chore: Setup notification service and change Java to LTS 21

server/application-server/build.gradle

@@ -13,7 +13,7 @@ version = '0.0.1-SNAPSHOT'
 
 java {
     toolchain {
-        languageVersion = JavaLanguageVersion.of(22)
+        languageVersion = JavaLanguageVersion.of(21)
     }
 }
 

server/application-server/src/main/java/de/tum/cit/aet/helios/syncing/NatsNotificationPublisherService.java

@@ -0,0 +1,95 @@
+package de.tum.cit.aet.helios.syncing;
+
+import io.nats.client.Connection;
+import io.nats.client.JetStream;
+import io.nats.client.Nats;
+import io.nats.client.Options;
+import io.nats.client.impl.NatsMessage;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Service;
+import org.springframework.boot.context.event.ApplicationReadyEvent;
+import org.springframework.context.event.EventListener;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.time.Duration;
+
+@Service
+public class NatsNotificationPublisherService {
+
+    private static final Logger logger = LoggerFactory.getLogger(NatsNotificationPublisherService.class);
+
+    private Connection natsConnection;
+    private JetStream jetStream;
+
+    @Value("${nats.enabled}")
+    private boolean isNatsEnabled;
+
+    @Value("${nats.server}")
+    private String natsServer;
+
+    @Value("${nats.auth.token}")
+    private String natsAuthToken;
+
+    @EventListener(ApplicationReadyEvent.class)
+    public void init() {
+        if (!isNatsEnabled) {
+            logger.info("NATS is disabled. Skipping initialization.");
+            return;
+        }
+
+        validateConfigurations();
+        Options options = buildNatsOptions();
+
+        while (true) {
+            try {
+                natsConnection = Nats.connect(options);
+                jetStream = natsConnection.jetStream();
+                logger.info("Connected to NATS at {}", natsServer);
+                // publishDummyNotification();
+                return;
+            } catch (IOException | InterruptedException e) {
+                logger.error("NATS connection error: {}", e.getMessage(), e);
+            }
+        }
+    }
+
+    private void validateConfigurations() {
+        if (natsServer == null || natsServer.trim().isEmpty()) {
+            throw new IllegalArgumentException("NATS server configuration is missing.");
+        }
+    }
+
+    private Options buildNatsOptions() {
+        return Options.builder()
+                .server(natsServer)
+                .token(natsAuthToken)
+                .connectionListener((conn, type) -> logger.info("Connection event - Server: {}, {}",
+                        conn.getServerInfo().getPort(), type))
+                .maxReconnects(-1)
+                .reconnectWait(Duration.ofSeconds(2))
+                .build();
+    }
+
+    public void publishNotification(String subject, byte[] message) throws IOException, InterruptedException {
+        NatsMessage msg = NatsMessage.builder()
+                .subject("notification." + subject)
+                .data(message)
+                .build();
+        natsConnection.publish(msg);
+        logger.info("Published message to subject '{}'", "notification." + subject);
+    }
+
+    private void publishDummyNotification() {
+        String dummyMessage = "This is a dummy notification message.";
+        try {
+            publishNotification("dummy", dummyMessage.getBytes(StandardCharsets.UTF_8));
+            logger.info("Dummy notification message published successfully.");
+        } catch (IOException | InterruptedException e) {
+            logger.error("Failed to publish dummy notification message: {}", e.getMessage(), e);
+        }
+    }
+}

server/notification/.env.example

@@ -0,0 +1,5 @@
+DATASOURCE_URL=jdbc:postgresql://127.0.0.1/helios
+DATASOURCE_USERNAME=helios
+DATASOURCE_PASSWORD=helios
+NATS_SERVER=localhost:4222
+NATS_AUTH_TOKEN=5760e8ae09adfb2756f9f8cd5cb2caa704cd3f549eaa9298be843ceb165185d815b81f90c680fa7f626b7cd63abf6ac9

server/notification/.gitattributes

@@ -0,0 +1,3 @@
+/gradlew text eol=lf
+*.bat text eol=crlf
+*.jar binary

server/notification/.gitignore

@@ -0,0 +1,38 @@
+HELP.md
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+.sdkmanrc

server/notification/build.gradle

@@ -0,0 +1,33 @@
+plugins {
+	id 'java'
+	id 'war'
+	id 'org.springframework.boot' version '3.3.4'
+	id 'io.spring.dependency-management' version '1.1.6'
+}
+
+group = 'de.tum.cit.aet'
+version = '0.0.1-SNAPSHOT'
+
+java {
+	toolchain {
+		languageVersion = JavaLanguageVersion.of(21)
+	}
+}
+
+repositories {
+	mavenCentral()
+}
+
+dependencies {
+	implementation 'org.springframework.boot:spring-boot-starter-web'
+	implementation 'org.springdoc:springdoc-openapi-starter-webmvc-ui:2.6.0'
+    implementation 'org.openapitools:jackson-databind-nullable:0.2.6'
+	implementation 'io.nats:jnats:2.20.4'
+	providedRuntime 'org.springframework.boot:spring-boot-starter-tomcat'
+	testImplementation 'org.springframework.boot:spring-boot-starter-test'
+	testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
+}
+
+tasks.named('test') {
+	useJUnitPlatform()
+}

server/notification/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.10.2-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists