Home » JVM Languages » Scala » Run code on startup with Play and Scala

About Emmanouil Gkatziouras

Emmanouil Gkatziouras
He is a versatile software engineer with experience in a wide variety of applications/services.He is enthusiastic about new projects, embracing new technologies, and getting to know people in the field of software.

Run code on startup with Play and Scala

Depending on various projects, sometimes there is the need to execute some actions on initialization just before our application starts to serve requests.

It was a common practice to call the functions that we wanted to get executed through GlobalSettings, however it is not recommended.

The other way around to achieve this is to implement a class which will be injected and thus add the code that we want to get executed on the class constructor.

We might believe that it is sufficient to implement a class which shall use the @Singleton annotation.

For example

@Singleton
class StartUpService {

    //The code that needs to be executed

}

But this will not work as expected since our component instances on play are created lazily when they are needed.

Instances are created lazily when they are needed. If a component is never used by another component, then it won’t be created at all. This is usually what you want. For most components there’s no point creating them until they’re needed. However, in some cases you want components to be started up straight away or even if they’re not used by another component. For example, you might want to send a message to a remote system or warm up a cache when the application starts. You can force a component to be created eagerly by using an eager binding.

To tackle this problem, our singleton has to be initialized eagerly. To achieve an eager initialization we will define an eager binding.

To define an eager binding we have to implement a class that extends the AbstractModule and then bind our service as an eager singleton.

package com.gkatzioura.eager

import com.google.inject.AbstractModule
import com.google.inject.name.Names

// A Module is needed to register bindings
class EagerLoaderModule extends AbstractModule {
  override def configure() = {

    bind(classOf[StartUpService]).asEagerSingleton
  }
}

Then we have to enable our module by declaring so to our conf/application.conf configuration.

play.modules.enabled += "com.gkatzioura.eager.EagerLoaderModule"

The above approach creates a module by defining it explicitly. The other approach is to use the default functionality where Play will load any class called Module that is defined in the root package.

In conclusion, play gives us the option to execute certain functions once the application has started. To do so we need to implement a component as an eager singleton. Skip the GlobalSettings as it is not advised by the official documentation.

Published on Java Code Geeks with permission by Emmanouil Gkatziouras, partner at our JCG program. See the original article here: Run code on startup with Play and Scala

Opinions expressed by Java Code Geeks contributors are their own.

(0 rating, 0 votes)
You need to be a registered member to rate this.
Start the discussion Views Tweet it!
Do you want to know how to develop your skillset to become a Java Rockstar?
Subscribe to our newsletter to start Rocking right now!
To get you started we give you our best selling eBooks for FREE!
1. JPA Mini Book
2. JVM Troubleshooting Guide
3. JUnit Tutorial for Unit Testing
4. Java Annotations Tutorial
5. Java Interview Questions
6. Spring Interview Questions
7. Android UI Design
and many more ....
Email address:

Leave a Reply

Be the First to Comment!

avatar
  Subscribe  
Notify of