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/json/JsonConfiguration.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.json;

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.Iterator;
import java.util.List;
import java.util.Map;

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
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.LoggerConfig;
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.Patterns;

/**
 * Creates a Node hierarchy from a JSON file.
 */
public class JsonConfiguration extends AbstractConfiguration implements Reconfigurable {

    private static final String[] VERBOSE_CLASSES = new String[] { ResolverUtil.class.getName() };
    private final List<Status> status = new ArrayList<>();
    private JsonNode root;

    public JsonConfiguration(final LoggerContext loggerContext, final ConfigurationSource configSource) {
        super(loggerContext, configSource);
        final File configFile = configSource.getFile();
        byte[] buffer;
        try {
            try (final InputStream configStream = configSource.getInputStream()) {
                buffer = toByteArray(configStream);
            }
            final InputStream is = new ByteArrayInputStream(buffer);
            root = getObjectMapper().readTree(is);
            if (root.size() == 1) {
                for (final JsonNode node : root) {
                    root = node;
                }
            }
            processAttributes(rootNode, root);
            final StatusConfiguration statusConfig = new StatusConfiguration().withVerboseClasses(VERBOSE_CLASSES)
                    .withStatus(getDefaultStatus());
            int monitorIntervalSeconds = 0;
            for (final Map.Entry<String, String> entry : rootNode.getAttributes().entrySet()) {
                final String key = entry.getKey();
                final String value = getStrSubstitutor().replace(entry.getValue());
                // TODO: this duplicates a lot of the XmlConfiguration constructor
                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(entry.getKey())) {
                    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 ("monitorInterval".equalsIgnoreCase(key)) {
                    monitorIntervalSeconds = Integer.parseInt(value);
                } else if ("advertiser".equalsIgnoreCase(key)) {
                    createAdvertiser(value, configSource, buffer, "application/json");
                }
            }
            initializeWatchers(this, configSource, monitorIntervalSeconds);
            statusConfig.initialize();
            if (getName() == null) {
                setName(configSource.getLocation());
            }
        } catch (final Exception ex) {
            LOGGER.error("Error parsing " + configSource.getLocation(), ex);
        }
    }

    protected ObjectMapper getObjectMapper() {
        return new ObjectMapper().configure(JsonParser.Feature.ALLOW_COMMENTS, true);
    }

    @Override
    public void setup() {
        final Iterator<Map.Entry<String, JsonNode>> iter = root.fields();
        final List<Node> children = rootNode.getChildren();
        while (iter.hasNext()) {
            final Map.Entry<String, JsonNode> entry = iter.next();
            final JsonNode n = entry.getValue();
            if (n.isObject()) {
                LOGGER.debug("Processing node for object {}", entry.getKey());
                children.add(constructNode(entry.getKey(), rootNode, n));
            } else if (n.isArray()) {
                LOGGER.error("Arrays are not supported at the root configuration.");
            }
        }
        LOGGER.debug("Completed parsing configuration");
        if (status.size() > 0) {
            for (final Status s : status) {
                LOGGER.error("Error processing element {}: {}", s.name, s.errorType);
            }
        }
    }

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

    private Node constructNode(final String name, final Node parent, final JsonNode jsonNode) {
        final PluginType<?> type = pluginManager.getPluginType(name);
        final Node node = new Node(parent, name, type);
        processAttributes(node, jsonNode);
        final Iterator<Map.Entry<String, JsonNode>> iter = jsonNode.fields();
        final List<Node> children = node.getChildren();
        while (iter.hasNext()) {
            final Map.Entry<String, JsonNode> entry = iter.next();
            final JsonNode n = entry.getValue();
            if (n.isArray() || n.isObject()) {
                if (type == null) {
                    status.add(new Status(name, n, ErrorType.CLASS_NOT_FOUND));
                }
                if (n.isArray()) {
                    LOGGER.debug("Processing node for array {}", entry.getKey());
                    for (int i = 0; i < n.size(); ++i) {
                        final String pluginType = getType(n.get(i), entry.getKey());
                        final PluginType<?> entryType = pluginManager.getPluginType(pluginType);
                        final Node item = new Node(node, entry.getKey(), entryType);
                        processAttributes(item, n.get(i));
                        if (pluginType.equals(entry.getKey())) {
                            LOGGER.debug("Processing {}[{}]", entry.getKey(), i);
                        } else {
                            LOGGER.debug("Processing {} {}[{}]", pluginType, entry.getKey(), i);
                        }
                        final Iterator<Map.Entry<String, JsonNode>> itemIter = n.get(i).fields();
                        final List<Node> itemChildren = item.getChildren();
                        while (itemIter.hasNext()) {
                            final Map.Entry<String, JsonNode> itemEntry = itemIter.next();
                            if (itemEntry.getValue().isObject()) {
                                LOGGER.debug("Processing node for object {}", itemEntry.getKey());
                                itemChildren.add(constructNode(itemEntry.getKey(), item, itemEntry.getValue()));
                            } else if (itemEntry.getValue().isArray()) {
                                final JsonNode array = itemEntry.getValue();
                                final String entryName = itemEntry.getKey();
                                LOGGER.debug("Processing array for object {}", entryName);
                                for (int j = 0; j < array.size(); ++j) {
                                    itemChildren.add(constructNode(entryName, item, array.get(j)));
                                }
                            }

                        }
                        children.add(item);
                    }
                } else {
                    LOGGER.debug("Processing node for object {}", entry.getKey());
                    children.add(constructNode(entry.getKey(), node, n));
                }
            } else {
                LOGGER.debug("Node {} is of type {}", entry.getKey(), n.getNodeType());
            }
        }

        String t;
        if (type == null) {
            t = "null";
        } else {
            t = type.getElementName() + ':' + type.getPluginClass();
        }

        final String p = node.getParent() == null ? "null"
                : node.getParent().getName() == null ? LoggerConfig.ROOT : node.getParent().getName();
        LOGGER.debug("Returning {} with parent {} of type {}", node.getName(), p, t);
        return node;
    }

    private String getType(final JsonNode node, final String name) {
        final Iterator<Map.Entry<String, JsonNode>> iter = node.fields();
        while (iter.hasNext()) {
            final Map.Entry<String, JsonNode> entry = iter.next();
            if (entry.getKey().equalsIgnoreCase("type")) {
                final JsonNode n = entry.getValue();
                if (n.isValueNode()) {
                    return n.asText();
                }
            }
        }
        return name;
    }

    private void processAttributes(final Node parent, final JsonNode node) {
        final Map<String, String> attrs = parent.getAttributes();
        final Iterator<Map.Entry<String, JsonNode>> iter = node.fields();
        while (iter.hasNext()) {
            final Map.Entry<String, JsonNode> entry = iter.next();
            if (!entry.getKey().equalsIgnoreCase("type")) {
                final JsonNode n = entry.getValue();
                if (n.isValueNode()) {
                    attrs.put(entry.getKey(), n.asText());
                }
            }
        }
    }

    @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 JsonNode node;
        private final String name;
        private final ErrorType errorType;

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

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

⏎ org/apache/logging/log4j/core/config/json/JsonConfiguration.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
Download 

⇒ Source Code for Apache Log4j JDK Logging Adapter

⇐ Source Code for Apache Log4j API

⇑ Downloading and Reviewing Apache Log4j Packages

⇑⇑ FAQ for Apache Log4j