[BAEL-6028] Guice Provider and @Provides

di-modules/guice/src/main/java/com/baeldung/examples/guice/provider/EmailNotifier.java

@@ -0,0 +1,26 @@
+package com.baeldung.examples.guice.provider;
+
+import com.google.inject.Provider;
+import java.util.logging.Logger;
+
+public class EmailNotifier implements Notifier, Provider<Notifier> {
+
+    private String smtpUrl;
+    private String user;
+    private String password;
+    private EmailNotifier emailNotifier;
+    Logger log = Logger.getLogger(EmailNotifier.class.getName());
+
+    @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) {
+        log.info("Sending email notification: " + message);
+    }
+}

di-modules/guice/src/main/java/com/baeldung/examples/guice/provider/Logger.java

@@ -0,0 +1,6 @@
+package com.baeldung.examples.guice.provider;
+
+
+public interface Logger {
+    String log(String message);
+}

di-modules/guice/src/main/java/com/baeldung/examples/guice/provider/MyGuiceModule.java

@@ -0,0 +1,31 @@
+package com.baeldung.examples.guice.provider;
+
+import com.google.inject.AbstractModule;
+import com.google.inject.Provides;
+import com.google.inject.name.Names;
+
+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).annotatedWith(Names.named("Email"))
+          .toProvider(EmailNotifier.class);
+
+        bind(Notifier.class).annotatedWith(Names.named("Phone"))
+          .toProvider(PhoneNotifier.class);
+    }
+
+    @Provides
+    public Logger provideLogger() {
+        return new Logger() {
+            @Override
+            public String log(String message) {
+                return "Logging message: " + message;
+            }
+        };
+    }
+}

di-modules/guice/src/main/java/com/baeldung/examples/guice/provider/MyService.java

@@ -0,0 +1,15 @@
+package com.baeldung.examples.guice.provider;
+
+import com.google.inject.Inject;
+import com.google.inject.name.Named;
+
+public class MyService {
+    private final Notifier emailNotifier;
+    private final Notifier phoneNotifier;
+
+    @Inject
+    public MyService(@Named("Email") Notifier emailNotifier, @Named("Phone") Notifier phoneNotifier) {
+        this.emailNotifier = emailNotifier;
+        this.phoneNotifier = phoneNotifier;
+    }
+}

di-modules/guice/src/main/java/com/baeldung/examples/guice/provider/Notifier.java

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

di-modules/guice/src/main/java/com/baeldung/examples/guice/provider/PhoneNotifier.java

@@ -0,0 +1,26 @@
+package com.baeldung.examples.guice.provider;
+
+import java.util.logging.Logger;
+
+import com.google.inject.Provider;
+
+public class PhoneNotifier implements Notifier, Provider<Notifier> {
+    private String fromNumber;
+    private String toNumber;
+
+    private PhoneNotifier phoneNotifier;
+    Logger log = Logger.getLogger(EmailNotifier.class.getName());
+
+    @Override
+    public Notifier get() {
+        // perform some initialization for email notifier
+        this.fromNumber = "baeldung";
+        phoneNotifier = new PhoneNotifier();
+        return phoneNotifier;
+    }
+
+    @Override
+    public void sendNotification(String message) {
+        log.info("Sending phone notification: " + message);
+    }
+}

di-modules/guice/src/test/java/com/baeldung/java/GuiceProviderUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.java;
+
+import org.junit.Test;
+import org.junit.jupiter.api.Assertions;
+import com.baeldung.examples.guice.provider.MyGuiceModule;
+import com.baeldung.examples.guice.provider.Notifier;
+import com.baeldung.examples.guice.provider.EmailNotifier;
+import com.baeldung.examples.guice.provider.Logger;
+
+import com.baeldung.examples.guice.provider.PhoneNotifier;
+import com.google.inject.Guice;
+import com.google.inject.Injector;
+
+public class GuiceProviderUnitTest {
+    @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 emailNotifier = injector.getInstance(EmailNotifier.class);
+        Notifier phoneNotifier = injector.getInstance(PhoneNotifier.class);
+        // Assert that notifier is of type EmailNotifier
+        assert emailNotifier != null;
+
+        assert emailNotifier instanceof EmailNotifier;
+        assert phoneNotifier instanceof PhoneNotifier;
+    }
+
+    @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"));
+    }
+}

di-modules/guice/src/test/java/com/baeldung/examples/GuiceUnitTest.java → di-modules/guice/src/test/java/com/baeldung/java/GuiceUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.examples;
+package com.baeldung.java;
 
 import static org.junit.Assert.assertNotNull;