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Friday, 6 July 2018

Google Guice - On-Demand Injection



Google Guice - On-Demand Injection

Injection is a process of injecting dependency into an object. Method and field injections can be used to initialize using exiting object using injector.injectMembers() method. See the example below.

Example

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

public class GuiceTester {
   public static void main(String[] args) {
      Injector injector = Guice.createInjector(new TextEditorModule());
      SpellChecker spellChecker = new SpellCheckerImpl();
      injector.injectMembers(spellChecker);
      
      TextEditor editor = injector.getInstance(TextEditor.class);     
      editor.makeSpellCheck();
   } 
}
class TextEditor {
   private SpellChecker spellChecker;

   @Inject
   public void setSpellChecker(SpellChecker spellChecker) {
      this.spellChecker = spellChecker;
   }
   public TextEditor() { }

   public void makeSpellCheck() {
      spellChecker.checkSpelling();
   } 
}

//Binding Module
class TextEditorModule extends AbstractModule {
   @Override
   protected void configure() {      
   } 
}
@ImplementedBy(SpellCheckerImpl.class)
interface SpellChecker {
   public void checkSpelling();
}

//spell checker implementation
class SpellCheckerImpl implements SpellChecker {
   public SpellCheckerImpl(){}
   
   @Override
   public void checkSpelling() { 
      System.out.println("Inside checkSpelling." );
   }
}
Compile and run the file, you will see the following output.
Inside checkSpelling.

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