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Pax Web JSP/EL/JSTL Support via Tomcat Jasper 2.
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/* Copyright 2008 Alin Dreghiciu.
 *
 * 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.ops4j.pax.web.jsp;

import java.io.IOException;
import java.net.URLClassLoader;
import java.util.concurrent.Callable;

import javax.servlet.RequestDispatcher;
import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import org.apache.jasper.servlet.JspServlet;
import org.ops4j.pax.swissbox.core.ContextClassLoaderUtils;
import org.osgi.framework.Bundle;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Wrapper of Jasper JspServlet that knows how to deal with resources loaded
 * from osgi context.
 *
 * @author Alin Dreghiciu
 * @since 0.3.0, January 07, 2008
 */
public class JspServletWrapper implements Servlet {

	/**
	 *
	 */
	private static final long serialVersionUID = 1L;
	/**
	 * Logger.
	 */
	private static final Logger LOG = LoggerFactory
			.getLogger(JspServletWrapper.class);
	/**
	 * Jasper Servlet.
	 */
	private final JspServlet jasperServlet;
	/**
	 * Jasper specific class loader.
	 */
	private final URLClassLoader jasperClassLoader;

	private final String jspFile;

	/**
	 * Constructor that provides a custom class loader, in order to be able to
	 * customize the behavior of Jasper with full control over the class loading
	 * mechanism. Only advanced users will need this, most others should simply
	 * use the other constructors that will provide a default class loader that
	 * delegates to the bundle.
	 *
	 * @param jspFile
	 * @param classLoader
	 */
	public JspServletWrapper(final String jspFile,
							 final URLClassLoader classLoader) {
		jasperServlet = new JspServlet();
		jasperClassLoader = classLoader;
		this.jspFile = jspFile;
	}

	public JspServletWrapper(final Bundle bundle, final String jspFile) {
		this(jspFile, new JasperClassLoader(bundle,
				JasperClassLoader.class.getClassLoader()));
	}

	public JspServletWrapper(final Bundle bundle) {
		this(bundle, null);
	}

	/**
	 * Delegates to jasper servlet with a controlled context class loader.
	 *
	 * @see JspServlet#init(ServletConfig)
	 */
	@Override
	public void init(final ServletConfig config) throws ServletException {
		try {
			ContextClassLoaderUtils.doWithClassLoader(jasperClassLoader,
					new Callable() {

						@Override
						public Void call() throws Exception {
							config.getServletContext().setAttribute(
									org.apache.tomcat.InstanceManager.class
											.getName(), new InstanceManager());
							jasperServlet.init(config);
							return null;
						}

					});
		} catch (ServletException e) {
			// re-thrown
			throw e;
			//CHECKSTYLE:OFF
		} catch (Exception ignore) {
			// ignored as it should never happen
			LOG.error("Ignored exception", ignore);
		}
		//CHECKSTYLE:ON
	}

	/**
	 * Delegates to jasper servlet.
	 *
	 * @see JspServlet#getServletConfig()
	 */
	@Override
	public ServletConfig getServletConfig() {
		return jasperServlet.getServletConfig();
	}

	/**
	 * Delegates to jasper servlet with a controlled context class loader.
	 *
	 * @see JspServlet#service(ServletRequest, ServletResponse)
	 */
	@Override
	public void service(final ServletRequest req, final ServletResponse res)
			throws ServletException, IOException {
		if (jspFile != null) {
			req.setAttribute(RequestDispatcher.INCLUDE_SERVLET_PATH, jspFile);
		}
		String includeRequestUri = (String) req
				.getAttribute(RequestDispatcher.INCLUDE_REQUEST_URI);

		if (includeRequestUri != null) {
			req.removeAttribute(RequestDispatcher.INCLUDE_REQUEST_URI);
		}

		try {
			ContextClassLoaderUtils.doWithClassLoader(jasperClassLoader,
					new Callable() {

						@Override
						public Void call() throws Exception {
							jasperServlet.service(req, res);
							return null;
						}

					});
		} catch (ServletException | IOException e) {
			// re-thrown
			throw e;
		} catch (Exception ignore) {
			// ignored as it should never happen
			LOG.error("Ignored exception", ignore);
		}
		//CHECKSTYLE:ON
	}

	/**
	 * Delegates to jasper servlet.
	 *
	 * @see JspServlet#getServletInfo()
	 */
	@Override
	public String getServletInfo() {
		return jasperServlet.getServletInfo();
	}

	/**
	 * Delegates to jasper servlet with a controlled context class loader.
	 *
	 * @see JspServlet#destroy()
	 */
	@Override
	public void destroy() {
		try {
			ContextClassLoaderUtils.doWithClassLoader(jasperClassLoader,
					new Callable() {

						@Override
						public Void call() throws Exception {
							jasperServlet.destroy();
							return null;
						}

					});
			//CHECKSTYLE:OFF
		} catch (Exception ignore) {
			// ignored as it should never happen
			LOG.error("Ignored exception", ignore);
		}
		//CHECKSTYLE:ON
	}

	/**
	 * Provides access to the embedded class loader, mostly useful for
	 * performing validation checks on the class loader in integration tests.
	 *
	 * @return the internal class loader used to dispatch to the underlying
	 * Jasper servlet.
	 */
	public URLClassLoader getClassLoader() {
		return jasperClassLoader;
	}
}