- Google Guice Tutorial
- Guice - Home
- Guice - Overview
- Guice - Environment Setup
- Guice - First Application
- Bindings Examples
- Guice - Linked binding
- Guice - Binding Annotations
- Guice - @Named binding
- Guice - Constant Bindings
- Guice - @Provides Annotation
- Guice - Provider Class
- Guice - Constructor Bindings
- Guice - Inbuilt Bindings
- Guice - Just-in-time Bindings
- Injection Examples
- Guice - Constructor Injection
- Guice - Method Injection
- Guice - Field Injection
- Guice - Optional Injection
- Guice - On-demand Injection
- Miscellaneous Examples
- Guice - Scopes
- Guice - AOP
- Guice Useful Resources
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Google Guice - Provider Class
As @provides method becomes more complex, this method can be moved to separate classes using Provider interface.
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, you have to map the provider to type.
bind(SpellChecker.class).toProvider(SpellCheckerProvider.class);
See the complete example below.
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.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
Now, compile and run the file. You can see the following output −
Inside checkSpelling. jdbc:mysql://localhost:5326/emp user 100
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