docs/modules/languages/pages/kotlin.adoc

= Writing Integrations in Kotlin

An integration written in Kotlin looks very similar to a Java one except it can leverages Kotlin's language enhancements over Java:

[source,kotlin]
----
from("timer:tick")
    .process { e -> e.getIn().body = "Hello Camel K!" }
    .to("log:info")
----

You can run it with the standard command:

```
kamel run example.kts
```

Camel K extends the Camel Java DSL making it easier to configure the context in which the integration runs using the top level _context_ block

[source,kotlin]
----
context {
  // configure the context here
}
----

At the moment the enhanced DSL provides a way to bind items to the registry, to configure the components the context creates and some improvements over the REST DSL.

== Registry Configuration

The registry is accessible using the _registry_ block inside the _context_ one:

[source,kotlin]
----
context {
    registry {
        bind("my-cache", Caffeine.newBuilder().build()) // <1>
        bind("my-processor", processor { // <2>
            e -> e.getIn().body = "Hello"
        })
        bind("my-predicate", predicate { // <3>
            e -> e.getIn().body != null
        })
    }
}
----
<1> bind a simple bean to the context
<2> define a custom processor to be used later in the routes by ref
<3> define a custom predicate to be used later in the routes by ref


== Components Configuration

Components can be configured within the _components_ block inside the _context_ one:

[source,kotlin]
----
context {
    components {
        component<SedaComponent>("seda") { //<1>
            queueSize = 1234
            concurrentConsumers = 12
        }

        component<SedaComponent>("mySeda") { // <2>
            queueSize = 4321
            concurrentConsumers = 21
        }

        component<LogComponent>("log") { // <3>
           setExchangeFormatter {
               e: Exchange -> "" + e.getIn().body
           }
       }
    }
}
----
<1> configure the properties of a component whit type _SedaComponent_ and name _seda_
<2> configure the properties of a component with type SedaComponent and name _mySeda_, note that as _mySeda_ does not represent a valid component scheme, a new component of the required type will be instantiated.
<3> configure the properties of the component whit name _log_

[NOTE]
====
As for Groovy, you can provide your custom extension to the DSL
====

== Rest Endpoints

Integrations's REST endpoints can be configured using the top level _rest_ block:

[source,kotlin]
----
rest {
    configuration { // <1>
        host = "my-host"
        port = "9192"
    }

    path("/my/path") { // <2>
        // standard Rest DSL
    }
}
----
<1> Configure the rest engine
<2> Configure the rest endpoint for the base path '/my/path'