LogSource.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.commons.logging;

import java.lang.reflect.Constructor;
import java.util.Hashtable;

import org.apache.commons.logging.impl.NoOpLog;

/**
 * Factory for creating {@link Log} instances.  Applications should call
 * the {@code makeNewLogInstance()} method to instantiate new instances
 * of the configured {@link Log} implementation class.
 * <p>
 * By default, calling {@code getInstance()} will use the following
 * algorithm:
 * <ul>
 * <li>If Log4J is available, return an instance of
 *     {@code org.apache.commons.logging.impl.Log4JLogger}.</li>
 * <li>If JDK 1.4 or later is available, return an instance of
 *     {@code org.apache.commons.logging.impl.Jdk14Logger}.</li>
 * <li>Otherwise, return an instance of
 *     {@code org.apache.commons.logging.impl.NoOpLog}.</li>
 * </ul>
 * <p>
 * You can change the default behavior in one of two ways:
 * <ul>
 * <li>On the startup command line, set the system property
 *     {@code org.apache.commons.logging.log} to the name of the
 *     {@code org.apache.commons.logging.Log} implementation class
 *     you want to use.</li>
 * <li>At runtime, call {@code LogSource.setLogImplementation()}.</li>
 * </ul>
 *
 * @deprecated Use {@link LogFactory} instead - The default factory
 *  implementation performs exactly the same algorithm as this class did
 */
@Deprecated
public class LogSource {

    /**
     * Logs.
     */
    static protected Hashtable<String, Log> logs = new Hashtable<>();

    /** Is Log4j available (in the current classpath) */
    static protected boolean log4jIsAvailable;

    /**
     * Is JDK 1.4 logging available, always true.
     *
     * @deprecated Java 8 is the baseline and includes JUL.
     */
    @Deprecated
    static protected boolean jdk14IsAvailable = true;

    /** Constructor for current log class */
    static protected Constructor<?> logImplctor;

    /**
     * An empty immutable {@code String} array.
     */
    private static final String[] EMPTY_STRING_ARRAY = {};

    static {

        // Is Log4J Available?
        log4jIsAvailable = isClassForName("org.apache.log4j.Logger");

        // Set the default Log implementation
        String name = null;
        try {
            name = System.getProperty("org.apache.commons.logging.log");
            if (name == null) {
                name = System.getProperty("org.apache.commons.logging.Log");
            }
        } catch (final Throwable ignore) {
            // Ignore
        }
        if (name != null) {
            try {
                setLogImplementation(name);
            } catch (final Throwable t) {
                try {
                    setLogImplementation("org.apache.commons.logging.impl.NoOpLog");
                } catch (final Throwable ignore) {
                    // Ignore
                }
            }
        } else {
            try {
                if (log4jIsAvailable) {
                    setLogImplementation("org.apache.commons.logging.impl.Log4JLogger");
                } else {
                    setLogImplementation("org.apache.commons.logging.impl.Jdk14Logger");
                }
            } catch (final Throwable t) {
                try {
                    setLogImplementation("org.apache.commons.logging.impl.NoOpLog");
                } catch (final Throwable ignore) {
                    // Ignore
                }
            }
        }

    }

    /**
     * Gets a {@code Log} instance by class.
     *
     * @param clazz a Class.
     * @return a {@code Log} instance.
     */
    static public Log getInstance(final Class<?> clazz) {
        return getInstance(clazz.getName());
    }

    /**
     * Gets a {@code Log} instance by class name.
     *
     * @param name Class name.
     * @return a {@code Log} instance.
     */
    static public Log getInstance(final String name) {
        return logs.computeIfAbsent(name, k -> makeNewLogInstance(name));
    }

    /**
     * Returns a {@link String} array containing the names of
     * all logs known to me.
     *
     * @return a {@link String} array containing the names of
     * all logs known to me.
     */
    static public String[] getLogNames() {
        return logs.keySet().toArray(EMPTY_STRING_ARRAY);
    }

    private static boolean isClassForName(final String className) {
        try {
            Class.forName(className);
            return true;
        } catch (final Throwable e) {
            return false;
        }
    }

    /**
     * Create a new {@link Log} implementation, based on the given <em>name</em>.
     * <p>
     * The specific {@link Log} implementation returned is determined by the
     * value of the {@code org.apache.commons.logging.log} property. The value
     * of {@code org.apache.commons.logging.log} may be set to the fully specified
     * name of a class that implements the {@link Log} interface. This class must
     * also have a public constructor that takes a single {@link String} argument
     * (containing the <em>name</em> of the {@link Log} to be constructed.
     * <p>
     * When {@code org.apache.commons.logging.log} is not set, or when no corresponding
     * class can be found, this method will return a Log4JLogger if the Log4j Logger
     * class is available in the {@link LogSource}'s classpath, or a Jdk14Logger if we
     * are on a JDK 1.4 or later system, or NoOpLog if neither of the above conditions is true.
     *
     * @param name the log name (or category)
     * @return a new instance.
     */
    static public Log makeNewLogInstance(final String name) {
        Log log;
        try {
            final Object[] args = { name };
            log = (Log) logImplctor.newInstance(args);
        } catch (final Throwable t) {
            log = null;
        }
        if (null == log) {
            log = new NoOpLog(name);
        }
        return log;
    }

    /**
     * Sets the log implementation/log implementation factory by class. The given class must implement {@link Log}, and provide a constructor that takes a single
     * {@link String} argument (containing the name of the log).
     *
     * @param logClass class.
     * @throws LinkageError                if there is missing dependency.
     * @throws ExceptionInInitializerError unexpected exception has occurred in a static initializer.
     * @throws NoSuchMethodException       if a matching method is not found.
     * @throws SecurityException           If a security manager, <em>s</em>, is present and the caller's class loader is not the same as or an ancestor of the
     *                                     class loader for the current class and invocation of {@link SecurityManager#checkPackageAccess
     *                                     s.checkPackageAccess()} denies access to the package of this class.
     */
    static public void setLogImplementation(final Class<?> logClass)
            throws LinkageError, ExceptionInInitializerError, NoSuchMethodException, SecurityException {
        logImplctor = logClass.getConstructor(String.class);
    }

    /**
     * Sets the log implementation/log implementation factory by the name of the class. The given class must implement {@link Log}, and provide a constructor
     * that takes a single {@link String} argument (containing the name of the log).
     *
     * @param className class name.
     * @throws LinkageError           if there is missing dependency.
     * @throws SecurityException      If a security manager, <em>s</em>, is present and the caller's class loader is not the same as or an ancestor of the class
     *                                loader for the current class and invocation of {@link SecurityManager#checkPackageAccess s.checkPackageAccess()} denies
     *                                access to the package of this class.
     */
    static public void setLogImplementation(final String className) throws LinkageError, SecurityException {
        try {
            final Class<?> logClass = Class.forName(className);
            logImplctor = logClass.getConstructor(String.class);
        } catch (final Throwable t) {
            logImplctor = null;
        }
    }

    /** Don't allow others to create instances. */
    private LogSource() {
    }
}