poi/src/ooxml/java/org/apache/poi/util/DocumentHelper.java

/* ====================================================================
   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.poi.util;

import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;

import javax.xml.XMLConstants;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.stream.events.Namespace;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.xml.sax.SAXException;

public final class DocumentHelper {
    private static POILogger logger = POILogFactory.getLogger(DocumentHelper.class);
    
    private DocumentHelper() {}

    /**
     * Creates a new document builder, with sensible defaults
     */
    public static synchronized DocumentBuilder newDocumentBuilder() {
        try {
            DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
            documentBuilder.setEntityResolver(SAXHelper.IGNORING_ENTITY_RESOLVER);
            return documentBuilder;
        } catch (ParserConfigurationException e) {
            throw new IllegalStateException("cannot create a DocumentBuilder", e);
        }
    }

    private static final DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
    static {
        documentBuilderFactory.setNamespaceAware(true);
        documentBuilderFactory.setValidating(false);
        trySetSAXFeature(documentBuilderFactory, XMLConstants.FEATURE_SECURE_PROCESSING, true);
        trySetXercesSecurityManager(documentBuilderFactory);
    }

    private static void trySetSAXFeature(DocumentBuilderFactory documentBuilderFactory, String feature, boolean enabled) {
        try {
            documentBuilderFactory.setFeature(feature, enabled);
        } catch (Exception e) {
            logger.log(POILogger.WARN, "SAX Feature unsupported", feature, e);
        } catch (AbstractMethodError ame) {
            logger.log(POILogger.WARN, "Cannot set SAX feature because outdated XML parser in classpath", feature, ame);
        }
    }
    
    private static void trySetXercesSecurityManager(DocumentBuilderFactory documentBuilderFactory) {
        // Try built-in JVM one first, standalone if not
        for (String securityManagerClassName : new String[] {
                "com.sun.org.apache.xerces.internal.util.SecurityManager",
                "org.apache.xerces.util.SecurityManager"
        }) {
            try {
                Object mgr = Class.forName(securityManagerClassName).newInstance();
                Method setLimit = mgr.getClass().getMethod("setEntityExpansionLimit", Integer.TYPE);
                setLimit.invoke(mgr, 4096);
                documentBuilderFactory.setAttribute("http://apache.org/xml/properties/security-manager", mgr);
                // Stop once one can be setup without error
                return;
            } catch (Exception e) {
                logger.log(POILogger.WARN, "SAX Security Manager could not be setup", e);
            }
        }
    }

    /**
     * Parses the given stream via the default (sensible)
     * DocumentBuilder
     * @param inp Stream to read the XML data from
     * @return the parsed Document 
     */
    public static Document readDocument(InputStream inp) throws IOException, SAXException {
        return newDocumentBuilder().parse(inp);
    }

    // must only be used to create empty documents, do not use it for parsing!
    private static final DocumentBuilder documentBuilderSingleton = newDocumentBuilder();

    /**
     * Creates a new DOM Document
     */
    public static synchronized Document createDocument() {
        return documentBuilderSingleton.newDocument();
    }

    /**
     * Adds a namespace declaration attribute to the given element.
     */
    public static void addNamespaceDeclaration(Element element, String namespacePrefix, String namespaceURI) {
        element.setAttributeNS(XMLConstants.XMLNS_ATTRIBUTE_NS_URI,
                XMLConstants.XMLNS_ATTRIBUTE + ':' + namespacePrefix,
                namespaceURI);
    }

    /**
     * Adds a namespace declaration attribute to the given element.
     */
    public static void addNamespaceDeclaration(Element element, Namespace namespace) {
        addNamespaceDeclaration(element, namespace.getPrefix(), namespace.getNamespaceURI());
    }

}