added case for length of map or JSONArray of values

json-path/src/main/java/com/jayway/jsonpath/internal/function/Length.java

@@ -5,6 +5,10 @@ import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import net.minidev.json.JSONArray;
 
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
 /**
  * Provides the length of a JSONArray Object
  *
@@ -18,6 +22,9 @@ public class Length implements Function {
             JSONArray array = (JSONArray)model;
             return Integer.valueOf(array.size());
         }
+        else if (model instanceof Map) {
+            return Integer.valueOf(((Map) model).size());
+        }
         return null;
     }
 }

json-path/src/test/java/com/jayway/jsonpath/functions/JSONEntityFunctionTest.java

@@ -60,6 +60,12 @@ public class JSONEntityFunctionTest extends BaseFunctionTest {
         verifyFunction("$.numbers.%length()", NUMBER_SERIES, 10);
     }
 
+
+    @Test
+    public void testLengthOfStructure() {
+        verifyFunction("$.batches.%length()", BATCH_JSON, 2);
+    }
+
     /**
      * The fictitious use-case/story - is we have a collection of batches with values indicating some quality metric.
      * We want to determine the average of the values for only the batch's values where the number of items in the batch