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- Guice - Provider Class
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- 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
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Google Guice - Optional Injection
Injection is a process of injecting dependeny into an object. Optional injection means injecting the dependency if exists. Method and Field injections may be optionally dependent and should have some default value if dependency is not present. 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; import com.google.inject.name.Named; 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() {} } @ImplementedBy(SpellCheckerImpl.class) interface SpellChecker { public void checkSpelling(); } //spell checker implementation class SpellCheckerImpl implements SpellChecker { private String dbUrl = "jdbc:mysql://localhost:5326/emp"; public SpellCheckerImpl(){} @Inject(optional=true) public void setDbUrl(@Named("JDBC") String dbUrl){ this.dbUrl = dbUrl; } @Override public void checkSpelling() { System.out.println("Inside checkSpelling." ); System.out.println(dbUrl); } }
Output
Compile and run the file, you will see the following output.
Inside checkSpelling. jdbc:mysql://localhost:5326/emp
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