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Pax Web JSP/EL/JSTL Support via Tomcat Jasper 2.
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/*
 * 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.ops4j.pax.web.jsp;

import java.io.IOException;
import java.util.Set;

import javax.servlet.ServletContainerInitializer;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.jsp.JspFactory;

import org.apache.jasper.Constants;
import org.apache.jasper.compiler.Localizer;
import org.apache.jasper.compiler.TldCache;
import org.apache.jasper.runtime.JspFactoryImpl;
import org.apache.jasper.security.SecurityClassLoad;
import org.apache.tomcat.InstanceManager;
import org.apache.tomcat.SimpleInstanceManager;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.xml.sax.SAXException;

/**
 * Initializer for the Jasper JSP Engine.
 */
public class JasperInitializer implements ServletContainerInitializer {

	private static final String MSG = "org.apache.jasper.servlet.JasperInitializer";
	private static final Logger LOG = LoggerFactory.getLogger(JasperInitializer.class);

	/**
	 * Preload classes required at runtime by a JSP servlet so that
	 * we don't get a defineClassInPackage security exception.
	 */
	static {
		JspFactoryImpl factory = new JspFactoryImpl();
		SecurityClassLoad.securityClassLoad(factory.getClass().getClassLoader());
		if (System.getSecurityManager() != null) {
			String basePackage = "org.apache.jasper.";
			try {
				factory.getClass().getClassLoader().loadClass(basePackage +
						"runtime.JspFactoryImpl$PrivilegedGetPageContext");
				factory.getClass().getClassLoader().loadClass(basePackage +
						"runtime.JspFactoryImpl$PrivilegedReleasePageContext");
				factory.getClass().getClassLoader().loadClass(basePackage +
						"runtime.JspRuntimeLibrary");
				factory.getClass().getClassLoader().loadClass(basePackage +
						"runtime.ServletResponseWrapperInclude");
				factory.getClass().getClassLoader().loadClass(basePackage +
						"servlet.JspServletWrapper");
			} catch (ClassNotFoundException ex) {
				throw new IllegalStateException(ex);
			}
		}

		if (JspFactory.getDefaultFactory() == null) {
			JspFactory.setDefaultFactory(factory);
		}
	}

	@Override
	public void onStartup(Set> types, ServletContext context) throws ServletException {
		if (LOG.isDebugEnabled()) {
			LOG.debug(Localizer.getMessage(MSG + ".onStartup", context.getServletContextName()));
		}

		// Setup a simple default Instance Manager
		if (context.getAttribute(InstanceManager.class.getName()) == null) {
			context.setAttribute(InstanceManager.class.getName(), new SimpleInstanceManager());
		}

		boolean validate = Boolean.parseBoolean(
				context.getInitParameter(Constants.XML_VALIDATION_TLD_INIT_PARAM));
		String blockExternalString = context.getInitParameter(
				Constants.XML_BLOCK_EXTERNAL_INIT_PARAM);
		boolean blockExternal;
		if (blockExternalString == null) {
			blockExternal = true;
		} else {
			blockExternal = Boolean.parseBoolean(blockExternalString);
		}

		// scan the application for TLDs
		TldScanner scanner = newTldScanner(context, true, validate, blockExternal);
		try {
			scanner.scan();
		} catch (IOException | SAXException e) {
			throw new ServletException(e);
		}

		// add any listeners defined in TLDs
		for (String listener : scanner.getListeners()) {
			try {
				context.addListener(listener);
			} catch (RuntimeException e) {
				if (e.getCause() instanceof ClassNotFoundException) {
					LOG.error("Could not add listener from scanned TLD to context. " +
							"The referenced class could not be found (missing import): {}", e.getMessage());
				} else {
					throw e;
				}
			}
		}

		context.setAttribute(TldCache.SERVLET_CONTEXT_ATTRIBUTE_NAME,
				new TldCache(context, scanner.getUriTldResourcePathMap(),
						scanner.getTldResourcePathTaglibXmlMap()));

		// context.addServlet("jsp", JspServlet.class);
		// context.getServletRegistration("jsp").addMapping("*.jsp");
	}

	protected TldScanner newTldScanner(ServletContext context, boolean namespaceAware,
									   boolean validate, boolean blockExternal) {
		return new TldScanner(context, namespaceAware, validate, blockExternal);
	}
}