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/lookup/Interpolator.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.lookup;

import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.ConfigurationAware;
import org.apache.logging.log4j.core.config.plugins.util.PluginManager;
import org.apache.logging.log4j.core.config.plugins.util.PluginType;
import org.apache.logging.log4j.core.util.Loader;
import org.apache.logging.log4j.core.util.ReflectionUtil;
import org.apache.logging.log4j.status.StatusLogger;
import org.apache.logging.log4j.util.Constants;

/**
 * Proxies all the other {@link StrLookup}s.
 */
public class Interpolator extends AbstractConfigurationAwareLookup {

    /** Constant for the prefix separator. */
    public static final char PREFIX_SEPARATOR = ':';

    private static final String LOOKUP_KEY_WEB = "web";

    private static final String LOOKUP_KEY_DOCKER = "docker";

    private static final String LOOKUP_KEY_KUBERNETES = "kubernetes";

    private static final String LOOKUP_KEY_SPRING = "spring";

    private static final String LOOKUP_KEY_JNDI = "jndi";

    private static final String LOOKUP_KEY_JVMRUNARGS = "jvmrunargs";

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

    private final Map<String, StrLookup> strLookupMap = new HashMap<>();

    private final StrLookup defaultLookup;

    public Interpolator(final StrLookup defaultLookup) {
        this(defaultLookup, null);
    }

    /**
     * Constructs an Interpolator using a given StrLookup and a list of packages to find Lookup plugins in.
     *
     * @param defaultLookup  the default StrLookup to use as a fallback
     * @param pluginPackages a list of packages to scan for Lookup plugins
     * @since 2.1
     */
    public Interpolator(final StrLookup defaultLookup, final List<String> pluginPackages) {
        this.defaultLookup = defaultLookup == null ? new MapLookup(new HashMap<String, String>()) : defaultLookup;
        final PluginManager manager = new PluginManager(CATEGORY);
        manager.collectPlugins(pluginPackages);
        final Map<String, PluginType<?>> plugins = manager.getPlugins();

        for (final Map.Entry<String, PluginType<?>> entry : plugins.entrySet()) {
            try {
                final Class<? extends StrLookup> clazz = entry.getValue().getPluginClass().asSubclass(StrLookup.class);
                strLookupMap.put(entry.getKey().toLowerCase(), ReflectionUtil.instantiate(clazz));
            } catch (final Throwable t) {
                handleError(entry.getKey(), t);
            }
        }
    }

    /**
     * Create the default Interpolator using only Lookups that work without an event.
     */
    public Interpolator() {
        this((Map<String, String>) null);
    }

    /**
     * Creates the Interpolator using only Lookups that work without an event and initial properties.
     */
    public Interpolator(final Map<String, String> properties) {
        this.defaultLookup = new MapLookup(properties == null ? new HashMap<String, String>() : properties);
        // TODO: this ought to use the PluginManager
        strLookupMap.put("log4j", new Log4jLookup());
        strLookupMap.put("sys", new SystemPropertiesLookup());
        strLookupMap.put("env", new EnvironmentLookup());
        strLookupMap.put("main", MainMapLookup.MAIN_SINGLETON);
        strLookupMap.put("marker", new MarkerLookup());
        strLookupMap.put("java", new JavaLookup());
        strLookupMap.put("lower", new LowerLookup());
        strLookupMap.put("upper", new UpperLookup());
        // JNDI
        try {
            // [LOG4J2-703] We might be on Android
            strLookupMap.put(LOOKUP_KEY_JNDI,
                Loader.newCheckedInstanceOf("org.apache.logging.log4j.core.lookup.JndiLookup", StrLookup.class));
        } catch (final LinkageError | Exception e) {
            handleError(LOOKUP_KEY_JNDI, e);
        }
        // JMX input args
        try {
            // We might be on Android
            strLookupMap.put(LOOKUP_KEY_JVMRUNARGS,
                Loader.newCheckedInstanceOf("org.apache.logging.log4j.core.lookup.JmxRuntimeInputArgumentsLookup",
                        StrLookup.class));
        } catch (final LinkageError | Exception e) {
            handleError(LOOKUP_KEY_JVMRUNARGS, e);
        }
        strLookupMap.put("date", new DateLookup());
        strLookupMap.put("ctx", new ContextMapLookup());
        if (Constants.IS_WEB_APP) {
            try {
                strLookupMap.put(LOOKUP_KEY_WEB,
                    Loader.newCheckedInstanceOf("org.apache.logging.log4j.web.WebLookup", StrLookup.class));
            } catch (final Exception ignored) {
                handleError(LOOKUP_KEY_WEB, ignored);
            }
        } else {
            LOGGER.debug("Not in a ServletContext environment, thus not loading WebLookup plugin.");
        }
        try {
            strLookupMap.put(LOOKUP_KEY_DOCKER,
                Loader.newCheckedInstanceOf("org.apache.logging.log4j.docker.DockerLookup", StrLookup.class));
        } catch (final Exception ignored) {
            handleError(LOOKUP_KEY_DOCKER, ignored);
        }
        try {
            strLookupMap.put(LOOKUP_KEY_SPRING,
                    Loader.newCheckedInstanceOf("org.apache.logging.log4j.spring.cloud.config.client.SpringLookup", StrLookup.class));
        } catch (final Exception ignored) {
            handleError(LOOKUP_KEY_SPRING, ignored);
        }
        try {
            strLookupMap.put(LOOKUP_KEY_KUBERNETES,
                    Loader.newCheckedInstanceOf("org.apache.logging.log4j.kubernetes.KubernetesLookup", StrLookup.class));
        } catch (final Exception | NoClassDefFoundError error) {
            handleError(LOOKUP_KEY_KUBERNETES, error);
        }
    }

    public Map<String, StrLookup> getStrLookupMap() {
        return strLookupMap;
    }

    private void handleError(final String lookupKey, final Throwable t) {
        switch (lookupKey) {
            case LOOKUP_KEY_JNDI:
                // java.lang.VerifyError: org/apache/logging/log4j/core/lookup/JndiLookup
                LOGGER.warn( // LOG4J2-1582 don't print the whole stack trace (it is just a warning...)
                        "JNDI lookup class is not available because this JRE does not support JNDI." +
                        " JNDI string lookups will not be available, continuing configuration. Ignoring " + t);
                break;
            case LOOKUP_KEY_JVMRUNARGS:
                // java.lang.VerifyError: org/apache/logging/log4j/core/lookup/JmxRuntimeInputArgumentsLookup
                LOGGER.warn(
                        "JMX runtime input lookup class is not available because this JRE does not support JMX. " +
                        "JMX lookups will not be available, continuing configuration. Ignoring " + t);
                break;
            case LOOKUP_KEY_WEB:
                LOGGER.info("Log4j appears to be running in a Servlet environment, but there's no log4j-web module " +
                        "available. If you want better web container support, please add the log4j-web JAR to your " +
                        "web archive or server lib directory.");
                break;
            case LOOKUP_KEY_DOCKER: case LOOKUP_KEY_SPRING:
                break;
            case LOOKUP_KEY_KUBERNETES:
                if (t instanceof NoClassDefFoundError) {
                    LOGGER.warn("Unable to create Kubernetes lookup due to missing dependency: {}", t.getMessage());
                }
                break;
            default:
                LOGGER.error("Unable to create Lookup for {}", lookupKey, t);
        }
    }

    /**
     * Resolves the specified variable. This implementation will try to extract
     * a variable prefix from the given variable name (the first colon (':') is
     * used as prefix separator). It then passes the name of the variable with
     * the prefix stripped to the lookup object registered for this prefix. If
     * no prefix can be found or if the associated lookup object cannot resolve
     * this variable, the default lookup object will be used.
     *
     * @param event The current LogEvent or null.
     * @param var the name of the variable whose value is to be looked up
     * @return the value of this variable or <b>null</b> if it cannot be
     * resolved
     */
    @Override
    public String lookup(final LogEvent event, String var) {
        if (var == null) {
            return null;
        }

        final int prefixPos = var.indexOf(PREFIX_SEPARATOR);
        if (prefixPos >= 0) {
            final String prefix = var.substring(0, prefixPos).toLowerCase(Locale.US);
            final String name = var.substring(prefixPos + 1);
            final StrLookup lookup = strLookupMap.get(prefix);
            if (lookup instanceof ConfigurationAware) {
                ((ConfigurationAware) lookup).setConfiguration(configuration);
            }
            String value = null;
            if (lookup != null) {
                value = event == null ? lookup.lookup(name) : lookup.lookup(event, name);
            }

            if (value != null) {
                return value;
            }
            var = var.substring(prefixPos + 1);
        }
        if (defaultLookup != null) {
            return event == null ? defaultLookup.lookup(var) : defaultLookup.lookup(event, var);
        }
        return null;
    }

    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder();
        for (final String name : strLookupMap.keySet()) {
            if (sb.length() == 0) {
                sb.append('{');
            } else {
                sb.append(", ");
            }

            sb.append(name);
        }
        if (sb.length() > 0) {
            sb.append('}');
        }
        return sb.toString();
    }

}

⏎ org/apache/logging/log4j/core/lookup/Interpolator.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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