fix issue #478: bugs in admin web page
diff --git a/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/service/impl/GenericServiceImpl.java b/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/service/impl/GenericServiceImpl.java
index eab74de..4677b71 100644
--- a/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/service/impl/GenericServiceImpl.java
+++ b/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/service/impl/GenericServiceImpl.java
@@ -52,16 +52,20 @@
         ReferenceConfig<GenericService> reference = new ReferenceConfig<>();
         String group = Tool.getGroup(service);
         String version = Tool.getVersion(service);
-        String interfaze = Tool.getInterface(service);
+        String intf = Tool.getInterface(service);
         reference.setGeneric(true);
         reference.setApplication(applicationConfig);
-        reference.setInterface(interfaze);
+        reference.setInterface(intf);
         reference.setVersion(version);
         reference.setGroup(group);
-        removeGenericSymbol(parameterTypes);
-        GenericService genericService = reference.get();
 
-        return genericService.$invoke(method, parameterTypes, params);
+        try {
+            removeGenericSymbol(parameterTypes);
+            GenericService genericService = reference.get();
+            return genericService.$invoke(method, parameterTypes, params);
+        } finally {
+            reference.destroy();
+        }
     }
 
     /**