Under heavy load the following occurs:

2005-09-09 10:44:05,345 ERROR [org.jboss.webservice.server.InvokerProvider] Cannot process WSDL document
java.lang.NullPointerException
at org.apache.xerces.dom.ParentNode.nodeListItem(Unknown Source)
at org.apache.xerces.dom.ParentNode.item(Unknown Source)
at com.ibm.wsdl.util.xml.DOM2Writer.print(Unknown Source)
at com.ibm.wsdl.util.xml.DOM2Writer.print(Unknown Source)
at com.ibm.wsdl.util.xml.DOM2Writer.print(Unknown Source)
at com.ibm.wsdl.util.xml.DOM2Writer.print(Unknown Source)
at com.ibm.wsdl.util.xml.DOM2Writer.serializeAsXML(Unknown Source)
at javax.wsdl.extensions.UnknownExtensionSerializer.marshall(Unknown Source)
at com.ibm.wsdl.xml.WSDLWriterImpl.printExtensibilityElements(Unknown Source)
at com.ibm.wsdl.xml.WSDLWriterImpl.printTypes(Unknown Source)
at com.ibm.wsdl.xml.WSDLWriterImpl.printDefinition(Unknown Source)
at com.ibm.wsdl.xml.WSDLWriterImpl.writeWSDL(Unknown Source)
at com.ibm.wsdl.xml.WSDLWriterImpl.getDocument(Unknown Source)
at org.jboss.webservice.server.WSDLRequestHandler.getWSDLDocument(WSDLRequestHandler.java:119)
at org.jboss.webservice.server.WSDLRequestHandler.getDocumentForPath(WSDLRequestHandler.java:73)
at org.jboss.webservice.server.InvokerProvider.generateWSDL(InvokerProvider.java:189)
at org.jboss.axis.strategies.WSDLGenStrategy.visit(WSDLGenStrategy.java:74)
at org.jboss.axis.SimpleChain.doVisiting(SimpleChain.java:160)
at org.jboss.axis.SimpleChain.generateWSDL(SimpleChain.java:143)
at org.jboss.axis.handlers.soap.SOAPService.generateWSDL(SOAPService.java:426)
at org.jboss.axis.server.AxisServer.generateWSDL(AxisServer.java:555)
at org.jboss.webservice.server.AbstractServlet.processWsdlRequest(AbstractServlet.java:138)
at org.jboss.webservice.server.ServiceEndpointServlet.doGet(ServiceEndpointServlet.java:108)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:697)
at org.jboss.axis.transport.http.AxisServletBase.service(AxisServletBase.java:370)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)

This is because the WSDL handling system reuses javax.wsdl.Definition objects across threads, which are not thread safe, because they internally use DOM elements.

-Jason