I have a Document object initialized in the init() method of the servlet and use it in the doPost() method to service the requests. selectNodeList() xpath query gives exception when the servlet services many request at same time. The Exception is shown below: Caused by: javax.xml.transform.TransformerException: -1 at org.apache.xpath.XPath.execute(XPath.java:331) at org.apache.xpath.CachedXPathAPI.eval(CachedXPathAPI.java:328) at org.apache.xpath.CachedXPathAPI.selectNodeList(CachedXPathAPI.java:255) at org.apache.xpath.CachedXPathAPI.selectNodeList(CachedXPathAPI.java:235) at com.pro.bb.servlets.Controller.getDataOrPeriodForReport(Controller.java:511) ... 23 more Caused by: java.lang.ArrayIndexOutOfBoundsException: -1 at org.apache.xpath.XPathContext.pushCurrentNode(XPathContext.java:808) at org.apache.xpath.axes.PredicatedNodeTest.acceptNode(PredicatedNodeTest.java:447) at org.apache.xpath.axes.AxesWalker.nextNode(AxesWalker.java:409) at org.apache.xpath.axes.WalkingIterator.nextNode(WalkingIterator.java:176) at org.apache.xpath.axes.NodeSequence.nextNode(NodeSequence.java:320) at org.apache.xpath.axes.NodeSequence.runTo(NodeSequence.java:474) at org.apache.xpath.axes.NodeSequence.setRoot(NodeSequence.java:257) at org.apache.xpath.axes.LocPathIterator.execute(LocPathIterator.java:257) at org.apache.xpath.XPath.execute(XPath.java:308) Help me sort out the issue.