Exception handling in async in Spring Boot - Mini Project: Build & Apply

Exception handling in async

📖 Scenario: You are building a Spring Boot application that performs a task asynchronously. Sometimes, errors happen during this task. You want to catch these errors properly so your app can handle them without crashing.

🎯 Goal: Create a Spring Boot service that runs a method asynchronously and handles exceptions thrown inside that method using a custom async exception handler.

📋 What You'll Learn

Create a service class with an asynchronous method

Configure a custom AsyncConfigurer to handle exceptions

Throw an exception inside the async method

Log the exception using the custom handler

💡 Why This Matters

🌍 Real World

Handling exceptions in asynchronous tasks is important in real-world apps to avoid crashes and to log errors for debugging.

💼 Career

Knowing how to manage async exceptions is a key skill for backend developers working with Spring Boot and microservices.

1

Create the async service class

Create a Spring service class called AsyncService with a method runAsyncTask annotated with @Async. Inside the method, throw a new RuntimeException with the message "Async error occurred".

Spring Boot

@Service
public class AsyncService {
    // Create the async method here
}

Need a hint?

Use @Service on the class and @Async on the method. Throw the exception inside the method body.

2

Add async configuration class

Create a configuration class called AsyncConfig that implements AsyncConfigurer. Override the method getAsyncUncaughtExceptionHandler() to return a new instance of SimpleAsyncUncaughtExceptionHandler.

Spring Boot

@Service
public class AsyncService {
    @Async
    public void runAsyncTask() {
        throw new RuntimeException("Async error occurred");
    }
}

// Create AsyncConfig class here

Need a hint?

Use @Configuration and @EnableAsync on the class. Implement AsyncConfigurer and override getAsyncUncaughtExceptionHandler().

3

Customize exception handler to log errors

Inside AsyncConfig, replace SimpleAsyncUncaughtExceptionHandler with a custom class CustomAsyncExceptionHandler that implements AsyncUncaughtExceptionHandler. In the handleUncaughtException method, log the exception message using System.out.println with the prefix "Async exception caught:".

Spring Boot

@Service
public class AsyncService {
    @Async
    public void runAsyncTask() {
        throw new RuntimeException("Async error occurred");
    }
}

@Configuration
@EnableAsync
public class AsyncConfig implements AsyncConfigurer {
    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
        // Return custom exception handler here
    }

    // Define CustomAsyncExceptionHandler class here
}

Need a hint?

Create a static inner class implementing AsyncUncaughtExceptionHandler. Override handleUncaughtException to print the exception message.

4

Call async method from main application

In your main Spring Boot application class, inject AsyncService and call runAsyncTask() inside the run method of CommandLineRunner to trigger the async method and see the exception handling in action.

Spring Boot

@Service
public class AsyncService {
    @Async
    public void runAsyncTask() {
        throw new RuntimeException("Async error occurred");
    }
}

@Configuration
@EnableAsync
public class AsyncConfig implements AsyncConfigurer {
    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
        return new CustomAsyncExceptionHandler();
    }

    public static class CustomAsyncExceptionHandler implements AsyncUncaughtExceptionHandler {
        @Override
        public void handleUncaughtException(Throwable ex, Method method, Object... params) {
            System.out.println("Async exception caught: " + ex.getMessage());
        }
    }
}

@SpringBootApplication
public class DemoApplication implements CommandLineRunner {

    private final AsyncService asyncService;

    public DemoApplication(AsyncService asyncService) {
        this.asyncService = asyncService;
    }

    @Override
    public void run(String... args) throws Exception {
        // Call async method here
    }

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

Need a hint?

Inject AsyncService via constructor. Call runAsyncTask() inside run method.