Issue #12279 ensure handlers added correctly for maven plugin

jetty-core/jetty-maven/src/main/java/org/eclipse/jetty/maven/ServerSupport.java

@@ -19,8 +19,6 @@
 import java.util.List;
 import java.util.Map;
 
-import org.eclipse.jetty.maven.MavenServerConnector;
-import org.eclipse.jetty.maven.PluginLog;
 import org.eclipse.jetty.security.LoginService;
 import org.eclipse.jetty.server.Connector;
 import org.eclipse.jetty.server.Handler;
@@ -65,7 +63,15 @@ public static void configureHandlers(Server server, List<ContextHandler> context
         if (contexts == null)
         {
             contexts = new ContextHandlerCollection();
-            server.setHandler(contexts);
+            if (server.getHandler() != null)
+            {
+                Handler.Sequence handlers = new Handler.Sequence();
+                handlers.addHandler(server.getHandler());
+                handlers.addHandler(contexts);
+                server.setHandler(handlers);
+            }
+            else
+                server.setHandler(contexts);
         } 
 
         if (contextHandlers != null)

jetty-core/jetty-maven/src/test/java/org/eclipse/jetty/maven/ServerSupportTest.java

@@ -0,0 +1,109 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.maven;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Set;
+
+import org.eclipse.jetty.server.Handler;
+import org.eclipse.jetty.server.Request;
+import org.eclipse.jetty.server.Response;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.server.handler.ContextHandler;
+import org.eclipse.jetty.server.handler.ContextHandlerCollection;
+import org.eclipse.jetty.util.Callback;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class ServerSupportTest
+{
+    @Test
+    public void testNoServerHandlers() throws Exception
+    {
+        //Test that a server will always create a ContextHandlerCollection and DefaultHandler
+        Server server = new Server();
+        assertNull(server.getHandler());
+        ServerSupport.configureHandlers(server, null, null);
+        assertNotNull(server.getDefaultHandler());
+        assertNotNull(server.getHandler());
+    }
+
+    @Test
+    public void testExistingServerHandler() throws Exception
+    {
+        //Test that if a Server already has a handler, we replace it with a
+        //sequence containing the original handler plus a ContextHandlerCollection
+        Server server = new Server();
+        Handler.Abstract testHandler = new Handler.Abstract()
+        {
+            @Override
+            public boolean handle(Request request, Response response, Callback callback) throws Exception
+            {
+                return false;
+            }
+        };
+
+        server.setHandler(testHandler);
+        ServerSupport.configureHandlers(server, null, null);
+        assertNotNull(server.getDefaultHandler());
+        assertInstanceOf(Handler.Sequence.class, server.getHandler());
+        Handler.Sequence handlers = (Handler.Sequence)server.getHandler();
+        assertTrue(handlers.contains(testHandler));
+        assertNotNull(handlers.getDescendant(ContextHandlerCollection.class));
+    }
+
+    @Test
+    public void testExistingServerHandlerWithContextHandlers() throws Exception
+    {
+        //Test that if a Server already has a handler, we replace it with
+        //a sequence containing the original handler plus a ContextHandlerCollection
+        //into which we add any supplied ContextHandlers
+        Server server = new Server();
+        Handler.Abstract testHandlerA = new Handler.Abstract()
+        {
+            @Override
+            public boolean handle(Request request, Response response, Callback callback) throws Exception
+            {
+                return false;
+            }
+        };
+
+        ContextHandler contextHandlerA = new ContextHandler();
+        contextHandlerA.setContextPath("/A");
+        ContextHandler contextHandlerB = new ContextHandler();
+        contextHandlerB.setContextPath("/B");
+        List<ContextHandler> contextHandlerList = Arrays.asList(contextHandlerA, contextHandlerB);
+
+        server.setHandler(testHandlerA);
+        ServerSupport.configureHandlers(server, contextHandlerList, null);
+        assertNotNull(server.getDefaultHandler());
+        assertInstanceOf(Handler.Sequence.class, server.getHandler());
+        Handler.Sequence handlers = (Handler.Sequence)server.getHandler();
+        List<Handler> handlerList = handlers.getHandlers();
+        assertEquals(testHandlerA, handlerList.get(0));
+        Handler second = handlerList.get(1);
+        assertInstanceOf(ContextHandlerCollection.class, second);
+        ContextHandlerCollection contextHandlers = (ContextHandlerCollection)second;
+        Set<String> contextPaths = contextHandlers.getContextPaths();
+        assertNotNull(contextPaths);
+        assertTrue(contextPaths.contains("/A"));
+        assertTrue(contextPaths.contains("/B"));
+    }
+}