For background, see:

http://www.netbeans.org/nonav/issues/show_bug.cgi?id=139048

To reproduce, run the following with Apache Xerces in the classpath:

---%<---
import java.net.URL;
import java.net.URLClassLoader;
import javax.xml.parsers.SAXParserFactory;
public class TestJAXP {
    public static void main(String[] args) throws Exception {
        Thread.currentThread().setContextClassLoader(new URLClassLoader(new URL[0], ClassLoader.getSystemClassLoader().getParent()));
        SAXParserFactory.newInstance();
    }
}
---%<---

Under JDK 6 I get:

Exception in thread "main" javax.xml.parsers.FactoryConfigurationError: Provider org.apache.xerces.jaxp.SAXParserFactoryImpl not found
        at javax.xml.parsers.SAXParserFactory.newInstance(SAXParserFactory.java:134)
        at TestJAXP.main(TestJAXP.java:7)

The reason is that FactoryFinder.findJarServiceProvider behaves as follows:

1. Check the thread's CCL for META-INF/services/javax.xml.parsers.SAXParserFactory. This is not found, since the CCL does not see the app class loader.

2. is == null, so set cl = null (bootstrap loader), and call SecuritySupport.getResourceAsStream.

3. ClassLoader.getSystemResourceAsStream(...) returns the resources from xerces.jar, because it checks the app class loader, not the bootstrap loader (which has no such resource).

4. newInstance(null, "org.apache.xerces....", false) is called, which asks for org.apache.xerces... from the CCL, which cannot see it.