/**
 * Created on Sep 12, 2005
 *
 * $Id: OpenSessionInViewFilter.java,v 1.2 2006/03/07 13:09:30 costin Exp $
 * $Revision: 1.2 $
 */
package org.springmodules.jcr.support;

import java.io.IOException;

import javax.jcr.Session;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;
import org.springframework.web.filter.OncePerRequestFilter;
import org.springmodules.jcr.SessionFactory;
import org.springmodules.jcr.SessionFactoryUtils;

/**
 * Servlet 2.3 Filter that binds a JCR Session to the thread for the
 * entire processing of the request. Intended for the "Open Session
 * in View" pattern, i.e. to allow for lazy loading in web views despite the
 * original transactions already being completed.
 * 
 * <p>
 * This filter works similar to the AOP JcrInterceptor: It just makes JCR
 * Sessions available via the thread. It is suitable for
 * non-transactional execution but also for business layer transactions via
 * JcrTransactionManager or JtaTransactionManager. In the latter case,
 * Sessions pre-bound by this filter will automatically be used for
 * the transactions.
 * 
 * <p>
 * Looks up the SessionFactory in Spring's root web application
 * context. Supports a "SessionFactoryBeanName" filter init-param in
 * <code>web.xml</code>; the default bean name is
 * "SessionFactory". Looks up the SessionFactory on each
 * request, to avoid initialization order issues (when using
 * ContextLoaderServlet, the root application context will get initialized
 * <i>after</i> this filter).
 * 
 * @author Costin Leau
 */
public class OpenSessionInViewFilter extends OncePerRequestFilter {
	public static final String DEFAULT_JCR_SESSION_FACTORY_FACTORY_BEAN_NAME = "sessionFactory";

	private String SessionFactoryBeanName = DEFAULT_JCR_SESSION_FACTORY_FACTORY_BEAN_NAME;

	/**
	 * Set the bean name of the SessionFactory to fetch from Spring's
	 * root application context. Default is "SessionFactory".
	 * 
	 * @see #DEFAULT_JCR_SESSION_FACTORY_FACTORY_BEAN_NAME
	 */
	public void setSessionFactoryBeanName(String SessionFactoryBeanName) {
		this.SessionFactoryBeanName = SessionFactoryBeanName;
	}

	/**
	 * Return the bean name of the SessionFactory to fetch from
	 * Spring's root application context.
	 */
	protected String getSessionFactoryBeanName() {
		return SessionFactoryBeanName;
	}


	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
			FilterChain filterChain) throws ServletException, IOException {

		SessionFactory sf = lookupSessionFactory(request);
		
		Session session = null;
		boolean participate = false;

		if (TransactionSynchronizationManager.hasResource(sf)) {
			// Do not modify the Session: just set the participate
			// flag.
			participate = true;
		}
		else {
			logger.debug("Opening JCR session in OpenSessionInViewFilter");
			session = SessionFactoryUtils.getSession(sf, true);
			TransactionSynchronizationManager.bindResource(sf, sf.getSessionHolder(session));
		}

		try {
			filterChain.doFilter(request, response);
		}

		finally {
			if (!participate) {
				TransactionSynchronizationManager.unbindResource(sf);
				logger.debug("Closing JCR session in OpenSessionInViewFilter");
				SessionFactoryUtils.releaseSession(session, sf);
			}
		}
	}

	/**
	 * Look up the SessionFactory that this filter should use, taking
	 * the current HTTP request as argument.
	 * <p>
	 * Default implementation delegates to the
	 * <code>lookupSessionFactory</code> without arguments.
	 * 
	 * @return the SessionFactory to use
	 * @see #lookupSessionFactory()
	 */
	protected SessionFactory lookupSessionFactory(HttpServletRequest request) {
		return lookupSessionFactory();
	}

	/**
	 * Look up the SessionFactory that this filter should use. The
	 * default implementation looks for a bean with the specified name in
	 * Spring's root application context.
	 * 
	 * @return the SessionFactory to use
	 * @see #getSessionFactoryBeanName
	 */
	protected SessionFactory lookupSessionFactory() {
		if (logger.isDebugEnabled()) {
			logger.debug("Using session factory '"
					+ getSessionFactoryBeanName()
					+ "' for OpenSessionInViewFilter");
		}
		WebApplicationContext wac = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());
		return (SessionFactory) wac.getBean(getSessionFactoryBeanName(), SessionFactory.class);
	}

}