Fix Embedded jetty NPE issue (#993)

Author: khandelwal-ayush

datastream-server-restli/src/main/java/com/linkedin/datastream/server/DatastreamServer.java

@@ -393,15 +393,17 @@ public synchronized void startup() throws DatastreamException {
     }
 
     // Start the DMS REST endpoint.
-    try {
-      _jettyLauncher.start();
-      _httpPort = _jettyLauncher.getPort();
-      // httpPort might be modified when _jettyLauncher start, so set the port of _serverComponentHealthAggregator.
-      _serverComponentHealthAggregator.setPort(_httpPort);
-      _isStarted = true;
-    } catch (Exception ex) {
-      ErrorLogger.logAndThrowDatastreamRuntimeException(LOG, "Failed to start embedded Jetty.", ex);
+    if (_jettyLauncher != null) {
+      try {
+        _jettyLauncher.start();
+        _httpPort = _jettyLauncher.getPort();
+        // httpPort might be modified when _jettyLauncher start, so set the port of _serverComponentHealthAggregator.
+        _serverComponentHealthAggregator.setPort(_httpPort);
+      } catch (Exception ex) {
+        ErrorLogger.logAndThrowDatastreamRuntimeException(LOG, "Failed to start embedded Jetty.", ex);
+      }
     }
+    _isStarted = true;
   }
 
   /**

datastream-server/src/main/java/com/linkedin/datastream/server/DatastreamServerConfigurationConstants.java

@@ -16,7 +16,7 @@ public final class DatastreamServerConfigurationConstants {
   public static final String CONFIG_CSV_METRICS_DIR = CONFIG_PREFIX + "csvMetricsDir";
   public static final String CONFIG_ZK_ADDRESS = CoordinatorConfig.CONFIG_ZK_ADDRESS;
   public static final String CONFIG_CLUSTER_NAME = CoordinatorConfig.CONFIG_CLUSTER;
-  public static final String CONFIG_ENABLE_EMBEDDED_JETTY = "enableEmbeddedJetty";
+  public static final String CONFIG_ENABLE_EMBEDDED_JETTY = CONFIG_PREFIX + "enableEmbeddedJetty";
   public static final String CONFIG_FACTORY_CLASS_NAME = "factoryClassName";
   public static final String CONFIG_CONNECTOR_BOOTSTRAP_TYPE = "bootstrapConnector";
   public static final String CONFIG_CONNECTOR_ASSIGNMENT_STRATEGY_FACTORY = "assignmentStrategyFactory";