GMLReader.java

/*
 * Copyright (c) 2016 Vivid Solutions.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * and Eclipse Distribution License v. 1.0 which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
 * and the Eclipse Distribution License is available at
 *
 * http://www.eclipse.org/org/documents/edl-v10.php.
 */
package org.locationtech.jts.io.gml2;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

import javax.xml.XMLConstants;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.geom.GeometryCollection;
import org.locationtech.jts.geom.GeometryFactory;
import org.locationtech.jts.geom.PrecisionModel;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.SAXNotRecognizedException;
import org.xml.sax.SAXNotSupportedException;
import org.xml.sax.helpers.DefaultHandler;


/**
 * Reads a GML2 geometry from an XML fragment into a {@link Geometry}.
 * <p>
 * An example of the GML2 format handled is:
 * <pre>
 *   &lt;LineString&gt;
 *  	&lt;coordinates&gt;
 *  		24824.045318333192,38536.15071012041
 *  		26157.378651666528,37567.42733944659 26666.666,36000.0
 *  		26157.378651666528,34432.57266055341
 *  		24824.045318333192,33463.84928987959
 *  		23175.954681666804,33463.84928987959
 *  		21842.621348333472,34432.57266055341 21333.333,36000.0
 *  		21842.621348333472,37567.42733944659
 *  		23175.954681666808,38536.15071012041
 *  	&lt;/coordinates&gt;
 *  &lt;/LineString&gt;
 * </pre>
 *
 * The reader ignores namespace prefixes, 
 * and disables both the validation and namespace options on the <tt>SAXParser</tt>.
 * This class requires the presence of a SAX Parser available via the 
 * {@link javax.xml.parsers.SAXParserFactory#newInstance()}
 * method.
 * <p>
 * A specification of the GML XML format 
 * can be found at the OGC web site: <a href='http://www.opengeospatial.org/'>http://www.opengeospatial.org/</a>.
 * <p>
 * It is the caller's responsibility to ensure that the supplied {@link PrecisionModel}
 * matches the precision of the incoming data.
 * If a lower precision for the data is required, a subsequent
 * process must be run on the data to reduce its precision.
 * <p>
 * To parse and build geometry directly from a SAX stream, see {@link GMLHandler}.
 *
 * @author David Zwiers, Vivid Solutions.
 * 
 * @see GMLHandler
 */
public class GMLReader 
{

	/**
	 * Reads a GML2 Geometry from a <tt>String</tt> into a single {@link Geometry}
	 *
	 * If a collection of geometries is found, a {@link GeometryCollection} is returned.
	 *
	 * @param gml The GML String to parse
	 * @param geometryFactory When null, a default will be used.
	 * @return the resulting JTS Geometry
	 * 
	 * @throws ParserConfigurationException
	 * @throws IOException
	 * @throws SAXException
	 *
	 * @see #read(Reader, GeometryFactory)
	 */
	public Geometry read(String gml, GeometryFactory geometryFactory) throws SAXException, IOException, ParserConfigurationException{
		return read(new StringReader(gml),geometryFactory);
	}

	/**
	 * Reads a GML2 Geometry from a {@link Reader} into a single {@link Geometry}
	 *
	 * If a collection of Geometries is found, a {@link GeometryCollection} is returned.
	 *
	 * @param reader The input source
	 * @param geometryFactory When null, a default will be used.
	 * @return The resulting JTS Geometry
	 * @throws SAXException
	 * @throws IOException
	 */
	public Geometry read(Reader reader, GeometryFactory geometryFactory) throws SAXException, IOException, ParserConfigurationException{
		SAXParserFactory fact = SAXParserFactory.newInstance();

		fact.setNamespaceAware(false);
		fact.setValidating(false);
		// GML does not require DOCTYPE
		boolean secureProcessing = setFeature(fact, XMLConstants.FEATURE_SECURE_PROCESSING, true);
		boolean disallowDocType = setFeature(fact, "http://apache.org/xml/features/disallow-doctype-decl", true);
		if (!secureProcessing && !disallowDocType) {
			throw new ParserConfigurationException("Parser does not support DOCTYPE restrictions");
		}
		setFeature(fact, "http://xml.org/sax/features/external-general-entities", false);
		setFeature(fact, "http://xml.org/sax/features/external-parameter-entities", false);
		setFeature(fact, "http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
		try {
			fact.setXIncludeAware(false);
		} catch (UnsupportedOperationException e) {
			// not supported by this parser
		}

		SAXParser parser = fact.newSAXParser();
		try {
			parser.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");
			parser.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");
		} catch (SAXNotRecognizedException | SAXNotSupportedException e) {
			// not supported by this parser
		}

		if(geometryFactory == null)
			geometryFactory = new GeometryFactory();

		GMLHandler gh = new GMLHandler(geometryFactory,null) {
			@Override
			public InputSource resolveEntity(String publicId, String systemId) throws SAXException {
				throw new SAXException("External entity resolution is not allowed: " + systemId);
			}
		};
		parser.parse(new InputSource(reader), (DefaultHandler)gh);

		return gh.getGeometry();
	}

	private static boolean setFeature(SAXParserFactory fact, String feature, boolean value) {
		try {
			fact.setFeature(feature, value);
			return true;
		} catch (ParserConfigurationException | SAXNotRecognizedException | SAXNotSupportedException e) {
			// not supported by this parser
			return false;
		}
	}

}