Plugins

Learn ContentNegotiation and StatusPages plugins.

What is a plugin?

A plugin is an add on that changes server behavior. In Ktor it is added with the install call. ContentNegotiation handles JSON, StatusPages catches errors.

Example: install(ContentNegotiation) { json() }. This plugin turns the body into a Kotlin object. With StatusPages the exception<Throwable> { call -> ... } block handles exceptions. Plugins can be installed in the Application module or in the routing block. Configuration happens once; all requests share the same behavior.

Exercise Add the ContentNegotiation plugin

Define fun Application.module(). Inside it call install(ContentNegotiation). In main, print println("Plugin added").

Show example solution

fun Application.module() {
    install(ContentNegotiation)
}

fun main() {
    println("Plugin added")
}

Error handling with StatusPages

StatusPages is the plugin that catches thrown exceptions on the server. install(StatusPages) { exception<Throwable> { call, cause -> call.respondText("Error", status = HttpStatusCode.InternalServerError) } }.

This block catches any exception and returns a consistent error response to the client. Different blocks can be written for specific exception types. StatusPages prevents the app from crashing and handles errors centrally. In production it is used alongside a logging plugin.

Test yourself

What does the StatusPages plugin do?
- Converts JSON
- Catches errors
- Routes URLs
- Picks engine
Show answer

Catches errors — StatusPages handles exceptions.

Complete the install call

fun Application.module() {
    ____(ContentNegotiation) { json() }
}

Show answer

fun Application.module() {
    install(ContentNegotiation) { json() }
}

Match plugins

ContentNegotiation

Converts JSON
StatusPages

Catches errors
install

Adds plugin
json()

Picks format

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