Velocity

Ktor allows you to use Velocity templates as views within your application by installing the Velocity feature.

Add Dependencies

To enable Velocity support, you need to include the ktor-velocity artifact in the build script:

Gradle (Groovy)

Gradle (Kotlin)

Maven

1. implementation "io.ktor:ktor-velocity:$ktor_version"

Install Velocity

To install the Velocity feature, pass it to the install function in the application initialization code. This can be the main function …

1. import io.ktor.features.*
2. // ...
3. fun Application.main() {
4. install(Velocity)
5. // ...
6. }

… or a specified module:

1. import io.ktor.features.*
2. // ...
3. fun Application.module() {
4. install(Velocity)
5. // ...
6. }

Configure Velocity

Configure Template Loading

Inside the install block, you can configure the VelocityEngine. For example, if you want to use templates from the classpath, use a resource loader for classpath:

1. import io.ktor.velocity.*
2. import org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader
3. import org.apache.velocity.runtime.RuntimeConstants

5. install(Velocity) {
6. setProperty(RuntimeConstants.RESOURCE_LOADER, "classpath")
7. setProperty("classpath.resource.loader.class", ClasspathResourceLoader::class.java.name)
8. }

Send a Template in Response

Imagine you have the index.vl template in resources/templates:

1. <html>
2. <body>
3. <h1>Hello, $user.name</h1>
4. </body>
5. </html>

A data model for a user looks as follows:

1. data class User(val id: Int, val name: String)

To use the template for the specified route, pass VelocityContent to the call.respond method in the following way:

1. get("/index") {
2. val sampleUser = User(1, "John")
3. call.respond(VelocityContent("templates/index.vl", mapOf("user" to sampleUser)))
4. }