[BACKLOG-39783] - Implemented a PentahoSystemPublisher that allows ar…

…bitrary events to be published to concerned subscribers

core/src/main/java/org/pentaho/platform/engine/core/system/PentahoSystem.java

@@ -400,7 +400,7 @@ public static boolean init( final IApplicationContext pApplicationContext, final
     if ( debug ) {
       Logger.debug( PentahoSystem.class, "PentahoSystem Init Complete" ); //$NON-NLS-1$
     }
-
+    PentahoSystemPublisher.getInstance().publish( PentahoSystemPublisher.START_UP_TOPIC, true );
     return true;
   }
 

core/src/main/java/org/pentaho/platform/engine/core/system/PentahoSystemPublisher.java

@@ -0,0 +1,66 @@
+/*!
+ *
+ * This program is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License, version 2.1 as published by the Free Software
+ * Foundation.
+ *
+ * You should have received a copy of the GNU Lesser General Public License along with this
+ * program; if not, you can obtain a copy at http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html
+ * or from the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU Lesser General Public License for more details.
+ *
+ *
+ * Copyright (c) 2002-2024 Hitachi Vantara. All rights reserved.
+ *
+ */
+
+package org.pentaho.platform.engine.core.system;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Consumer;
+
+public class PentahoSystemPublisher {
+  public static final String START_UP_TOPIC = "system_startup";
+  public static final String SHUT_DOWN_TOPIC = "system_shutdown";
+  private final Map<String, ArrayList<Consumer<?>>> topicsSubscribers = new HashMap<>();
+  private static PentahoSystemPublisher instance = null;
+
+  public static PentahoSystemPublisher getInstance() {
+    if ( instance == null ) {
+      instance = new PentahoSystemPublisher();
+    }
+    return instance;
+  }
+
+  public int topicCount() {
+    return topicsSubscribers.size();
+  }
+
+  public <T> void publish( String topic, T value ) {
+    ArrayList<Consumer<?>> subscribers = topicsSubscribers.get( topic );
+    if ( subscribers == null ) {
+      return;
+    }
+
+    for ( Consumer subscriberConsumer : subscribers ) {
+      subscriberConsumer.accept( value );
+    }
+  }
+
+  public synchronized <T> void subscribe( String topicName, Consumer<T> subscriberCallback ) {
+    ArrayList<Consumer<?>> subscribers = topicsSubscribers.get( topicName );
+    if ( subscribers == null ) {
+      subscribers = new ArrayList<>();
+      subscribers.add( subscriberCallback );
+      topicsSubscribers.put( topicName, subscribers );
+    } else {
+      subscribers.add( subscriberCallback );
+    }
+  }
+}

core/src/test/java/org/pentaho/platform/engine/core/system/PentahoSystemPublisherTest.java

@@ -0,0 +1,23 @@
+package org.pentaho.platform.engine.core.system;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class PentahoSystemPublisherTest {
+  @Test
+  public void subscribeTest() {
+    PentahoSystemPublisher.getInstance().subscribe( PentahoSystemPublisher.START_UP_TOPIC, this::startupSubscriber );
+    PentahoSystemPublisher.getInstance().subscribe( PentahoSystemPublisher.SHUT_DOWN_TOPIC, this::shutdownSubscriber );
+    Assert.assertEquals( 2,  PentahoSystemPublisher.getInstance().topicCount() );
+    PentahoSystemPublisher.getInstance().publish( PentahoSystemPublisher.START_UP_TOPIC, true );
+    PentahoSystemPublisher.getInstance().publish( PentahoSystemPublisher.SHUT_DOWN_TOPIC, true );
+  }
+
+  private void shutdownSubscriber( boolean isStopping ) {
+    Assert.assertTrue( isStopping );
+  }
+
+  public void startupSubscriber( boolean isStarting ) {
+    Assert.assertTrue( isStarting );
+  }
+}