Merged HotSwapHandler from ee9 to common

jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/Handler.java

@@ -534,9 +534,7 @@ public interface Handler extends LifeCycle, Destroyable, Invocable
         public List<Handler> getHandlers()
         {
             Handler next = getHandler();
-            if (next == null)
-                return Collections.emptyList();
-            return List.of(next);
+            return (next == null) ? Collections.emptyList() : Collections.singletonList(next);
         }
 
         @Override

jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/handler/HotSwapHandler.java

@@ -13,13 +13,113 @@
 
 package org.eclipse.jetty.server.handler;
 
+import java.util.Collections;
+import java.util.List;
+
 import org.eclipse.jetty.server.Handler;
+import org.eclipse.jetty.server.Request;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.util.thread.Invocable;
 
 /**
  * A <code>HandlerContainer</code> that allows a hot swap of a wrapped handler.
- * @deprecated
  */
-@Deprecated
-public class HotSwapHandler extends Handler.Wrapper
+public class HotSwapHandler extends Handler.AbstractContainer implements Handler.Nested
 {
+    // TODO unit tests
+
+    private volatile Handler _handler;
+
+    /**
+     *
+     */
+    public HotSwapHandler()
+    {
+    }
+
+    /**
+     * @return Returns the handlers.
+     */
+    public Handler getHandler()
+    {
+        return _handler;
+    }
+
+    /**
+     * @return Returns the handlers.
+     */
+    @Override
+    public List<Handler> getHandlers()
+    {
+        Handler next = _handler;
+        return (next == null) ? Collections.emptyList() : Collections.singletonList(next);
+    }
+
+    /**
+     * @param handler Set the {@link Handler} which should be wrapped.
+     */
+    public void setHandler(Handler handler)
+    {
+        // check state
+        Server server1 = ((Nested)this).getServer();
+        if (server1 != null && server1.isStarted() && handler != null &&
+            server1.getInvocationType() != Invocable.combine(server1.getInvocationType(), handler.getInvocationType()))
+            throw new IllegalArgumentException("Cannot change invocation type of started server");
+
+        // Check for loops.
+        if (handler == this || (handler instanceof Container container &&
+            container.getDescendants().contains(this)))
+            throw new IllegalStateException("setHandler loop");
+
+        try
+        {
+            Server server = getServer();
+            if (handler == _handler)
+                return;
+
+            Handler oldHandler = _handler;
+            if (handler != null)
+            {
+                handler.setServer(server);
+                addBean(handler, true);
+                if (oldHandler != null && oldHandler.isStarted())
+                    handler.start();
+            }
+            _handler = handler;
+            if (oldHandler != null)
+                removeBean(oldHandler);
+        }
+        catch (Exception e)
+        {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Override
+    public Request.Processor handle(Request request) throws Exception
+    {
+        Handler next = _handler;
+        return next == null ? null : next.handle(request);
+    }
+
+    @Override
+    public InvocationType getInvocationType()
+    {
+        Handler next = getHandler();
+        return next == null ? InvocationType.NON_BLOCKING : next.getInvocationType();
+    }
+
+    @Override
+    public void destroy()
+    {
+        if (!isStopped())
+            throw new IllegalStateException("!STOPPED");
+        Handler child = getHandler();
+        if (child != null)
+        {
+            setHandler((Handler)null);
+            child.destroy();
+        }
+        super.destroy();
+    }
 }

jetty-ee9/jetty-ee9-nested/src/main/java/org/eclipse/jetty/ee9/nested/HotSwapHandler.java

@@ -84,18 +84,6 @@ public class HotSwapHandler extends AbstractHandlerContainer
         }
     }
 
-    @Override
-    protected void doStart() throws Exception
-    {
-        super.doStart();
-    }
-
-    @Override
-    protected void doStop() throws Exception
-    {
-        super.doStop();
-    }
-
     @Override
     public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException
     {