Merge pull request #329 from jochenberger/negative-array-index

Add support for negative array indexes

README.md

@@ -155,6 +155,7 @@ Given the json
 | <a href="http://jsonpath.herokuapp.com/?path=$.store.*" target="_blank">$.store.*</a>                  | All things, both books and bicycles  |
 | <a href="http://jsonpath.herokuapp.com/?path=$.store..price" target="_blank">$.store..price</a>             | The price of everything         |
 | <a href="http://jsonpath.herokuapp.com/?path=$..book[2]" target="_blank">$..book[2]</a>                 | The third book                      |
+| <a href="http://jsonpath.herokuapp.com/?path=$..book[2]" target="_blank">$..book[-2]</a>                 | The second to last book            |
 | <a href="http://jsonpath.herokuapp.com/?path=$..book[0,1]" target="_blank">$..book[0,1]</a>               | The first two books               |
 | <a href="http://jsonpath.herokuapp.com/?path=$..book[:2]" target="_blank">$..book[:2]</a>                | All books from index 0 (inclusive) until index 2 (exclusive) |
 | <a href="http://jsonpath.herokuapp.com/?path=$..book[1:2]" target="_blank">$..book[1:2]</a>                | All books from index 1 (inclusive) until index 2 (exclusive) |

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

@@ -42,7 +42,7 @@ public class ArrayIndexOperation {
         //check valid chars
         for (int i = 0; i < operation.length(); i++) {
             char c = operation.charAt(i);
-            if (!isDigit(c) && c != ',' && c != ' ') {
+            if (!isDigit(c) && c != ',' && c != ' ' && c != '-') {
                 throw new InvalidPathException("Failed to parse ArrayIndexOperation: " + operation);
             }
         }

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

@@ -125,8 +125,9 @@ public abstract class PathToken {
     protected void handleArrayIndex(int index, String currentPath, Object model, EvaluationContextImpl ctx) {
         String evalPath = Utils.concat(currentPath, "[", String.valueOf(index), "]");
         PathRef pathRef = ctx.forUpdate() ? PathRef.create(model, index) : PathRef.NO_OP;
+        int effectiveIndex = index < 0 ? ctx.jsonProvider().length(model) + index : index;
         try {
-            Object evalHit = ctx.jsonProvider().getArrayIndex(model, index);
+            Object evalHit = ctx.jsonProvider().getArrayIndex(model, effectiveIndex);
             if (isLeaf()) {
                 ctx.addResult(evalPath, pathRef, evalHit);
             } else {

json-path/src/test/java/com/jayway/jsonpath/old/internal/ArrayIndexFilterTest.java

@@ -1,6 +1,9 @@
 package com.jayway.jsonpath.old.internal;
 
 import com.jayway.jsonpath.JsonPath;
+
+import org.junit.Assert;
+
 import org.hamcrest.Matchers;
 import org.junit.Test;
 
@@ -43,4 +46,10 @@ public class ArrayIndexFilterTest {
         assertThat(result, Matchers.contains(1, 3, 5));
     }
 
+    @Test
+    public void can_access_items_from_end_with_negative_index() {
+        int result = JsonPath.parse(JSON).read("$[-3]");
+        Assert.assertEquals(8, result);
+    }
+
 }