How-To Guide on Advanced Beginner

Coroutine Debugging

d8lzz1gpw@mozmail.com (kimbenji) — Wed, 13 May 2026 00:00:00 +0000

A step-by-step procedure for tracing where exceptions originate in asynchronous coroutine code and which coroutines are stuck.

Estimated time: about 15-20 minutes

TL;DR

Adding the JVM option -Dkotlinx.coroutines.debug shows the coroutine name in the thread name.

Use CoroutineName("name") to give a coroutine a name for easy identification in logs.

The IntelliJ Coroutines tab visually shows the state of every running coroutine.

DebugProbes from kotlinx-coroutines-debug restores stack traces.

What This Guide Solves#

Use this guide in the following situations:

Null Safety Migration

d8lzz1gpw@mozmail.com (kimbenji) — Wed, 13 May 2026 00:00:00 +0000

Step-by-step instructions for safely handling null-related issues when porting Java code to Kotlin.

Estimated time: about 15-20 minutes

TL;DR

Types coming from Java are inferred in Kotlin as platform types (e.g., String!).

Adding @Nullable/@NotNull annotations on Java code lets Kotlin infer the correct type.

Handle platform types defensively with ?. or ?: default instead of !!.

Migrate incrementally per class and verify with tests at each step.

What This Guide Solves#

Use this guide in the following situations:

Gradle Kotlin DSL Tips

d8lzz1gpw@mozmail.com (kimbenji) — Wed, 13 May 2026 00:00:00 +0000

Practical know-how and frequently used patterns for using Gradle Kotlin DSL effectively.

Estimated time: about 10-15 minutes

TL;DR

Manage all dependency versions in one place with libs.versions.toml (Version Catalog).

Reuse build logic via buildSrc or composite builds.

The plugins { } block is the modern alternative to apply(plugin = "...").

Keep multi-module configuration DRY with convention plugins.

What This Guide Solves#

Use this guide in the following situations:

When you keep copy-pasting the same Gradle configuration across modules
When dependency versions are scattered across files and updates are tedious
When you’re migrating from Groovy DSL to Kotlin DSL and the syntax is confusing

Step 1: Set Up Version Catalog (libs.versions.toml)#

gradle/libs.versions.toml is the centralized dependency-version file supported since Gradle 7.4.

Kotest vs JUnit

d8lzz1gpw@mozmail.com (kimbenji) — Wed, 13 May 2026 00:00:00 +0000

Compare the Kotest and JUnit 5 stacks and walk through choosing the right one for your project and migrating between them.

Estimated time: about 15-20 minutes

TL;DR

JUnit 5 + AssertJ + MockK: easier for teams migrating from Java, mature Spring Boot integration

Kotest: Kotlin-native style, BDD specs, built-in property-based testing

Both work with Spring Boot and can even be mixed in the same project.

For new pure-Kotlin projects, Kotest is recommended. For Java mix or teams in transition, JUnit 5.

What This Guide Solves#

Use this guide in the following situations:

Performance Profiling

d8lzz1gpw@mozmail.com (kimbenji) — Wed, 13 May 2026 00:00:00 +0000

Step-by-step instructions for finding and optimizing performance bottlenecks in Kotlin/JVM applications.

Estimated time: about 20-25 minutes

TL;DR

Don’t guess — measure first. Find real hotspots with Async Profiler or JFR.

Coroutine dispatcher choice has the biggest impact. Use Dispatchers.IO for I/O and Dispatchers.Default for CPU.

Reduce lambda capture and boxing costs with inline functions and primitive types.

Measurements taken before JIT warm-up don’t reflect real production performance.

What This Guide Solves#

Use this guide in the following situations: