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/plugins/visitors/PluginElementVisitor.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.plugins.visitors;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;

import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.Node;
import org.apache.logging.log4j.core.config.plugins.PluginElement;
import org.apache.logging.log4j.core.config.plugins.util.PluginType;

/**
 * PluginVisitor implementation for {@link PluginElement}. Supports arrays as well as singular values.
 */
public class PluginElementVisitor extends AbstractPluginVisitor<PluginElement> {
    public PluginElementVisitor() {
        super(PluginElement.class);
    }

    @Override
    public Object visit(final Configuration configuration, final Node node, final LogEvent event,
                        final StringBuilder log) {
        final String name = this.annotation.value();
        if (this.conversionType.isArray()) {
            setConversionType(this.conversionType.getComponentType());
            final List<Object> values = new ArrayList<>();
            final Collection<Node> used = new ArrayList<>();
            log.append("={");
            boolean first = true;
            for (final Node child : node.getChildren()) {
                final PluginType<?> childType = child.getType();
                if (name.equalsIgnoreCase(childType.getElementName()) ||
                    this.conversionType.isAssignableFrom(childType.getPluginClass())) {
                    if (!first) {
                        log.append(", ");
                    }
                    first = false;
                    used.add(child);
                    final Object childObject = child.getObject();
                    if (childObject == null) {
                        LOGGER.error("Null object returned for {} in {}.", child.getName(), node.getName());
                        continue;
                    }
                    if (childObject.getClass().isArray()) {
                        log.append(Arrays.toString((Object[]) childObject)).append('}');
                        node.getChildren().removeAll(used);
                        return childObject;
                    }
                    log.append(child.toString());
                    values.add(childObject);
                }
            }
            log.append('}');
            // note that we need to return an empty array instead of null if the types are correct
            if (!values.isEmpty() && !this.conversionType.isAssignableFrom(values.get(0).getClass())) {
                LOGGER.error("Attempted to assign attribute {} to list of type {} which is incompatible with {}.",
                    name, values.get(0).getClass(), this.conversionType);
                return null;
            }
            node.getChildren().removeAll(used);
            // we need to use reflection here because values.toArray() will cause type errors at runtime
            final Object[] array = (Object[]) Array.newInstance(this.conversionType, values.size());
            for (int i = 0; i < array.length; i++) {
                array[i] = values.get(i);
            }
            return array;
        }
        final Node namedNode = findNamedNode(name, node.getChildren());
        if (namedNode == null) {
            log.append(name).append("=null");
            return null;
        }
        log.append(namedNode.getName()).append('(').append(namedNode.toString()).append(')');
        node.getChildren().remove(namedNode);
        return namedNode.getObject();
    }

    private Node findNamedNode(final String name, final Iterable<Node> children) {
        for (final Node child : children) {
            final PluginType<?> childType = child.getType();
            if (childType == null) {
                //System.out.println();
            }
            if (name.equalsIgnoreCase(childType.getElementName()) ||
                this.conversionType.isAssignableFrom(childType.getPluginClass())) {
                // FIXME: check child.getObject() for null?
                // doing so would be more consistent with the array version
                return child;
            }
        }
        return null;
    }
}

⏎ org/apache/logging/log4j/core/config/plugins/visitors/PluginElementVisitor.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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