SLF4JLogFactory

/*
 * Copyright 2001-2004 The Apache Software Foundation.
 *
 * Licensed 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.impl;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogConfigurationException;
import org.apache.commons.logging.LogFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.spi.LocationAwareLogger;

import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * <p>
 * Concrete subclass of {@link LogFactory} which always delegates to the
 * {@link LoggerFactory org.slf4j.LoggerFactory} class.
 *
 * <p>
 * This factory generates instances of {@link SLF4JLog}. It will remember
 * previously created instances for the same name, and will return them on
 * repeated requests to the <code>getInstance()</code> method.
 *
 * <p>
 * This implementation ignores any configured attributes.
 *
 *
 * @author Rod Waldhoff
 * @author Craig R. McClanahan
 * @author Richard A. Sitze
 * @author Ceki G&uuml;lc&uuml;
 */
@SuppressWarnings("rawtypes")
public class SLF4JLogFactory extends LogFactory {

    // ----------------------------------------------------------- Constructors

    /**
     * The {@link org.apache.commons.logging.Log}instances that have already been
     * created, keyed by logger name.
     */
    ConcurrentMap<String, Log> loggerMap;

    /**
     * Public no-arguments constructor required by the lookup mechanism.
     */
    public SLF4JLogFactory() {
        loggerMap = new ConcurrentHashMap<>();
    }

    // ----------------------------------------------------- Manifest Constants

    /**
     * The name of the system property identifying our {@link Log}implementation
     * class.
     */
    public static final String LOG_PROPERTY = "org.apache.commons.logging.Log";

    // ----------------------------------------------------- Instance Variables

    /**
     * Configuration attributes.
     */
    protected Hashtable attributes = new Hashtable();

    // --------------------------------------------------------- Public Methods

    /**
     * Return the configuration attribute with the specified name (if any), or
     * <code>null</code> if there is no such attribute.
     *
     * @param name
     *          Name of the attribute to return
     */
    public Object getAttribute(String name) {

        return (attributes.get(name));

    }

    /**
     * Return an array containing the names of all currently defined configuration
     * attributes. If there are no such attributes, a zero length array is
     * returned.
     */
    @SuppressWarnings("unchecked")
    public String[] getAttributeNames() {

        List<String> names = new ArrayList<>();
        Enumeration<String> keys = attributes.keys();
        while (keys.hasMoreElements()) {
            names.add((String) keys.nextElement());
        }
        String[] results = new String[names.size()];
        for (int i = 0; i < results.length; i++) {
            results[i] = (String) names.get(i);
        }
        return (results);

    }

    /**
     * Convenience method to derive a name from the specified class and call
     * <code>getInstance(String)</code> with it.
     *
     * @param clazz
     *          Class for which a suitable Log name will be derived
     *
     * @exception LogConfigurationException
     *              if a suitable <code>Log</code> instance cannot be returned
     */
    public Log getInstance(Class clazz) throws LogConfigurationException {
        return (getInstance(clazz.getName()));
    }

    /**
     * <p>
     * Construct (if necessary) and return a <code>Log</code> instance, using
     * the factory's current set of configuration attributes.
     *
     *
     * @param name
     *          Logical name of the <code>Log</code> instance to be returned
     *          (the meaning of this name is only known to the underlying logging
     *          implementation that is being wrapped)
     *
     * @exception LogConfigurationException
     *              if a suitable <code>Log</code> instance cannot be returned
     */
    public Log getInstance(String name) throws LogConfigurationException {
        Log instance = loggerMap.get(name);
        if (instance != null) {
            return instance;
        } else {
            Log newInstance;
            Logger slf4jLogger = LoggerFactory.getLogger(name);
            if (slf4jLogger instanceof LocationAwareLogger) {
                newInstance = new SLF4JLocationAwareLog((LocationAwareLogger) slf4jLogger);
            } else {
                newInstance = new SLF4JLog(slf4jLogger);
            }
            Log oldInstance = loggerMap.putIfAbsent(name, newInstance);
            return oldInstance == null ? newInstance : oldInstance;
        }
    }

    /**
     * Release any internal references to previously created
     * {@link org.apache.commons.logging.Log}instances returned by this factory.
     * This is useful in environments like servlet containers, which implement
     * application reloading by throwing away a ClassLoader. Dangling references
     * to objects in that class loader would prevent garbage collection.
     */
    public void release() {
        // This method is never called by jcl-over-slf4j classes. However,
        // in certain deployment scenarios, in particular if jcl-over-slf4j.jar
        // is
        // in the the web-app class loader and the official commons-logging.jar is
        // deployed in some parent class loader (e.g. commons/lib), then it is
        // possible
        // for the parent class loader to mask the classes shipping in
        // jcl-over-slf4j.jar.
        System.out.println("WARN: The method " + SLF4JLogFactory.class + "#release() was invoked.");
        System.out.println("WARN: Please see http://www.slf4j.org/codes.html#release for an explanation.");
        System.out.flush();
    }

    /**
     * Remove any configuration attribute associated with the specified name. If
     * there is no such attribute, no action is taken.
     *
     * @param name
     *          Name of the attribute to remove
     */
    public void removeAttribute(String name) {
        attributes.remove(name);
    }

    /**
     * Set the configuration attribute with the specified name. Calling this with
     * a <code>null</code> value is equivalent to calling
     * <code>removeAttribute(name)</code>.
     *
     * @param name
     *          Name of the attribute to set
     * @param value
     *          Value of the attribute to set, or <code>null</code> to remove
     *          any setting for this attribute
     */
    @SuppressWarnings("unchecked")
    public void setAttribute(String name, Object value) {

        if (value == null) {
            attributes.remove(name);
        } else {
            attributes.put(name, value);
        }

    }
}