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

Fetching entities

Following the REST practices, the URL for fetching all cats should be /cats, while for fetching a single cat, it should be /cats/123, where 123 is the ID of the cat we are trying to fetch.

Let's add two new routes for that:

get("/cats") {
    ...
}
get("/cats/{id}") {
    ...
}

The first route is very similar to the /status route we introduced earlier in this chapter. But the second round is slightly different: it uses a query parameter in the URL. You can recognize query parameters by the curly brackets around their name.

To read a query parameter, we can access the parameters map:

val id = requireNotNull(call.parameters["id"]).toInt()

If there is an ID on the URL, we need to try and fetch a cat from the database:

val cat = transaction {
    CatsTable.select {
        CatsTable.id.eq(id)
    ...