src/main/java/org/apache/sling/launchpad/webapp/SlingServlet.java - sling-org-apache-sling-launchpad-base - Git at Google

 /*
  * 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.apache.sling.launchpad.webapp;

 import java.io.File;
 import java.io.IOException;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.Map;

 import javax.servlet.GenericServlet;
 import javax.servlet.Servlet;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletRequestWrapper;
 import javax.servlet.http.HttpServletResponse;

 import org.apache.sling.launchpad.base.shared.Launcher;
 import org.apache.sling.launchpad.base.shared.Loader;
 import org.apache.sling.launchpad.base.shared.Notifiable;
 import org.apache.sling.launchpad.base.shared.SharedConstants;
 import org.apache.sling.launchpad.base.shared.Util;

 /**
  * The <code>SlingServlet</code> is the externally visible Web Application
  * launcher for Sling. Please refer to the full description <i>The Sling
  * Launchpad</i> on the Sling Wiki for a full description of this class.
  * <p>
  * Logging goes to ServletContext.log methods.
  * <p>
  * This class goes into the secondary artifact with the classifier <i>webapp</i>
  * to be used as the main servlet to be registered in the servlet container.
  *
  * @see <a href="http://cwiki.apache.org/SLING/the-sling-launchpad.html">The
  *      Sling Launchpad</a>
  */
 @SuppressWarnings("serial")
 public class SlingServlet extends GenericServlet implements Notifiable {

     /**
      * The number times Sling will be tried to be started before giving up
      * (value is 20). This number is chosen deliberately as generally Sling
      * should start up smoothly. Whether any bundles within Sling start or not
      * is not counted here.
      */
     private static final int MAX_START_FAILURES = 20;

     /**
      * The name of the system property which may be set to define the default
      * prefix for the sling.home value generated from the Sling servlet context
      * path.
      *
      * @see #toSlingHome(String)
      */
     private static final String SLING_HOME_PREFIX = "sling.home.prefix";

     /**
      * The default value to be used as the prefix for the sling.home value
      * generated from the Sling servlet context path if the
      * {@link #SLING_HOME_PREFIX sling.home.prefix} system property is not set.
      *
      * @see #toSlingHome(String)
      */
     private static final String SLING_HOME_PREFIX_DEFAULT = "sling/";

     private Map<String, String> properties;

     private String slingHome;

     private Loader loader;

     private Servlet sling;

     /**
      * Field managed by the {@link #startSling(String)} method to indicate
      * whether Sling is in the process of being started.
      */
     private Thread startingSling;

     /**
      * Counter to count the number of failed startups. After this number
      * expires, the SlingServlet will not try to start Sling any more.
      */
     private int startFailureCounter = 0;

     // ---------- GenericServlet

     /**
      * Launches the SLing framework if the sling.home setting can be derived
      * from the configuration or the SerlvetContext. Otherwise Sling is not
      * started yet and will be started when the first request comes in.
      */
     @Override
     public void init() {
         this.properties = collectInitParameters();

         this.slingHome = getSlingHome(null);
         if (this.slingHome != null) {
             startSling();
         } else {
             log("Apache Sling cannot be started yet, because sling.home is not defined yet");
         }

         log("Servlet " + getServletName() + " initialized");
     }

     @Override
     public String getServletInfo() {
         if (sling != null) {
             return sling.getServletInfo();
         }

         return "Sling Launchpad Proxy";
     }

     /**
      * If Sling has already been started, the request is forwarded to the
      * started Sling framework. Otherwise the Sling framework is started unless
      * there were too many startup failures.
      * <p>
      * If the request is not forwarded to Sling, this method returns a 404/NOT
      * FOUND if the startup failure counter has exceeded or 503/SERVICE
      * UNAVAILABLE if the Sling framework is starting up.
      * <p>
      * If a request causes the framework to start, it is immediately terminated
      * with said response status and framework is started in a separate thread.
      */
     @Override
     public void service(ServletRequest req, ServletResponse res)
             throws ServletException, IOException {

         // delegate the request to the registered delegatee servlet
         Servlet delegatee = sling;
         if (delegatee != null) {

             // check for problematic application servers like WebSphere
             // where path info and servlet path is set wrong SLING-2410
             final HttpServletRequest request = (HttpServletRequest) req;
             if ( request.getPathInfo() == null && request.getServletPath() != null
                     && request.getServletPath().endsWith(".jsp") ) {
                 req = new HttpServletRequestWrapper(request) {

                     @Override
                     public String getPathInfo() {
                         return request.getServletPath();
                     }

                     @Override
                     public String getServletPath() {
                         return "";
                     }

                 };
             }
             delegatee.service(req, res);

         } else if (startFailureCounter > MAX_START_FAILURES) {

             // too many startup retries, fail for ever
             ((HttpServletResponse) res).sendError(HttpServletResponse.SC_NOT_FOUND);

         } else {

             startSling(req);

             ((HttpServletResponse) res).sendError(
                 HttpServletResponse.SC_SERVICE_UNAVAILABLE,
                 "Apache Sling is currently starting up, please try again");
         }
     }

     /**
      * Stop the Sling framework when the web application is being stopped
      */
     @Override
     public void destroy() {
         if (sling != null) {
             sling.destroy();
         }

         // clear fields
         slingHome = null;
         loader = null;
         sling = null;
     }

     // ---------- Notifiable interface

     /**
      * The framework has been stopped by calling the <code>Bundle.stop()</code>
      * on the system bundle. This actually terminates the Sling Standalone
      * application.
      * <p>
      * Note, that a new request coming in while the web application is still
      * running, will actually cause Sling to restart !
      */
     @Override
     public void stopped() {
         /**
          * This method is called if the framework is stopped from within by
          * calling stop on the system bundle or if the framework is stopped
          * because the VM is going down and the shutdown hook has initated the
          * shutdown In any case we ensure the reference to the framework is
          * removed and remove the shutdown hook (but don't care if that fails).
          */

         log("Apache Sling has been stopped");

         // clear the reference to the framework
         sling = null;
     }

     /**
      * The framework has been stopped with the intent to be restarted by calling
      * either of the <code>Bundle.update</code> methods on the system bundle.
      * <p>
      * If an <code>InputStream</code> was provided, this has been copied to a
      * temporary file, which will be used in place of the existing launcher jar
      * file.
      *
      * @param updateFile The temporary file to replace the existing launcher jar
      *            file. If <code>null</code> the existing launcher jar will be
      *            used again.
      */
     @Override
     public void updated(File updateFile) {

         // drop the sling reference to be able to restart
         synchronized (this) {
             if (startingSling == null) {
                 sling = null;
             }
         }

         // ensure we have a VM as clean as possible
         loader.cleanupVM();

         if (updateFile == null) {

             log("Restarting Framework and Apache Sling");
             startSling((URL) null);

         } else {

             log("Restarting Framework with update from " + updateFile);
             try {
                 startSling(updateFile.toURI().toURL());
             } catch (MalformedURLException mue) {
                 log("Cannot get URL for file " + updateFile, mue);
             } finally {
                 updateFile.delete();
             }

         }
     }

     // --------- internal

     /**
      * If Sling is not currently starting up, a thread is started to start Sling
      * in the background.
      */
     private void startSling(final ServletRequest request) {
         if (startingSling == null) {
             slingHome = getSlingHome((HttpServletRequest) request);
             Thread starter = new Thread(new Runnable() {
                 @Override
                 public void run() {
                     startSling();
                 }
             }, "SlingStarter_" + System.currentTimeMillis());

             starter.setDaemon(true);
             starter.start();
         }
     }

     /**
      * Called from the startup thread initiated by a request or from
      * {@link #init()} to install the launcher jar and actually start sling.
      */
     private void startSling() {

         try {
             File launchpadHome = getLaunchpadHome(slingHome);
             this.loader = new Loader(launchpadHome) {
                 @Override
                 protected void info(String msg) {
                     log(msg);
                 }
             };
         } catch (IllegalArgumentException iae) {
             startupFailure(null, iae);
             return;
         }

         try {
             URL launcherJar = getServletContext().getResource(
                 SharedConstants.DEFAULT_SLING_LAUNCHER_JAR);
             if (launcherJar == null) {
                 launcherJar = getServletContext().getResource(
                     "/WEB-INF" + SharedConstants.DEFAULT_SLING_LAUNCHER_JAR);
             }

             startSling(launcherJar);
         } catch (MalformedURLException mue) {
             log("Cannot load Apache Sling Launcher JAR "
                 + SharedConstants.DEFAULT_SLING_LAUNCHER_JAR, mue);
         }
     }

     /**
      * Installs the launcher jar from the given URL (if not <code>null</code>)
      * and launches Sling from that launcher.
      */
     private void startSling(URL launcherJar) {
         synchronized (this) {
             if (sling != null) {
                 log("Apache Sling already started, nothing to do");
                 return;
             } else if (startingSling != null) {
                 log("Apache Sling being started by Thread " + startingSling);
                 return;
             }

             startingSling = Thread.currentThread();
         }

         if (launcherJar != null) {
             try {
                 log("Checking launcher JAR in " + slingHome);
                 loader.installLauncherJar(launcherJar);
             } catch (IOException ioe) {
                 startupFailure("Failed installing " + launcherJar, ioe);
                 return;
             }
         } else {
             log("No Launcher JAR to install");
         }

         Object object = null;
         try {
             object = loader.loadLauncher(SharedConstants.DEFAULT_SLING_SERVLET);
         } catch (IllegalArgumentException iae) {
             startupFailure("Cannot load Launcher Servlet "
                 + SharedConstants.DEFAULT_SLING_SERVLET, iae);
             return;
         }

         if (object instanceof Servlet) {
             Servlet sling = (Servlet) object;

             if (sling instanceof Launcher) {
                 Launcher slingLauncher = (Launcher) sling;
                 slingLauncher.setNotifiable(this);
                 slingLauncher.setCommandLine(properties);
                 slingLauncher.setSlingHome(slingHome);
             }

             try {
                 log("Starting launcher ...");
                 sling.init(getServletConfig());
                 this.sling = sling;
                 this.startFailureCounter = 0;
                 log("Startup completed");
             } catch (ServletException se) {
                 startupFailure(null, se);
             }
         }

         // reset the starting flag
         synchronized (this) {
             startingSling = null;
         }
     }

     /**
      * Define the sling.home parameter implementing the algorithme defined on
      * the wiki page to find the setting according to this algorithm:
      * <ol>
      * <li>Servlet parameter <code>sling.home</code></li>
      * <li>Context <code>sling.home</code></li>
      * <li>Derived from ServletContext path</li>
      * </ol>
      * <p>
      * <code>null</code> may be returned by this method if no
      * <code>sling.home</code> parameter is set and if the servlet container
      * does not provide the Servlet API 2.5
      * <code>ServletContext.getContextPath()</code> method and the
      * <code>request</code> parameter is <code>null</code>.
      * <p>
      * If <code>sling.home</code> can be retrieved, it is returned as an
      * absolute path.
      *
      * @param args The command line arguments
      * @return The value to use for sling.home or <code>null</code> if the value
      *         cannot be retrieved.
      */
     private String getSlingHome(HttpServletRequest request) {

         String source = null;

         // access config and context to be able to log the sling.home source

         // 1. servlet config parameter
         String slingHome = getServletConfig().getInitParameter(
             SharedConstants.SLING_HOME);
         if (slingHome != null) {

             source = "servlet parameter sling.home";

         } else {

             // 2. servlet context parameter
             slingHome = getServletContext().getInitParameter(
                 SharedConstants.SLING_HOME);
             if (slingHome != null) {

                 source = "servlet context parameter sling.home";

             } else {

                 // 3. servlet context path (Servlet API 2.5 and later)
                 try {

                     String contextPath = getServletContext().getContextPath();
                     slingHome = toSlingHome(contextPath);
                     source = "servlet context path";

                 } catch (NoSuchMethodError nsme) {

                     // 4.servlet context path (Servlet API 2.4 and earlier)
                     if (request != null) {

                         String contextPath = request.getContextPath();
                         slingHome = toSlingHome(contextPath);
                         source = "servlet context path (from request)";

                     } else {

                         log("ServletContext path not available here, delaying startup until first request");
                         return null;

                     }
                 }

             }
         }

         // substitute any ${...} references and make absolute
         slingHome = Util.substVars(slingHome, SharedConstants.SLING_HOME, null, properties);
         slingHome = new File(slingHome).getAbsolutePath();

         log("Setting sling.home=" + slingHome + " (" + source + ")");
         return slingHome;
     }

     /**
      * Define the sling.launchpad parameter implementing the algorithme defined
      * on the wiki page to find the setting according to this algorithm:
      * <ol>
      * <li>Servlet init parameter <code>sling.launchpad</code>. This path is
      * resolved against the <code>slingHome</code> folder if relative.</li>
      * <li>Servlet context init parameter <code>sling.launchpad</code>. This
      * path is resolved against the <code>slingHome</code> folder if relative.</li>
      * <li>Default to same as <code>sling.home</code></li>
      * </ol>
      * <p>
      * The absolute path of the returned file is stored as the
      * <code>sling.launchpad</code> property in the {@link #properties} map.
      *
      * @param slingHome The absolute path to the Sling Home folder (aka the
      *            <code>sling.home</code>.
      * @return The absolute <code>File</code> indicating the launchpad folder.
      */
     private File getLaunchpadHome(final String slingHome) {
         String launchpadHomeParam = properties.get(SharedConstants.SLING_LAUNCHPAD);
         if (launchpadHomeParam == null || launchpadHomeParam.length() == 0) {
             properties.put(SharedConstants.SLING_LAUNCHPAD, slingHome);
             return new File(slingHome);
         }

         File launchpadHome = new File(launchpadHomeParam);
         if (!launchpadHome.isAbsolute()) {
             launchpadHome = new File(slingHome, launchpadHomeParam);
         }

         properties.put(SharedConstants.SLING_LAUNCHPAD,
             launchpadHome.getAbsolutePath());
         return launchpadHome;
     }

     /**
      * Converts the servlet context path to a path used for the sling.home
      * property. The servlet context path is converted to a simple name by
      * replacing all slash characters in the path with underscores (or a single
      * underscore for the root context path being empty or null). Next the
      * result is prefixed with either value of the
      * <code>sling.home.prefix</code> system property or the (default prefix)
      * <code>sling/</code>.
      *
      * @param contextPath
      * @return
      */
     private String toSlingHome(String contextPath) {
         String prefix = System.getProperty(SLING_HOME_PREFIX,
             SLING_HOME_PREFIX_DEFAULT);

         if (!prefix.endsWith("/")) {
             prefix = prefix.concat("/");
         }

         if (contextPath == null || contextPath.length() == 0) {
             return prefix + "_";
         }

         return prefix + contextPath.replace('/', '_');
     }

     private void startupFailure(String message, Throwable cause) {

         // ensure message
         if (message == null) {
             message = "Failed to start Apache Sling in " + slingHome;
         }

         // unwrap to get the real cause
         while (cause.getCause() != null) {
             cause = cause.getCause();
         }

         // log it now and increase the failure counter
         log(message, cause);
         startFailureCounter++;

         // ensure the startingSling fields is not set
         synchronized (this) {
             startingSling = null;
         }
     }

     // ---------- Property file variable substition support --------------------

     private Map<String, String> collectInitParameters() {
         HashMap<String, String> props = new HashMap<String, String>();
         for (Enumeration<String> keys = getServletContext().getInitParameterNames(); keys.hasMoreElements();) {
             String key = keys.nextElement();
             props.put(key, getServletContext().getInitParameter(key));
         }
         for (Enumeration<String> keys = getServletConfig().getInitParameterNames(); keys.hasMoreElements();) {
             String key = keys.nextElement();
             props.put(key, getServletConfig().getInitParameter(key));
         }
         return props;
     }

 }
	/*
	* 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.apache.sling.launchpad.webapp;

	import java.io.File;
	import java.io.IOException;
	import java.net.MalformedURLException;
	import java.net.URL;
	import java.util.Enumeration;
	import java.util.HashMap;
	import java.util.Map;

	import javax.servlet.GenericServlet;
	import javax.servlet.Servlet;
	import javax.servlet.ServletException;
	import javax.servlet.ServletRequest;
	import javax.servlet.ServletResponse;
	import javax.servlet.http.HttpServletRequest;
	import javax.servlet.http.HttpServletRequestWrapper;
	import javax.servlet.http.HttpServletResponse;

	import org.apache.sling.launchpad.base.shared.Launcher;
	import org.apache.sling.launchpad.base.shared.Loader;
	import org.apache.sling.launchpad.base.shared.Notifiable;
	import org.apache.sling.launchpad.base.shared.SharedConstants;
	import org.apache.sling.launchpad.base.shared.Util;

	/**
	* The <code>SlingServlet</code> is the externally visible Web Application
	* launcher for Sling. Please refer to the full description <i>The Sling
	* Launchpad</i> on the Sling Wiki for a full description of this class.
	* <p>
	* Logging goes to ServletContext.log methods.
	* <p>
	* This class goes into the secondary artifact with the classifier <i>webapp</i>
	* to be used as the main servlet to be registered in the servlet container.
	*
	* @see <a href="http://cwiki.apache.org/SLING/the-sling-launchpad.html">The
	* Sling Launchpad</a>
	*/
	@SuppressWarnings("serial")
	public class SlingServlet extends GenericServlet implements Notifiable {

	/**
	* The number times Sling will be tried to be started before giving up
	* (value is 20). This number is chosen deliberately as generally Sling
	* should start up smoothly. Whether any bundles within Sling start or not
	* is not counted here.
	*/
	private static final int MAX_START_FAILURES = 20;

	/**
	* The name of the system property which may be set to define the default
	* prefix for the sling.home value generated from the Sling servlet context
	* path.
	*
	* @see #toSlingHome(String)
	*/
	private static final String SLING_HOME_PREFIX = "sling.home.prefix";

	/**
	* The default value to be used as the prefix for the sling.home value
	* generated from the Sling servlet context path if the
	* {@link #SLING_HOME_PREFIX sling.home.prefix} system property is not set.
	*
	* @see #toSlingHome(String)
	*/
	private static final String SLING_HOME_PREFIX_DEFAULT = "sling/";

	private Map<String, String> properties;

	private String slingHome;

	private Loader loader;

	private Servlet sling;

	/**
	* Field managed by the {@link #startSling(String)} method to indicate
	* whether Sling is in the process of being started.
	*/
	private Thread startingSling;

	/**
	* Counter to count the number of failed startups. After this number
	* expires, the SlingServlet will not try to start Sling any more.
	*/
	private int startFailureCounter = 0;

	// ---------- GenericServlet

	/**
	* Launches the SLing framework if the sling.home setting can be derived
	* from the configuration or the SerlvetContext. Otherwise Sling is not
	* started yet and will be started when the first request comes in.
	*/
	@Override
	public void init() {
	this.properties = collectInitParameters();

	this.slingHome = getSlingHome(null);
	if (this.slingHome != null) {
	startSling();
	} else {
	log("Apache Sling cannot be started yet, because sling.home is not defined yet");
	}

	log("Servlet " + getServletName() + " initialized");
	}

	@Override
	public String getServletInfo() {
	if (sling != null) {
	return sling.getServletInfo();
	}

	return "Sling Launchpad Proxy";
	}

	/**
	* If Sling has already been started, the request is forwarded to the
	* started Sling framework. Otherwise the Sling framework is started unless
	* there were too many startup failures.
	* <p>
	* If the request is not forwarded to Sling, this method returns a 404/NOT
	* FOUND if the startup failure counter has exceeded or 503/SERVICE
	* UNAVAILABLE if the Sling framework is starting up.
	* <p>
	* If a request causes the framework to start, it is immediately terminated
	* with said response status and framework is started in a separate thread.
	*/
	@Override
	public void service(ServletRequest req, ServletResponse res)
	throws ServletException, IOException {

	// delegate the request to the registered delegatee servlet
	Servlet delegatee = sling;
	if (delegatee != null) {

	// check for problematic application servers like WebSphere
	// where path info and servlet path is set wrong SLING-2410
	final HttpServletRequest request = (HttpServletRequest) req;
	if ( request.getPathInfo() == null && request.getServletPath() != null
	&& request.getServletPath().endsWith(".jsp") ) {
	req = new HttpServletRequestWrapper(request) {

	@Override
	public String getPathInfo() {
	return request.getServletPath();
	}

	@Override
	public String getServletPath() {
	return "";
	}

	};
	}
	delegatee.service(req, res);

	} else if (startFailureCounter > MAX_START_FAILURES) {

	// too many startup retries, fail for ever
	((HttpServletResponse) res).sendError(HttpServletResponse.SC_NOT_FOUND);

	} else {

	startSling(req);

	((HttpServletResponse) res).sendError(
	HttpServletResponse.SC_SERVICE_UNAVAILABLE,
	"Apache Sling is currently starting up, please try again");
	}
	}

	/**
	* Stop the Sling framework when the web application is being stopped
	*/
	@Override
	public void destroy() {
	if (sling != null) {
	sling.destroy();
	}

	// clear fields
	slingHome = null;
	loader = null;
	sling = null;
	}

	// ---------- Notifiable interface

	/**
	* The framework has been stopped by calling the <code>Bundle.stop()</code>
	* on the system bundle. This actually terminates the Sling Standalone
	* application.
	* <p>
	* Note, that a new request coming in while the web application is still
	* running, will actually cause Sling to restart !
	*/
	@Override
	public void stopped() {
	/**
	* This method is called if the framework is stopped from within by
	* calling stop on the system bundle or if the framework is stopped
	* because the VM is going down and the shutdown hook has initated the
	* shutdown In any case we ensure the reference to the framework is
	* removed and remove the shutdown hook (but don't care if that fails).
	*/

	log("Apache Sling has been stopped");

	// clear the reference to the framework
	sling = null;
	}

	/**
	* The framework has been stopped with the intent to be restarted by calling
	* either of the <code>Bundle.update</code> methods on the system bundle.
	* <p>
	* If an <code>InputStream</code> was provided, this has been copied to a
	* temporary file, which will be used in place of the existing launcher jar
	* file.
	*
	* @param updateFile The temporary file to replace the existing launcher jar
	* file. If <code>null</code> the existing launcher jar will be
	* used again.
	*/
	@Override
	public void updated(File updateFile) {

	// drop the sling reference to be able to restart
	synchronized (this) {
	if (startingSling == null) {
	sling = null;
	}
	}

	// ensure we have a VM as clean as possible
	loader.cleanupVM();

	if (updateFile == null) {

	log("Restarting Framework and Apache Sling");
	startSling((URL) null);

	} else {

	log("Restarting Framework with update from " + updateFile);
	try {
	startSling(updateFile.toURI().toURL());
	} catch (MalformedURLException mue) {
	log("Cannot get URL for file " + updateFile, mue);
	} finally {
	updateFile.delete();
	}

	}
	}

	// --------- internal

	/**
	* If Sling is not currently starting up, a thread is started to start Sling
	* in the background.
	*/
	private void startSling(final ServletRequest request) {
	if (startingSling == null) {
	slingHome = getSlingHome((HttpServletRequest) request);
	Thread starter = new Thread(new Runnable() {
	@Override
	public void run() {
	startSling();
	}
	}, "SlingStarter_" + System.currentTimeMillis());

	starter.setDaemon(true);
	starter.start();
	}
	}

	/**
	* Called from the startup thread initiated by a request or from
	* {@link #init()} to install the launcher jar and actually start sling.
	*/
	private void startSling() {

	try {
	File launchpadHome = getLaunchpadHome(slingHome);
	this.loader = new Loader(launchpadHome) {
	@Override
	protected void info(String msg) {
	log(msg);
	}
	};
	} catch (IllegalArgumentException iae) {
	startupFailure(null, iae);
	return;
	}

	try {
	URL launcherJar = getServletContext().getResource(
	SharedConstants.DEFAULT_SLING_LAUNCHER_JAR);
	if (launcherJar == null) {
	launcherJar = getServletContext().getResource(
	"/WEB-INF" + SharedConstants.DEFAULT_SLING_LAUNCHER_JAR);
	}

	startSling(launcherJar);
	} catch (MalformedURLException mue) {
	log("Cannot load Apache Sling Launcher JAR "
	+ SharedConstants.DEFAULT_SLING_LAUNCHER_JAR, mue);
	}
	}

	/**
	* Installs the launcher jar from the given URL (if not <code>null</code>)
	* and launches Sling from that launcher.
	*/
	private void startSling(URL launcherJar) {
	synchronized (this) {
	if (sling != null) {
	log("Apache Sling already started, nothing to do");
	return;
	} else if (startingSling != null) {
	log("Apache Sling being started by Thread " + startingSling);
	return;
	}

	startingSling = Thread.currentThread();
	}

	if (launcherJar != null) {
	try {
	log("Checking launcher JAR in " + slingHome);
	loader.installLauncherJar(launcherJar);
	} catch (IOException ioe) {
	startupFailure("Failed installing " + launcherJar, ioe);
	return;
	}
	} else {
	log("No Launcher JAR to install");
	}

	Object object = null;
	try {
	object = loader.loadLauncher(SharedConstants.DEFAULT_SLING_SERVLET);
	} catch (IllegalArgumentException iae) {
	startupFailure("Cannot load Launcher Servlet "
	+ SharedConstants.DEFAULT_SLING_SERVLET, iae);
	return;
	}

	if (object instanceof Servlet) {
	Servlet sling = (Servlet) object;

	if (sling instanceof Launcher) {
	Launcher slingLauncher = (Launcher) sling;
	slingLauncher.setNotifiable(this);
	slingLauncher.setCommandLine(properties);
	slingLauncher.setSlingHome(slingHome);
	}

	try {
	log("Starting launcher ...");
	sling.init(getServletConfig());
	this.sling = sling;
	this.startFailureCounter = 0;
	log("Startup completed");
	} catch (ServletException se) {
	startupFailure(null, se);
	}
	}

	// reset the starting flag
	synchronized (this) {
	startingSling = null;
	}
	}

	/**
	* Define the sling.home parameter implementing the algorithme defined on
	* the wiki page to find the setting according to this algorithm:
	* <ol>
	* <li>Servlet parameter <code>sling.home</code></li>
	* <li>Context <code>sling.home</code></li>
	* <li>Derived from ServletContext path</li>
	* </ol>
	* <p>
	* <code>null</code> may be returned by this method if no
	* <code>sling.home</code> parameter is set and if the servlet container
	* does not provide the Servlet API 2.5
	* <code>ServletContext.getContextPath()</code> method and the
	* <code>request</code> parameter is <code>null</code>.
	* <p>
	* If <code>sling.home</code> can be retrieved, it is returned as an
	* absolute path.
	*
	* @param args The command line arguments
	* @return The value to use for sling.home or <code>null</code> if the value
	* cannot be retrieved.
	*/
	private String getSlingHome(HttpServletRequest request) {

	String source = null;

	// access config and context to be able to log the sling.home source

	// 1. servlet config parameter
	String slingHome = getServletConfig().getInitParameter(
	SharedConstants.SLING_HOME);
	if (slingHome != null) {

	source = "servlet parameter sling.home";

	} else {

	// 2. servlet context parameter
	slingHome = getServletContext().getInitParameter(
	SharedConstants.SLING_HOME);
	if (slingHome != null) {

	source = "servlet context parameter sling.home";

	} else {

	// 3. servlet context path (Servlet API 2.5 and later)
	try {

	String contextPath = getServletContext().getContextPath();
	slingHome = toSlingHome(contextPath);
	source = "servlet context path";

	} catch (NoSuchMethodError nsme) {

	// 4.servlet context path (Servlet API 2.4 and earlier)
	if (request != null) {

	String contextPath = request.getContextPath();
	slingHome = toSlingHome(contextPath);
	source = "servlet context path (from request)";

	} else {

	log("ServletContext path not available here, delaying startup until first request");
	return null;

	}
	}

	}
	}

	// substitute any ${...} references and make absolute
	slingHome = Util.substVars(slingHome, SharedConstants.SLING_HOME, null, properties);
	slingHome = new File(slingHome).getAbsolutePath();

	log("Setting sling.home=" + slingHome + " (" + source + ")");
	return slingHome;
	}

	/**
	* Define the sling.launchpad parameter implementing the algorithme defined
	* on the wiki page to find the setting according to this algorithm:
	* <ol>
	* <li>Servlet init parameter <code>sling.launchpad</code>. This path is
	* resolved against the <code>slingHome</code> folder if relative.</li>
	* <li>Servlet context init parameter <code>sling.launchpad</code>. This
	* path is resolved against the <code>slingHome</code> folder if relative.</li>
	* <li>Default to same as <code>sling.home</code></li>
	* </ol>
	* <p>
	* The absolute path of the returned file is stored as the
	* <code>sling.launchpad</code> property in the {@link #properties} map.
	*
	* @param slingHome The absolute path to the Sling Home folder (aka the
	* <code>sling.home</code>.
	* @return The absolute <code>File</code> indicating the launchpad folder.
	*/
	private File getLaunchpadHome(final String slingHome) {
	String launchpadHomeParam = properties.get(SharedConstants.SLING_LAUNCHPAD);
	if (launchpadHomeParam == null \|\| launchpadHomeParam.length() == 0) {
	properties.put(SharedConstants.SLING_LAUNCHPAD, slingHome);
	return new File(slingHome);
	}

	File launchpadHome = new File(launchpadHomeParam);
	if (!launchpadHome.isAbsolute()) {
	launchpadHome = new File(slingHome, launchpadHomeParam);
	}

	properties.put(SharedConstants.SLING_LAUNCHPAD,
	launchpadHome.getAbsolutePath());
	return launchpadHome;
	}

	/**
	* Converts the servlet context path to a path used for the sling.home
	* property. The servlet context path is converted to a simple name by
	* replacing all slash characters in the path with underscores (or a single
	* underscore for the root context path being empty or null). Next the
	* result is prefixed with either value of the
	* <code>sling.home.prefix</code> system property or the (default prefix)
	* <code>sling/</code>.
	*
	* @param contextPath
	* @return
	*/
	private String toSlingHome(String contextPath) {
	String prefix = System.getProperty(SLING_HOME_PREFIX,
	SLING_HOME_PREFIX_DEFAULT);

	if (!prefix.endsWith("/")) {
	prefix = prefix.concat("/");
	}

	if (contextPath == null \|\| contextPath.length() == 0) {
	return prefix + "_";
	}

	return prefix + contextPath.replace('/', '_');
	}

	private void startupFailure(String message, Throwable cause) {

	// ensure message
	if (message == null) {
	message = "Failed to start Apache Sling in " + slingHome;
	}

	// unwrap to get the real cause
	while (cause.getCause() != null) {
	cause = cause.getCause();
	}

	// log it now and increase the failure counter
	log(message, cause);
	startFailureCounter++;

	// ensure the startingSling fields is not set
	synchronized (this) {
	startingSling = null;
	}
	}

	// ---------- Property file variable substition support --------------------

	private Map<String, String> collectInitParameters() {
	HashMap<String, String> props = new HashMap<String, String>();
	for (Enumeration<String> keys = getServletContext().getInitParameterNames(); keys.hasMoreElements();) {
	String key = keys.nextElement();
	props.put(key, getServletContext().getInitParameter(key));
	}
	for (Enumeration<String> keys = getServletConfig().getInitParameterNames(); keys.hasMoreElements();) {
	String key = keys.nextElement();
	props.put(key, getServletConfig().getInitParameter(key));
	}
	return props;
	}

	}