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Friday, 6 July 2018

Google Guice - @Named Binding



Google Guice - @Named Binding

Guice provides another way also to map bindings without creating a custom annotation. It allows so using @Named annotation.

Mapping using named annotation

bind(SpellChecker.class).annotatedWith(Names.named("OpenOffice")).to(OpenOfficeWordSpellCheckerImpl.class);

Inject using @Named annotation

@Inject
public TextEditor(@Named("OpenOffice") SpellChecker spellChecker) {
   this.spellChecker = spellChecker;
}

Complete Example

Create a java class named GuiceTester.
GuiceTester.java
import com.google.inject.AbstractModule;
import com.google.inject.Guice;
import com.google.inject.Inject;
import com.google.inject.Injector;
import com.google.inject.name.Named;
import com.google.inject.name.Names;

public class GuiceTester {
   public static void main(String[] args) {
      Injector injector = Guice.createInjector(new TextEditorModule());
      TextEditor editor = injector.getInstance(TextEditor.class);
      editor.makeSpellCheck();
   } 
}
class TextEditor {
   private SpellChecker spellChecker;
   
   @Inject
   public TextEditor(@Named("OpenOffice") SpellChecker spellChecker) {
      this.spellChecker = spellChecker;      
   }
   public void makeSpellCheck() {
      spellChecker.checkSpelling(); 
   }  
}

//Binding Module
class TextEditorModule extends AbstractModule {
   @Override
   
   protected void configure() {
      bind(SpellChecker.class).annotatedWith(Names.named("OpenOffice"))
         .to(OpenOfficeWordSpellCheckerImpl.class);
   } 
}

//spell checker interface
interface SpellChecker {
   public void checkSpelling();
}

//spell checker implementation
class SpellCheckerImpl implements SpellChecker {
   @Override
   
   public void checkSpelling() {
      System.out.println("Inside checkSpelling." );
   } 
}

//subclass of SpellCheckerImpl
class OpenOfficeWordSpellCheckerImpl extends SpellCheckerImpl {
   @Override
   
   public void checkSpelling() {
      System.out.println("Inside OpenOfficeWordSpellCheckerImpl.checkSpelling." );
   } 
}

Output

Compile and run the file, you will see the following output.
Inside OpenOfficeWordSpellCheckerImpl.checkSpelling.

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