Application

Learn Application and module structure.

What is Application?

Application is the central point of a Ktor server. Plugins, routing and lifecycle are attached here. It is configured through an Application.module() function.

Example: fun Application.module() { install(ContentNegotiation); routing { ... } }. This function is referenced by module name in the embeddedServer call. module is a common name; any name works. You can define several modules and connect them in sequence. This structure breaks the server configuration into pieces.

Binding a module

You bind a module in the embeddedServer call. Example: embeddedServer(Netty, port = 8080, module = Application::module).

Here the module parameter takes a reference to the module function. The default module name is module; if it differs you must specify it. Modules are used to split the server: authentication in one module, reporting in another. This separation improves readability.

Exercise Define Application.module

Define fun Application.module(). Inside main, print println("Module ready").

Show example solution

fun Application.module() {
}

fun main() {
    println("Module ready")
}

Test yourself

Match Application parts

Application

Central point
module()

Configuration
install

Adds plugin
routing

Route definition
What does Application.module() do?
- Holds configuration
- Picks engine
- Starts the server
- Makes HTTP request
Show answer

Holds configuration — module() holds plugin and routing configuration.

Complete the Application.module definition

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

Show answer

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

Next lesson: Plugins

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