/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed 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
 *
 *      https://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.springframework.beans.factory.xml;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.net.URLDecoder;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.lang.Nullable;

EntityResolver implementation that tries to resolve entity references through a ResourceLoader (usually, relative to the resource base of an ApplicationContext), if applicable. Extends DelegatingEntityResolver to also provide DTD and XSD lookup. 
Allows to use standard XML entities to include XML snippets into an
application context definition, for example to split a large XML file
into various modules. The include paths can be relative to the
application context's resource base as usual, instead of relative
to the JVM working directory (the XML parser's default).
Note: In addition to relative paths, every URL that specifies a
file in the current system root, i.e. the JVM working directory,
will be interpreted relative to the application context too.
Author:
Juergen Hoeller
See Also:
ResourceLoader
ApplicationContext
Since:
31.07.2003/**
 * {@code EntityResolver} implementation that tries to resolve entity references
 * through a {@link org.springframework.core.io.ResourceLoader} (usually,
 * relative to the resource base of an {@code ApplicationContext}), if applicable.
 * Extends {@link DelegatingEntityResolver} to also provide DTD and XSD lookup.
 *
 * <p>Allows to use standard XML entities to include XML snippets into an
 * application context definition, for example to split a large XML file
 * into various modules. The include paths can be relative to the
 * application context's resource base as usual, instead of relative
 * to the JVM working directory (the XML parser's default).
 *
 * <p>Note: In addition to relative paths, every URL that specifies a
 * file in the current system root, i.e. the JVM working directory,
 * will be interpreted relative to the application context too.
 *
 * @author Juergen Hoeller
 * @since 31.07.2003
 * @see org.springframework.core.io.ResourceLoader
 * @see org.springframework.context.ApplicationContext
 */
public class ResourceEntityResolver extends DelegatingEntityResolver {

	private static final Log logger = LogFactory.getLog(ResourceEntityResolver.class);

	private final ResourceLoader resourceLoader;


	
Create a ResourceEntityResolver for the specified ResourceLoader
(usually, an ApplicationContext).
Params:
resourceLoader – the ResourceLoader (or ApplicationContext)
to load XML entity includes with/**
	 * Create a ResourceEntityResolver for the specified ResourceLoader
	 * (usually, an ApplicationContext).
	 * @param resourceLoader the ResourceLoader (or ApplicationContext)
	 * to load XML entity includes with
	 */
	public ResourceEntityResolver(ResourceLoader resourceLoader) {
		super(resourceLoader.getClassLoader());
		this.resourceLoader = resourceLoader;
	}


	@Override
	@Nullable
	public InputSource resolveEntity(@Nullable String publicId, @Nullable String systemId)
			throws SAXException, IOException {

		InputSource source = super.resolveEntity(publicId, systemId);

		if (source == null && systemId != null) {
			String resourcePath = null;
			try {
				String decodedSystemId = URLDecoder.decode(systemId, "UTF-8");
				String givenUrl = new URL(decodedSystemId).toString();
				String systemRootUrl = new File("").toURI().toURL().toString();
				// Try relative to resource base if currently in system root.
				if (givenUrl.startsWith(systemRootUrl)) {
					resourcePath = givenUrl.substring(systemRootUrl.length());
				}
			}
			catch (Exception ex) {
				// Typically a MalformedURLException or AccessControlException.
				if (logger.isDebugEnabled()) {
					logger.debug("Could not resolve XML entity [" + systemId + "] against system root URL", ex);
				}
				// No URL (or no resolvable URL) -> try relative to resource base.
				resourcePath = systemId;
			}
			if (resourcePath != null) {
				if (logger.isTraceEnabled()) {
					logger.trace("Trying to locate XML entity [" + systemId + "] as resource [" + resourcePath + "]");
				}
				Resource resource = this.resourceLoader.getResource(resourcePath);
				source = new InputSource(resource.getInputStream());
				source.setPublicId(publicId);
				source.setSystemId(systemId);
				if (logger.isDebugEnabled()) {
					logger.debug("Found XML entity [" + systemId + "]: " + resource);
				}
			}
			else if (systemId.endsWith(DTD_SUFFIX) || systemId.endsWith(XSD_SUFFIX)) {
				// External dtd/xsd lookup via https even for canonical http declaration
				String url = systemId;
				if (url.startsWith("http:")) {
					url = "https:" + url.substring(5);
				}
				try {
					source = new InputSource(new URL(url).openStream());
					source.setPublicId(publicId);
					source.setSystemId(systemId);
				}
				catch (IOException ex) {
					if (logger.isDebugEnabled()) {
						logger.debug("Could not resolve XML entity [" + systemId + "] through URL [" + url + "]", ex);
					}
					// Fall back to the parser's default behavior.
					source = null;
				}
			}
		}

		return source;
	}

}