Support for getting the length of an array.

json-path/src/main/java/com/jayway/jsonpath/internal/token/PathToken.java

@@ -128,6 +128,17 @@ public abstract class PathToken {
         }
     }
 
+    void handleArrayLength(String currentPath, Object model, EvaluationContextImpl ctx) {
+        String evalPath = currentPath + ".length";
+        PathRef pathRef = ctx.forUpdate() ? PathRef.create(model, "length") : PathRef.NO_OP;
+        Object evalHit = ctx.jsonProvider().length(model);
+        if (isLeaf()) {
+            ctx.addResult(evalPath, pathRef, evalHit);
+        } else {
+            next().evaluate(evalPath, pathRef, evalHit, ctx);
+        }
+    }
+
     PathToken prev(){
         return prev;
     }

json-path/src/main/java/com/jayway/jsonpath/internal/token/PropertyPathToken.java

@@ -38,6 +38,11 @@ public class PropertyPathToken extends PathToken {
     @Override
     public void evaluate(String currentPath, PathRef parent, Object model, EvaluationContextImpl ctx) {
         if (!ctx.jsonProvider().isMap(model)) {
+            // Special case handling of the 'length' property of arrays.
+            if (isLeaf() && ctx.jsonProvider().isArray(model) && properties.size() == 1 && properties.get(0).equals("length")) {
+                handleArrayLength(currentPath, model, ctx);
+                return;
+            }
             throw new PathNotFoundException("Property " + getPathFragment() + " not found in path " + currentPath);
         }
 

json-path/src/test/java/com/jayway/jsonpath/JsonProviderTest.java

@@ -75,6 +75,13 @@ public class JsonProviderTest extends BaseTest {
         assertThat(using(GSON_CONFIGURATION).parse(JSON).read("$", typeRef)).extracting("foo").containsExactly("foo0", "foo1", "foo2");
     }
 
+    @Test
+    public void length_of_array() {
+        assertThat(using(JACKSON_CONFIGURATION).parse(JSON_DOCUMENT).read("$.store.book.length", Integer.class)).isEqualTo(4);
+        assertThat(using(JACKSON_JSON_NODE_CONFIGURATION).parse(JSON_DOCUMENT).read("$.store.book.length", Integer.class)).isEqualTo(4);
+        assertThat(using(JSON_SMART_CONFIGURATION).parse(JSON_DOCUMENT).read("$.store.book.length", Integer.class)).isEqualTo(4);
+        assertThat(using(GSON_CONFIGURATION).parse(JSON_DOCUMENT).read("$.store.book.length", Integer.class)).isEqualTo(4);
+    }
 
     public static class FooBarBaz<T> {
         public T gen;