floodlight/OFStatisticsMessageBase: add convenience method that returns the...

floodlight/OFStatisticsMessageBase: add convenience method that returns the first stats-req/reply message dcontained in the body

src/main/java/org/openflow/protocol/OFStatisticsMessageBase.java

@@ -78,6 +78,23 @@ public abstract class OFStatisticsMessageBase extends OFMessage implements
         return statistics;
     }
 
+    /**
+     * return the first statistics request in the list of statistics, for
+     * statistics messages that expect exactly one message in their body (e.g.,
+     * flow stats request, port statsrequest)
+     *
+     * @return the first and only element in the list of statistics
+     * @throw NoSuchElementException if the list does not contain exactly one
+     *        element
+     */
+    public OFStatistics getFirstStatistics() {
+        if (statistics == null || statistics.size() != 1) {
+            throw new IllegalArgumentException("Invariant violation: statistics message of type "+statisticType+" contains "+statistics.size() +" statreq/reply messages in its body (should be 1)");
+        }
+
+        return statistics.get(0);
+    }
+
     /**
      * @param statistics the statistics to set
      */