Add example of unique keys
diff --git a/src/test/java/org/yaml/snakeyaml/issues/issue139/UniqueKeyTest.java b/src/test/java/org/yaml/snakeyaml/issues/issue139/UniqueKeyTest.java
new file mode 100644
index 0000000..1fdd7fd
--- /dev/null
+++ b/src/test/java/org/yaml/snakeyaml/issues/issue139/UniqueKeyTest.java
@@ -0,0 +1,64 @@
+/**
+ * Copyright (c) 2008-2012, http://www.snakeyaml.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.yaml.snakeyaml.issues.issue139;
+
+import java.util.List;
+import java.util.Map;
+
+import junit.framework.TestCase;
+
+import org.yaml.snakeyaml.Yaml;
+import org.yaml.snakeyaml.constructor.Constructor;
+import org.yaml.snakeyaml.error.YAMLException;
+import org.yaml.snakeyaml.nodes.MappingNode;
+import org.yaml.snakeyaml.nodes.Node;
+import org.yaml.snakeyaml.nodes.NodeTuple;
+
+public class UniqueKeyTest extends TestCase {
+
+ public void testNotUnique() {
+ String data = "{key: 1, key: 2}";
+ Yaml yaml = new Yaml(new UniqueKeyConstructor());
+ try {
+ yaml.load(data);
+ fail("The same key must be rejected");
+ } catch (Exception e) {
+ assertEquals("The key is not unique key", e.getMessage());
+ }
+ }
+
+ private class UniqueKeyConstructor extends Constructor {
+
+ @Override
+ protected void constructMapping2ndStep(MappingNode node, Map<Object, Object> mapping) {
+ List<NodeTuple> nodeValue = (List<NodeTuple>) node.getValue();
+ for (NodeTuple tuple : nodeValue) {
+ Node keyNode = tuple.getKeyNode();
+ Node valueNode = tuple.getValueNode();
+ Object key = constructObject(keyNode);
+ if (key != null) {
+ key.hashCode();// check circular dependencies
+ }
+ Object value = constructObject(valueNode);
+ Object old = mapping.put(key, value);
+ if (old != null) {
+ throw new YAMLException("The key is not unique " + key);
+ }
+ }
+ }
+ }
+
+}
