httpdns 缓存策略，特殊接口获取 httpdns 服务

foudations/mogo-utils/src/main/java/com/mogo/utils/network/OkHttpFactory.java

@@ -1,11 +1,11 @@
 package com.mogo.utils.network;
 
 import java.net.InetAddress;
-import java.net.UnknownHostException;
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
+import okhttp3.ConnectionPool;
 import okhttp3.Dns;
 import okhttp3.Interceptor;
 import okhttp3.OkHttpClient;
@@ -52,7 +52,11 @@ public final class OkHttpFactory {
                     HttpDns httpDns = NetConfig.instance().getHttpDns();
                     if ( httpDns != null ) {
                         builder.dns( hostname -> {
-                            return httpDns.lookup( hostname );
+                            List< InetAddress > addresses = httpDns.lookup( hostname );
+                            if ( addresses != null && !addresses.isEmpty() ) {
+                                return addresses;
+                            }
+                            return Dns.SYSTEM.lookup( hostname );
                         } );
                     }