pmd: fix #958 Intermittent NullPointerException while loading XPath node attributes

* synchronizing the method cache
 * adding additional null check

pmd/etc/changelog.txt

@@ -1,5 +1,6 @@
 ????? ??, 2013 - 5.0.3:
 
+Fixed bug  958: Intermittent NullPointerException while loading XPath node attributes
 Fixed bug  968: Issues with JUnit4 @Test annotation with expected exception (Thanks to Yiannis Paschalidis)
 Fixed bug  975: false positive in ClassCastExceptionWithToArray
 Fixed bug  976: UselessStringValueOf wrong when appending character arrays

pmd/src/main/java/net/sourceforge/pmd/lang/ast/xpath/AttributeAxisIterator.java

@@ -5,6 +5,7 @@ package net.sourceforge.pmd.lang.ast.xpath;
 
 import java.lang.reflect.Method;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
@@ -48,7 +49,8 @@ public class AttributeAxisIterator implements Iterator<Attribute> {
     private int position;
     private Node node;
 
-    private static Map<Class<?>, MethodWrapper[]> methodCache = new HashMap<Class<?>, MethodWrapper[]>();
+    private static Map<Class<?>, MethodWrapper[]> methodCache =
+            Collections.synchronizedMap(new HashMap<Class<?>, MethodWrapper[]>());
 
     public AttributeAxisIterator(Node contextNode) {
         this.node = contextNode;
@@ -86,7 +88,7 @@ public class AttributeAxisIterator implements Iterator<Attribute> {
     }
 
     private Attribute getNextAttribute() {
-        if (position == methodWrappers.length) {
+        if (methodWrappers == null || position == methodWrappers.length) {
             return null;
         }
         MethodWrapper m = methodWrappers[position++];

pmd/src/test/java/net/sourceforge/pmd/lang/ast/xpath/AttributeAxisIteratorTest.java

@@ -0,0 +1,43 @@
+/**
+ * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+ */
+package net.sourceforge.pmd.lang.ast.xpath;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import net.sourceforge.pmd.lang.java.ast.DummyJavaNode;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Unit test for {@link AttributeAxisIterator}
+ */
+public class AttributeAxisIteratorTest {
+
+    /**
+     * Test hasNext and next.
+     */
+    @Test
+    public void testAttributeAxisIterator() {
+        DummyJavaNode dummyNode = new DummyJavaNode(1);
+        dummyNode.testingOnly__setBeginLine(1);
+        dummyNode.testingOnly__setBeginColumn(1);
+
+        AttributeAxisIterator it = new AttributeAxisIterator(dummyNode);
+        Map<String, Attribute> atts = new HashMap<String, Attribute>();
+        while (it.hasNext()) {
+            Attribute attribute = it.next();
+            atts.put(attribute.getName(), attribute);
+        }
+        Assert.assertEquals(7, atts.size());
+        Assert.assertTrue(atts.containsKey("BeginColumn"));
+        Assert.assertTrue(atts.containsKey("BeginLine"));
+        Assert.assertTrue(atts.containsKey("FindBoundary"));
+        Assert.assertTrue(atts.containsKey("Image"));
+        Assert.assertTrue(atts.containsKey("SingleLine"));
+        Assert.assertTrue(atts.containsKey("EndColumn"));
+        Assert.assertTrue(atts.containsKey("EndLine"));
+    }
+}