntelliJ IDEA)

Folder Structure

The folder structure should be as follows.

aopexceptionhandling:

├── build.gradle
└── src    
        ├── main    
        │   └── java
        │       └── net    
        │           └── asifhossain    
        │               └── aopexceptionhandling    
        │                   ├── aop    
        │                   │   └── ExceptionLoggerPointCut.java    
        │                   ├── AopExampleApp.java    
        │                   └── service    
        │                       └── ExceptionalService.java    
        └── test        
                └── java            
                         └── net                
                             └── asifhossain
                                 └── aopexceptionhandling
                                    └── AopExampleAppTest.java

Creating a Gradle Build File

Create a file named build.gradle in the application with the following content:

build.gradle:

group 'net.asifhossain'

buildscript {
    ext {
        springBootVersion = '1.5.9.RELEASE'
    }
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'

group = 'net.asifhossain'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    compile('org.springframework.boot:spring-boot-starter-aop')
    compile('org.springframework.boot:spring-boot-starter-web')
    testCompile('org.springframework.boot:spring-boot-starter-test')
}

Creating the Service

Now let's create a service method that will throw an exception.

ExceptionalService.java:

package net.asifhossain.aopexceptionhandling.service;

import org.springframework.stereotype.Service;

@Service
public class ExceptionalService {
    public void throwException() throws Exception {
        throw new Exception();
    }
}

Now let's create an aspect configuration file to log all the exceptions thrown from the service method.

ExceptionLoggerPointCut.java:

package net.asifhossain.aopexceptionhandling.aop;

import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Aspect;
import org.springframework.context.annotation.Configuration;

@Configuration
@Aspect
public class ExceptionLoggerPointCut {
    @AfterThrowing(pointcut = "execution(* net.asifhossain.aopexceptionhandling.*.*.*(..))", throwing = "ex")
    public void logError(Exception ex) {
        ex.printStackTrace();
    }
}

Making the Application Runnable

Now create the application class with all the components.

AopExampleApp.java:

package net.asifhossain.aopexceptionhandling;

import net.asifhossain.aopexceptionhandling.service.ExceptionalService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.EnableAspectJAutoProxy;

@SpringBootApplication
@EnableAspectJAutoProxy
public class AopExampleApp implements CommandLineRunner {

    @Autowired
    ExceptionalService service;

    @Override
    public void run(String... args) throws Exception {
        try {
            service.throwException();
        } catch (Exception ex) {
            
        }
    }

    public static void main(String[] args) {
        SpringApplication.run(AopExampleApp.class);
    }
}

Running the Application

To run the application, run the following command:

gradle bootRun 

You will see the thrown exception is logged on the console.

You can find all the codes in my GitHub repository.

That's all for today. Thanks for reading.