fix: prevent duplicate shutdown hooks and replace e.printStackTrace() in CassandraConnector (#1183)

Two issues fixed:
1. prepareSession() called registerShutdownHook() on every invocation.
   If getSession() triggered re-preparation (stale/closed session),
   multiple hooks were registered for the same operation. Added a
   shutdownHookRegistered boolean guard to ensure exactly one hook is
   registered for the lifetime of the process.
2. e.printStackTrace() in the catch block sent stack traces to stderr
   without context. Replaced with TelemetryManager.error() for consistent,
   structured logging.
3. close() now iterates sessions individually with per-session error
   handling so a failure on one session does not abort closing others,
   and clears the map after shutdown.

Co-authored-by: Claude <claude@anthropic.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: pallakartheekreddy

platform-core/cassandra-connector/src/main/java/org/sunbird/cassandra/CassandraConnector.java

@@ -22,6 +22,9 @@ public class CassandraConnector {
 	/** Cassandra Session Map. */
 	private static Map<String, Session> sessionMap = new HashMap<String, Session>();
 
+	/** Guard to prevent registering duplicate JVM shutdown hooks. */
+	private static boolean shutdownHookRegistered = false;
+
 	static {
 		if (Platform.getBoolean("service.db.cassandra.enabled", true))
 			prepareSession("lp", getConsistencyLevel("lp"));
@@ -77,9 +80,11 @@ private static void prepareSession(String sessionKey, ConsistencyLevel level) {
 						.build().connect());
 			}
 
-			registerShutdownHook();
+			if (!shutdownHookRegistered) {
+				registerShutdownHook();
+				shutdownHookRegistered = true;
+			}
 		} catch (Exception e) {
-			e.printStackTrace();
 			TelemetryManager.error("Error! While Loading Cassandra Properties." + e.getMessage(), e);
 		}
 	}
@@ -129,21 +134,33 @@ private static List<InetSocketAddress> getSocketAddress(List<String> hosts) {
 	}
 
 	/**
-	 * Close connection with the cluster.
-	 *
+	 * Close all Cassandra sessions gracefully.
+	 * Each session is closed individually so a failure in one does not
+	 * prevent closing the others.
 	 */
 	public static void close() {
-		sessionMap.entrySet().stream().forEach(stream -> stream.getValue().close());
+		sessionMap.forEach((key, session) -> {
+			if (session != null && !session.isClosed()) {
+				try {
+					session.close();
+				} catch (Exception e) {
+					TelemetryManager.error("Error closing Cassandra session for key: " + key + " — " + e.getMessage(), e);
+				}
+			}
+		});
+		sessionMap.clear();
 	}
 
 	/**
-	 * Register JVM shutdown hook to close cassandra open session.
+	 * Register a single JVM shutdown hook to close all open Cassandra sessions.
+	 * Protected by shutdownHookRegistered so it is called only once even when
+	 * prepareSession() is invoked multiple times.
 	 */
 	private static void registerShutdownHook() {
 		Runtime.getRuntime().addShutdownHook(new Thread() {
 			@Override
 			public void run() {
-				TelemetryManager.log("Shutting down Cassandra connector session");
+				TelemetryManager.log("Shutting down Cassandra connector — closing all sessions");
 				CassandraConnector.close();
 			}
 		});