Quelle LogFactory.java Sprache: 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.juli.logging;

import java.lang.reflect.Constructor;
import java.nio.file.FileSystems;
import java.util.ServiceLoader;
import java.util.logging.LogManager;

import aQute.bnd.annotation.spi.ServiceConsumer;

/**
* This is a modified LogFactory that uses a simple {@link ServiceLoader} based
* discovery mechanism with a default of using JDK based logging. An
* implementation that uses the full Commons Logging discovery mechanism is
* available as part of the Tomcat extras download.
*
* Why? It is an attempt to strike a balance between simpler code (no discovery)
* and providing flexibility - particularly for those projects that embed Tomcat
* or some of Tomcat's components - is an alternative logging
* implementation is desired.
*
* Note that this implementation is not just a wrapper around JDK logging (like
* the original commons-logging impl). It adds 2 features - a simpler
* configuration (which is in fact a subset of log4j.properties) and a
* formatter that is less ugly.
*
* The removal of 'abstract' preserves binary backward compatibility. It is
* possible to preserve the abstract - and introduce another (hardcoded) factory
* - but I see no benefit.
*
* Since this class is not intended to be extended - all protected methods are
* removed. This can be changed - but again, there is little value in keeping
* dead code. Just take a quick look at the removed code ( and it's complexity).
*
* --------------
*
* Original comment:
* Factory for creating {@link Log} instances, with discovery and
* configuration features similar to that employed by standard Java APIs
* such as JAXP.
*
* IMPLEMENTATION NOTE - This implementation is heavily
* based on the SAXParserFactory and DocumentBuilderFactory implementations
* (corresponding to the JAXP pluggability APIs) found in Apache Xerces.
*
*
* @author Craig R. McClanahan
* @author Costin Manolache
* @author Richard A. Sitze
*/
@ServiceConsumer(value=Log.class)
public class LogFactory {

 private static final LogFactory singleton = new LogFactory();

 private final Constructor<? extends Log> discoveredLogConstructor;

 /**
 * Private constructor that is not available for public use.
 */
 private LogFactory() {
 /*
 * Work-around known a JRE bug.
 * https://bugs.openjdk.java.net/browse/JDK-8194653
 *
 * Pre-load the default file system. No performance impact as we need to
 * load the default file system anyway. Just do it earlier to avoid the
 * potential deadlock.
 *
 * This can be removed once the oldest JRE supported by Tomcat includes
 * a fix.
 */
 FileSystems.getDefault();

 // Look via a ServiceLoader for a Log implementation that has a
 // constructor taking the String name.
 ServiceLoader<Log> logLoader = ServiceLoader.load(Log.class);
 Constructor<? extends Log> m=null;
 for (Log log: logLoader) {
 Class<? extends Log> c=log.getClass();
 try {
 m=c.getConstructor(String.class);
 break;
 }
 catch (NoSuchMethodException | SecurityException e) {
 throw new Error(e);
 }
 }
 discoveredLogConstructor=m;
 }

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

 // only those 2 methods need to change to use a different direct logger.

 /**
 * Construct (if necessary) and return a <code>Log</code> instance,
 * using the factory's current set of configuration attributes.
 *
 * NOTE - Depending upon the implementation of
 * the <code>LogFactory</code> you are using, the <code>Log</code>
 * instance you are returned may or may not be local to the current
 * application, and may or may not be returned again on a subsequent
 * call with the same name argument.
 *
 * @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)
 *
 * @return A log instance with the requested name
 *
 * @exception LogConfigurationException if a suitable <code>Log</code>
 * instance cannot be returned
 */
 public Log getInstance(String name) throws LogConfigurationException {
 if (discoveredLogConstructor == null) {
 return DirectJDKLog.getInstance(name);
 }

 try {
 return discoveredLogConstructor.newInstance(name);
 } catch (ReflectiveOperationException | IllegalArgumentException e) {
 throw new LogConfigurationException(e);
 }
 }

 /**
 * 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
 *
 * @return A log instance with a name of clazz.getName()
 *
 * @exception LogConfigurationException if a suitable <code>Log</code>
 * instance cannot be returned
 */
 public Log getInstance(Class<?> clazz) throws LogConfigurationException {
 return getInstance( clazz.getName());
 }

 // ------------------------------------------------------- Static Variables

 // --------------------------------------------------------- Static Methods

 /**
 * Construct (if necessary) and return a <code>LogFactory</code>
 * instance, using the following ordered lookup procedure to determine
 * the name of the implementation class to be loaded.
 * <ul>
 * <li>The <code>org.apache.commons.logging.LogFactory</code> system
 * property.</li>
 * <li>The JDK 1.3 Service Discovery mechanism</li>
 * <li>Use the properties file <code>commons-logging.properties</code>
 * file, if found in the class path of this class. The configuration
 * file is in standard <code>java.util.Properties</code> format and
 * contains the fully qualified name of the implementation class
 * with the key being the system property defined above.</li>
 * <li>Fall back to a default implementation class
 * (<code>org.apache.commons.logging.impl.LogFactoryImpl</code>).</li>
 * </ul>
 *
 * NOTE - If the properties file method of identifying the
 * <code>LogFactory</code> implementation class is utilized, all of the
 * properties defined in this file will be set as configuration attributes
 * on the corresponding <code>LogFactory</code> instance.
 *
 * @return The singleton LogFactory instance
 *
 * @exception LogConfigurationException if the implementation class is not
 * available or cannot be instantiated.
 */
 public static LogFactory getFactory() throws LogConfigurationException {
 return singleton;
 }

 /**
 * Convenience method to return a named logger, without the application
 * having to care about factories.
 *
 * @param clazz Class from which a log name will be derived
 *
 * @return A log instance with a name of clazz.getName()
 *
 * @exception LogConfigurationException if a suitable <code>Log</code>
 * instance cannot be returned
 */
 public static Log getLog(Class<?> clazz)
 throws LogConfigurationException {
 return getFactory().getInstance(clazz);
 }

 /**
 * Convenience method to return a named logger, without the application
 * having to care about factories.
 *
 * @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)
 *
 * @return A log instance with the requested name
 *
 * @exception LogConfigurationException if a suitable <code>Log</code>
 * instance cannot be returned
 */
 public static Log getLog(String name)
 throws LogConfigurationException {
 return getFactory().getInstance(name);
 }

 /**
 * Release any internal references to previously created {@link LogFactory}
 * instances that have been associated with the specified class loader
 * (if any), after calling the instance method <code>release()</code> on
 * each of them.
 *
 * @param classLoader ClassLoader for which to release the LogFactory
 */
 public static void release(ClassLoader classLoader) {
 // JULI's log manager looks at the current classLoader so there is no
 // need to use the passed in classLoader, the default implementation
 // does not so calling reset in that case will break things
 if (!LogManager.getLogManager().getClass().getName().equals(
 "java.util.logging.LogManager")) {
 LogManager.getLogManager().reset();
 }
 }
}

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