用 Java 玩 2.6 - 添加环境依赖注入

Question

I need to use the Play.Environment in one of my java class as below. I am using Play 2.6.x. Can you please help me in understanding, how to add dependency injection here. I tried using as below, but the env object is coming as NULL.

MyFile.java

public final class MyFinalClass  {

 @Inject
 static Environment env;

public static String getFilePath(String fileName)  {
        return env.rootPath().getAbsolutePath();
}
static {
//It has a static block and some code here. I dont have any constructor.
}
}

Thanks

/***************************************************************************/ I have modified the above code and make it Singleton as below:

MyFinalClass.java
public class MyFinalClass   implements IConfigurationManager {

    @Inject Environment env;
    private static MyFinalClass   INSTANCE;

    //Pvt Constructor
    private MyFinalClass  () {

    }

    //Create Singleton Instance
    public static MyFinalClass instance() {
        if(INSTANCE == null) {
            INSTANCE = new MyFinalClass();
        }
        return INSTANCE;
    }
}

//Module.java
class Module extends AbstractModule {
    @Override 
    protected void configure( {

        bind(MyFinalClass.class).asEagerSingleton();
      }

Here I am getting Error as: Classes must have either one (and only one) constructor annotated with @Inject or a zero-argument constructor that is not private.

Then I modified as below:

Environment env;
//Pvt Constructor
@Inject private MyFinalClass  (Environment env) {
    this.env = env;
}

Here I am getting compilation issue the new MyFinalClass expects argument. Can you please help in this.

Thanks

Answer 1

Static field injection is not recommended . If you really need to have your class and method static you should use Guice's requestStaticInjection(..) . You could also make MyFinalClass a Singleton, inject Environment in the constructor and then inject MyFinalClass wherever you need to use getFilePath(..).

Edit : I see your comment about requestStaticInjection, so here is a short description about how to use it. Honestly I think it's more tidy to just make the class a Singleton. If you have stuff in MyFinalClass that you don't want to include in a Singleton maybe you should create a new class.

To use requestStaticInjection() you have to do the request from a module, and this module needs to be loaded .

public class InjectorModule extends AbstractModule {
    @Override
    protected void configure() {
        requestStaticInjection(MyFinalClass.class);
    }
}

Edit 2 : You have changed your question now to use Singleton, but you are doing it wrong. Check the Play Docs , you just have to add the @Singleton annotation to your class.

Example where we create a singleton and a controller class that injects it (I'm writing this directly in the editor, not tested code but you get the idea):

@Singleton
public class MyFinalClass {
    private Environment env;

    @Inject
    public MyFinalClass(Environment env) {
        this.env = env;
    }

    public String getFilePath(String fileName) {
        return env.rootPath().getAbsolutePath();
    }
}

public class TestController extends Controller {
    @Inject
    private MyFinalClass myFinalClass;

    public Result index() {
        String fileName = "test.tst";
        String filePath = myFinalClass.getFilePath(fileName);

        return ok(filePath);
    }
}