consistently use setArrayIndex for arrays instead of setProperty

json-path/src/main/java/com/jayway/jsonpath/JsonPath.java

@@ -178,7 +178,7 @@ public class JsonPath {
                 Object res = path.evaluate(jsonObject, jsonObject, configuration).getValue(false);
                 if(optAlwaysReturnList && path.isDefinite()){
                     Object array = configuration.jsonProvider().createArray();
-                    configuration.jsonProvider().setProperty(array, 0, res);
+                    configuration.jsonProvider().setArrayIndex(array, 0, res);
                     return (T)array;
                 } else {
                     return (T)res;

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

@@ -89,7 +89,7 @@ public abstract class PathRef implements Comparable<PathRef>  {
         @Override
         public void add(Object newVal, Configuration configuration) {
             if(configuration.jsonProvider().isArray(parent)){
-                configuration.jsonProvider().setProperty(parent, null, newVal);
+                configuration.jsonProvider().setArrayIndex(parent, configuration.jsonProvider().length(parent), newVal);
             } else {
                 throw new InvalidModificationException("Invalid add operation. $ is not an array");
             }
@@ -185,7 +185,7 @@ public abstract class PathRef implements Comparable<PathRef>  {
                 return;
             }
             if(configuration.jsonProvider().isArray(target)){
-                configuration.jsonProvider().setProperty(target, null, value);
+                configuration.jsonProvider().setArrayIndex(target, configuration.jsonProvider().length(target), value);
             } else {
                 throw new InvalidModificationException("Can only add to an array");
             }

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

@@ -80,8 +80,8 @@ public class EvaluationContextImpl implements EvaluationContext {
             updateOperations.add(operation);
         }
 
-        configuration.jsonProvider().setProperty(valueResult, resultIndex, model);
+        configuration.jsonProvider().setArrayIndex(valueResult, resultIndex, model);
-        configuration.jsonProvider().setProperty(pathResult, resultIndex, path);
+        configuration.jsonProvider().setArrayIndex(pathResult, resultIndex, path);
         resultIndex++;
         if(!configuration().getEvaluationListeners().isEmpty()){
             int idx = resultIndex - 1;

json-path/src/main/java/com/jayway/jsonpath/spi/json/AbstractJsonProvider.java

@@ -56,7 +56,12 @@ public abstract class AbstractJsonProvider implements JsonProvider {
         if (!isArray(array)) {
             throw new UnsupportedOperationException();
         } else {
-            ((List) array).set(index, newValue);
+            List l = (List) array;
+            if (index == l.size()){
+                l.add(newValue);
+            }else {
+                l.set(index, newValue);
+            }
         }
     }
 
@@ -78,10 +83,10 @@ public abstract class AbstractJsonProvider implements JsonProvider {
     }
 
     /**
-     * Sets a value in an object or array
+     * Sets a value in an object
      *
-     * @param obj   an array or an object
+     * @param obj   an object
-     * @param key   a String key or a numerical index
+     * @param key   a String key
      * @param value the value to set
      */
     @SuppressWarnings("unchecked")
@@ -89,14 +94,7 @@ public abstract class AbstractJsonProvider implements JsonProvider {
         if (isMap(obj))
             ((Map) obj).put(key.toString(), value);
         else {
-            List list = (List) obj;
+            throw new JsonPathException("setProperty operation cannot be used with " + obj!=null?obj.getClass().getName():"null");
-            int index;
-            if (key != null) {
-                index = key instanceof Integer ? (Integer) key : Integer.parseInt(key.toString());
-            } else {
-                index = list.size();
-            }
-            list.add(index, value);
         }
     }
 
@@ -159,7 +157,7 @@ public abstract class AbstractJsonProvider implements JsonProvider {
         } else if(obj instanceof String){
             return ((String)obj).length();
         }
-        throw new JsonPathException("length operation can not applied to " + obj!=null?obj.getClass().getName():"null");
+        throw new JsonPathException("length operation cannot be applied to " + obj!=null?obj.getClass().getName():"null");
     }
 
     /**

json-path/src/main/java/com/jayway/jsonpath/spi/json/GsonJsonProvider.java

@@ -134,10 +134,11 @@ public class GsonJsonProvider extends AbstractJsonProvider {
 
     @Override
     public void setArrayIndex(Object array, int index, Object newValue) {
-        if (!isArray(array)) {
+        JsonArray a = toJsonArray(array);
-            throw new UnsupportedOperationException();
+        if (index == a.size()) {
+            a.add(createJsonElement(newValue));
         } else {
-            toJsonArray(array).set (index, createJsonElement(newValue));
+            a.set(index, createJsonElement(newValue));
         }
     }
 

json-path/src/main/java/com/jayway/jsonpath/spi/json/JsonProvider.java

@@ -113,7 +113,7 @@ public interface JsonProvider {
     Object getArrayIndex(Object obj, int idx, boolean unwrap);
 
     /**
-     * Sets a value in an array
+     * Sets a value in an array. If the array is too small, the provider is supposed to enlarge it.
      *
      * @param array an array
      * @param idx index
@@ -131,10 +131,10 @@ public interface JsonProvider {
     Object getMapValue(Object obj, String key);
 
     /**
-     * Sets a value in an object or array
+     * Sets a value in an object
      *
-     * @param obj   an array or an object
+     * @param obj   an object
-     * @param key   a String key or a numerical index
+     * @param key   a String key
      * @param value the value to set
      */
     void setProperty(Object obj, Object key, Object value);