Fix issue when reconnecting after connected via REST (#127)

* Fix issue when reconnecting after connected via REST
* Minor cleanup

Author: tmiddlet2666

coherence-visualvm-plugin/src/main/java/com/oracle/coherence/plugin/visualvm/MockApplication.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2025 Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code 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 General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package com.oracle.coherence.plugin.visualvm;
+
+import org.graalvm.visualvm.application.Application;
+
+import static org.graalvm.visualvm.host.Host.UNKNOWN_HOST;
+
+/**
+ * MockApplication is a class used to register a REST connection to fix
+ * issue when unregistering application..
+ */
+public class MockApplication extends Application
+    {
+    // ---- constructors ----------------------------------------------------
+
+    /**
+     * Constructs a new MockApplication instance.
+     *
+     * @param id the unique identifier for this application
+     */
+    public MockApplication(String id)
+        {
+        super(UNKNOWN_HOST, id);
+        }
+    }

coherence-visualvm-plugin/src/main/java/com/oracle/coherence/plugin/visualvm/VisualVMView.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2022 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2025 Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -58,11 +58,9 @@
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
 
-import java.util.LinkedHashSet;
-import java.util.List;
-import java.util.Map;
-import java.util.Set;
+import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
@@ -167,6 +165,12 @@ protected DataViewComponent createComponent()
             addModelForApplication(m_application, model);
             }
 
+        if (m_application == null)
+            {
+            // this is called from REST, so create a dummy application, so the visual VM Model gets cleaned up
+            m_application = new MockApplication(String.valueOf(f_counter.incrementAndGet()));
+            }
+
         boolean fClusterSnapshotEnabled = com.oracle.coherence.plugin.visualvm.GlobalPreferences
                 .sharedInstance().isClusterSnapshotEnabled();
 
@@ -516,4 +520,6 @@ public static void addModelForApplication(Application application, VisualVMModel
      * Set of panels to refresh and update.
      */
     private final Set<AbstractCoherencePanel> f_setPanels = new LinkedHashSet<>();
+
+    private static final AtomicInteger f_counter = new AtomicInteger(0);
     }