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/util/Loader.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.util;

import java.io.InputStream;
import java.lang.reflect.InvocationTargetException;
import java.net.URL;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.status.StatusLogger;
import org.apache.logging.log4j.util.LoaderUtil;
import org.apache.logging.log4j.util.PropertiesUtil;

/**
 * Load resources (or images) from various sources.
 */
public final class Loader {

    private static final Logger LOGGER = StatusLogger.getLogger();

    private static final String TSTR = "Caught Exception while in Loader.getResource. This may be innocuous.";

    private Loader() {
    }

    /**
     * Returns the ClassLoader to use.
     * @return the ClassLoader.
     */
    public static ClassLoader getClassLoader() {
        return getClassLoader(Loader.class, null);
    }

    /**
     * Returns the ClassLoader of current thread if possible, or falls back to the system ClassLoader if none is
     * available.
     *
     * @return the TCCL.
     * @see org.apache.logging.log4j.util.LoaderUtil#getThreadContextClassLoader()
     */
    public static ClassLoader getThreadContextClassLoader() {
        return LoaderUtil.getThreadContextClassLoader();
    }

    // TODO: this method could use some explanation
    public static ClassLoader getClassLoader(final Class<?> class1, final Class<?> class2) {
        final ClassLoader threadContextClassLoader = getThreadContextClassLoader();
        final ClassLoader loader1 = class1 == null ? null : class1.getClassLoader();
        final ClassLoader loader2 = class2 == null ? null : class2.getClassLoader();

        if (isChild(threadContextClassLoader, loader1)) {
            return isChild(threadContextClassLoader, loader2) ? threadContextClassLoader : loader2;
        }
        return isChild(loader1, loader2) ? loader1 : loader2;
    }

    /**
     * This method will search for {@code resource} in different
     * places. The search order is as follows:
     *
     * <ol>
     *
     * <li>Search for {@code resource} using the thread context
     * class loader under Java2. If that fails, search for
     * {@code resource} using the class loader that loaded this
     * class ({@code Loader}). Under JDK 1.1, only the class
     * loader that loaded this class ({@code Loader}) is used.</li>
     * <li>Try one last time with
     * {@code ClassLoader.getSystemResource(resource)}, that is is
     * using the system class loader in JDK 1.2 and virtual machine's
     * built-in class loader in JDK 1.1.</li>
     * </ol>
     * @param resource The resource to load.
     * @param defaultLoader The default ClassLoader.
     * @return A URL to the resource.
     */
    public static URL getResource(final String resource, final ClassLoader defaultLoader) {
        try {
            ClassLoader classLoader = getThreadContextClassLoader();
            if (classLoader != null) {
                LOGGER.trace("Trying to find [{}] using context class loader {}.", resource, classLoader);
                final URL url = classLoader.getResource(resource);
                if (url != null) {
                    return url;
                }
            }

            // We could not find resource. Let us now try with the classloader that loaded this class.
            classLoader = Loader.class.getClassLoader();
            if (classLoader != null) {
                LOGGER.trace("Trying to find [{}] using {} class loader.", resource, classLoader);
                final URL url = classLoader.getResource(resource);
                if (url != null) {
                    return url;
                }
            }
            // We could not find resource. Finally try with the default ClassLoader.
            if (defaultLoader != null) {
                LOGGER.trace("Trying to find [{}] using {} class loader.", resource, defaultLoader);
                final URL url = defaultLoader.getResource(resource);
                if (url != null) {
                    return url;
                }
            }
        } catch (final Throwable t) {
            //
            //  can't be InterruptedException or InterruptedIOException
            //    since not declared, must be error or RuntimeError.
            LOGGER.warn(TSTR, t);
        }

        // Last ditch attempt: get the resource from the class path. It
        // may be the case that clazz was loaded by the Extension class
        // loader which the parent of the system class loader. Hence the
        // code below.
        LOGGER.trace("Trying to find [{}] using ClassLoader.getSystemResource().", resource);
        return ClassLoader.getSystemResource(resource);
    }

    /**
     * This method will search for {@code resource} in different
     * places. The search order is as follows:
     *
     * <ol>
     * <li>Search for {@code resource} using the thread context
     * class loader under Java2. If that fails, search for
     * {@code resource} using the class loader that loaded this
     * class ({@code Loader}). Under JDK 1.1, only the class
     * loader that loaded this class ({@code Loader}) is used.</li>
     * <li>Try one last time with
     * {@code ClassLoader.getSystemResource(resource)}, that is is
     * using the system class loader in JDK 1.2 and virtual machine's
     * built-in class loader in JDK 1.1.</li>
     * </ol>
     * @param resource The resource to load.
     * @param defaultLoader The default ClassLoader.
     * @return An InputStream to read the resouce.
     */
    public static InputStream getResourceAsStream(final String resource, final ClassLoader defaultLoader) {
        try {
            ClassLoader classLoader = getThreadContextClassLoader();
            InputStream is;
            if (classLoader != null) {
                LOGGER.trace("Trying to find [{}] using context class loader {}.", resource, classLoader);
                is = classLoader.getResourceAsStream(resource);
                if (is != null) {
                    return is;
                }
            }

            // We could not find resource. Let us now try with the classloader that loaded this class.
            classLoader = Loader.class.getClassLoader();
            if (classLoader != null) {
                LOGGER.trace("Trying to find [{}] using {} class loader.", resource, classLoader);
                is = classLoader.getResourceAsStream(resource);
                if (is != null) {
                    return is;
                }
            }

            // We could not find resource. Finally try with the default ClassLoader.
            if (defaultLoader != null) {
                LOGGER.trace("Trying to find [{}] using {} class loader.", resource, defaultLoader);
                is = defaultLoader.getResourceAsStream(resource);
                if (is != null) {
                    return is;
                }
            }
        } catch (final Throwable t) {
            //
            //  can't be InterruptedException or InterruptedIOException
            //    since not declared, must be error or RuntimeError.
            LOGGER.warn(TSTR, t);
        }

        // Last ditch attempt: get the resource from the class path. It
        // may be the case that clazz was loaded by the Extension class
        // loader which the parent of the system class loader. Hence the
        // code below.
        LOGGER.trace("Trying to find [{}] using ClassLoader.getSystemResource().", resource);
        return ClassLoader.getSystemResourceAsStream(resource);
    }

    /**
     * Determines if one ClassLoader is a child of another ClassLoader. Note that a {@code null} ClassLoader is
     * interpreted as the system ClassLoader as per convention.
     *
     * @param loader1 the ClassLoader to check for childhood.
     * @param loader2 the ClassLoader to check for parenthood.
     * @return {@code true} if the first ClassLoader is a strict descendant of the second ClassLoader.
     */
    private static boolean isChild(final ClassLoader loader1, final ClassLoader loader2) {
        if (loader1 != null && loader2 != null) {
            ClassLoader parent = loader1.getParent();
            while (parent != null && parent != loader2) {
                parent = parent.getParent();
            }
            // once parent is null, we're at the system CL, which would indicate they have separate ancestry
            return parent != null;
        }
        return loader1 != null;
    }

    /**
     * Loads and initializes a named Class using a given ClassLoader.
     *
     * @param className The class name.
     * @param loader The class loader.
     * @return The class.
     * @throws ClassNotFoundException if the class could not be found.
     */
    public static Class<?> initializeClass(final String className, final ClassLoader loader)
            throws ClassNotFoundException {
        return Class.forName(className, true, loader);
    }

    /**
     * Loads a named Class using a given ClassLoader.
     *
     * @param className The class name.
     * @param loader The class loader.
     * @return The class, or null if loader is null.
     * @throws ClassNotFoundException if the class could not be found.
     */
    public static Class<?> loadClass(final String className, final ClassLoader loader)
            throws ClassNotFoundException {
        return loader != null ? loader.loadClass(className) : null;
    }

    /**
     * Load a Class in the {@code java.*} namespace by name. Useful for peculiar scenarios typically involving
     * Google App Engine.
     *
     * @param className The class name.
     * @return The Class.
     * @throws ClassNotFoundException if the Class could not be found.
     */
    public static Class<?> loadSystemClass(final String className) throws ClassNotFoundException {
        try {
            return Class.forName(className, true, ClassLoader.getSystemClassLoader());
        } catch (final Throwable t) {
            LOGGER.trace("Couldn't use SystemClassLoader. Trying Class.forName({}).", className, t);
            return Class.forName(className);
        }
    }

    /**
     * Loads and instantiates a Class using the default constructor.
     *
     * @param className The class name.
     * @return new instance of the class.
     * @throws ClassNotFoundException if the class isn't available to the usual ClassLoaders
     * @throws IllegalAccessException if the class can't be instantiated through a public constructor
     * @throws InstantiationException if there was an exception whilst instantiating the class
     * @throws NoSuchMethodException if there isn't a no-args constructor on the class
     * @throws InvocationTargetException if there was an exception whilst constructing the class
     */
    @SuppressWarnings("unchecked")
    public static <T> T newInstanceOf(final String className)
        throws ClassNotFoundException,
        IllegalAccessException,
        InstantiationException,
        NoSuchMethodException,
        InvocationTargetException {
        final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(getClassLoader());
            return LoaderUtil.newInstanceOf(className);
        } finally {
            Thread.currentThread().setContextClassLoader(contextClassLoader);
        }
    }

    /**
     * Loads, instantiates, and casts a Class using the default constructor.
     *
     * @param className The class name.
     * @param clazz The class to cast it to.
     * @param <T> The type to cast it to.
     * @return new instance of the class cast to {@code T}
     * @throws ClassNotFoundException if the class isn't available to the usual ClassLoaders
     * @throws IllegalAccessException if the class can't be instantiated through a public constructor
     * @throws InstantiationException if there was an exception whilst instantiating the class
     * @throws NoSuchMethodException if there isn't a no-args constructor on the class
     * @throws InvocationTargetException if there was an exception whilst constructing the class
     * @throws ClassCastException if the constructed object isn't type compatible with {@code T}
     */
    public static <T> T newCheckedInstanceOf(final String className, final Class<T> clazz)
        throws ClassNotFoundException,
        NoSuchMethodException,
        IllegalAccessException,
        InvocationTargetException,
        InstantiationException {
        final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(getClassLoader());
            return LoaderUtil.newCheckedInstanceOf(className, clazz);
        } finally {
            Thread.currentThread().setContextClassLoader(contextClassLoader);
        }
    }

    /**
     * Loads and instantiates a class given by a property name.
     *
     * @param propertyName The property name to look up a class name for.
     * @param clazz        The class to cast it to.
     * @param <T>          The type to cast it to.
     * @return new instance of the class given in the property or {@code null} if the property was unset.
     * @throws ClassNotFoundException    if the class isn't available to the usual ClassLoaders
     * @throws IllegalAccessException    if the class can't be instantiated through a public constructor
     * @throws InstantiationException    if there was an exception whilst instantiating the class
     * @throws NoSuchMethodException     if there isn't a no-args constructor on the class
     * @throws InvocationTargetException if there was an exception whilst constructing the class
     * @throws ClassCastException        if the constructed object isn't type compatible with {@code T}
     */
    public static <T> T newCheckedInstanceOfProperty(final String propertyName, final Class<T> clazz)
        throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException,
        IllegalAccessException {
        final String className = PropertiesUtil.getProperties().getStringProperty(propertyName);
        final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(getClassLoader());
            return LoaderUtil.newCheckedInstanceOfProperty(propertyName, clazz);
        } finally {
            Thread.currentThread().setContextClassLoader(contextClassLoader);
        }
    }

    /**
     * Determines if a named Class can be loaded or not.
     *
     * @param className The class name.
     * @return {@code true} if the class could be found or {@code false} otherwise.
     */
    public static boolean isClassAvailable(final String className) {
        final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(getClassLoader());
            return LoaderUtil.isClassAvailable(className);
        } finally {
            Thread.currentThread().setContextClassLoader(contextClassLoader);
        }
    }

    public static boolean isJansiAvailable() {
        return isClassAvailable("org.fusesource.jansi.AnsiRenderer");
    }

    /**
     * Loads a class by name. This method respects the {@link #IGNORE_TCCL_PROPERTY} Log4j property. If this property is
     * specified and set to anything besides {@code false}, then the default ClassLoader will be used.
     *
     * @param className The class name.
     * @return the Class for the given name.
     * @throws ClassNotFoundException if the specified class name could not be found
     */
    public static Class<?> loadClass(final String className) throws ClassNotFoundException {

        final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(getClassLoader());
            return LoaderUtil.loadClass(className);
        } finally {
            Thread.currentThread().setContextClassLoader(contextClassLoader);
        }
    }
}

⏎ org/apache/logging/log4j/core/util/Loader.java

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