log4j-core/src/main/java/org/apache/logging/log4j/core/layout/HtmlLayout.java - logging-log4j2 - 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.logging.log4j.core.layout;

 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.io.IOException;
 import java.io.InterruptedIOException;
 import java.io.LineNumberReader;
 import java.io.PrintWriter;
 import java.io.StringReader;
 import java.io.StringWriter;
 import java.lang.management.ManagementFactory;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Date;
 import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.core.Layout;
 import org.apache.logging.log4j.core.LogEvent;
 import org.apache.logging.log4j.core.config.Configuration;
 import org.apache.logging.log4j.core.config.LoggerConfig;
 import org.apache.logging.log4j.core.config.plugins.PluginConfiguration;
 import org.apache.logging.log4j.core.pattern.DatePatternConverter;
 import org.apache.logging.log4j.core.util.Transform;
 import org.apache.logging.log4j.plugins.Configurable;
 import org.apache.logging.log4j.plugins.Plugin;
 import org.apache.logging.log4j.plugins.PluginBuilderAttribute;
 import org.apache.logging.log4j.plugins.PluginFactory;
 import org.apache.logging.log4j.util.Strings;

 /**
  * Outputs events as rows in an HTML table on an HTML page.
  * <p>
  * Appenders using this layout should have their encoding set to UTF-8 or UTF-16, otherwise events containing non ASCII
  * characters could result in corrupted log files.
  * </p>
  */
 @Configurable(elementType = Layout.ELEMENT_TYPE, printObject = true)
 @Plugin
 public final class HtmlLayout extends AbstractStringLayout {

     /**
      * Default font family: {@value}.
      */
     public static final String DEFAULT_FONT_FAMILY = "arial,sans-serif";

     private static final String TRACE_PREFIX = "<br />&nbsp;&nbsp;&nbsp;&nbsp;";
     private static final String REGEXP = Strings.LINE_SEPARATOR.equals("\n") ? "\n" : Strings.LINE_SEPARATOR + "|\n";
     private static final String DEFAULT_TITLE = "Log4j Log Messages";
     private static final String DEFAULT_CONTENT_TYPE = "text/html";
     private static final String DEFAULT_DATE_PATTERN = "JVM_ELAPSE_TIME";

     private final long jvmStartTime = ManagementFactory.getRuntimeMXBean().getStartTime();

     // Print no location info by default
     private final boolean locationInfo;
     private final String title;
     private final String contentType;
     private final String font;
     private final String fontSize;
     private final String headerSize;
     private final DatePatternConverter datePatternConverter;

     /**Possible font sizes */
     public enum FontSize {
         SMALLER("smaller"),
         XXSMALL("xx-small"),
         XSMALL("x-small"),
         SMALL("small"),
         MEDIUM("medium"),
         LARGE("large"),
         XLARGE("x-large"),
         XXLARGE("xx-large"),
         LARGER("larger");

         private final String size;

         FontSize(final String size) {
             this.size = size;
         }

         public String getFontSize() {
             return size;
         }

         public static FontSize getFontSize(final String size) {
             for (final FontSize fontSize : values()) {
                 if (fontSize.size.equals(size)) {
                     return fontSize;
                 }
             }
             return SMALL;
         }

         public FontSize larger() {
             return this.ordinal() < XXLARGE.ordinal() ? FontSize.values()[this.ordinal() + 1] : this;
         }
     }

     private HtmlLayout(
             final Configuration configuration,
             final boolean locationInfo,
             final String title,
             final String contentType,
             final Charset charset,
             final String font,
             final String fontSize,
             final String headerSize,
             final String datePattern,
             final String timezone) {
         super(configuration, charset);
         this.locationInfo = locationInfo;
         this.title = title;
         this.contentType = addCharsetToContentType(contentType);
         this.font = font;
         this.fontSize = fontSize;
         this.headerSize = headerSize;
         this.datePatternConverter = DEFAULT_DATE_PATTERN.equals(datePattern)
                 ? null
                 : DatePatternConverter.newInstance(configuration, new String[] {datePattern, timezone});
     }

     /**
      * For testing purposes.
      */
     public String getTitle() {
         return title;
     }

     /**
      * For testing purposes.
      */
     public boolean isLocationInfo() {
         return locationInfo;
     }

     @Override
     public boolean requiresLocation() {
         return locationInfo;
     }

     private String addCharsetToContentType(final String contentType) {
         if (contentType == null) {
             return DEFAULT_CONTENT_TYPE + "; charset=" + getCharset();
         }
         return contentType.contains("charset") ? contentType : contentType + "; charset=" + getCharset();
     }

     /**
      * Formats as a String.
      *
      * @param event The Logging Event.
      * @return A String containing the LogEvent as HTML.
      */
     @Override
     public String toSerializable(final LogEvent event) {
         final StringBuilder sbuf = stringBuilderRecycler.acquire();
         try {

             sbuf.append(Strings.LINE_SEPARATOR).append("<tr>").append(Strings.LINE_SEPARATOR);

             sbuf.append("<td>");

             if (datePatternConverter == null) {
                 sbuf.append(event.getTimeMillis() - jvmStartTime);
             } else {
                 datePatternConverter.format(event, sbuf);
             }
             sbuf.append("</td>").append(Strings.LINE_SEPARATOR);

             final String escapedThread = Transform.escapeHtmlTags(event.getThreadName());
             sbuf.append("<td title=\"").append(escapedThread).append(" thread\">");
             sbuf.append(escapedThread);
             sbuf.append("</td>").append(Strings.LINE_SEPARATOR);

             sbuf.append("<td title=\"Level\">");
             if (event.getLevel().equals(Level.DEBUG)) {
                 sbuf.append("<font color=\"#339933\">");
                 sbuf.append(Transform.escapeHtmlTags(String.valueOf(event.getLevel())));
                 sbuf.append("</font>");
             } else if (event.getLevel().isMoreSpecificThan(Level.WARN)) {
                 sbuf.append("<font color=\"#993300\"><strong>");
                 sbuf.append(Transform.escapeHtmlTags(String.valueOf(event.getLevel())));
                 sbuf.append("</strong></font>");
             } else {
                 sbuf.append(Transform.escapeHtmlTags(String.valueOf(event.getLevel())));
             }
             sbuf.append("</td>").append(Strings.LINE_SEPARATOR);

             String escapedLogger = Transform.escapeHtmlTags(event.getLoggerName());
             if (Strings.isEmpty(escapedLogger)) {
                 escapedLogger = LoggerConfig.ROOT;
             }
             sbuf.append("<td title=\"").append(escapedLogger).append(" logger\">");
             sbuf.append(escapedLogger);
             sbuf.append("</td>").append(Strings.LINE_SEPARATOR);

             if (locationInfo) {
                 final StackTraceElement element = event.getSource();
                 sbuf.append("<td>");
                 sbuf.append(Transform.escapeHtmlTags(element.getFileName()));
                 sbuf.append(':');
                 sbuf.append(element.getLineNumber());
                 sbuf.append("</td>").append(Strings.LINE_SEPARATOR);
             }

             sbuf.append("<td title=\"Message\">");
             sbuf.append(Transform.escapeHtmlTags(event.getMessage().getFormattedMessage())
                     .replaceAll(REGEXP, "<br />"));
             sbuf.append("</td>").append(Strings.LINE_SEPARATOR);
             sbuf.append("</tr>").append(Strings.LINE_SEPARATOR);

             if (event.getContextStack() != null && !event.getContextStack().isEmpty()) {
                 sbuf.append("<tr><td bgcolor=\"#EEEEEE\" style=\"font-size : ").append(fontSize);
                 sbuf.append(";\" colspan=\"6\" ");
                 sbuf.append("title=\"Nested Diagnostic Context\">");
                 sbuf.append("NDC: ")
                         .append(Transform.escapeHtmlTags(event.getContextStack().toString()));
                 sbuf.append("</td></tr>").append(Strings.LINE_SEPARATOR);
             }

             if (event.getContextData() != null && !event.getContextData().isEmpty()) {
                 sbuf.append("<tr><td bgcolor=\"#EEEEEE\" style=\"font-size : ").append(fontSize);
                 sbuf.append(";\" colspan=\"6\" ");
                 sbuf.append("title=\"Mapped Diagnostic Context\">");
                 sbuf.append("MDC: ")
                         .append(Transform.escapeHtmlTags(
                                 event.getContextData().toMap().toString()));
                 sbuf.append("</td></tr>").append(Strings.LINE_SEPARATOR);
             }

             final Throwable throwable = event.getThrown();
             if (throwable != null) {
                 sbuf.append("<tr><td bgcolor=\"#993300\" style=\"color:White; font-size : ")
                         .append(fontSize);
                 sbuf.append(";\" colspan=\"6\">");
                 appendThrowableAsHtml(throwable, sbuf);
                 sbuf.append("</td></tr>").append(Strings.LINE_SEPARATOR);
             }

             return sbuf.toString();
         } finally {
             stringBuilderRecycler.release(sbuf);
         }
     }

     @Override
     public String getContentType() {
         return contentType;
     }

     @SuppressFBWarnings(
             value = "INFORMATION_EXPOSURE_THROUGH_AN_ERROR_MESSAGE",
             justification = "Log4j prints stacktraces only to logs, which should be private.")
     private void appendThrowableAsHtml(final Throwable throwable, final StringBuilder sbuf) {
         final StringWriter sw = new StringWriter();
         final PrintWriter pw = new PrintWriter(sw);
         try {
             throwable.printStackTrace(pw);
         } catch (final RuntimeException ex) {
             // Ignore the exception.
         }
         pw.flush();
         final LineNumberReader reader = new LineNumberReader(new StringReader(sw.toString()));
         final ArrayList<String> lines = new ArrayList<>();
         try {
             String line = reader.readLine();
             while (line != null) {
                 lines.add(line);
                 line = reader.readLine();
             }
         } catch (final IOException ex) {
             if (ex instanceof InterruptedIOException) {
                 Thread.currentThread().interrupt();
             }
             lines.add(ex.toString());
         }
         boolean first = true;
         for (final String line : lines) {
             if (!first) {
                 sbuf.append(TRACE_PREFIX);
             } else {
                 first = false;
             }
             sbuf.append(Transform.escapeHtmlTags(line));
             sbuf.append(Strings.LINE_SEPARATOR);
         }
     }

     private StringBuilder appendLs(final StringBuilder sbuilder, final String s) {
         sbuilder.append(s).append(Strings.LINE_SEPARATOR);
         return sbuilder;
     }

     private StringBuilder append(final StringBuilder sbuilder, final String s) {
         sbuilder.append(s);
         return sbuilder;
     }

     /**
      * Returns appropriate HTML headers.
      * @return The header as a byte array.
      */
     @Override
     public byte[] getHeader() {
         final StringBuilder sbuf = stringBuilderRecycler.acquire();
         try {
             append(sbuf, "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" ");
             appendLs(sbuf, "\"http://www.w3.org/TR/html4/loose.dtd\">");
             appendLs(sbuf, "<html>");
             appendLs(sbuf, "<head>");
             append(sbuf, "<meta charset=\"");
             append(sbuf, getCharset().toString());
             appendLs(sbuf, "\"/>");
             append(sbuf, "<title>").append(title);
             appendLs(sbuf, "</title>");
             appendLs(sbuf, "<style type=\"text/css\">");
             appendLs(sbuf, "<!--");
             append(sbuf, "body, table {font-family:").append(font).append("; font-size: ");
             appendLs(sbuf, headerSize).append(";}");
             appendLs(sbuf, "th {background: #336699; color: #FFFFFF; text-align: left;}");
             appendLs(sbuf, "-->");
             appendLs(sbuf, "</style>");
             appendLs(sbuf, "</head>");
             appendLs(sbuf, "<body bgcolor=\"#FFFFFF\" topmargin=\"6\" leftmargin=\"6\">");
             appendLs(sbuf, "<hr size=\"1\" noshade=\"noshade\">");
             appendLs(sbuf, "Log session start time " + new Date() + "<br>");
             appendLs(sbuf, "<br>");
             appendLs(
                     sbuf,
                     "<table cellspacing=\"0\" cellpadding=\"4\" border=\"1\" bordercolor=\"#224466\" width=\"100%\">");
             appendLs(sbuf, "<tr>");
             appendLs(sbuf, "<th>Time</th>");
             appendLs(sbuf, "<th>Thread</th>");
             appendLs(sbuf, "<th>Level</th>");
             appendLs(sbuf, "<th>Logger</th>");
             if (locationInfo) {
                 appendLs(sbuf, "<th>File:Line</th>");
             }
             appendLs(sbuf, "<th>Message</th>");
             appendLs(sbuf, "</tr>");
             return sbuf.toString().getBytes(getCharset());
         } finally {
             stringBuilderRecycler.release(sbuf);
         }
     }

     /**
      * Returns the appropriate HTML footers.
      * @return the footer as a byte array.
      */
     @Override
     public byte[] getFooter() {
         final StringBuilder sbuf = stringBuilderRecycler.acquire();
         try {
             appendLs(sbuf, "</table>");
             appendLs(sbuf, "<br>");
             appendLs(sbuf, "</body></html>");
             return getBytes(sbuf.toString());
         } finally {
             stringBuilderRecycler.release(sbuf);
         }
     }

     @PluginFactory
     public static Builder newBuilder() {
         return new Builder();
     }

     public static class Builder implements org.apache.logging.log4j.plugins.util.Builder<HtmlLayout> {

         @PluginConfiguration
         private Configuration configuration;

         @PluginBuilderAttribute
         private boolean locationInfo = false;

         @PluginBuilderAttribute
         private String title = DEFAULT_TITLE;

         @PluginBuilderAttribute
         private String contentType = null; // defer default value in order to use specified charset

         @PluginBuilderAttribute
         private Charset charset = StandardCharsets.UTF_8;

         @PluginBuilderAttribute
         private FontSize fontSize = FontSize.SMALL;

         @PluginBuilderAttribute
         private String fontName = DEFAULT_FONT_FAMILY;

         @PluginBuilderAttribute
         private String datePattern = DEFAULT_DATE_PATTERN;

         @PluginBuilderAttribute
         private String timezone = null; // null means default timezone

         private Builder() {}

         public Builder setConfiguration(final Configuration configuration) {
             this.configuration = configuration;
             return this;
         }

         public Builder setLocationInfo(final boolean locationInfo) {
             this.locationInfo = locationInfo;
             return this;
         }

         public Builder setTitle(final String title) {
             this.title = title;
             return this;
         }

         public Builder setContentType(final String contentType) {
             this.contentType = contentType;
             return this;
         }

         public Builder setCharset(final Charset charset) {
             this.charset = charset;
             return this;
         }

         public Builder setFontSize(final FontSize fontSize) {
             this.fontSize = fontSize;
             return this;
         }

         public Builder setFontName(final String fontName) {
             this.fontName = fontName;
             return this;
         }

         public Builder setDatePattern(final String datePattern) {
             this.datePattern = datePattern;
             return this;
         }

         public Builder setTimezone(final String timezone) {
             this.timezone = timezone;
             return this;
         }

         @Override
         public HtmlLayout build() {
             // TODO: extract charset from content-type
             if (contentType == null) {
                 contentType = DEFAULT_CONTENT_TYPE + "; charset=" + charset;
             }
             return new HtmlLayout(
                     configuration,
                     locationInfo,
                     title,
                     contentType,
                     charset,
                     fontName,
                     fontSize.getFontSize(),
                     fontSize.larger().getFontSize(),
                     datePattern,
                     timezone);
         }
     }
 }
	/*
	* 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.logging.log4j.core.layout;

	import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
	import java.io.IOException;
	import java.io.InterruptedIOException;
	import java.io.LineNumberReader;
	import java.io.PrintWriter;
	import java.io.StringReader;
	import java.io.StringWriter;
	import java.lang.management.ManagementFactory;
	import java.nio.charset.Charset;
	import java.nio.charset.StandardCharsets;
	import java.util.ArrayList;
	import java.util.Date;
	import org.apache.logging.log4j.Level;
	import org.apache.logging.log4j.core.Layout;
	import org.apache.logging.log4j.core.LogEvent;
	import org.apache.logging.log4j.core.config.Configuration;
	import org.apache.logging.log4j.core.config.LoggerConfig;
	import org.apache.logging.log4j.core.config.plugins.PluginConfiguration;
	import org.apache.logging.log4j.core.pattern.DatePatternConverter;
	import org.apache.logging.log4j.core.util.Transform;
	import org.apache.logging.log4j.plugins.Configurable;
	import org.apache.logging.log4j.plugins.Plugin;
	import org.apache.logging.log4j.plugins.PluginBuilderAttribute;
	import org.apache.logging.log4j.plugins.PluginFactory;
	import org.apache.logging.log4j.util.Strings;

	/**
	* Outputs events as rows in an HTML table on an HTML page.
	* <p>
	* Appenders using this layout should have their encoding set to UTF-8 or UTF-16, otherwise events containing non ASCII
	* characters could result in corrupted log files.
	* </p>
	*/
	@Configurable(elementType = Layout.ELEMENT_TYPE, printObject = true)
	@Plugin
	public final class HtmlLayout extends AbstractStringLayout {

	/**
	* Default font family: {@value}.
	*/
	public static final String DEFAULT_FONT_FAMILY = "arial,sans-serif";

	private static final String TRACE_PREFIX = "<br />    ";
	private static final String REGEXP = Strings.LINE_SEPARATOR.equals("\n") ? "\n" : Strings.LINE_SEPARATOR + "\|\n";
	private static final String DEFAULT_TITLE = "Log4j Log Messages";
	private static final String DEFAULT_CONTENT_TYPE = "text/html";
	private static final String DEFAULT_DATE_PATTERN = "JVM_ELAPSE_TIME";

	private final long jvmStartTime = ManagementFactory.getRuntimeMXBean().getStartTime();

	// Print no location info by default
	private final boolean locationInfo;
	private final String title;
	private final String contentType;
	private final String font;
	private final String fontSize;
	private final String headerSize;
	private final DatePatternConverter datePatternConverter;

	/*Possible font sizes /
	public enum FontSize {
	SMALLER("smaller"),
	XXSMALL("xx-small"),
	XSMALL("x-small"),
	SMALL("small"),
	MEDIUM("medium"),
	LARGE("large"),
	XLARGE("x-large"),
	XXLARGE("xx-large"),
	LARGER("larger");

	private final String size;

	FontSize(final String size) {
	this.size = size;
	}

	public String getFontSize() {
	return size;
	}

	public static FontSize getFontSize(final String size) {
	for (final FontSize fontSize : values()) {
	if (fontSize.size.equals(size)) {
	return fontSize;
	}
	}
	return SMALL;
	}

	public FontSize larger() {
	return this.ordinal() < XXLARGE.ordinal() ? FontSize.values()[this.ordinal() + 1] : this;
	}
	}

	private HtmlLayout(
	final Configuration configuration,
	final boolean locationInfo,
	final String title,
	final String contentType,
	final Charset charset,
	final String font,
	final String fontSize,
	final String headerSize,
	final String datePattern,
	final String timezone) {
	super(configuration, charset);
	this.locationInfo = locationInfo;
	this.title = title;
	this.contentType = addCharsetToContentType(contentType);
	this.font = font;
	this.fontSize = fontSize;
	this.headerSize = headerSize;
	this.datePatternConverter = DEFAULT_DATE_PATTERN.equals(datePattern)
	? null
	: DatePatternConverter.newInstance(configuration, new String[] {datePattern, timezone});
	}

	/**
	* For testing purposes.
	*/
	public String getTitle() {
	return title;
	}

	/**
	* For testing purposes.
	*/
	public boolean isLocationInfo() {
	return locationInfo;
	}

	@Override
	public boolean requiresLocation() {
	return locationInfo;
	}

	private String addCharsetToContentType(final String contentType) {
	if (contentType == null) {
	return DEFAULT_CONTENT_TYPE + "; charset=" + getCharset();
	}
	return contentType.contains("charset") ? contentType : contentType + "; charset=" + getCharset();
	}

	/**
	* Formats as a String.
	*
	* @param event The Logging Event.
	* @return A String containing the LogEvent as HTML.
	*/
	@Override
	public String toSerializable(final LogEvent event) {
	final StringBuilder sbuf = stringBuilderRecycler.acquire();
	try {

	sbuf.append(Strings.LINE_SEPARATOR).append("<tr>").append(Strings.LINE_SEPARATOR);

	sbuf.append("<td>");

	if (datePatternConverter == null) {
	sbuf.append(event.getTimeMillis() - jvmStartTime);
	} else {
	datePatternConverter.format(event, sbuf);
	}
	sbuf.append("</td>").append(Strings.LINE_SEPARATOR);

	final String escapedThread = Transform.escapeHtmlTags(event.getThreadName());
	sbuf.append("<td title=\"").append(escapedThread).append(" thread\">");
	sbuf.append(escapedThread);
	sbuf.append("</td>").append(Strings.LINE_SEPARATOR);

	sbuf.append("<td title=\"Level\">");
	if (event.getLevel().equals(Level.DEBUG)) {
	sbuf.append("<font color=\"#339933\">");
	sbuf.append(Transform.escapeHtmlTags(String.valueOf(event.getLevel())));
	sbuf.append("</font>");
	} else if (event.getLevel().isMoreSpecificThan(Level.WARN)) {
	sbuf.append("<font color=\"#993300\"><strong>");
	sbuf.append(Transform.escapeHtmlTags(String.valueOf(event.getLevel())));
	sbuf.append("</strong></font>");
	} else {
	sbuf.append(Transform.escapeHtmlTags(String.valueOf(event.getLevel())));
	}
	sbuf.append("</td>").append(Strings.LINE_SEPARATOR);

	String escapedLogger = Transform.escapeHtmlTags(event.getLoggerName());
	if (Strings.isEmpty(escapedLogger)) {
	escapedLogger = LoggerConfig.ROOT;
	}
	sbuf.append("<td title=\"").append(escapedLogger).append(" logger\">");
	sbuf.append(escapedLogger);
	sbuf.append("</td>").append(Strings.LINE_SEPARATOR);

	if (locationInfo) {
	final StackTraceElement element = event.getSource();
	sbuf.append("<td>");
	sbuf.append(Transform.escapeHtmlTags(element.getFileName()));
	sbuf.append(':');
	sbuf.append(element.getLineNumber());
	sbuf.append("</td>").append(Strings.LINE_SEPARATOR);
	}

	sbuf.append("<td title=\"Message\">");
	sbuf.append(Transform.escapeHtmlTags(event.getMessage().getFormattedMessage())
	.replaceAll(REGEXP, "<br />"));
	sbuf.append("</td>").append(Strings.LINE_SEPARATOR);
	sbuf.append("</tr>").append(Strings.LINE_SEPARATOR);

	if (event.getContextStack() != null && !event.getContextStack().isEmpty()) {
	sbuf.append("<tr><td bgcolor=\"#EEEEEE\" style=\"font-size : ").append(fontSize);
	sbuf.append(";\" colspan=\"6\" ");
	sbuf.append("title=\"Nested Diagnostic Context\">");
	sbuf.append("NDC: ")
	.append(Transform.escapeHtmlTags(event.getContextStack().toString()));
	sbuf.append("</td></tr>").append(Strings.LINE_SEPARATOR);
	}

	if (event.getContextData() != null && !event.getContextData().isEmpty()) {
	sbuf.append("<tr><td bgcolor=\"#EEEEEE\" style=\"font-size : ").append(fontSize);
	sbuf.append(";\" colspan=\"6\" ");
	sbuf.append("title=\"Mapped Diagnostic Context\">");
	sbuf.append("MDC: ")
	.append(Transform.escapeHtmlTags(
	event.getContextData().toMap().toString()));
	sbuf.append("</td></tr>").append(Strings.LINE_SEPARATOR);
	}

	final Throwable throwable = event.getThrown();
	if (throwable != null) {
	sbuf.append("<tr><td bgcolor=\"#993300\" style=\"color:White; font-size : ")
	.append(fontSize);
	sbuf.append(";\" colspan=\"6\">");
	appendThrowableAsHtml(throwable, sbuf);
	sbuf.append("</td></tr>").append(Strings.LINE_SEPARATOR);
	}

	return sbuf.toString();
	} finally {
	stringBuilderRecycler.release(sbuf);
	}
	}

	@Override
	public String getContentType() {
	return contentType;
	}

	@SuppressFBWarnings(
	value = "INFORMATION_EXPOSURE_THROUGH_AN_ERROR_MESSAGE",
	justification = "Log4j prints stacktraces only to logs, which should be private.")
	private void appendThrowableAsHtml(final Throwable throwable, final StringBuilder sbuf) {
	final StringWriter sw = new StringWriter();
	final PrintWriter pw = new PrintWriter(sw);
	try {
	throwable.printStackTrace(pw);
	} catch (final RuntimeException ex) {
	// Ignore the exception.
	}
	pw.flush();
	final LineNumberReader reader = new LineNumberReader(new StringReader(sw.toString()));
	final ArrayList<String> lines = new ArrayList<>();
	try {
	String line = reader.readLine();
	while (line != null) {
	lines.add(line);
	line = reader.readLine();
	}
	} catch (final IOException ex) {
	if (ex instanceof InterruptedIOException) {
	Thread.currentThread().interrupt();
	}
	lines.add(ex.toString());
	}
	boolean first = true;
	for (final String line : lines) {
	if (!first) {
	sbuf.append(TRACE_PREFIX);
	} else {
	first = false;
	}
	sbuf.append(Transform.escapeHtmlTags(line));
	sbuf.append(Strings.LINE_SEPARATOR);
	}
	}

	private StringBuilder appendLs(final StringBuilder sbuilder, final String s) {
	sbuilder.append(s).append(Strings.LINE_SEPARATOR);
	return sbuilder;
	}

	private StringBuilder append(final StringBuilder sbuilder, final String s) {
	sbuilder.append(s);
	return sbuilder;
	}

	/**
	* Returns appropriate HTML headers.
	* @return The header as a byte array.
	*/
	@Override
	public byte[] getHeader() {
	final StringBuilder sbuf = stringBuilderRecycler.acquire();
	try {
	append(sbuf, "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" ");
	appendLs(sbuf, "\"http://www.w3.org/TR/html4/loose.dtd\">");
	appendLs(sbuf, "<html>");
	appendLs(sbuf, "<head>");
	append(sbuf, "<meta charset=\"");
	append(sbuf, getCharset().toString());
	appendLs(sbuf, "\"/>");
	append(sbuf, "<title>").append(title);
	appendLs(sbuf, "</title>");
	appendLs(sbuf, "<style type=\"text/css\">");
	appendLs(sbuf, "<!--");
	append(sbuf, "body, table {font-family:").append(font).append("; font-size: ");
	appendLs(sbuf, headerSize).append(";}");
	appendLs(sbuf, "th {background: #336699; color: #FFFFFF; text-align: left;}");
	appendLs(sbuf, "-->");
	appendLs(sbuf, "</style>");
	appendLs(sbuf, "</head>");
	appendLs(sbuf, "<body bgcolor=\"#FFFFFF\" topmargin=\"6\" leftmargin=\"6\">");
	appendLs(sbuf, "<hr size=\"1\" noshade=\"noshade\">");
	appendLs(sbuf, "Log session start time " + new Date() + "<br>");
	appendLs(sbuf, "<br>");
	appendLs(
	sbuf,
	"<table cellspacing=\"0\" cellpadding=\"4\" border=\"1\" bordercolor=\"#224466\" width=\"100%\">");
	appendLs(sbuf, "<tr>");
	appendLs(sbuf, "<th>Time</th>");
	appendLs(sbuf, "<th>Thread</th>");
	appendLs(sbuf, "<th>Level</th>");
	appendLs(sbuf, "<th>Logger</th>");
	if (locationInfo) {
	appendLs(sbuf, "<th>File:Line</th>");
	}
	appendLs(sbuf, "<th>Message</th>");
	appendLs(sbuf, "</tr>");
	return sbuf.toString().getBytes(getCharset());
	} finally {
	stringBuilderRecycler.release(sbuf);
	}
	}

	/**
	* Returns the appropriate HTML footers.
	* @return the footer as a byte array.
	*/
	@Override
	public byte[] getFooter() {
	final StringBuilder sbuf = stringBuilderRecycler.acquire();
	try {
	appendLs(sbuf, "</table>");
	appendLs(sbuf, "<br>");
	appendLs(sbuf, "</body></html>");
	return getBytes(sbuf.toString());
	} finally {
	stringBuilderRecycler.release(sbuf);
	}
	}

	@PluginFactory
	public static Builder newBuilder() {
	return new Builder();
	}

	public static class Builder implements org.apache.logging.log4j.plugins.util.Builder<HtmlLayout> {

	@PluginConfiguration
	private Configuration configuration;

	@PluginBuilderAttribute
	private boolean locationInfo = false;

	@PluginBuilderAttribute
	private String title = DEFAULT_TITLE;

	@PluginBuilderAttribute
	private String contentType = null; // defer default value in order to use specified charset

	@PluginBuilderAttribute
	private Charset charset = StandardCharsets.UTF_8;

	@PluginBuilderAttribute
	private FontSize fontSize = FontSize.SMALL;

	@PluginBuilderAttribute
	private String fontName = DEFAULT_FONT_FAMILY;

	@PluginBuilderAttribute
	private String datePattern = DEFAULT_DATE_PATTERN;

	@PluginBuilderAttribute
	private String timezone = null; // null means default timezone

	private Builder() {}

	public Builder setConfiguration(final Configuration configuration) {
	this.configuration = configuration;
	return this;
	}

	public Builder setLocationInfo(final boolean locationInfo) {
	this.locationInfo = locationInfo;
	return this;
	}

	public Builder setTitle(final String title) {
	this.title = title;
	return this;
	}

	public Builder setContentType(final String contentType) {
	this.contentType = contentType;
	return this;
	}

	public Builder setCharset(final Charset charset) {
	this.charset = charset;
	return this;
	}

	public Builder setFontSize(final FontSize fontSize) {
	this.fontSize = fontSize;
	return this;
	}

	public Builder setFontName(final String fontName) {
	this.fontName = fontName;
	return this;
	}

	public Builder setDatePattern(final String datePattern) {
	this.datePattern = datePattern;
	return this;
	}

	public Builder setTimezone(final String timezone) {
	this.timezone = timezone;
	return this;
	}

	@Override
	public HtmlLayout build() {
	// TODO: extract charset from content-type
	if (contentType == null) {
	contentType = DEFAULT_CONTENT_TYPE + "; charset=" + charset;
	}
	return new HtmlLayout(
	configuration,
	locationInfo,
	title,
	contentType,
	charset,
	fontName,
	fontSize.getFontSize(),
	fontSize.larger().getFontSize(),
	datePattern,
	timezone);
	}
	}
	}