Merge pull request apolloconfig#698 from powerYao/master

use emptyList instead of creating a new list every time.

Author: nobodyiam

apollo-configservice/src/main/java/com/ctrip/framework/apollo/metaservice/service/DiscoveryService.java

@@ -9,7 +9,7 @@
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Service;
 
-import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
 @Service
@@ -23,22 +23,22 @@ public List<InstanceInfo> getConfigServiceInstances() {
     if (application == null) {
       Tracer.logEvent("Apollo.EurekaDiscovery.NotFound", ServiceNameConsts.APOLLO_CONFIGSERVICE);
     }
-    return application != null ? application.getInstances() : new ArrayList<>();
+    return application != null ? application.getInstances() : Collections.emptyList();
   }
 
   public List<InstanceInfo> getMetaServiceInstances() {
     Application application = eurekaClient.getApplication(ServiceNameConsts.APOLLO_METASERVICE);
     if (application == null) {
       Tracer.logEvent("Apollo.EurekaDiscovery.NotFound", ServiceNameConsts.APOLLO_METASERVICE);
     }
-    return application != null ? application.getInstances() : new ArrayList<>();
+    return application != null ? application.getInstances() : Collections.emptyList();
   }
 
   public List<InstanceInfo> getAdminServiceInstances() {
     Application application = eurekaClient.getApplication(ServiceNameConsts.APOLLO_ADMINSERVICE);
     if (application == null) {
       Tracer.logEvent("Apollo.EurekaDiscovery.NotFound", ServiceNameConsts.APOLLO_ADMINSERVICE);
     }
-    return application != null ? application.getInstances() : new ArrayList<>();
+    return application != null ? application.getInstances() : Collections.emptyList();
   }
 }