Apache Log4j Core Implementation provides the functional components of the logging system. Users are free to create their own plugins and include them in the logging configuration. Apache Log4j Core is a required module to use Apache Log4j.

Bytecode (Java 8) for Apache Log4j Core Implementation is provided in a separate JAR file like log4j-core-2.14.1.jar.

Source Code files for Apache Log4j API are provided in both binary packge like apache-log4j-2.14.1-bin.zip and source package like apache-log4j-2.14.1-src.zip. You can download them at Apache Log4j Website.

You can also browse Source Code files for Apache Log4j Core Implementation 2.14.1 below.

⏎ org/apache/logging/log4j/core/layout/HtmlLayout.java

/*
 * 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.pattern.DatePatternConverter;
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 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 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, String datePattern, String timezone) {
        super(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(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 = getStringBuilder();

        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();
    }

    @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.
     */
    @Deprecated
    @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, DEFAULT_DATE_PATTERN,
                null);
    }

    /**
     * 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;

        @PluginBuilderAttribute
        private String datePattern = DEFAULT_DATE_PATTERN;

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

        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;
        }

        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(locationInfo, title, contentType, charset, fontName, fontSize.getFontSize(),
                fontSize.larger().getFontSize(), datePattern, timezone);
        }
    }
}

⏎ org/apache/logging/log4j/core/layout/HtmlLayout.java

Or download all of them as a single archive file:

File name: log4j-core-2.14.1-sources.jar
File size: 1281358 bytes
Release date: 2021-03-06
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