diff --git a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingFloatingIpHandler.java b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingFloatingIpHandler.java
index b34ae9c..16607b1 100644
--- a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingFloatingIpHandler.java
+++ b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingFloatingIpHandler.java
@@ -144,7 +144,8 @@
                                     boolean install) {
         Network osNet = osNetworkService.network(osPort.getNetworkId());
         if (osNet == null) {
-            final String error = String.format(ERR_FLOW + "no network(%s) exists",
+            final String errorFormat = ERR_FLOW + "no network(%s) exists";
+            final String error = String.format(errorFormat,
                     floatingIp.getFloatingIpAddress(),
                     osPort.getNetworkId());
             throw new IllegalStateException(error);
@@ -153,7 +154,8 @@
         MacAddress srcMac = MacAddress.valueOf(osPort.getMacAddress());
         InstancePort instPort = instancePortService.instancePort(srcMac);
         if (instPort == null) {
-            final String error = String.format(ERR_FLOW + "no host(MAC:%s) found",
+            final String errorFormat = ERR_FLOW + "no host(MAC:%s) found";
+            final String error = String.format(errorFormat,
                     floatingIp.getFloatingIpAddress(), srcMac);
             throw new IllegalStateException(error);
         }
@@ -222,13 +224,13 @@
             throw new IllegalStateException(error);
         }
         if (osNet.getNetworkType() == NetworkType.VXLAN && cNode.dataIp() == null) {
-            final String error = String.format(ERR_FLOW +
-                    "VXLAN mode is not ready for %s", floatingIp, cNode.hostname());
+            final String errorFormat = ERR_FLOW + "VXLAN mode is not ready for %s";
+            final String error = String.format(errorFormat, floatingIp, cNode.hostname());
             throw new IllegalStateException(error);
         }
         if (osNet.getNetworkType() == NetworkType.VLAN && cNode.vlanIntf() == null) {
-            final String error = String.format(ERR_FLOW +
-                    "VLAN mode is not ready for %s", floatingIp, cNode.hostname());
+            final String errorFormat = ERR_FLOW + "VLAN mode is not ready for %s";
+            final String error = String.format(errorFormat, floatingIp, cNode.hostname());
             throw new IllegalStateException(error);
         }
 
@@ -460,7 +462,8 @@
         private void associateFloatingIp(NetFloatingIP osFip) {
             Port osPort = osNetworkService.port(osFip.getPortId());
             if (osPort == null) {
-                final String error = String.format(ERR_FLOW + "port(%s) not found",
+                final String errorFormat = ERR_FLOW + "port(%s) not found";
+                final String error = String.format(errorFormat,
                         osFip.getFloatingIpAddress(), osFip.getPortId());
                 throw new IllegalStateException(error);
             }
diff --git a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingHandler.java b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingHandler.java
index 11b3247..6d2f70b 100644
--- a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingHandler.java
+++ b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingHandler.java
@@ -108,7 +108,6 @@
 
     private static final String MSG_ENABLED = "Enabled ";
     private static final String MSG_DISABLED = "Disabled ";
-    private static final String ERR_SET_FLOWS = "Failed to set flows for router %s:";
     private static final String ERR_UNSUPPORTED_NET_TYPE = "Unsupported network type";
     private static final boolean USE_STATEFUL_SNAT = false;
 
@@ -237,7 +236,7 @@
         Subnet osSubnet = osNetworkService.subnet(osRouterIface.getSubnetId());
         if (osSubnet == null) {
             final String error = String.format(
-                    ERR_SET_FLOWS + "subnet %s does not exist",
+                    "Failed to set flows for router %s: subnet %s does not exist",
                     osRouterIface.getId(),
                     osRouterIface.getSubnetId());
             throw new IllegalStateException(error);
@@ -261,7 +260,7 @@
         Subnet osSubnet = osNetworkService.subnet(osRouterIface.getSubnetId());
         if (osSubnet == null) {
             final String error = String.format(
-                    ERR_SET_FLOWS + "subnet %s does not exist",
+                    "Failed to set flows for router %s: subnet %s does not exist",
                     osRouterIface.getId(),
                     osRouterIface.getSubnetId());
             throw new IllegalStateException(error);
@@ -421,8 +420,8 @@
                                 install));
                 break;
             default:
-                final String error = String.format(
-                        ERR_UNSUPPORTED_NET_TYPE + "%s",
+                final String error = String.format("%s %s",
+                        ERR_UNSUPPORTED_NET_TYPE,
                         network.getNetworkType().toString());
                 throw new IllegalStateException(error);
         }
@@ -615,8 +614,8 @@
                         install);
                 break;
             default:
-                final String error = String.format(
-                        ERR_UNSUPPORTED_NET_TYPE + "%s",
+                final String error = String.format("%s %s",
+                        ERR_UNSUPPORTED_NET_TYPE,
                         networkType.toString());
                 throw new IllegalStateException(error);
         }
@@ -645,8 +644,8 @@
                 sBuilder.matchVlanId(VlanId.vlanId(segmentId));
                 break;
             default:
-                final String error = String.format(
-                        ERR_UNSUPPORTED_NET_TYPE + "%s",
+                final String error = String.format("%s %s",
+                        ERR_UNSUPPORTED_NET_TYPE,
                         networkType.toString());
                 throw new IllegalStateException(error);
         }
@@ -811,8 +810,8 @@
                         .matchEthDst(osNodeService.node(deviceId).vlanPortMac());
                 break;
             default:
-                final String error = String.format(
-                        ERR_UNSUPPORTED_NET_TYPE + "%s",
+                final String error = String.format("%s %s",
+                        ERR_UNSUPPORTED_NET_TYPE,
                         networkType.toString());
                 throw new IllegalStateException(error);
         }
@@ -870,8 +869,8 @@
                 sBuilder.matchVlanId(VlanId.vlanId(segmentId));
                 break;
             default:
-                final String error = String.format(
-                        ERR_UNSUPPORTED_NET_TYPE + "%s",
+                final String error = String.format("%s %s",
+                        ERR_UNSUPPORTED_NET_TYPE,
                         networkType.toString());
                 throw new IllegalStateException(error);
         }
diff --git a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingSnatHandler.java b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingSnatHandler.java
index 5ea8442..9f792bd 100644
--- a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingSnatHandler.java
+++ b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingSnatHandler.java
@@ -285,8 +285,8 @@
                                        TpPort patPort, IpAddress externalIp, MacAddress externalPeerRouterMac) {
         Network osNet = osNetworkService.network(srcInstPort.networkId());
         if (osNet == null) {
-            final String error = String.format(ERR_PACKETIN + "network %s not found",
-                    srcInstPort.networkId());
+            final String error = String.format("%s network %s not found",
+                                        ERR_PACKETIN, srcInstPort.networkId());
             throw new IllegalStateException(error);
         }
 
@@ -333,9 +333,8 @@
                         .setEthSrc(DEFAULT_GATEWAY_MAC);
                 break;
             default:
-                final String error = String.format(
-                        ERR_UNSUPPORTED_NET_TYPE + "%s",
-                        networkType.toString());
+                final String error = String.format("%s %s",
+                        ERR_UNSUPPORTED_NET_TYPE, networkType.toString());
                 throw new IllegalStateException(error);
         }
 
@@ -373,8 +372,8 @@
                     tmpBuilder.setOutput(gNode.vlanPortNum());
                     break;
                 default:
-                    final String error = String.format(ERR_UNSUPPORTED_NET_TYPE + "%s",
-                            networkType.toString());
+                    final String error = String.format("%s %s",
+                            ERR_UNSUPPORTED_NET_TYPE, networkType.toString());
                     throw new IllegalStateException(error);
             }
 
@@ -412,8 +411,8 @@
                 tBuilder.popVlan();
                 break;
             default:
-                final String error = String.format(ERR_UNSUPPORTED_NET_TYPE + "%s",
-                        networkType.toString());
+                final String error = String.format("%s %s",
+                        ERR_UNSUPPORTED_NET_TYPE, networkType.toString());
                 throw new IllegalStateException(error);
         }
 
diff --git a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingHandler.java b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingHandler.java
index 37cabf4..3cba0e3 100644
--- a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingHandler.java
+++ b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackSwitchingHandler.java
@@ -74,7 +74,7 @@
 
     private final Logger log = getLogger(getClass());
 
-    private static final String ERR_SET_FLOWS = "Failed to set flows for %s: ";
+    private static final String ERR_SET_FLOWS_VNI = "Failed to set flows for %s: Failed to get VNI for %s";
 
     @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
     CoreService coreService;
@@ -341,9 +341,9 @@
         Network osNet = osNetworkService.network(instPort.networkId());
 
         if (osNet == null || Strings.isNullOrEmpty(osNet.getProviderSegID())) {
-            final String error = String.format(
-                    ERR_SET_FLOWS + "Failed to get VNI for %s",
-                    instPort, osNet == null ? "<none>" : osNet.getName());
+            final String error =
+                    String.format(ERR_SET_FLOWS_VNI,
+                        instPort, osNet == null ? "<none>" : osNet.getName());
             throw new IllegalStateException(error);
         }
 
@@ -354,9 +354,9 @@
     private Long getVni(InstancePort instPort) {
         Network osNet = osNetworkService.network(instPort.networkId());
         if (osNet == null || Strings.isNullOrEmpty(osNet.getProviderSegID())) {
-            final String error = String.format(
-                    ERR_SET_FLOWS + "Failed to get VNI for %s",
-                    instPort, osNet == null ? "<none>" : osNet.getName());
+            final String error =
+                    String.format(ERR_SET_FLOWS_VNI,
+                        instPort, osNet == null ? "<none>" : osNet.getName());
             throw new IllegalStateException(error);
         }
         return Long.valueOf(osNet.getProviderSegID());