CoroutineExceptionHandler in Kotlin - Mini Project: Build & Apply

Handling Errors with CoroutineExceptionHandler in Kotlin

📖 Scenario: You are building a simple Kotlin program that runs coroutines to perform tasks. Sometimes, these tasks can fail with errors. You want to catch these errors gracefully and print a message instead of crashing the program.

🎯 Goal: Learn how to use CoroutineExceptionHandler to catch exceptions in coroutines and handle them by printing a friendly error message.

📋 What You'll Learn

Create a coroutine scope with a CoroutineExceptionHandler

Launch a coroutine that throws an exception

Handle the exception using the CoroutineExceptionHandler

Print the error message from the handler

💡 Why This Matters

🌍 Real World

In real apps, coroutines often run background tasks like network calls. Handling errors with CoroutineExceptionHandler helps keep apps stable and user-friendly.

💼 Career

Understanding CoroutineExceptionHandler is important for Kotlin developers working on Android apps or backend services that use coroutines for concurrency.

1

Create a CoroutineExceptionHandler

Create a val called handler and assign it a CoroutineExceptionHandler that prints the message "Caught exception: " followed by the exception's message.

Kotlin

# Your code here
// Create CoroutineExceptionHandler called handler

Need a hint?

Use CoroutineExceptionHandler { _, exception -> } and inside the lambda, print the exception message.

2

Create a CoroutineScope with the handler

Create a val called scope and assign it a CoroutineScope using Dispatchers.Default combined with the handler.

Kotlin

import kotlinx.coroutines.*

val handler = CoroutineExceptionHandler { _, exception ->
    println("Caught exception: ${exception.message}")
}

# Your code here
// Create CoroutineScope called scope with Dispatchers.Default + handler

Need a hint?

Use CoroutineScope(Dispatchers.Default + handler) to combine dispatcher and handler.

3

Launch a coroutine that throws an exception

Use scope.launch to start a coroutine that immediately throws an IllegalArgumentException with the message "Something went wrong".

Kotlin

import kotlinx.coroutines.*

val handler = CoroutineExceptionHandler { _, exception ->
    println("Caught exception: ${exception.message}")
}

val scope = CoroutineScope(Dispatchers.Default + handler)

# Your code here
// Launch coroutine that throws IllegalArgumentException("Something went wrong")

Need a hint?

Inside scope.launch { }, throw the exception with the exact message.

4

Print the error message from the handler

Run the program and print the output. The program should print Caught exception: Something went wrong.

Kotlin

import kotlinx.coroutines.*

val handler = CoroutineExceptionHandler { _, exception ->
    println("Caught exception: ${exception.message}")
}

val scope = CoroutineScope(Dispatchers.Default + handler)

fun main() {
    scope.launch {
        throw IllegalArgumentException("Something went wrong")
    }
    Thread.sleep(100) // Wait to see the output
}

# Your code here
// Run and print output

Need a hint?

Run the program and check the console output matches exactly.