[play 2.5.3][Using dependency injection to get configuration values]

[miguel...@gmail.com]

I'm trying to migrate a Playframework application from 2.4 to 2.5.3 and I have problems to get values from application.conf file:

Before to get a value of from application.conf what I do was:

Play.application().configuration().getString("label")

Now as Play.application() is deprecated, I should use Dependency injection. Based on the framework documentation I use the following instructions:

1. Define import: import javax.inject.*; import play.Configuration;
2. Define class property: @Inject private Configuration configuration;
3. Use the configuration class property on my class

When I follow these instructions on my controller Application.java it is working perfectly.

But when I try to use it on an other class object from my project, the dependency injection is not working and I always get a NullPointerException.

Can someone give me an example about how to get values from application.conf using dependency Injection?

Some part of my java code where I try to use the DI:

import javax.inject.Inject;
import play.Configuration;
import play.Logger;

public class Zipper {

    @Inject private  Configuration configuration;

    public void unZip(String zipFilePath) {
        Logger.debug("Display : zipFilePath"+zipFilePath);
        Logger.debug("before call parameter from application.conf");
        Logger.debug("configuration.getString = "+configuration.getString("Unzipedfile.path"));
        Logger.debug("aftercall parameter from application.conf");
    }
}

And I always get a null pointer exception, at the line with configuration.getString("Unzipedfile.path")




FYI: i call the class Zipper from an other java class like this : Zipper zipTest = new Zipper();




Is it a limitation, meaning only my controller "application.java" is able to inject correctly the Configuration class ?




[Igmar Palsenberg]

But when I try to use it on an other class object from my project, the dependency injection is not working and I always get a NullPointerException.

Can someone give me an example about how to get values from application.conf using dependency Injection?

 

public class Zipper {

    @Inject private  Configuration configuration;

    public void unZip(String zipFilePath) {
        Logger.debug("Display : zipFilePath"+zipFilePath);
        Logger.debug("before call parameter from application.conf");
        Logger.debug("configuration.getString = "+configuration.getString("Unzipedfile.path"));
        Logger.debug("aftercall parameter from application.conf");
    }
}

And I always get a null pointer exception, at the line with configuration.getString("Unzipedfile.path")




FYI: i call the class Zipper from an other java class like this : Zipper zipTest = new Zipper();

This bypasses dependency injection. You have a few options : 

 public class Zipper {

    @Inject

    public  Zipper(Configuration configuration) {

    }

}

@Inject Injector somewhere, and do :

Zipper zipper = injector.instanceOf(Zipper.class);

Or, in a module, bind it (to a singleton) (assuming is is suitable as such)

public class GlobalBootstrapModule extends AbstractModule {

     @Override

      protected void configure() {

            bind(Zipper.class).in(Singleton.class);

      }

}

or just bind it if it's not suppose to be a Singleton

Or better, use a Guice module, and give a specialised instance back (using a provider).

Igmar 

[Simon Jacobs]

The NPE occurs because the Zipper class is not instantiated by the DI Framework.

Add @Singleton to your Zipper class and inject Zipper to e.q. a controller to make sure Guice will instantiate the class for you and inject it's dependencies.

Regards

[miguel...@gmail.com]

It works, thx a lot :)