Adding Ktor to an existing Gradle project

1. On the Welcome screen, click New Project.

   Otherwise, from the main menu, select File | New | Project.

2. In the New Project wizard, choose Gradle from the list on the left and specify the following settings:

   

   • Choose the Project SDK from the list.

   • (Optional) Enable the Kotlin DSL build script option to use Kotlin instead of Groovy DSL.

   • Select Kotlin/JVM in the Additional Libraries and Frameworks area.

   Click Next.

3. On the next wizard page, specify a project's name and location.

   

   Click Finish and wait until IntelliJ IDEA creates and builds a project.

1. Open the build.gradle or build.gradle.kts file. It should look as follows:

   Gradle (Groovy)

   Gradle (Kotlin)

   plugins {
       id 'org.jetbrains.kotlin.jvm' version '1.5.31'
   }
   
   group 'org.example'
   version '1.0-SNAPSHOT'
   
   repositories {
       mavenCentral()
   }
   
   dependencies {
       implementation "org.jetbrains.kotlin:kotlin-stdlib"
   }

   plugins {
       kotlin("jvm") version "1.5.31"
   }
   
   group = "org.example"
   version = "1.0-SNAPSHOT"
   
   repositories {
       mavenCentral()
   }
   
   dependencies {
       implementation(kotlin("stdlib"))
   }

   Besides other settings, this build script declares the Maven Central repository. Since Ktor dependencies are stored in Maven Central, we don't need to change anything here.

2. To create a simple Ktor application, we need to add at least the following dependencies:

   • ktor-server-core: contains core Ktor functionality.

   • A dependency for an engine (for example, ktor-server-netty).

   • Logback artifacts for logging.

   The dependencies block might look as follows:

   Gradle (Groovy)

   Gradle (Kotlin)

   dependencies {
       implementation "io.ktor:ktor-server-core:1.6.8"
       implementation "io.ktor:ktor-server-netty:1.6.8"
       implementation "ch.qos.logback:logback-classic:1.2.5"
   }

   dependencies {
       implementation("io.ktor:ktor-server-core:1.6.8")
       implementation("io.ktor:ktor-server-netty:1.6.8")
       implementation("ch.qos.logback:logback-classic:1.2.5")
   }

   Note that other engines and plugins that extend Ktor functionality might required additional dependencies. You can learn more from corresponding topics.

Create a server using embeddedServer

• Add the following code to Application.kt to use the embeddedServer function for starting a Ktor server:

  package com.example
  
  import io.ktor.application.*
  import io.ktor.response.*
  import io.ktor.routing.*
  import io.ktor.server.engine.*
  import io.ktor.server.netty.*
  
  fun main() {
      embeddedServer(Netty, port = 8080) {
          routing {
              get("/") {
                  call.respondText("Hello, world!")
              }
          }
      }.start(wait = true)
  }

Create a server using EngineMain

1. Add the following code to Application.kt to use EngineMain for starting a Ktor server:

   package com.example
   
   import io.ktor.application.*
   import io.ktor.response.*
   import io.ktor.routing.*
   
   fun main(args: Array<String>): Unit = io.ktor.server.netty.EngineMain.main(args)
   
   fun Application.module(testing: Boolean = false) {
       routing {
           get("/") {
               call.respondText("Hello, world!")
           }
       }
   }

   The Application.module function is a module loaded by the server. Modules to load should be specified in the application.conf file, which will be created in the next step.

2. Create the application.conf file in the src/main/resources folder and copy the following configuration:

   ktor {
       deployment {
           port = 8080
       }
       application {
           modules = [ com.example.ApplicationKt.module ]
       }
   }

   This file specifies a fully qualified name of the Application.module module to load and sets a listening port to 8080.

1. Add the following code in the plugins block to use the Application plugin:

   Gradle (Groovy)

   Gradle (Kotlin)

   plugins {
       id 'application'
   }

   plugins {
       application
   }

2. Depending on the way you used to create a server, specify the application main class in one of the following ways:

   • If you use embeddedServer, specify the main class as follows:

     Gradle (Groovy)

     Gradle (Kotlin)

     application {
         mainClass = 'com.example.ApplicationKt'
     }

     application {
         mainClass.set("com.example.ApplicationKt")
     }

   • If you use EngineMain, you need to configure it as the main class. For Netty, it will look as follows:

     Gradle (Groovy)

     Gradle (Kotlin)

     application {
         mainClass = 'io.ktor.server.netty.EngineMain'
     }

     application {
         mainClass.set("io.ktor.server.netty.EngineMain")
     }

3. The resulting build.gradle/build.gradle.kts file should look something like this:

   Gradle (Groovy)

   Gradle (Kotlin)

   plugins {
       id 'application'
       id 'org.jetbrains.kotlin.jvm' version '1.5.31'
   }
   
   group 'org.example'
   version '1.0-SNAPSHOT'
   
   application {
       mainClass = 'io.ktor.server.netty.EngineMain'
   }
   
   repositories {
       mavenCentral()
   }
   
   dependencies {
       implementation "org.jetbrains.kotlin:kotlin-stdlib"
       implementation "io.ktor:ktor-server-core:1.6.8"
       implementation "io.ktor:ktor-server-netty:1.6.8"
       implementation "ch.qos.logback:logback-classic:1.2.5"
   }

   plugins {
       application
       kotlin("jvm") version "1.5.31"
   }
   
   group = "org.example"
   version = "1.0-SNAPSHOT"
   
   application {
       mainClass.set("io.ktor.server.netty.EngineMain")
   }
   
   repositories {
       mavenCentral()
   }
   
   dependencies {
       implementation(kotlin("stdlib"))
       implementation("io.ktor:ktor-server-core:1.6.8")
       implementation("io.ktor:ktor-server-netty:1.6.8")
       implementation("ch.qos.logback:logback-classic:1.2.5")
   }

1. Open the terminal.

2. Execute the ./gradlew run command. The following message should be shown:

   [main] INFO  Application - Responding at http://0.0.0.0:8080

   This means that the server is ready to accept requests at the http://0.0.0.0:8080 address. You can click this link to open the application in a default browser: