[Dubbo-3106]Make getRegistered return unmodifiable collection. #3106 (#3425)

* make getRegistered return unmodifiable collection. #3106

* fix ci failure

Author: kezhenxu94

dubbo-registry/dubbo-registry-api/src/main/java/org/apache/dubbo/registry/support/AbstractRegistry.java

@@ -37,6 +37,7 @@
 import java.nio.channels.FileChannel;
 import java.nio.channels.FileLock;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -118,15 +119,15 @@ protected void setUrl(URL url) {
     }
 
     public Set<URL> getRegistered() {
-        return registered;
+        return Collections.unmodifiableSet(registered);
     }
 
     public Map<URL, Set<NotifyListener>> getSubscribed() {
-        return subscribed;
+        return Collections.unmodifiableMap(subscribed);
     }
 
     public Map<URL, Map<String, List<URL>>> getNotified() {
-        return notified;
+        return Collections.unmodifiableMap(notified);
     }
 
     public File getCacheFile() {

dubbo-registry/dubbo-registry-api/src/test/java/org/apache/dubbo/registry/support/AbstractRegistryTest.java

@@ -96,7 +96,9 @@ public void testRegister() throws Exception {
         abstractRegistry.register(mockUrl);
         assert abstractRegistry.getRegistered().contains(mockUrl);
         //test multiple urls
-        abstractRegistry.getRegistered().clear();
+        for (URL url : abstractRegistry.getRegistered()) {
+            abstractRegistry.unregister(url);
+        }
         List<URL> urlList = getList();
         for (URL url : urlList) {
             abstractRegistry.register(url);
@@ -122,14 +124,16 @@ public void testRegisterIfURLNULL() throws Exception {
     public void testUnregister() throws Exception {
         //test one unregister
         URL url = new URL("dubbo", "192.168.0.1", 2200);
-        abstractRegistry.getRegistered().add(url);
+        abstractRegistry.register(url);
         abstractRegistry.unregister(url);
         MatcherAssert.assertThat(false, Matchers.equalTo(abstractRegistry.getRegistered().contains(url)));
         //test multiple unregisters
-        abstractRegistry.getRegistered().clear();
+        for (URL u : abstractRegistry.getRegistered()) {
+            abstractRegistry.unregister(u);
+        }
         List<URL> urlList = getList();
         for (URL urlSub : urlList) {
-            abstractRegistry.getRegistered().add(urlSub);
+            abstractRegistry.register(urlSub);
         }
         for (URL urlSub : urlList) {
             abstractRegistry.unregister(urlSub);

dubbo-registry/dubbo-registry-multicast/src/test/java/org/apache/dubbo/registry/multicast/MulticastRegistryTest.java

@@ -92,7 +92,9 @@ public void testRegister() {
         Set<URL> registered;
         // clear first
         registered = registry.getRegistered();
-        registered.clear();
+        for (URL url : registered) {
+            registry.unregister(url);
+        }
 
         for (int i = 0; i < 2; i++) {
             registry.register(serviceUrl);