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 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 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.LoggerConfig;
 import org.apache.logging.log4j.core.config.Node;
 import org.apache.logging.log4j.core.config.plugins.Plugin;
 import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
 import org.apache.logging.log4j.core.config.plugins.PluginBuilderAttribute;
 import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
 import org.apache.logging.log4j.core.config.plugins.PluginFactory;
 import org.apache.logging.log4j.core.util.Transform;
 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>
  */
 @Plugin(name = "HtmlLayout", category = Node.CATEGORY, elementType = Layout.ELEMENT_TYPE, printObject = true)
 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 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;

     /**Possible font sizes */
     public static 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;

         private 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 boolean locationInfo, final String title, final String contentType, final Charset charset,
             final String font, final String fontSize, final String headerSize) {
         super(charset);
         this.locationInfo = locationInfo;
         this.title = title;
         this.contentType = addCharsetToContentType(contentType);
         this.font = font;
         this.fontSize = fontSize;
         this.headerSize = headerSize;
     }

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

     /**
      * For testing purposes.
      */
     public boolean isLocationInfo() {
         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 = getStringBuilder();

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

         sbuf.append("<td>");
         sbuf.append(event.getTimeMillis() - jvmStartTime);
         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();
     }

     @Override
     /**
      * @return The content type.
      */
     public String getContentType() {
         return contentType;
     }

     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 = new StringBuilder();
         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 java.util.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());
     }

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

     /**
      * Creates an HTML Layout.
      * @param locationInfo If "true", location information will be included. The default is false.
      * @param title The title to include in the file header. If none is specified the default title will be used.
      * @param contentType The content type. Defaults to "text/html".
      * @param charset The character set to use. If not specified, the default will be used.
      * @param fontSize The font size of the text.
      * @param font The font to use for the text.
      * @return An HTML Layout.
      */
     @PluginFactory
     public static HtmlLayout createLayout(
             @PluginAttribute(value = "locationInfo") final boolean locationInfo,
             @PluginAttribute(value = "title", defaultString = DEFAULT_TITLE) final String title,
             @PluginAttribute("contentType") String contentType,
             @PluginAttribute(value = "charset", defaultString = "UTF-8") final Charset charset,
             @PluginAttribute("fontSize") String fontSize,
             @PluginAttribute(value = "fontName", defaultString = DEFAULT_FONT_FAMILY) final String font) {
         final FontSize fs = FontSize.getFontSize(fontSize);
         fontSize = fs.getFontSize();
         final String headerSize = fs.larger().getFontSize();
         if (contentType == null) {
             contentType = DEFAULT_CONTENT_TYPE + "; charset=" + charset;
         }
         return new HtmlLayout(locationInfo, title, contentType, charset, font, fontSize, headerSize);
     }

     /**
      * Creates an HTML Layout using the default settings.
      *
      * @return an HTML Layout.
      */
     public static HtmlLayout createDefaultLayout() {
         return newBuilder().build();
     }

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

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

         @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;

         private Builder() {
         }

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

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

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

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

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

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

         @Override
         public HtmlLayout build() {
             // TODO: extract charset from content-type
             if (contentType == null) {
                 contentType = DEFAULT_CONTENT_TYPE + "; charset=" + charset;
             }
             return new HtmlLayout(locationInfo, title, contentType, charset, fontName, fontSize.getFontSize(),
                 fontSize.larger().getFontSize());
         }
     }
 }
	/*
	* 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 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 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.LoggerConfig;
	import org.apache.logging.log4j.core.config.Node;
	import org.apache.logging.log4j.core.config.plugins.Plugin;
	import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
	import org.apache.logging.log4j.core.config.plugins.PluginBuilderAttribute;
	import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
	import org.apache.logging.log4j.core.config.plugins.PluginFactory;
	import org.apache.logging.log4j.core.util.Transform;
	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>
	*/
	@Plugin(name = "HtmlLayout", category = Node.CATEGORY, elementType = Layout.ELEMENT_TYPE, printObject = true)
	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 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;

	/*Possible font sizes /
	public static 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;

	private 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 boolean locationInfo, final String title, final String contentType, final Charset charset,
	final String font, final String fontSize, final String headerSize) {
	super(charset);
	this.locationInfo = locationInfo;
	this.title = title;
	this.contentType = addCharsetToContentType(contentType);
	this.font = font;
	this.fontSize = fontSize;
	this.headerSize = headerSize;
	}

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

	/**
	* For testing purposes.
	*/
	public boolean isLocationInfo() {
	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 = getStringBuilder();

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

	sbuf.append("<td>");
	sbuf.append(event.getTimeMillis() - jvmStartTime);
	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();
	}

	@Override
	/**
	* @return The content type.
	*/
	public String getContentType() {
	return contentType;
	}

	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 = new StringBuilder();
	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 java.util.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());
	}

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

	/**
	* Creates an HTML Layout.
	* @param locationInfo If "true", location information will be included. The default is false.
	* @param title The title to include in the file header. If none is specified the default title will be used.
	* @param contentType The content type. Defaults to "text/html".
	* @param charset The character set to use. If not specified, the default will be used.
	* @param fontSize The font size of the text.
	* @param font The font to use for the text.
	* @return An HTML Layout.
	*/
	@PluginFactory
	public static HtmlLayout createLayout(
	@PluginAttribute(value = "locationInfo") final boolean locationInfo,
	@PluginAttribute(value = "title", defaultString = DEFAULT_TITLE) final String title,
	@PluginAttribute("contentType") String contentType,
	@PluginAttribute(value = "charset", defaultString = "UTF-8") final Charset charset,
	@PluginAttribute("fontSize") String fontSize,
	@PluginAttribute(value = "fontName", defaultString = DEFAULT_FONT_FAMILY) final String font) {
	final FontSize fs = FontSize.getFontSize(fontSize);
	fontSize = fs.getFontSize();
	final String headerSize = fs.larger().getFontSize();
	if (contentType == null) {
	contentType = DEFAULT_CONTENT_TYPE + "; charset=" + charset;
	}
	return new HtmlLayout(locationInfo, title, contentType, charset, font, fontSize, headerSize);
	}

	/**
	* Creates an HTML Layout using the default settings.
	*
	* @return an HTML Layout.
	*/
	public static HtmlLayout createDefaultLayout() {
	return newBuilder().build();
	}

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

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

	@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;

	private Builder() {
	}

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

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

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

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

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

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

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