added an activator to com.sap.sse which registers a shutdown hook so the OSGi framework will shut down gracefully upon SIGTERM

Change-Id: Ic1d5741878e5139d1757585a5a96aaa2facba170

java/com.sap.sse/META-INF/MANIFEST.MF

@@ -30,3 +30,4 @@ Import-Package: javax.servlet;version="3.1.0",
  org.osgi.framework;version="1.8.0",
  org.osgi.util.tracker;version="1.5.1"
 Automatic-Module-Name: com.sap.sse
+Bundle-Activator: com.sap.sse.impl.Activator

java/com.sap.sse/src/com/sap/sse/impl/Activator.java

@@ -0,0 +1,38 @@
+package com.sap.sse.impl;
+
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import org.osgi.framework.Bundle;
+import org.osgi.framework.BundleActivator;
+import org.osgi.framework.BundleContext;
+import org.osgi.framework.BundleException;
+
+/**
+ * Registers a shutdown hook that gracefully stops the OSGi framework by
+ * grabbing the system bundle and stopping it.
+ * 
+ * @author Axel Uhl (D043530)
+ *
+ */
+public class Activator implements BundleActivator {
+    private static final Logger logger = Logger.getLogger(Activator.class.getName());
+    
+    @Override
+    public void start(BundleContext context) throws Exception {
+        Runtime.getRuntime().addShutdownHook(new Thread(()->{
+            logger.info("Executing shutdown hook, gracefully shutting down OSGi framework");
+            try {
+                final Bundle systemBundle = context.getBundle(0);
+                logger.info("Found system bundle "+systemBundle.getSymbolicName());
+                systemBundle.stop();
+            } catch (BundleException e) {
+                logger.log(Level.WARNING, "Exception while trying to gracefully stop the OSGi framework", e);
+            }
+        }));
+    }
+
+    @Override
+    public void stop(BundleContext context) throws Exception {
+    }
+}