Guice - @Provides Annotation

Introduction

Guice provides a way to create bindings with complex objects using @Provides annotation. This way, we can initialize the object before injecting as dependency.

@Provides
public SpellChecker provideSpellChecker(){
   String dbUrl = "jdbc:mysql://localhost:5326/emp";
   String user = "user";
   int timeout = 100;
   SpellChecker SpellChecker = new SpellCheckerImpl(dbUrl, user, timeout);
   return SpellChecker;
}

This method is being part of Binding Module and provides the complex object to be mapped. See the complete example below.

Example - Usage of @Provides Annotation

GuiceTester.java

package com.tutorialspoint;

import com.google.inject.AbstractModule;
import com.google.inject.Guice;
import com.google.inject.Inject;
import com.google.inject.Injector;
import com.google.inject.Provides;

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( SpellChecker spellChecker) {
      this.spellChecker = spellChecker;
   }
   public void makeSpellCheck(){
      spellChecker.checkSpelling();
   } 
}

//Binding Module
class TextEditorModule extends AbstractModule {

   @Override
   protected void configure() {} 

   @Provides
   public SpellChecker provideSpellChecker(){

      String dbUrl = "jdbc:mysql://localhost:5326/emp";
      String user = "user";
      int timeout = 100;

      SpellChecker SpellChecker = new SpellCheckerImpl(dbUrl, user, timeout);
      return SpellChecker;
   }
}

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

//spell checker implementation
class SpellCheckerImpl implements SpellChecker {

   private String dbUrl;
   private String user;
   private Integer timeout;

   @Inject
   public SpellCheckerImpl(String dbUrl, 
      String user, 
      Integer timeout){
      this.dbUrl = dbUrl;
      this.user = user;
      this.timeout = timeout;
   } 

   @Override
   public void checkSpelling() { 
      System.out.println("Inside checkSpelling." );
      System.out.println(dbUrl);
      System.out.println(user);
      System.out.println(timeout);
   }
}

Output

Compile and run the file, you will see the following output −

Inside checkSpelling.
jdbc:mysql://localhost:5326/emp
user
100