FacesConfigXml.java

/*
 * Copyright 2017 OmniFaces
 *
 * 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
 *
 *     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.omnifaces.config;

import static org.omnifaces.util.Beans.getReference;
import static org.omnifaces.util.Faces.getServletContext;
import static org.omnifaces.util.Faces.hasContext;
import static org.omnifaces.util.Utils.isEmpty;
import static org.omnifaces.util.Utils.parseLocale;
import static org.omnifaces.util.Xml.createDocument;
import static org.omnifaces.util.Xml.getNodeList;
import static org.omnifaces.util.Xml.getTextContent;

import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;

import javax.faces.application.Application;
import javax.servlet.ServletContext;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

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

/**
 * <p>
 * This configuration enum parses the <code>/WEB-INF/faces-config.xml</code> and all
 * <code>/META-INF/faces-config.xml</code> files found in the classpath and offers methods to obtain information from
 * them which is not available by the standard JSF API.
 *
 * <h3>Usage</h3>
 * <p>
 * Some examples:
 * <pre>
 * // Get a mapping of all <resource-bundle> vars and base names.
 * Map<String, String> resourceBundles = FacesConfigXml.INSTANCE.getResourceBundles();
 * </pre>
 * <pre>
 * // Get an ordered list of all <supported-locale> values with <default-locale> as first item.
 * List<Locale> supportedLocales = FacesConfigXml.INSTANCE.getSupportedLocales();
 * </pre>
 *
 * @author Bauke Scholtz
 * @author Michele Mariotti
 * @since 2.1
 */
public enum FacesConfigXml {

	// Enum singleton -------------------------------------------------------------------------------------------------

	/**
	 * Returns the lazily loaded enum singleton instance.
	 */
	INSTANCE;

	// Private constants ----------------------------------------------------------------------------------------------

	private static final String APP_FACES_CONFIG_XML =
		"/WEB-INF/faces-config.xml";
	private static final String LIB_FACES_CONFIG_XML =
		"META-INF/faces-config.xml";
	private static final String XPATH_RESOURCE_BUNDLE =
		"application/resource-bundle";
	private static final String XPATH_DEFAULT_LOCALE =
		"application/locale-config/default-locale";
	private static final String XPATH_SUPPORTED_LOCALE =
		"application/locale-config/supported-locale";
	private static final String XPATH_VAR =
		"var";
	private static final String XPATH_BASE_NAME =
		"base-name";
	private static final String ERROR_INITIALIZATION_FAIL =
		"FacesConfigXml failed to initialize. Perhaps your faces-config.xml contains a typo?";

	// Properties -----------------------------------------------------------------------------------------------------

	private Map<String, String> resourceBundles;
	private List<Locale> supportedLocales;

	// Init -----------------------------------------------------------------------------------------------------------

	/**
	 * Perform automatic initialization whereby the servlet context is obtained from CDI.
	 */
	private FacesConfigXml() {
		ServletContext servletContext = hasContext() ? getServletContext() : getReference(ServletContext.class);

		try {
			Element facesConfigXml = loadFacesConfigXml(servletContext).getDocumentElement();
			XPath xpath = XPathFactory.newInstance().newXPath();
			resourceBundles = parseResourceBundles(facesConfigXml, xpath);
			supportedLocales = parseSupportedLocales(facesConfigXml, xpath);
		}
		catch (Exception e) {
			throw new IllegalStateException(ERROR_INITIALIZATION_FAIL, e);
		}
	}

	// Getters --------------------------------------------------------------------------------------------------------

	/**
	 * Returns a mapping of all resource bundle base names by var.
	 * @return A mapping of all resource bundle base names by var.
	 */
	public Map<String, String> getResourceBundles() {
		return resourceBundles;
	}

	/**
	 * Returns an ordered list of all supported locales on this application, with the default locale as the first
	 * item, if any. This will return an empty list if there are no locales definied in <code>faces-config.xml</code>.
	 * @return An ordered list of all supported locales on this application, with the default locale as the first
	 * item, if any.
	 * @see Application#getDefaultLocale()
	 * @see Application#getSupportedLocales()
	 * @since 2.2
	 */
	public List<Locale> getSupportedLocales() {
		return supportedLocales;
	}

	// Helpers --------------------------------------------------------------------------------------------------------

	/**
	 * Load, merge and return all <code>faces-config.xml</code> files found in the classpath
	 * into a single {@link Document}.
	 */
	private static Document loadFacesConfigXml(ServletContext context) throws IOException, SAXException {
		List<URL> facesConfigURLs = new ArrayList<>();
		facesConfigURLs.add(context.getResource(APP_FACES_CONFIG_XML));
		facesConfigURLs.addAll(Collections.list(Thread.currentThread().getContextClassLoader().getResources(LIB_FACES_CONFIG_XML)));
		return createDocument(facesConfigURLs);
	}

	/**
	 * Create and return a mapping of all resource bundle base names by var found in the given document.
	 * @throws XPathExpressionException
	 */
	private static Map<String, String> parseResourceBundles(Element facesConfigXml, XPath xpath) throws XPathExpressionException {
		Map<String, String> resourceBundles = new LinkedHashMap<>();
		NodeList resourceBundleNodes = getNodeList(facesConfigXml, xpath, XPATH_RESOURCE_BUNDLE);

		for (int i = 0; i < resourceBundleNodes.getLength(); i++) {
			Node node = resourceBundleNodes.item(i);

			String var = xpath.compile(XPATH_VAR).evaluate(node).trim();
			String baseName = xpath.compile(XPATH_BASE_NAME).evaluate(node).trim();

			if (!resourceBundles.containsKey(var)) {
				resourceBundles.put(var, baseName);
			}
		}

		return Collections.unmodifiableMap(resourceBundles);
	}

	/**
	 * Create and return a list of default locale and all supported locales in same order as in the given document.
	 * @throws XPathExpressionException
	 */
	private static List<Locale> parseSupportedLocales(Element facesConfigXml, XPath xpath) throws XPathExpressionException {
		List<Locale> supportedLocales = new ArrayList<>();
		String defaultLocale = xpath.compile(XPATH_DEFAULT_LOCALE).evaluate(facesConfigXml).trim();

		if (!isEmpty(defaultLocale)) {
			supportedLocales.add(parseLocale(defaultLocale));
		}

		NodeList supportedLocaleNodes = getNodeList(facesConfigXml, xpath, XPATH_SUPPORTED_LOCALE);

		for (int i = 0; i < supportedLocaleNodes.getLength(); i++) {
			Locale supportedLocale = parseLocale(getTextContent(supportedLocaleNodes.item(i)));

			if (!supportedLocales.contains(supportedLocale)) {
				supportedLocales.add(supportedLocale);
			}
		}

		return Collections.unmodifiableList(supportedLocales);
	}

}