[JXPATH-68] StackOverflow error on a call to 'JXPathContext.createPath()'

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.2 Final, Nightly Builds
• Fix Version/s: 1.3

Environment

Windows XP Professional, Sun JDK 1.4.2
Run with JXPath v1.2 and v20060530

• Assignee: Unassigned
• Reporter: Joseph Campolongo
• Created: 07/Jun/06 01:49
• Updated: 10/Jan/07 23:00
• Resolved: 10/Jan/07 23:00

Description

I'm running into a StackOverflow error on a call to
'JXPathContext.createPath()' whenever I have a path that looks like
'a/b[1]/c'. I took a quick look at the code and it appears JXPath, when
trying to create its parent pointer, simply recreates an equivalent
pointer(???).

Here is code to reproduce the problem.

Map map = new HashMap();
map.put("a", null);

JXPathContext pathContext = JXPathContext.newContext(map);
pathContext.setFactory(new AbstractFactory() {
public boolean createObject(
JXPathContext context, Pointer pointer, Object parent, String
name, int index) {

Map parentMap = (Map)parent;
System.out.println(parent + ":" + name + ":" + index);
if (index > -1) {
List list = (List)parentMap.get(name);
if (list == null)

{ list = new ArrayList(); }
int size = list.size();
for (int i = size; i <= index; i++) { list.add(i, null); }
parentMap.put(name, list);
} else { parentMap.put(name, new HashMap()); }
return true;
}

});
pathContext.createPath("a/b[1]/c");

***************

I have continued looking into this, and found that the problem is that, if
the List is created with a 'null' element, JXPath gets stuck in infinite
recursion.

To discover this, I changed my Factory to implement the following method:

public boolean createObject(
JXPathContext context, Pointer pointer, Object parent,
String name, int index) {

if (pointer instanceof NodePointer) { index = ((NodePointer)pointer).getIndex(); }
System.out.println(parent + ":" + name + ":" + index);
Map parentMap = (Map)parent;
if (index > -1) {
List list = (List)parentMap.get(name);
if (list == null) { list = new ArrayList(); }

int size = list.size();
for (int i = size; i <= index; i++)

{ list.add(i, new HashMap()); // !!!!!! Don't set to 'null' }

parentMap.put(name, list);
} else

{ parentMap.put(name, new HashMap()); }

return true;
}

Then I ran the following code:

pathContext.createPath("a/b[1]/c");
pathContext.createPath("a/b[2]/c"); // STACK OVERFLOW HERE

Here is the stack trace at the beginning, where
'ValueUtils.expandCollection()' is called. It puts 'null' into the list,
thus causing the stack overflow as we cycle between createPath() &
createChild().

Thread [main] (Suspended (breakpoint at line 227 in DynamicPropertyPointer))
DynamicPropertyPointer.createPath(JXPathContext) line: 227
DynamicPropertyPointer(PropertyPointer).createChild(JXPathContext,
QName, int) line: 188
NullElementPointer.createPath(JXPathContext) line: 82
NullPointer.createPath(JXPathContext) line: 86
NullPropertyPointer.createPath(JXPathContext) line: 103
NullPointer.createPath(JXPathContext) line: 86
NullPropertyPointer.createPath(JXPathContext) line: 103
JXPathContextReferenceImpl.createPath(String, Expression) line: 447
JXPathContextReferenceImpl.createPath(String) line: 427
Test.test4() line: 75
Test.main(String[]) line: 38