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/config/xml/XmlConfiguration.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.config.xml;

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import javax.xml.XMLConstants;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;

import org.apache.logging.log4j.core.LoggerContext;
import org.apache.logging.log4j.core.config.AbstractConfiguration;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.ConfigurationSource;
import org.apache.logging.log4j.core.config.Node;
import org.apache.logging.log4j.core.config.Reconfigurable;
import org.apache.logging.log4j.core.config.plugins.util.PluginType;
import org.apache.logging.log4j.core.config.plugins.util.ResolverUtil;
import org.apache.logging.log4j.core.config.status.StatusConfiguration;
import org.apache.logging.log4j.core.util.Closer;
import org.apache.logging.log4j.core.util.Loader;
import org.apache.logging.log4j.core.util.Patterns;
import org.apache.logging.log4j.core.util.Throwables;
import org.w3c.dom.Attr;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.NodeList;
import org.w3c.dom.Text;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

/**
 * Creates a Node hierarchy from an XML file.
 */
public class XmlConfiguration extends AbstractConfiguration implements Reconfigurable {

    private static final String XINCLUDE_FIXUP_LANGUAGE =
            "http://apache.org/xml/features/xinclude/fixup-language";
    private static final String XINCLUDE_FIXUP_BASE_URIS =
            "http://apache.org/xml/features/xinclude/fixup-base-uris";
    private static final String[] VERBOSE_CLASSES = new String[] {ResolverUtil.class.getName()};
    private static final String LOG4J_XSD = "Log4j-config.xsd";

    private final List<Status> status = new ArrayList<>();
    private Element rootElement;
    private boolean strict;
    private String schemaResource;

    public XmlConfiguration(final LoggerContext loggerContext, final ConfigurationSource configSource) {
        super(loggerContext, configSource);
        final File configFile = configSource.getFile();
        byte[] buffer = null;

        try {
            final InputStream configStream = configSource.getInputStream();
            try {
                buffer = toByteArray(configStream);
            } finally {
                Closer.closeSilently(configStream);
            }
            final InputSource source = new InputSource(new ByteArrayInputStream(buffer));
            source.setSystemId(configSource.getLocation());
            final DocumentBuilder documentBuilder = newDocumentBuilder(true);
            Document document;
            try {
                document = documentBuilder.parse(source);
            } catch (final Exception e) {
                // LOG4J2-1127
                final Throwable throwable = Throwables.getRootCause(e);
                if (throwable instanceof UnsupportedOperationException) {
                    LOGGER.warn(
                            "The DocumentBuilder {} does not support an operation: {}."
                            + "Trying again without XInclude...",
                            documentBuilder, e);
                    document = newDocumentBuilder(false).parse(source);
                } else {
                    throw e;
                }
            }
            rootElement = document.getDocumentElement();
            final Map<String, String> attrs = processAttributes(rootNode, rootElement);
            final StatusConfiguration statusConfig = new StatusConfiguration().withVerboseClasses(VERBOSE_CLASSES)
                    .withStatus(getDefaultStatus());
            int monitorIntervalSeconds = 0;
            for (final Map.Entry<String, String> entry : attrs.entrySet()) {
                final String key = entry.getKey();
                final String value = getStrSubstitutor().replace(entry.getValue());
                if ("status".equalsIgnoreCase(key)) {
                    statusConfig.withStatus(value);
                } else if ("dest".equalsIgnoreCase(key)) {
                    statusConfig.withDestination(value);
                } else if ("shutdownHook".equalsIgnoreCase(key)) {
                    isShutdownHookEnabled = !"disable".equalsIgnoreCase(value);
                } else if ("shutdownTimeout".equalsIgnoreCase(key)) {
                    shutdownTimeoutMillis = Long.parseLong(value);
                } else if ("verbose".equalsIgnoreCase(key)) {
                    statusConfig.withVerbosity(value);
                } else if ("packages".equalsIgnoreCase(key)) {
                    pluginPackages.addAll(Arrays.asList(value.split(Patterns.COMMA_SEPARATOR)));
                } else if ("name".equalsIgnoreCase(key)) {
                    setName(value);
                } else if ("strict".equalsIgnoreCase(key)) {
                    strict = Boolean.parseBoolean(value);
                } else if ("schema".equalsIgnoreCase(key)) {
                    schemaResource = value;
                } else if ("monitorInterval".equalsIgnoreCase(key)) {
                    monitorIntervalSeconds = Integer.parseInt(value);
                } else if ("advertiser".equalsIgnoreCase(key)) {
                    createAdvertiser(value, configSource, buffer, "text/xml");
                }
            }
            initializeWatchers(this, configSource, monitorIntervalSeconds);
            statusConfig.initialize();
        } catch (final SAXException | IOException | ParserConfigurationException e) {
            LOGGER.error("Error parsing " + configSource.getLocation(), e);
        }
        if (strict && schemaResource != null && buffer != null) {
            try (InputStream is = Loader.getResourceAsStream(schemaResource, XmlConfiguration.class.getClassLoader())) {
                if (is != null) {
                    final javax.xml.transform.Source src = new StreamSource(is, LOG4J_XSD);
                    final SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
                    Schema schema = null;
                    try {
                        schema = factory.newSchema(src);
                    } catch (final SAXException ex) {
                        LOGGER.error("Error parsing Log4j schema", ex);
                    }
                    if (schema != null) {
                        final Validator validator = schema.newValidator();
                        try {
                            validator.validate(new StreamSource(new ByteArrayInputStream(buffer)));
                        } catch (final IOException ioe) {
                            LOGGER.error("Error reading configuration for validation", ioe);
                        } catch (final SAXException ex) {
                            LOGGER.error("Error validating configuration", ex);
                        }
                    }
                }
            } catch (final Exception ex) {
                LOGGER.error("Unable to access schema {}", this.schemaResource, ex);
            }
        }

        if (getName() == null) {
            setName(configSource.getLocation());
        }
    }

    /**
     * Creates a new DocumentBuilder suitable for parsing a configuration file.
     *
     * @param xIncludeAware enabled XInclude
     * @return a new DocumentBuilder
     * @throws ParserConfigurationException
     */
    static DocumentBuilder newDocumentBuilder(final boolean xIncludeAware) throws ParserConfigurationException {
        final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(true);

        disableDtdProcessing(factory);

        if (xIncludeAware) {
            enableXInclude(factory);
        }
        return factory.newDocumentBuilder();
    }

    private static void disableDtdProcessing(final DocumentBuilderFactory factory) {
        factory.setValidating(false);
        factory.setExpandEntityReferences(false);
        setFeature(factory, "http://xml.org/sax/features/external-general-entities", false);
        setFeature(factory, "http://xml.org/sax/features/external-parameter-entities", false);
        setFeature(factory, "http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
    }

    private static void setFeature(final DocumentBuilderFactory factory, final String featureName, final boolean value) {
        try {
            factory.setFeature(featureName, value);
        } catch (Exception | LinkageError e) {
            getStatusLogger().error("Caught {} setting feature {} to {} on DocumentBuilderFactory {}: {}",
                    e.getClass().getCanonicalName(), featureName, value, factory, e, e);
        }
    }

    /**
     * Enables XInclude for the given DocumentBuilderFactory
     *
     * @param factory a DocumentBuilderFactory
     */
    private static void enableXInclude(final DocumentBuilderFactory factory) {
        try {
            // Alternative: We set if a system property on the command line is set, for example:
            // -DLog4j.XInclude=true
            factory.setXIncludeAware(true);
        } catch (final UnsupportedOperationException e) {
            LOGGER.warn("The DocumentBuilderFactory [{}] does not support XInclude: {}", factory, e);
        } catch (@SuppressWarnings("ErrorNotRethrown") final AbstractMethodError | NoSuchMethodError err) {
            LOGGER.warn("The DocumentBuilderFactory [{}] is out of date and does not support XInclude: {}", factory,
                    err);
        }
        try {
            // Alternative: We could specify all features and values with system properties like:
            // -DLog4j.DocumentBuilderFactory.Feature="http://apache.org/xml/features/xinclude/fixup-base-uris true"
            factory.setFeature(XINCLUDE_FIXUP_BASE_URIS, true);
        } catch (final ParserConfigurationException e) {
            LOGGER.warn("The DocumentBuilderFactory [{}] does not support the feature [{}]: {}", factory,
                    XINCLUDE_FIXUP_BASE_URIS, e);
        } catch (@SuppressWarnings("ErrorNotRethrown") final AbstractMethodError err) {
            LOGGER.warn("The DocumentBuilderFactory [{}] is out of date and does not support setFeature: {}", factory,
                    err);
        }
        try {
            factory.setFeature(XINCLUDE_FIXUP_LANGUAGE, true);
        } catch (final ParserConfigurationException e) {
            LOGGER.warn("The DocumentBuilderFactory [{}] does not support the feature [{}]: {}", factory,
                    XINCLUDE_FIXUP_LANGUAGE, e);
        } catch (@SuppressWarnings("ErrorNotRethrown") final AbstractMethodError err) {
            LOGGER.warn("The DocumentBuilderFactory [{}] is out of date and does not support setFeature: {}", factory,
                    err);
        }
    }

    @Override
    public void setup() {
        if (rootElement == null) {
            LOGGER.error("No logging configuration");
            return;
        }
        constructHierarchy(rootNode, rootElement);
        if (status.size() > 0) {
            for (final Status s : status) {
                LOGGER.error("Error processing element {} ({}): {}", s.name, s.element, s.errorType);
            }
            return;
        }
        rootElement = null;
    }

    @Override
    public Configuration reconfigure() {
        try {
            final ConfigurationSource source = getConfigurationSource().resetInputStream();
            if (source == null) {
                return null;
            }
            final XmlConfiguration config = new XmlConfiguration(getLoggerContext(), source);
            return config.rootElement == null ? null : config;
        } catch (final IOException ex) {
            LOGGER.error("Cannot locate file {}", getConfigurationSource(), ex);
        }
        return null;
    }

    private void constructHierarchy(final Node node, final Element element) {
        processAttributes(node, element);
        final StringBuilder buffer = new StringBuilder();
        final NodeList list = element.getChildNodes();
        final List<Node> children = node.getChildren();
        for (int i = 0; i < list.getLength(); i++) {
            final org.w3c.dom.Node w3cNode = list.item(i);
            if (w3cNode instanceof Element) {
                final Element child = (Element) w3cNode;
                final String name = getType(child);
                final PluginType<?> type = pluginManager.getPluginType(name);
                final Node childNode = new Node(node, name, type);
                constructHierarchy(childNode, child);
                if (type == null) {
                    final String value = childNode.getValue();
                    if (!childNode.hasChildren() && value != null) {
                        node.getAttributes().put(name, value);
                    } else {
                        status.add(new Status(name, element, ErrorType.CLASS_NOT_FOUND));
                    }
                } else {
                    children.add(childNode);
                }
            } else if (w3cNode instanceof Text) {
                final Text data = (Text) w3cNode;
                buffer.append(data.getData());
            }
        }

        final String text = buffer.toString().trim();
        if (text.length() > 0 || (!node.hasChildren() && !node.isRoot())) {
            node.setValue(text);
        }
    }

    private String getType(final Element element) {
        if (strict) {
            final NamedNodeMap attrs = element.getAttributes();
            for (int i = 0; i < attrs.getLength(); ++i) {
                final org.w3c.dom.Node w3cNode = attrs.item(i);
                if (w3cNode instanceof Attr) {
                    final Attr attr = (Attr) w3cNode;
                    if (attr.getName().equalsIgnoreCase("type")) {
                        final String type = attr.getValue();
                        attrs.removeNamedItem(attr.getName());
                        return type;
                    }
                }
            }
        }
        return element.getTagName();
    }

    private Map<String, String> processAttributes(final Node node, final Element element) {
        final NamedNodeMap attrs = element.getAttributes();
        final Map<String, String> attributes = node.getAttributes();

        for (int i = 0; i < attrs.getLength(); ++i) {
            final org.w3c.dom.Node w3cNode = attrs.item(i);
            if (w3cNode instanceof Attr) {
                final Attr attr = (Attr) w3cNode;
                if (attr.getName().equals("xml:base")) {
                    continue;
                }
                attributes.put(attr.getName(), attr.getValue());
            }
        }
        return attributes;
    }

    @Override
    public String toString() {
        return getClass().getSimpleName() + "[location=" + getConfigurationSource() + "]";
    }

    /**
     * The error that occurred.
     */
    private enum ErrorType {
        CLASS_NOT_FOUND
    }

    /**
     * Status for recording errors.
     */
    private static class Status {
        private final Element element;
        private final String name;
        private final ErrorType errorType;

        public Status(final String name, final Element element, final ErrorType errorType) {
            this.name = name;
            this.element = element;
            this.errorType = errorType;
        }

        @Override
        public String toString() {
            return "Status [name=" + name + ", element=" + element + ", errorType=" + errorType + "]";
        }

    }

}

⏎ org/apache/logging/log4j/core/config/xml/XmlConfiguration.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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