Book Image

Kotlin Design Patterns and Best Practices - Second Edition

By : Alexey Soshin
Book Image

Kotlin Design Patterns and Best Practices - Second Edition

By: Alexey Soshin

Overview of this book

This book shows you how easy it can be to implement traditional design patterns in the modern multi-paradigm Kotlin programming language, and takes you through the new patterns and paradigms that have emerged. This second edition is updated to cover the changes introduced from Kotlin 1.2 up to 1.5 and focuses more on the idiomatic usage of coroutines, which have become a stable language feature. You'll begin by learning about the practical aspects of smarter coding in Kotlin, as well as understanding basic Kotlin syntax and the impact of design patterns on your code. The book also provides an in-depth explanation of the classical design patterns, such as Creational, Structural, and Behavioral families, before moving on to functional programming. You'll go through reactive and concurrent patterns, and finally, get to grips with coroutines and structured concurrency to write performant, extensible, and maintainable code. By the end of this Kotlin book, you'll have explored the latest trends in architecture and design patterns for microservices. You’ll also understand the tradeoffs when choosing between different architectures and make informed decisions.
Table of Contents (17 chapters)
1
Section 1: Classical Patterns
6
Section 2: Reactive and Concurrent Patterns
11
Section 3: Practical Application of Design Patterns

Connecting to a database

To store and retrieve cats, we'll need to connect to a database. We'll use PostgreSQL for that purpose, although using another SQL database won't be any different.

First, we'll need a new library to connect to the database. We'll use the Exposed library, which is also developed by JetBrains.

Let's add the following dependency to our build.gradle.kts file:

dependencies {
    implementation("org.jetbrains.exposed:exposed:0.17.14")
    implementation("org.postgresql:postgresql:42.2.24")
    ...
}

Once the libraries are in place, we need to connect to them. To do that, let's create a new file called DB.kt under /src/main/kotlin with the following contents:

object DB {
    private val host=System.getenv("DB_HOST")?:"localhost"
    private val port =     ...