/*
 * 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.catalina.valves;


import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;
import java.util.TimeZone;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpSession;

import org.apache.catalina.Lifecycle;
import org.apache.catalina.LifecycleException;
import org.apache.catalina.LifecycleListener;
import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.Response;
import org.apache.catalina.util.LifecycleSupport;
import org.apache.catalina.util.StringManager;


/**
 * <p>Implementation of the <b>Valve</b> interface that generates a web server
 * access log with the detailed line contents matching a configurable pattern.
 * The syntax of the available patterns is similar to that supported by the
 * Apache <code>mod_log_config</code> module.  As an additional feature,
 * automatic rollover of log files when the date changes is also supported.</p>
 *
 * <p>Patterns for the logged message may include constant text or any of the
 * following replacement strings, for which the corresponding information
 * from the specified Response is substituted:</p>
 * <ul>
 * <li><b>%a</b> - Remote IP address
 * <li><b>%A</b> - Local IP address
 * <li><b>%b</b> - Bytes sent, excluding HTTP headers, or '-' if no bytes
 *     were sent
 * <li><b>%B</b> - Bytes sent, excluding HTTP headers
 * <li><b>%h</b> - Remote host name
 * <li><b>%H</b> - Request protocol
 * <li><b>%l</b> - Remote logical username from identd (always returns '-')
 * <li><b>%m</b> - Request method
 * <li><b>%p</b> - Local port
 * <li><b>%q</b> - Query string (prepended with a '?' if it exists, otherwise
 *     an empty string
 * <li><b>%r</b> - First line of the request
 * <li><b>%s</b> - HTTP status code of the response
 * <li><b>%S</b> - User session ID
 * <li><b>%t</b> - Date and time, in Common Log Format format
 * <li><b>%u</b> - Remote user that was authenticated
 * <li><b>%U</b> - Requested URL path
 * <li><b>%v</b> - Local server name
 * <li><b>%D</b> - Time taken to process the request, in millis
 * <li><b>%T</b> - Time taken to process the request, in seconds
 * </ul>
 * <p>In addition, the caller can specify one of the following aliases for
 * commonly utilized patterns:</p>
 * <ul>
 * <li><b>common</b> - <code>%h %l %u %t "%r" %s %b</code>
 * <li><b>combined</b> -
 *   <code>%h %l %u %t "%r" %s %b "%{Referer}i" "%{User-Agent}i"</code>
 * </ul>
 *
 * <p>
 * There is also support to write information from the cookie, incoming
 * header, the Session or something else in the ServletRequest.<br>
 * It is modeled after the apache syntax:
 * <ul>
 * <li><code>%{xxx}i</code> for incoming headers
 * <li><code>%{xxx}c</code> for a specific cookie
 * <li><code>%{xxx}r</code> xxx is an attribute in the ServletRequest
 * <li><code>%{xxx}s</code> xxx is an attribute in the HttpSession
 * </ul>
 * </p>
 *
 * <p>
 * Conditional logging is also supported. This can be done with the
 * <code>condition</code> property.
 * If the value returned from ServletRequest.getAttribute(condition)
 * yields a non-null value. The logging will be skipped.
 * </p>
 *
 * @author Craig R. McClanahan
 * @author Jason Brittain
 * @author Remy Maucherat
 * @author Takayuki Kaneko
 * @version $Revision: 494191 $ $Date: 2007-01-04 12:17:11 +0900
 */

public class AccessLogValve
    extends ValveBase
    implements Lifecycle {


    // ----------------------------------------------------------- Constructors


    /**
     * Construct a new instance of this class with default property values.
     */
    public AccessLogValve() {
        setPattern("common");
    }


    // ----------------------------------------------------- Instance Variables


    /**
     * The as-of date for the currently open log file, or a zero-length
     * string if there is no open log file.
     */
    private String dateStamp = "";


    /**
     * The directory in which log files are created.
     */
    private String directory = "logs";


    /**
     * The descriptive information about this implementation.
     */
    protected static final String info =
        "org.apache.catalina.valves.FastAccessLogValve/1.0";


    /**
     * The lifecycle event support for this component.
     */
    protected LifecycleSupport lifecycle = new LifecycleSupport(this);


    /**
     * The set of month abbreviations for log messages.
     */
    protected static final String months[] =
    { "Jan", "Feb", "Mar", "Apr", "May", "Jun",
      "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };


    /**
     * The pattern used to format our access log lines.
     */
    private String pattern = null;


    /**
     * The prefix that is added to log file filenames.
     */
    private String prefix = "access_log.";


    /**
     * Should we rotate our log file? Default is true (like old behavior)
     */
    private boolean rotatable = true;


    /**
     * Buffered logging.
     */
    private boolean buffered = true;


    /**
     * The string manager for this package.
     */
    private StringManager sm =
        StringManager.getManager(Constants.Package);


    /**
     * Has this component been started yet?
     */
    private boolean started = false;


    /**
     * The suffix that is added to log file filenames.
     */
    private String suffix = "";


    /**
     * The PrintWriter to which we are currently logging, if any.
     */
    private PrintWriter writer = null;


    /**
     * A date formatter to format a Date into a date in the format
     * "yyyy-MM-dd".
     */
    private SimpleDateFormat dateFormatter = null;


    /**
     * A date formatter to format Dates into a day string in the format
     * "dd".
     */
    private SimpleDateFormat dayFormatter = null;


    /**
     * A date formatter to format a Date into a month string in the format
     * "MM".
     */
    private SimpleDateFormat monthFormatter = null;


    /**
     * A date formatter to format a Date into a year string in the format
     * "yyyy".
     */
    private SimpleDateFormat yearFormatter = null;


    /**
     * A date formatter to format a Date into a time in the format
     * "kk:mm:ss" (kk is a 24-hour representation of the hour).
     */
    private SimpleDateFormat timeFormatter = null;


    /**
     * The system timezone.
     */
    private TimeZone timezone = null;

    
    /**
     * The time zone offset relative to GMT in text form when daylight saving
     * is not in operation.
     */
    private String timeZoneNoDST = null;


    /**
     * The time zone offset relative to GMT in text form when daylight saving
     * is in operation.
     */
    private String timeZoneDST = null;
    
    
    /**
     * The system time when we last updated the Date that this valve
     * uses for log lines.
     */
    private Date currentDate = null;
    
    private long currentMillis = 0;


    /**
     * Resolve hosts.
     */
    private boolean resolveHosts = false;


    /**
     * Instant when the log daily rotation was last checked.
     */
    private long rotationLastChecked = 0L;


    /**
     * Are we doing conditional logging. default false.
     */
    private String condition = null;


    /**
     * Date format to place in log file name. Use at your own risk!
     */
    private String fileDateFormat = null;
    
    /**
     * Array of AccessLogElement, they will be used to make log message.
     */
    private AccessLogElement[] logElements = null;

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


    /**
     * Return the directory in which we create log files.
     */
    public String getDirectory() {
        return (directory);
    }


    /**
     * Set the directory in which we create log files.
     *
     * @param directory The new log file directory
     */
    public void setDirectory(String directory) {
        this.directory = directory;
    }


    /**
     * Return descriptive information about this implementation.
     */
    public String getInfo() {
        return (info);
    }


    /**
     * Return the format pattern.
     */
    public String getPattern() {
        return (this.pattern);
    }


    /**
     * Set the format pattern, first translating any recognized alias.
     *
     * @param pattern The new pattern
     */
    public void setPattern(String pattern) {
        if (pattern == null)
            pattern = "";
        if (pattern.equals(Constants.AccessLog.COMMON_ALIAS))
            pattern = Constants.AccessLog.COMMON_PATTERN;
        if (pattern.equals(Constants.AccessLog.COMBINED_ALIAS))
            pattern = Constants.AccessLog.COMBINED_PATTERN;
        this.pattern = pattern;
        logElements = createLogElements();
    }


    /**
     * Return the log file prefix.
     */
    public String getPrefix() {
        return (prefix);
    }


    /**
     * Set the log file prefix.
     *
     * @param prefix The new log file prefix
     */
    public void setPrefix(String prefix) {
        this.prefix = prefix;
    }


    /**
     * Should we rotate the logs
     */
    public boolean isRotatable() {
        return rotatable;
    }


    /**
     * Set the value is we should we rotate the logs
     *
     * @param rotatable true is we should rotate.
     */
    public void setRotatable(boolean rotatable) {
        this.rotatable = rotatable;
    }


    /**
     * Is the logging buffered
     */
    public boolean isBuffered() {
        return buffered;
    }


    /**
     * Set the value if the logging should be buffered
     *
     * @param buffered true if buffered.
     */
    public void setBuffered(boolean buffered) {
        this.buffered = buffered;
    }


    /**
     * Return the log file suffix.
     */
    public String getSuffix() {
        return (suffix);
    }


    /**
     * Set the log file suffix.
     *
     * @param suffix The new log file suffix
     */
    public void setSuffix(String suffix) {
        this.suffix = suffix;
    }


    /**
     * Set the resolve hosts flag.
     *
     * @param resolveHosts The new resolve hosts value
     */
    public void setResolveHosts(boolean resolveHosts) {
        this.resolveHosts = resolveHosts;
    }


    /**
     * Get the value of the resolve hosts flag.
     */
    public boolean isResolveHosts() {
        return resolveHosts;
    }


    /**
     * Return whether the attribute name to look for when
     * performing conditional loggging. If null, every
     * request is logged.
     */
    public String getCondition() {
        return condition;
    }


    /**
     * Set the ServletRequest.attribute to look for to perform
     * conditional logging. Set to null to log everything.
     *
     * @param condition Set to null to log everything
     */
    public void setCondition(String condition) {
        this.condition = condition;
    }

    /**
     *  Return the date format date based log rotation.
     */
    public String getFileDateFormat() {
        return fileDateFormat;
    }


    /**
     *  Set the date format date based log rotation.
     */
    public void setFileDateFormat(String fileDateFormat) {
        this.fileDateFormat =  fileDateFormat;
    }

    // --------------------------------------------------------- Public Methods

    /**
     * Execute a periodic task, such as reloading, etc. This method will be
     * invoked inside the classloading context of this container. Unexpected
     * throwables will be caught and logged.
     */
    public void backgroundProcess() {
        if (writer != null && buffered) {
            writer.flush();
        }
    }    

    /**
     * Log a message summarizing the specified request and response, according
     * to the format specified by the <code>pattern</code> property.
     *
     * @param request Request being processed
     * @param response Response being processed
     *
     * @exception IOException if an input/output error has occurred
     * @exception ServletException if a servlet error has occurred
     */
    public void invoke(Request request, Response response) throws IOException,
            ServletException {

        // Pass this request on to the next valve in our pipeline
        long t1 = System.currentTimeMillis();

        getNext().invoke(request, response);

        long t2 = System.currentTimeMillis();
        long time = t2 - t1;

        if (condition != null
                && null != request.getRequest().getAttribute(condition)) {
            return;
        }

        Date date = getDate();
        StringBuffer result = new StringBuffer();

        for (int i = 0; i < logElements.length; i++) {
            logElements[i].addElement(result, date, request, response, time);
        }

        log(result.toString());
    }


    // -------------------------------------------------------- Private Methods


    /**
     * Close the currently open log file (if any)
     */
    private synchronized void close() {
        if (writer == null) {
            return;
        }
        writer.flush();
        writer.close();
        writer = null;
        dateStamp = "";
    }


    /**
     * Log the specified message to the log file, switching files if the date
     * has changed since the previous log call.
     *
     * @param message Message to be logged
     */
    public void log(String message) {
        if (rotatable) {
            // Only do a logfile switch check once a second, max.
            long systime = System.currentTimeMillis();
            if ((systime - rotationLastChecked) > 1000) {

                // We need a new currentDate
                currentDate = new Date(systime);
                rotationLastChecked = systime;

                // Check for a change of date
                String tsDate = dateFormatter.format(currentDate);

                // If the date has changed, switch log files
                if (!dateStamp.equals(tsDate)) {
                    synchronized (this) {
                        if (!dateStamp.equals(tsDate)) {
                            close();
                            dateStamp = tsDate;
                            open();
                        }
                    }
                }
            }
        }

        // Log this message
        if (writer != null) {
            writer.println(message);
            if (!buffered) {
                writer.flush();
            }
        }

    }


    /**
     * Return the month abbreviation for the specified month, which must
     * be a two-digit String.
     *
     * @param month Month number ("01" .. "12").
     */
    private String lookup(String month) {
        int index;
        try {
            index = Integer.parseInt(month) - 1;
        } catch (Throwable t) {
            index = 0;  // Can not happen, in theory
        }
        return (months[index]);
    }


    /**
     * Open the new log file for the date specified by <code>dateStamp</code>.
     */
    private synchronized void open() {
        // Create the directory if necessary
        File dir = new File(directory);
        if (!dir.isAbsolute())
            dir = new File(System.getProperty("catalina.base"), directory);
        dir.mkdirs();

        // Open the current log file
        try {
            String pathname;
            // If no rotate - no need for dateStamp in fileName
            if (rotatable) {
                pathname = dir.getAbsolutePath() + File.separator + prefix
                        + dateStamp + suffix;
            } else {
                pathname = dir.getAbsolutePath() + File.separator + prefix
                        + suffix;
            }
            writer = new PrintWriter(new BufferedWriter(new FileWriter(
                    pathname, true), 128000), false);
        } catch (IOException e) {
            writer = null;
        }
    }
 
    /**
     * This method returns a Date object that is accurate to within one second.
     * If a thread calls this method to get a Date and it's been less than 1
     * second since a new Date was created, this method simply gives out the
     * same Date again so that the system doesn't spend time creating Date
     * objects unnecessarily.
     * 
     * @return Date
     */
    private Date getDate() {
        // Only create a new Date once per second, max.
        long systime = System.currentTimeMillis();
        if ((systime - currentMillis) > 1000) {
            synchronized (this) {
                if ((systime - currentMillis) > 1000) {
                    currentDate = new Date(systime);
                    currentMillis = systime;
                }
            }
        }
        return currentDate;
    }


    private String getTimeZone(Date date) {
        if (timezone.inDaylightTime(date)) {
            return timeZoneDST;
        } else {
            return timeZoneNoDST;
        }
    }
    
    
    private String calculateTimeZoneOffset(long offset) {
        StringBuffer tz = new StringBuffer();
        if ((offset < 0)) {
            tz.append("-");
            offset = -offset;
        } else {
            tz.append("+");
        }

        long hourOffset = offset / (1000 * 60 * 60);
        long minuteOffset = (offset / (1000 * 60)) % 60;

        if (hourOffset < 10)
            tz.append("0");
        tz.append(hourOffset);

        if (minuteOffset < 10)
            tz.append("0");
        tz.append(minuteOffset);

        return tz.toString();
    }


    // ------------------------------------------------------ Lifecycle Methods


    /**
     * Add a lifecycle event listener to this component.
     *
     * @param listener The listener to add
     */
    public void addLifecycleListener(LifecycleListener listener) {
        lifecycle.addLifecycleListener(listener);
    }


    /**
     * Get the lifecycle listeners associated with this lifecycle. If this
     * Lifecycle has no listeners registered, a zero-length array is returned.
     */
    public LifecycleListener[] findLifecycleListeners() {
        return lifecycle.findLifecycleListeners();
    }


    /**
     * Remove a lifecycle event listener from this component.
     *
     * @param listener The listener to add
     */
    public void removeLifecycleListener(LifecycleListener listener) {
        lifecycle.removeLifecycleListener(listener);
    }


    /**
     * Prepare for the beginning of active use of the public methods of this
     * component.  This method should be called after <code>configure()</code>,
     * and before any of the public methods of the component are utilized.
     *
     * @exception LifecycleException if this component detects a fatal error
     *  that prevents this component from being used
     */
    public void start() throws LifecycleException {

        // Validate and update our current component state
        if (started)
            throw new LifecycleException(sm
                    .getString("accessLogValve.alreadyStarted"));
        lifecycle.fireLifecycleEvent(START_EVENT, null);
        started = true;

        // Initialize the timeZone, Date formatters, and currentDate
        timezone = TimeZone.getDefault();
        timeZoneNoDST = calculateTimeZoneOffset(timezone.getRawOffset());
        Calendar calendar = Calendar.getInstance(timezone);
        int offset = calendar.get(Calendar.DST_OFFSET);
        timeZoneDST = calculateTimeZoneOffset(timezone.getRawOffset() + offset);

        if (fileDateFormat == null || fileDateFormat.length() == 0)
            fileDateFormat = "yyyy-MM-dd";
        dateFormatter = new SimpleDateFormat(fileDateFormat);
        dateFormatter.setTimeZone(timezone);
        dayFormatter = new SimpleDateFormat("dd");
        dayFormatter.setTimeZone(timezone);
        monthFormatter = new SimpleDateFormat("MM");
        monthFormatter.setTimeZone(timezone);
        yearFormatter = new SimpleDateFormat("yyyy");
        yearFormatter.setTimeZone(timezone);
        timeFormatter = new SimpleDateFormat("HH:mm:ss");
        timeFormatter.setTimeZone(timezone);
        currentDate = new Date();
        dateStamp = dateFormatter.format(currentDate);
        open();
    }


    /**
     * Gracefully terminate the active use of the public methods of this
     * component.  This method should be the last one called on a given
     * instance of this component.
     *
     * @exception LifecycleException if this component detects a fatal error
     *  that needs to be reported
     */
    public void stop() throws LifecycleException {

        // Validate and update our current component state
        if (!started)
            throw new LifecycleException(sm
                    .getString("accessLogValve.notStarted"));
        lifecycle.fireLifecycleEvent(STOP_EVENT, null);
        started = false;
        close();
    }
    
    /**
     * AccessLogElement writes the partial message into the buffer.
     */
    private interface AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time);

    }
    
    /**
     * write local IP address - %A
     */
    private class LocalAddrElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            String value;
            try {
                value = InetAddress.getLocalHost().getHostAddress();
            } catch (Throwable e) {
                value = "127.0.0.1";
            }
            buf.append(value);
        }
    }
    
    /**
     * write remote IP address - %a
     */
    private class RemoteAddrElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            buf.append(request.getRemoteAddr());
        }
    }
    
    /**
     * write remote host name - %h
     */
    private class HostElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            buf.append(request.getRemoteHost());
        }
    }
    
    /**
     * write remote logical username from identd (always returns '-') - %l
     */
    private class LogicalUserNameElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            buf.append('-');
        }
    }
    
    /**
     * write request protocol - %H
     */
    private class ProtocolElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            buf.append(request.getProtocol());
        }
    }

    /**
     * write remote user that was authenticated (if any), else '-' - %u
     */
    private class UserElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            if (request != null) {
                String value = request.getRemoteUser();
                if (value != null) {
                    buf.append(value);
                } else {
                    buf.append('-');
                }
            } else {
                buf.append('-');
            }
        }
    }

    /**
     * write date and time, in Common Log Format - %t
     */
    private class DateAndTimeElement implements AccessLogElement {
        private Date currentDate = new Date(0);

        private String currentDateString = null;
        
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            if (currentDate != date) {
                synchronized (this) {
                    if (currentDate != date) {
                        StringBuffer current = new StringBuffer(32);
                        current.append('[');
                        current.append(dayFormatter.format(date)); // Day
                        current.append('/');
                        current.append(lookup(monthFormatter.format(date))); // Month
                        current.append('/');
                        current.append(yearFormatter.format(date)); // Year
                        current.append(':');
                        current.append(timeFormatter.format(date)); // Time
                        current.append(' ');
                        current.append(getTimeZone(date)); // Timezone
                        current.append(']');
                        currentDateString = current.toString();
                        currentDate = date;
                    }
                }
            }
            buf.append(currentDateString);
        }
    }

    /**
     * write first line of the request (method and request URI) - %r
     */
    private class RequestElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            if (request != null) {
                buf.append(request.getMethod());
                buf.append(' ');
                buf.append(request.getRequestURI());
                if (request.getQueryString() != null) {
                    buf.append('?');
                    buf.append(request.getQueryString());
                }
                buf.append(' ');
                buf.append(request.getProtocol());
            } else {
                buf.append("- - ");
                buf.append(request.getProtocol());
            }
        }
    }

    /**
     * write HTTP status code of the response - %s
     */
    private class HttpStatusCodeElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            if (response != null) {
                buf.append(response.getStatus());
            } else {
                buf.append('-');
            }
        }
    }

    /**
     * write local port on which this request was received - %p
     */
    private class LocalPortElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            buf.append(request.getServerPort());
        }
    }

    /**
     * write bytes sent, excluding HTTP headers - %b, %B
     */
    private class ByteSentElement implements AccessLogElement {
        private boolean conversion;

        /**
         * if conversion is true, write '-' instead of 0 - %b
         */
        public ByteSentElement(boolean conversion) {
            this.conversion = conversion;
        }

        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            int length = response.getContentCount();
            if (length <= 0 && conversion) {
                buf.append('-');
            } else {
                buf.append(length);
            }
        }
    }

    /**
     * write request method (GET, POST, etc.) - %m
     */
    private class MethodElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            if (request != null) {
                buf.append(request.getMethod());
            }
        }
    }

    /**
     * write time taken to process the request - %D, %T
     */
    private class ElapsedTimeElement implements AccessLogElement {
        private boolean millis;

        /**
         * if millis is true, write time in millis - %D
         * if millis is false, write time in seconds - %T
         */
        public ElapsedTimeElement(boolean millis) {
            this.millis = millis;
        }

        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            if (millis) {
                buf.append(time);
            } else {
                // second
                buf.append(time / 1000);
                buf.append('.');
                int remains = (int) (time % 1000);
                buf.append(remains / 100);
                remains = remains % 100;
                buf.append(remains / 10);
                buf.append(remains % 10);
            }
        }
    }
    
    /**
     * write Query string (prepended with a '?' if it exists) - %q
     */
    private class QueryElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            String query = null;
            if (request != null)
                query = request.getQueryString();
            if (query != null) {
                buf.append('?');
                buf.append(query);
            }
        }
    }

    /**
     * write user session ID - %S
     */
    private class SessionIdElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            if (request != null) {
                if (request.getSession(false) != null) {
                    buf.append(request.getSessionInternal(false)
                            .getIdInternal());
                } else {
                    buf.append('-');
                }
            } else {
                buf.append('-');
            }
        }
    }

    /**
     * write requested URL path - %U
     */
    private class RequestURIElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            if (request != null) {
                buf.append(request.getRequestURI());
            } else {
                buf.append('-');
            }
        }
    }

    /**
     * write local server name - %v
     */
    private class LocalServerNameElement implements AccessLogElement {
        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            buf.append(request.getServerName());
        }
    }
    
    /**
     * write any string
     */
    private class StringElement implements AccessLogElement {
        private String str;

        public StringElement(String str) {
            this.str = str;
        }

        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            buf.append(str);
        }
    }

    /**
     * write incoming headers - %{xxx}i
     */
    private class HeaderElement implements AccessLogElement {
        private String header;

        public HeaderElement(String header) {
            this.header = header;
        }

        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            buf.append(request.getHeader(header));
        }
    }

    /**
     * write a specific cookie - %{xxx}c
     */
    private class CookieElement implements AccessLogElement {
        private String header;

        public CookieElement(String header) {
            this.header = header;
        }

        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            String value = "-";
            Cookie[] c = request.getCookies();
            if (c != null) {
                for (int i = 0; i < c.length; i++) {
                    if (header.equals(c[i].getName())) {
                        value = c[i].getValue();
                        break;
                    }
                }
            }
            buf.append(value);
        }
    }

    /**
     * write an attribute in the ServletRequest - %{xxx}r
     */
    private class RequestAttributeElement implements AccessLogElement {
        private String header;

        public RequestAttributeElement(String header) {
            this.header = header;
        }

        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            Object value = null;
            if (request != null) {
                value = request.getAttribute(header);
            } else {
                value = "??";
            }
            if (value != null) {
                if (value instanceof String) {
                    buf.append((String) value);
                } else {
                    buf.append(value.toString());
                }
            } else {
                buf.append('-');
            }
        }
    }

    /**
     * write an attribute in the HttpSession - %{xxx}s
     */
    private class SessionAttributeElement implements AccessLogElement {
        private String header;

        public SessionAttributeElement(String header) {
            this.header = header;
        }

        public void addElement(StringBuffer buf, Date date, Request request,
                Response response, long time) {
            Object value = null;
            if (null != request) {
                HttpSession sess = request.getSession(false);
                if (null != sess)
                    value = sess.getAttribute(header);
            } else {
                value = "??";
            }
            if (value != null) {
                if (value instanceof String) {
                    buf.append((String) value);
                } else {
                    buf.append(value.toString());
                }
            } else {
                buf.append('-');
            }
        }
    }




    /**
     * parse pattern string and create the array of AccessLogElement
     */
    private AccessLogElement[] createLogElements() {
        List list = new ArrayList();
        boolean replace = false;
        StringBuffer buf = new StringBuffer();
        for (int i = 0; i < pattern.length(); i++) {
            char ch = pattern.charAt(i);
            if (replace) {
                /*
                 * For code that processes {, the behavior will be ... if I do
                 * not enounter a closing } - then I ignore the {
                 */
                if ('{' == ch) {
                    StringBuffer name = new StringBuffer();
                    int j = i + 1;
                    for (; j < pattern.length() && '}' != pattern.charAt(j); j++) {
                        name.append(pattern.charAt(j));
                    }
                    if (j + 1 < pattern.length()) {
                        /* the +1 was to account for } which we increment now */
                        j++;
                        list.add(createAccessLogElement(name.toString(),
                                pattern.charAt(j)));
                        i = j; /* Since we walked more than one character */
                    } else {
                        // D'oh - end of string - pretend we never did this
                        // and do processing the "old way"
                        list.add(createAccessLogElement(ch));
                    }
                } else {
                    list.add(createAccessLogElement(ch));
                }
                replace = false;
            } else if (ch == '%') {
                replace = true;
                list.add(new StringElement(buf.toString()));
                buf = new StringBuffer();
            } else {
                buf.append(ch);
            }
        }
        if (buf.length() > 0) {
            list.add(new StringElement(buf.toString()));
        }
        return (AccessLogElement[]) list.toArray(new AccessLogElement[0]);
    }

    /**
     * create an AccessLogElement implementation which needs header string
     */
    private AccessLogElement createAccessLogElement(String header, char pattern) {
        switch (pattern) {
        case 'i':
            return new HeaderElement(header);
        case 'c':
            return new CookieElement(header);
        case 'r':
            return new RequestAttributeElement(header);
        case 's':
            return new SessionAttributeElement(header);
        default:
            return new StringElement("???");
        }
    }

    /**
     * create an AccessLogElement implementation
     */
    private AccessLogElement createAccessLogElement(char pattern) {
        switch (pattern) {
        case 'a':
            return new RemoteAddrElement();
        case 'A':
            return new LocalAddrElement();
        case 'b':
            return new ByteSentElement(true);
        case 'B':
            return new ByteSentElement(false);
        case 'D':
            return new ElapsedTimeElement(true);
        case 'h':
            return new HostElement();
        case 'H':
            return new ProtocolElement();
        case 'l':
            return new LogicalUserNameElement();
        case 'm':
            return new MethodElement();
        case 'p':
            return new LocalPortElement();
        case 'q':
            return new QueryElement();
        case 'r':
            return new RequestElement();
        case 's':
            return new HttpStatusCodeElement();
        case 'S':
            return new SessionIdElement();
        case 't':
            return new DateAndTimeElement();
        case 'T':
            return new ElapsedTimeElement(false);
        case 'u':
            return new UserElement();
        case 'U':
            return new RequestURIElement();
        case 'v':
            return new LocalServerNameElement();
        default:
            return new StringElement("???" + pattern + "???");
        }
    }
}
