Fixes #4020 - Deprecate ExtensionFactory

+ This class is removed in Jetty 10 anyway.
+ If all you want is to access available extension names
  then use the Factory.getAvailableExtensionNames() method
  (which exists in Jetty 10.0.0 as well)

Signed-off-by: Joakim Erdfelt <joakim.erdfelt@gmail.com>

jetty-websocket/websocket-api/src/main/java/org/eclipse/jetty/websocket/api/extensions/ExtensionFactory.java

@@ -24,6 +24,12 @@ import java.util.Map;
 import java.util.ServiceLoader;
 import java.util.Set;
 
+/**
+ * The Factory for Extensions.
+ *
+ * @deprecated this class is removed from Jetty 10.0.0+
+ */
+@Deprecated
 public abstract class ExtensionFactory implements Iterable<Class<? extends Extension>>
 {
     private ServiceLoader<Extension> extensionLoader = ServiceLoader.load(Extension.class);

jetty-websocket/websocket-server/src/main/java/org/eclipse/jetty/websocket/server/WebSocketServerFactory.java

@@ -29,6 +29,7 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
 import java.util.concurrent.Executor;
 import javax.servlet.ServletContext;
 import javax.servlet.http.HttpServletRequest;
@@ -450,6 +451,13 @@ public class WebSocketServerFactory extends ContainerLifeCycle implements WebSoc
         return eventDriverFactory;
     }
 
+    @Override
+    public Set<String> getAvailableExtensionNames()
+    {
+        return Collections.unmodifiableSet(extensionFactory.getExtensionNames());
+    }
+
+    @Deprecated
     @Override
     public ExtensionFactory getExtensionFactory()
     {

jetty-websocket/websocket-servlet/src/main/java/org/eclipse/jetty/websocket/servlet/WebSocketServletFactory.java

@@ -21,6 +21,7 @@ package org.eclipse.jetty.websocket.servlet;
 import java.io.IOException;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
+import java.util.Set;
 import javax.servlet.ServletContext;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
@@ -66,8 +67,24 @@ public interface WebSocketServletFactory
 
     void stop() throws Exception;
 
+    /**
+     * Get the set of available Extensions by registered name.
+     *
+     * @return the set of available extensions by registered name.
+     */
+    Set<String> getAvailableExtensionNames();
+
     WebSocketCreator getCreator();
 
+    /**
+     * Get the registered extensions for this WebSocket factory.
+     *
+     * @return the ExtensionFactory
+     * @see #getAvailableExtensionNames()
+     * @deprecated this class is removed from Jetty 10.0.0+.  To remove specific extensions
+     * from negotiation use {@link WebSocketCreator} to remove then during handshake.
+     */
+    @Deprecated
     ExtensionFactory getExtensionFactory();
 
     /**