Guice - Provider Interface

Introduction

Using @provides annotation of multiple methods can become more complex when code base become large in size. We can move these methods to seperate classes by implementing the Provider interface as shown below −

class SpellCheckerProvider implements Provider<SpellChecker>{
   @Override
   public SpellChecker get() {
      String dbUrl = "jdbc:mysql://localhost:5326/emp";
      String user = "user";
      int timeout = 100;
      SpellChecker SpellChecker = new SpellCheckerImpl(dbUrl, user, timeout);
      return SpellChecker;
   } 
}

Next step is to map the provider to type.

bind(SpellChecker.class).toProvider(SpellCheckerProvider.class);

See the complete example below.

Example - Usage of Provider Interface

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.Provider;

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() {
      bind(SpellChecker.class)
         .toProvider(SpellCheckerProvider.class);
   } 
}

//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);
   }
}

class SpellCheckerProvider implements Provider<SpellChecker>{

   @Override
   public SpellChecker get() {
      String dbUrl = "jdbc:mysql://localhost:5326/emp";
      String user = "user";
      int timeout = 100;

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

Output

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

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