diff --git a/common/base/src/constants.rs b/common/base/src/constants.rs
index b1faf270..070ac727 100644
--- a/common/base/src/constants.rs
+++ b/common/base/src/constants.rs
@@ -17,6 +17,8 @@
 pub const REGISTRY_PROTOCOL: &str = "registry_protocol";
 pub const PROTOCOL: &str = "protocol";
 pub const REGISTRY: &str = "registry";
+pub const INVOKE: &str = "$invoke";
+pub const INVOKE_ASYNC: &str = "$invokeAsync";
 
 // URL key
 pub const DUBBO_KEY: &str = "dubbo";
diff --git a/dubbo/src/cluster/loadbalance/impls/random.rs b/dubbo/src/cluster/loadbalance/impls/random.rs
index 3e1cf651..d1b2b18e 100644
--- a/dubbo/src/cluster/loadbalance/impls/random.rs
+++ b/dubbo/src/cluster/loadbalance/impls/random.rs
@@ -21,7 +21,7 @@ use std::{
 };
 
 use crate::{
-    cluster::loadbalance::types::{LoadBalance, Metadata},
+    cluster::loadbalance::types::{AbstractLoadBalance, Metadata},
     codegen::RpcInvocation,
 };
 
@@ -43,16 +43,13 @@ impl Debug for RandomLoadBalance {
     }
 }
 
-impl LoadBalance for RandomLoadBalance {
-    fn select(
+impl AbstractLoadBalance for RandomLoadBalance {
+    fn do_select(
         &self,
         invokers: Arc<Vec<Url>>,
         _url: Option<Url>,
         _invocation: Arc<RpcInvocation>,
     ) -> Option<Url> {
-        if invokers.is_empty() {
-            return None;
-        }
         let index = rand::random::<usize>() % invokers.len();
         Some(invokers[index].clone())
     }
diff --git a/dubbo/src/cluster/loadbalance/impls/roundrobin.rs b/dubbo/src/cluster/loadbalance/impls/roundrobin.rs
index 5fd0ed49..f07c7707 100644
--- a/dubbo/src/cluster/loadbalance/impls/roundrobin.rs
+++ b/dubbo/src/cluster/loadbalance/impls/roundrobin.rs
@@ -25,7 +25,7 @@ use std::{
 };
 
 use crate::{
-    cluster::loadbalance::types::{LoadBalance, Metadata},
+    cluster::loadbalance::types::{AbstractLoadBalance, Metadata},
     codegen::RpcInvocation,
 };
 
@@ -61,16 +61,13 @@ impl RoundRobinLoadBalance {
     }
 }
 
-impl LoadBalance for RoundRobinLoadBalance {
-    fn select(
+impl AbstractLoadBalance for RoundRobinLoadBalance {
+    fn do_select(
         &self,
         invokers: Arc<Vec<Url>>,
         _url: Option<Url>,
         invocation: Arc<RpcInvocation>,
     ) -> Option<Url> {
-        if invokers.is_empty() {
-            return None;
-        }
         let fingerprint = invocation.unique_fingerprint();
         self.guarantee_counter_key(fingerprint.as_str());
         let index = self
diff --git a/dubbo/src/cluster/loadbalance/types.rs b/dubbo/src/cluster/loadbalance/types.rs
index 9273d07e..d7a403dd 100644
--- a/dubbo/src/cluster/loadbalance/types.rs
+++ b/dubbo/src/cluster/loadbalance/types.rs
@@ -31,6 +31,32 @@ pub trait LoadBalance: Debug {
     ) -> Option<Url>;
 }
 
+pub trait AbstractLoadBalance: LoadBalance {
+    fn do_select(
+        &self,
+        invokers: Arc<Vec<Url>>,
+        url: Option<Url>,
+        invocation: Arc<RpcInvocation>,
+    ) -> Option<Url>;
+}
+
+impl<AbstractLoadBalanceImpl: AbstractLoadBalance> LoadBalance for AbstractLoadBalanceImpl {
+    fn select(
+        &self,
+        invokers: Arc<Vec<Url>>,
+        url: Option<Url>,
+        invocation: Arc<RpcInvocation>,
+    ) -> Option<Url> {
+        if invokers.is_empty() {
+            return None;
+        }
+        if invokers.len() == 1 {
+            return Some(invokers[0].clone());
+        }
+        self.do_select(invokers, url, invocation)
+    }
+}
+
 pub struct Metadata {
     pub name: &'static str,
 }