[BAEL-6028] Guice Provider class vs @provides

Author: bhaskar16

libraries-data/pom.xml

@@ -105,6 +105,11 @@
             <artifactId>javax.persistence-api</artifactId>
             <version>2.2</version>
         </dependency>
+        <dependency>
+            <groupId>com.google.inject</groupId>
+            <artifactId>guice</artifactId>
+            <version>7.0.0</version>
+        </dependency>
         <dependency>
             <groupId>com.github.ben-manes.caffeine</groupId>
             <artifactId>caffeine</artifactId>

libraries-data/src/main/java/com/baeldung/guice/EmailNotifier.java

@@ -0,0 +1,24 @@
+package com.baeldung.guice;
+
+import com.google.inject.Provider;
+
+public class EmailNotifier implements Notifier, Provider<Notifier> {
+
+    private String smtpUrl;
+    private String user;
+    private String password;
+    private EmailNotifier emailNotifier;
+
+    @Override
+    public Notifier get() {
+        // perform some initialization for email notifier
+        this.smtpUrl = "smtp://localhost:25";
+        emailNotifier = new EmailNotifier();
+        return emailNotifier;
+    }
+
+    @Override
+    public void sendNotification(String message) {
+        System.out.println("Sending email notification: " + message);
+    }
+}

libraries-data/src/main/java/com/baeldung/guice/Logger.java

@@ -0,0 +1,5 @@
+package com.baeldung.guice;
+
+public interface Logger {
+    String log(String message);
+}

libraries-data/src/main/java/com/baeldung/guice/MyGuiceModule.java

@@ -0,0 +1,26 @@
+package com.baeldung.guice;
+
+import com.google.inject.AbstractModule;
+import com.google.inject.Provides;
+
+public class MyGuiceModule extends AbstractModule {
+    /**
+     * This method is called when the Guice injector is created.
+     * It binds the Notifier interface to the EmailNotifier implementation.
+     */
+
+    @Override
+    protected void configure() {
+        bind(Notifier.class).to(EmailNotifier.class);
+    }
+
+    @Provides
+    public Logger provideLogger() {
+        return new Logger() {
+            @Override
+            public String log(String message) {
+                return "Logging message: " + message;
+            }
+        };
+    }
+}

libraries-data/src/main/java/com/baeldung/guice/Notifier.java

@@ -0,0 +1,5 @@
+package com.baeldung.guice;
+
+public interface Notifier {
+    void sendNotification(String message);
+}

libraries-data/src/test/java/com/baeldung/guice/GuiceProviderTester.java

@@ -0,0 +1,30 @@
+package com.baeldung.guice;
+
+import org.junit.Test;
+import org.junit.jupiter.api.Assertions;
+
+import com.google.inject.Guice;
+import com.google.inject.Injector;
+
+public class GuiceProviderTester {
+    @Test
+    public void givenGuiceProvider_whenInjecting_thenShouldReturnEmailNotifier() {
+        // Create a Guice injector with the NotifierModule
+        Injector injector = Guice.createInjector(new MyGuiceModule());
+        // Get an instance of Notifier from the injector
+        Notifier notifier = injector.getInstance(Notifier.class);
+        // Assert that notifier is of type EmailNotifier
+        assert notifier != null;
+        assert notifier instanceof EmailNotifier;
+    }
+
+    @Test
+    public void givenGuiceProvider_whenInjectingWithProvides_thenShouldReturnCustomLogger() {
+        // Create a Guice injector with the NotifierModule
+        Injector injector = Guice.createInjector(new MyGuiceModule());
+        // Get an instance of Logger from the injector
+        Logger logger = injector.getInstance(Logger.class);
+        assert logger != null;
+        Assertions.assertNotNull(logger.log("Hello world"));
+    }
+}