Gain insights into Kotlin language essentials and delve into design patterns and best practices. Discover functional programming techniques to enhance code reuse, robustness, and build reliable, scalable projects.

Packt MBE - Kotlin Design Patterns and Best Practices.png

Kotlin_optimized.tar.gz

Kotlin

Kotlin_Co

Kotlin_SPA

Cats_Hostel

Cats_Shelter(1..5)

Cats_Shelter(6-7-8)

Design patterns enable developers to speed up the development process by providing proven development paradigms. Reusing design patterns helps prevent complex issues that can cause major problems. Moreover, it improves your codebase, promotes code reuse, and makes an architecture more robust.

In this course, you will start with a gentle introduction of the Kotlin language. You will explore design patterns that are part of the best practices that help developers use Kotlin efficiently. Design patterns appeared in the era of object-oriented languages such as C++ and Java. You will learn the language features that Kotlin provides, which allow developers to program in a functional style and implement the design patterns.

After taking this course, you’ll be able to take your knowledge of Kotlin, design patterns, and associated best practices to the software industry and apply it to build reliable, scalable, and maintainable projects.

Kotlin Design Patterns and Best Practices

## Adding code to `App.kt` file
Now, let’s add the following content to our main file, the `App.kt` file (in some cases, it could be `server.kt`). We can follow the path in the directory on the left side of the IDE---`/CatsHostel/app/src/main/kotlin/catshostel/App.kt`---to see the code:

```
fun main() {
    embeddedServer(Netty, port = 8080) {
         routing {
              get("/") {
                 call.respondText("OK")
              }
         }
    }.start(wait = true)
    println("open http://localhost:8080")
}
```

That's all the code we need to write to start a web server that will respond with OK when we open the app in our browser.


Now, let's understand what happens here:
* To interact with the request and return a response, we can use the `call` object, also known as the context. This object provides all the convenient methods for parsing requests and returning responses in different formats, and we'll see the different methods available for it throughout this chapter .
* The `embeddedServer()` function is an implementation of the Builder pattern. It allows us to configure our server. Most of the arguments have the same defaults. We override port to 8080 just for convenience.
* We specify the `wait` argument to be `true` so that our server will wait for incoming requests.

* The only mandatory argument to the `embeddedServer()` function is the server engine. In our example, we use `Netty`, which is a very well-known JVM library, but there are others as well. The most interesting of them is `CIO`, which was developed by JetBrains themselves.

## CIO and Netty
Now, let's understand what `CIO` and `Netty` are. They are both Factory patterns that create the actual instance of our server when invoked. This is a really interesting combination of different design patterns in one place to create a very flexible and extensible architecture.


To switch to using `CIO`, all we need to do is add a new dependency in our configuration file:
```
dependencies {
...
implementation("io.ktor:ktor-server-cio:$ktorVersion")
...
}
```
See the `build.gradle.kts` file.

Then, we need to pass another server engine, `CIO`, to our `embeddedServer()` function:

```
embeddedServer(CIO, port = 8080) {
...
}.start(wait = true)
```
>**Note**: We can uncomment this part and check with `Netty` Server and then we can check the code below it by commenting it again.
    
Notice that we didn't have to change anything else in our code when we switched the server engine. That is because `embeddedServer()` uses the Bridge design pattern to make components interchangeable.

Now that our server has been started let's investigate how we define different responses for each request to the server.

## Executing the application

Now let's go ahead and execute the application:



Learn how to start the server in a Ktor application with the CIO server engine. 

Getting Started with Kotlin

Working with Creational Patterns

Understanding Structural Patterns

Getting Familiar with Behavioral Patterns

Introducing Functional Programming

Threads and Coroutines

Controlling the Data Flow

Designing for Concurrency

Idioms and Anti-Patterns

Concurrent Microservices with Ktor

Reactive Microservices with Vert.x

Conclusion

Starting the Server

Adding code to `App.kt` file

Starting the Server

Adding code to App.kt file

Adding code to `App.kt` file