allow addressListner to return new addressList for filtering (#3572)

Author: Jeff-Lv

dubbo-registry/dubbo-registry-api/src/main/java/org/apache/dubbo/registry/AddressListener.java

@@ -29,6 +29,6 @@ public interface AddressListener {
      *
      * @param addresses
      */
-    void notify(List<URL> addresses);
+    List<URL> notify(List<URL> addresses);
 
 }

dubbo-registry/dubbo-registry-api/src/main/java/org/apache/dubbo/registry/integration/RegistryDirectory.java

@@ -188,11 +188,12 @@ public synchronized void notify(List<URL> urls) {
          */
         ExtensionLoader<AddressListener> addressListenerExtensionLoader = ExtensionLoader.getExtensionLoader(AddressListener.class);
         Set<String> surpportedListeners = addressListenerExtensionLoader.getSupportedExtensions();
-        for (String addressListenerName : surpportedListeners) {
-            addressListenerExtensionLoader.getExtension(addressListenerName).notify(categoryUrls);
+        if (surpportedListeners != null && !surpportedListeners.isEmpty()) {
+            for (String addressListenerName : surpportedListeners) {
+                categoryUrls = addressListenerExtensionLoader.getExtension(addressListenerName).notify(categoryUrls);
+            }
         }
 
-
         /**
          * TODO Try to refactor the processing of these three type of urls using Collectors.groupBy()?
          */