Skip to content

Kotlin Details

Kotlin entails a few differences. The jte-kotlin dependency is needed to enable .kte templates that contain Kotlin code. Keep in mind that Kotlin application code can use either Java (.jte) or Kotlin (.kte) templates. .kte files are only needed for Kotlin based templates.

Add required dependencies

This dependency is a compile time dependency to avoid including the Kotlin compiler in the resulting build.

compileOnly "gg.jte:jte-kotlin:3.1.12"

Common errors

Non-null parameters

@param name: String
@param name: String?

If a non-null parameter exists in the template, the template will fail to load with an error in the line where the parameter is being included.

Error rendering template:

Failed to render admin/index.kte, error at admin/index.kte:1
(many many lines of stack trace)
Caused by: java.lang.NullPointerException: null cannot be cast to non-null type kotlin.String

Writing a non-supported type to a template

@param myList: List


This will generate an error like so:

gg.jte.TemplateException: Failed to compile template, error at myPage/index.kte:3
Reason: None of the following functions can be called with the arguments supplied: 
public open fun writeUserContent(p0: Content!): Unit defined in gg.jte.html.HtmlTemplateOutput
public open fun writeUserContent(p0: Boolean): Unit defined in gg.jte.html.HtmlTemplateOutput

This will be improved in the future.

Nulls in @for expressions

@for loops use an iterator. If a variable is null then the following error will appear:

Failed to compile template, error at myApp/index.kte:5
        for (s in things) {
Reason: Not nullable value required to call an 'iterator()' method on for-loop range

A quick fix is to make the parameter have an empty list by default.

@for(things in (things ?: listOf()))