MyApp.groovy

package com.example

import ratpack.guice.Guice
import ratpack.server.RatpackServer

public class MyApp {
  public static void main(String[] args) throws Exception {

    RatpackServer.start { spec ->
      spec.registry {
        Guice.registry { r ->
          r.bind(MyService.class)
        }
      }
      .handlers { chain ->
        chain.get { ctx ->
          MyService myService = ctx.get(MyService.class)
          myService.myMethod()
          ctx.render("Finished!")
        }
      }
    }
  }
}

MyApp.java

package example;

import ratpack.guice.Guice;
import ratpack.server.RatpackServer;

public class MyApp {

  public static void main(String[] args) throws Exception {
    RatpackServer.start(spec -> spec
      .registry(Guice.registry(r -> r
        .bind(MyService.class)
      ))
      .handlers(chain -> chain
        .get(ctx -> {
          MyService myService = ctx.get(MyService.class);
          myService.myMethod();
          ctx.render("Finished");
        })
      ));
  }
}

MyService.java

package com.example

class MyService {
  void myMethod() {
    System.out.println("calling myMethod");
  }
}

Yes, just change to

public class MyApp {
  public static void main(String[] args) throws Exception {
    RatpackServer.start { spec ->
      spec.registry(
        Guice.registry { r ->
          r.bind(MyService.class)
        }
      )
      .handlers { chain ->
        chain.get { ctx ->
          MyService myService = ctx.get(MyService.class)
          myService.myMethod()
          ctx.render("Finished!")
        }
      }
    }
  }
}

Excellent! :)