Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, * software distributed under the License is distributed on an * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * KIND, either express or implied. See the License for the * specific language governing permissions and limitations * under the License. */ package org.apache.xml.security.utils; import java.lang.reflect.Constructor; import java.lang.reflect.Method; import java.lang.reflect.Modifier; import javax.xml.transform.ErrorListener; import javax.xml.transform.SourceLocator; import javax.xml.transform.TransformerException; import org.apache.xml.security.transforms.implementations.FuncHere; import org.apache.xml.utils.PrefixResolver; import org.apache.xml.utils.PrefixResolverDefault; import org.apache.xpath.Expression; import org.apache.xpath.XPath; import org.apache.xpath.XPathContext; import org.apache.xpath.compiler.FunctionTable; import org.apache.xpath.objects.XObject; import org.w3c.dom.Document; import org.w3c.dom.Node; import org.w3c.dom.NodeList; /** * An implementation of XPathAPI using Xalan. This supports the "here()" function defined in the digital * signature spec. */ public class XalanXPathAPI implements XPathAPI { private static org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory .getLog(XalanXPathAPI.class); private String xpathStr = null; private XPath xpath = null; private static FunctionTable funcTable = null; private static boolean installed; private XPathContext context; static { fixupFunctionTable(); } /** * Use an XPath string to select a nodelist. * XPath namespace prefixes are resolved from the namespaceNode. * * @param contextNode The node to start searching from. * @param xpathnode * @param str * @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces. * @return A NodeIterator, should never be null. * * @throws TransformerException */ public NodeList selectNodeList(Node contextNode, Node xpathnode, String str, Node namespaceNode) throws TransformerException { // Execute the XPath, and have it return the result XObject list = eval(contextNode, xpathnode, str, namespaceNode); // Return a NodeList. return list.nodelist(); } /** * Evaluate an XPath string and return true if the output is to be included or not. * @param contextNode The node to start searching from. * @param xpathnode The XPath node * @param str The XPath expression * @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces. */ public boolean evaluate(Node contextNode, Node xpathnode, String str, Node namespaceNode) throws TransformerException { XObject object = eval(contextNode, xpathnode, str, namespaceNode); return object.bool(); } /** * Clear any context information from this object */ public void clear() { xpathStr = null; xpath = null; context = null; } public synchronized static boolean isInstalled() { return installed; } private XObject eval(Node contextNode, Node xpathnode, String str, Node namespaceNode) throws TransformerException { if (context == null) { context = new XPathContext(xpathnode); context.setSecureProcessing(true); } // Create an object to resolve namespace prefixes. // XPath namespaces are resolved from the input context node's document element // if it is a root node, or else the current context node (for lack of a better // resolution space, given the simplicity of this sample code). Node resolverNode = (namespaceNode.getNodeType() == Node.DOCUMENT_NODE) ? ((Document) namespaceNode).getDocumentElement() : namespaceNode; PrefixResolverDefault prefixResolver = new PrefixResolverDefault(resolverNode); if (!str.equals(xpathStr)) { if (str.indexOf("here()") > 0) { context.reset(); } xpath = createXPath(str, prefixResolver); xpathStr = str; } // Execute the XPath, and have it return the result int ctxtNode = context.getDTMHandleFromNode(contextNode); return xpath.execute(context, ctxtNode, prefixResolver); } private XPath createXPath(String str, PrefixResolver prefixResolver) throws TransformerException { XPath xpath = null; Class<?>[] classes = new Class[] { String.class, SourceLocator.class, PrefixResolver.class, int.class, ErrorListener.class, FunctionTable.class }; Object[] objects = new Object[] { str, null, prefixResolver, Integer.valueOf(XPath.SELECT), null, funcTable }; try { Constructor<?> constructor = XPath.class.getConstructor(classes); xpath = (XPath) constructor.newInstance(objects); } catch (Exception ex) { if (log.isDebugEnabled()) { log.debug(ex); } } if (xpath == null) { xpath = new XPath(str, null, prefixResolver, XPath.SELECT, null); } return xpath; } private synchronized static void fixupFunctionTable() { installed = false; if (log.isDebugEnabled()) { log.debug("Registering Here function"); } /** * Try to register our here() implementation as internal function. */ try { Class<?>[] args = { String.class, Expression.class }; Method installFunction = FunctionTable.class.getMethod("installFunction", args); if ((installFunction.getModifiers() & Modifier.STATIC) != 0) { Object[] params = { "here", new FuncHere() }; installFunction.invoke(null, params); installed = true; } } catch (Exception ex) { log.debug("Error installing function using the static installFunction method", ex); } if (!installed) { try { funcTable = new FunctionTable(); Class<?>[] args = { String.class, Class.class }; Method installFunction = FunctionTable.class.getMethod("installFunction", args); Object[] params = { "here", FuncHere.class }; installFunction.invoke(funcTable, params); installed = true; } catch (Exception ex) { log.debug("Error installing function using the static installFunction method", ex); } } if (log.isDebugEnabled()) { if (installed) { log.debug("Registered class " + FuncHere.class.getName() + " for XPath function 'here()' function in internal table"); } else { log.debug("Unable to register class " + FuncHere.class.getName() + " for XPath function 'here()' function in internal table"); } } } }