Ktor server
- Kotlin course
- Advanced
- Lesson 19/83
- 5 min
Learn HTTP servers with Ktor server.
What is Ktor server?
Ktor server is a coroutine based framework for writing HTTP servers in Kotlin. It works with engines like Netty, Jetty or CIO.
A server is started with the embeddedServer function. Example: embeddedServer(Netty, port = 8080) { ... }.start(wait = true). Routing and plugins are declared inside this block. Because it is coroutine based, each request is handled as a coroutine; this differs from a thread per request model. In this lesson you will set up the basic server skeleton.
Engine choice
A Ktor server runs on an engine. On JVM the common choices are Netty, Jetty and CIO.
The engine handles sockets and request dispatch. In embeddedServer(Netty, port = 8080) { ... } the engine is the first parameter. Netty is a common, mature choice for production. CIO is written in Kotlin and needs no extra dependency. The choice depends on performance and dependency needs.
Practice Set up the server skeleton
Define a server with val server = embeddedServer(Netty, port = 8080) { }. Print println("Server ready").
Starter code
// Ktor server
// write here
import io.ktor.server.application.*
import io.ktor.server.engine.*
import io.ktor.server.netty.*
fun main() {
}Sample solution
fun main() {
val server = embeddedServer(Netty, port = 8080) {
}
println("Server ready")
}Expected output
Server ready
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 How is a Ktor server started?
- main()
- HttpClient()
- embeddedServer() Correct answer
- runBlocking()
Explanation: The embeddedServer function starts the server.
2 Complete the embeddedServer call
val server = ____(Netty, port = 8080) {
}val server = embeddedServer(Netty, port = 8080) {
}Explanation: embeddedServer starts the server.
3 Match Ktor server parts
| Term | Meaning |
|---|---|
embeddedServer |
Starts server |
Netty |
Engine |
port |
Port number |
routing |
Route definition |