Automatic hot reloading of Scala classes
Hottie is small library to recompile, reload and reinstantiate individual Scala classes on the fly without application restart.
It works by creating dynamic class proxy which watches on scala source file, reloading it when necessary and switching to new implementation.
I use Hottie to reload Scalatags templates but it surely can be used more widely.
libraryDependencies += "me.scf37" %% "hottie" % "1.0.5"
package me.scf37.hottie.demo
class Hello {
def sayHello(): String = "hello, world!"
}package me.scf37.hottie.demo
import java.nio.file.Paths
import me.scf37.hottie.Hottie
object Main {
// handler to be called when reload occurs
@volatile var onChange: () => Unit = () => ()
// create new Hottie instance with reload handler
val h: Hottie = Hottie(_ => onChange())
def main(args: Array[String]): Unit = {
// create instance of watched class
val hello: Hello = h.newInstance[Hello](
classOf[Hello],
// source file to watch
Paths.get("src/test/scala/me/scf37/hottie/demo/Hello.scala")
) { cls =>
// create Hello instance by Class[Hello]
cls.newInstance()
}
// say hello
println(hello.sayHello())
// when reload occurs, say hello again
onChange = () => println(hello.sayHello())
Thread.sleep(Long.MaxValue)
}
}Run Main and change sayHello function in Hello.scala in your IDE. Changes will be recompiled and new value of sayHello function will be printed to console.
