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/processor/PluginProcessor.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.processor;

import java.io.IOException;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Locale;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.Messager;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.ElementVisitor;
import javax.lang.model.element.TypeElement;
import javax.lang.model.util.Elements;
import javax.lang.model.util.SimpleElementVisitor7;
import javax.tools.Diagnostic.Kind;
import javax.tools.FileObject;
import javax.tools.StandardLocation;

import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginAliases;
import org.apache.logging.log4j.util.Strings;

/**
 * Annotation processor for pre-scanning Log4j 2 plugins.
 */
@SupportedAnnotationTypes("org.apache.logging.log4j.core.config.plugins.*")
public class PluginProcessor extends AbstractProcessor {

    // TODO: this could be made more abstract to allow for compile-time and run-time plugin processing

    /**
     * The location of the plugin cache data file. This file is written to by this processor, and read from by
     * {@link org.apache.logging.log4j.core.config.plugins.util.PluginManager}.
     */
    public static final String PLUGIN_CACHE_FILE =
            "META-INF/org/apache/logging/log4j/core/config/plugins/Log4j2Plugins.dat";

    private final PluginCache pluginCache = new PluginCache();

    @Override
    public SourceVersion getSupportedSourceVersion() {
        return SourceVersion.latest();
    }

    @Override
    public boolean process(final Set<? extends TypeElement> annotations, final RoundEnvironment roundEnv) {
        Messager messager = processingEnv.getMessager();
        messager.printMessage(Kind.NOTE, "Processing Log4j annotations");
        try {
            final Set<? extends Element> elements = roundEnv.getElementsAnnotatedWith(Plugin.class);
            if (elements.isEmpty()) {
                messager.printMessage(Kind.NOTE, "No elements to process");
                return false;
            }
            collectPlugins(elements);
            writeCacheFile(elements.toArray(new Element[elements.size()]));
            messager.printMessage(Kind.NOTE, "Annotations processed");
            return true;
        } catch (final Exception ex) {
            ex.printStackTrace();
            error(ex.getMessage());
            return false;
        }
    }

    private void error(final CharSequence message) {
        processingEnv.getMessager().printMessage(Kind.ERROR, message);
    }

    private void collectPlugins(final Iterable<? extends Element> elements) {
        final Elements elementUtils = processingEnv.getElementUtils();
        final ElementVisitor<PluginEntry, Plugin> pluginVisitor = new PluginElementVisitor(elementUtils);
        final ElementVisitor<Collection<PluginEntry>, Plugin> pluginAliasesVisitor = new PluginAliasesElementVisitor(
                elementUtils);
        for (final Element element : elements) {
            final Plugin plugin = element.getAnnotation(Plugin.class);
            if (plugin == null) {
                continue;
            }
            final PluginEntry entry = element.accept(pluginVisitor, plugin);
            final Map<String, PluginEntry> category = pluginCache.getCategory(entry.getCategory());
            category.put(entry.getKey(), entry);
            final Collection<PluginEntry> entries = element.accept(pluginAliasesVisitor, plugin);
            for (final PluginEntry pluginEntry : entries) {
                category.put(pluginEntry.getKey(), pluginEntry);
            }
        }
    }

    private void writeCacheFile(final Element... elements) throws IOException {
        final FileObject fileObject = processingEnv.getFiler().createResource(StandardLocation.CLASS_OUTPUT, Strings.EMPTY,
                PLUGIN_CACHE_FILE, elements);
        try (final OutputStream out = fileObject.openOutputStream()) {
            pluginCache.writeCache(out);
        }
    }

    /**
     * ElementVisitor to scan the Plugin annotation.
     */
    private static class PluginElementVisitor extends SimpleElementVisitor7<PluginEntry, Plugin> {

        private final Elements elements;

        private PluginElementVisitor(final Elements elements) {
            this.elements = elements;
        }

        @Override
        public PluginEntry visitType(final TypeElement e, final Plugin plugin) {
            Objects.requireNonNull(plugin, "Plugin annotation is null.");
            final PluginEntry entry = new PluginEntry();
            entry.setKey(plugin.name().toLowerCase(Locale.US));
            entry.setClassName(elements.getBinaryName(e).toString());
            entry.setName(Plugin.EMPTY.equals(plugin.elementType()) ? plugin.name() : plugin.elementType());
            entry.setPrintable(plugin.printObject());
            entry.setDefer(plugin.deferChildren());
            entry.setCategory(plugin.category());
            return entry;
        }
    }

    /**
     * ElementVisitor to scan the PluginAliases annotation.
     */
    private static class PluginAliasesElementVisitor extends SimpleElementVisitor7<Collection<PluginEntry>, Plugin> {

        private final Elements elements;

        private PluginAliasesElementVisitor(final Elements elements) {
            super(Collections.<PluginEntry> emptyList());
            this.elements = elements;
        }

        @Override
        public Collection<PluginEntry> visitType(final TypeElement e, final Plugin plugin) {
            final PluginAliases aliases = e.getAnnotation(PluginAliases.class);
            if (aliases == null) {
                return DEFAULT_VALUE;
            }
            final Collection<PluginEntry> entries = new ArrayList<>(aliases.value().length);
            for (final String alias : aliases.value()) {
                final PluginEntry entry = new PluginEntry();
                entry.setKey(alias.toLowerCase(Locale.US));
                entry.setClassName(elements.getBinaryName(e).toString());
                entry.setName(Plugin.EMPTY.equals(plugin.elementType()) ? alias : plugin.elementType());
                entry.setPrintable(plugin.printObject());
                entry.setDefer(plugin.deferChildren());
                entry.setCategory(plugin.category());
                entries.add(entry);
            }
            return entries;
        }
    }
}

⏎ org/apache/logging/log4j/core/config/plugins/processor/PluginProcessor.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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