Re: [xmlblaster] server side exception: Can't process XPath expression

[Marcel Ruff <mr at marcelruff.info>]

Am 24.08.2012 05:01, schrieb Andrew Yinger:
> i believe this issue was identified before, but i occasionally see a
> server-side exception that starts off like:
>
>     errorCode=user.query.invalid message=#exported Sorry, can't access,
> query syntax of
>     ....
>     XmlBlasterException errorCode=[resource.configuration]
> serverSideException=true location=[XmlNotPortable]
>      message=[#exported Can't process XPath expression .....
>
>
> it was first suggested that this was a parsing issue -- a possible xml
> parser library conflict.  (i have verified that i do *not* have any
> extraneous xml parsing libs in my 'java\lib\endorsed' directory.)
>
> later, a user noticed that a similar error was happening during unit
> testing, and that it was a bug on the server:
>
> The issues are:
> 1. The null check (method_newXPath == null) is outside the
> synchronization block. Thread A and thread B could both pass through
> the null check at the same time. Thread A will create the xpath
> objects while B waits. Then thread B will go through and recreate
> xpath objects while A is using them.
>
> 2. XPathFactory is, in general, not thread-safe (see
> http://java.sun.com/javase/6/docs/api/javax/xml/xpath/XPathFactory.html),
> and a method on that object is invoked outside the synchro block.
In the current code it looks like this:

            Object xpath = null;
            synchronized(XmlNotPortable.class) {
               if (method_newXPath == null) {
                  clazz_XPathFactory = java.lang.Class.forName("javax.xml.xpath.XPathFactory");
                  Class[] paramCls = new Class[0];
                  Object[] params = new Object[0];
                  java.lang.reflect.Method method = clazz_XPathFactory.getMethod("newInstance", 
paramCls);
                  instance_XPathFactory = method.invoke(clazz_XPathFactory, params);
                  method_newXPath = clazz_XPathFactory.getMethod("newXPath", paramCls);

                  clazz_XPath = java.lang.Class.forName("javax.xml.xpath.XPath");

                  Class clazz_XPathConstants = 
java.lang.Class.forName("javax.xml.xpath.XPathConstants");
                  clazz_QName = java.lang.Class.forName("javax.xml.namespace.QName");
                  java.lang.reflect.Field field = clazz_XPathConstants.getDeclaredField("NODESET");
                  field_NODESET = field.get(null);
                  paramCls_StringDocument = new Class[] {
                                   java.lang.String.class,
                                   java.lang.Object.class, // org.w3c.dom.Document.class,
                                   clazz_QName };
               }
               xpath = method_newXPath.invoke(instance_XPathFactory, new Object[0]);
            }

so it seems to be correctly synchronized, or do I overlook your issue?

Thank you
Marcel
> has this bug been fixed?  if so, what version should i be using now?
> (i am currently using xmlBlaster version 1.6.2 2007-12-03
> 'Openroads'.)
>
> a response to this ongoing issue would be greatly appreciated, as it
> is impacting our automated unit tests.
>
>
> thanks,
> andrew yinger