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/*
 * 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;


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Properties;


/**
 * 

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 * @version $Revision: 1.27 $ $Date: 2004/06/06 21:15:12 $ */ public abstract class LogFactory { // ----------------------------------------------------- Manifest Constants /** * The name of the property used to identify the LogFactory implementation * class name. */ public static final String FACTORY_PROPERTY = "org.apache.commons.logging.LogFactory"; /** * The fully qualified class name of the fallback LogFactory * implementation class to use, if no other can be found. */ public static final String FACTORY_DEFAULT = "org.apache.commons.logging.impl.LogFactoryImpl"; /** * The name of the properties file to search for. */ public static final String FACTORY_PROPERTIES = "commons-logging.properties"; /** * JDK1.3+ * 'Service Provider' specification. * */ protected static final String SERVICE_ID = "META-INF/services/org.apache.commons.logging.LogFactory"; // ----------------------------------------------------------- Constructors /** * Protected constructor that is not available for public use. */ protected LogFactory() { } // --------------------------------------------------------- Public Methods /** * Return the configuration attribute with the specified name (if any), * or null if there is no such attribute. * * @param name Name of the attribute to return */ public abstract Object getAttribute(String 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. */ public abstract String[] getAttributeNames(); /** * Convenience method to derive a name from the specified class and * call getInstance(String) with it. * * @param clazz Class for which a suitable Log name will be derived * * @exception LogConfigurationException if a suitable Log * instance cannot be returned */ public abstract Log getInstance(Class clazz) throws LogConfigurationException; /** *

Construct (if necessary) and return a Log instance, * using the factory's current set of configuration attributes.

* *

NOTE - Depending upon the implementation of * the LogFactory you are using, the Log * 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 Log 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 Log * instance cannot be returned */ public abstract Log getInstance(String name) throws LogConfigurationException; /** * Release any internal references to previously created {@link 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 abstract void release(); /** * 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 abstract void removeAttribute(String name); /** * Set the configuration attribute with the specified name. Calling * this with a null value is equivalent to calling * removeAttribute(name). * * @param name Name of the attribute to set * @param value Value of the attribute to set, or null * to remove any setting for this attribute */ public abstract void setAttribute(String name, Object value); // ------------------------------------------------------- Static Variables /** * The previously constructed LogFactory instances, keyed by * the ClassLoader with which it was created. */ protected static Hashtable factories = new Hashtable(); // --------------------------------------------------------- Static Methods /** *

Construct (if necessary) and return a LogFactory * instance, using the following ordered lookup procedure to determine * the name of the implementation class to be loaded.

*
    *
  • The org.apache.commons.logging.LogFactory system * property.
  • *
  • The JDK 1.3 Service Discovery mechanism
  • *
  • Use the properties file commons-logging.properties * file, if found in the class path of this class. The configuration * file is in standard java.util.Properties format and * contains the fully qualified name of the implementation class * with the key being the system property defined above.
  • *
  • Fall back to a default implementation class * (org.apache.commons.logging.impl.LogFactoryImpl).
  • *
* *

NOTE - If the properties file method of identifying the * LogFactory implementation class is utilized, all of the * properties defined in this file will be set as configuration attributes * on the corresponding LogFactory instance.

* * @exception LogConfigurationException if the implementation class is not * available or cannot be instantiated. */ public static LogFactory getFactory() throws LogConfigurationException { // Identify the class loader we will be using ClassLoader contextClassLoader = (ClassLoader)AccessController.doPrivileged( new PrivilegedAction() { public Object run() { return getContextClassLoader(); } }); // Return any previously registered factory for this class loader LogFactory factory = getCachedFactory(contextClassLoader); if (factory != null) return factory; // Load properties file. // Will be used one way or another in the end. Properties props=null; try { InputStream stream = getResourceAsStream(contextClassLoader, FACTORY_PROPERTIES); if (stream != null) { props = new Properties(); props.load(stream); stream.close(); } } catch (IOException e) { } catch (SecurityException e) { } // First, try the system property try { String factoryClass = System.getProperty(FACTORY_PROPERTY); if (factoryClass != null) { factory = newFactory(factoryClass, contextClassLoader); } } catch (SecurityException e) { ; // ignore } // Second, try to find a service by using the JDK1.3 jar // discovery mechanism. This will allow users to plug a logger // by just placing it in the lib/ directory of the webapp ( or in // CLASSPATH or equivalent ). This is similar to the second // step, except that it uses the (standard?) jdk1.3 location in the jar. if (factory == null) { try { InputStream is = getResourceAsStream(contextClassLoader, SERVICE_ID); if( is != null ) { // This code is needed by EBCDIC and other strange systems. // It's a fix for bugs reported in xerces BufferedReader rd; try { rd = new BufferedReader(new InputStreamReader(is, "UTF-8")); } catch (java.io.UnsupportedEncodingException e) { rd = new BufferedReader(new InputStreamReader(is)); } String factoryClassName = rd.readLine(); rd.close(); if (factoryClassName != null && ! "".equals(factoryClassName)) { factory= newFactory( factoryClassName, contextClassLoader ); } } } catch( Exception ex ) { ; } } // Third try a properties file. // If the properties file exists, it'll be read and the properties // used. IMHO ( costin ) System property and JDK1.3 jar service // should be enough for detecting the class name. The properties // should be used to set the attributes ( which may be specific to // the webapp, even if a default logger is set at JVM level by a // system property ) if (factory == null && props != null) { String factoryClass = props.getProperty(FACTORY_PROPERTY); if (factoryClass != null) { factory = newFactory(factoryClass, contextClassLoader); } } // Fourth, try the fallback implementation class if (factory == null) { factory = newFactory(FACTORY_DEFAULT, LogFactory.class.getClassLoader()); } if (factory != null) { /** * Always cache using context class loader. */ cacheFactory(contextClassLoader, factory); if( props!=null ) { Enumeration names = props.propertyNames(); while (names.hasMoreElements()) { String name = (String) names.nextElement(); String value = props.getProperty(name); factory.setAttribute(name, value); } } } return factory; } /** * 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 * * @exception LogConfigurationException if a suitable Log * 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 Log 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 Log * 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 release() on * each of them. * * @param classLoader ClassLoader for which to release the LogFactory */ public static void release(ClassLoader classLoader) { synchronized (factories) { LogFactory factory = (LogFactory) factories.get(classLoader); if (factory != null) { factory.release(); factories.remove(classLoader); } } } /** * Release any internal references to previously created {@link LogFactory} * instances, after calling the instance method release() on * each of them. 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 static void releaseAll() { synchronized (factories) { Enumeration elements = factories.elements(); while (elements.hasMoreElements()) { LogFactory element = (LogFactory) elements.nextElement(); element.release(); } factories.clear(); } } // ------------------------------------------------------ Protected Methods /** * Return the thread context class loader if available. * Otherwise return null. * * The thread context class loader is available for JDK 1.2 * or later, if certain security conditions are met. * * @exception LogConfigurationException if a suitable class loader * cannot be identified. */ protected static ClassLoader getContextClassLoader() throws LogConfigurationException { ClassLoader classLoader = null; try { // Are we running on a JDK 1.2 or later system? Method method = Thread.class.getMethod("getContextClassLoader", null); // Get the thread context class loader (if there is one) try { classLoader = (ClassLoader)method.invoke(Thread.currentThread(), null); } catch (IllegalAccessException e) { throw new LogConfigurationException ("Unexpected IllegalAccessException", e); } catch (InvocationTargetException e) { /** * InvocationTargetException is thrown by 'invoke' when * the method being invoked (getContextClassLoader) throws * an exception. * * getContextClassLoader() throws SecurityException when * the context class loader isn't an ancestor of the * calling class's class loader, or if security * permissions are restricted. * * In the first case (not related), we want to ignore and * keep going. We cannot help but also ignore the second * with the logic below, but other calls elsewhere (to * obtain a class loader) will trigger this exception where * we can make a distinction. */ if (e.getTargetException() instanceof SecurityException) { ; // ignore } else { // Capture 'e.getTargetException()' exception for details // alternate: log 'e.getTargetException()', and pass back 'e'. throw new LogConfigurationException ("Unexpected InvocationTargetException", e.getTargetException()); } } } catch (NoSuchMethodException e) { // Assume we are running on JDK 1.1 classLoader = LogFactory.class.getClassLoader(); } // Return the selected class loader return classLoader; } /** * Check cached factories (keyed by contextClassLoader) */ private static LogFactory getCachedFactory(ClassLoader contextClassLoader) { LogFactory factory = null; if (contextClassLoader != null) factory = (LogFactory) factories.get(contextClassLoader); return factory; } private static void cacheFactory(ClassLoader classLoader, LogFactory factory) { if (classLoader != null && factory != null) factories.put(classLoader, factory); } /** * Return a new instance of the specified LogFactory * implementation class, loaded by the specified class loader. * If that fails, try the class loader used to load this * (abstract) LogFactory. * * @param factoryClass Fully qualified name of the LogFactory * implementation class * @param classLoader ClassLoader from which to load this class * * @exception LogConfigurationException if a suitable instance * cannot be created */ protected static LogFactory newFactory(final String factoryClass, final ClassLoader classLoader) throws LogConfigurationException { Object result = AccessController.doPrivileged( new PrivilegedAction() { public Object run() { // This will be used to diagnose bad configurations // and allow a useful message to be sent to the user Class logFactoryClass = null; try { if (classLoader != null) { try { // First the given class loader param (thread class loader) // Warning: must typecast here & allow exception // to be generated/caught & recast properly. logFactoryClass = classLoader.loadClass(factoryClass); return (LogFactory) logFactoryClass.newInstance(); } catch (ClassNotFoundException ex) { if (classLoader == LogFactory.class.getClassLoader()) { // Nothing more to try, onwards. throw ex; } // ignore exception, continue } catch (NoClassDefFoundError e) { if (classLoader == LogFactory.class.getClassLoader()) { // Nothing more to try, onwards. throw e; } } catch(ClassCastException e){ if (classLoader == LogFactory.class.getClassLoader()) { // Nothing more to try, onwards (bug in loader implementation). throw e; } } // Ignore exception, continue } /* At this point, either classLoader == null, OR * classLoader was unable to load factoryClass. * Try the class loader that loaded this class: * LogFactory.getClassLoader(). * * Notes: * a) LogFactory.class.getClassLoader() may return 'null' * if LogFactory is loaded by the bootstrap classloader. * b) The Java endorsed library mechanism is instead * Class.forName(factoryClass); */ // Warning: must typecast here & allow exception // to be generated/caught & recast properly. logFactoryClass = Class.forName(factoryClass); return (LogFactory) logFactoryClass.newInstance(); } catch (Exception e) { // Check to see if we've got a bad configuration if (logFactoryClass != null && !LogFactory.class.isAssignableFrom(logFactoryClass)) { return new LogConfigurationException( "The chosen LogFactory implementation does not extend LogFactory." + " Please check your configuration.", e); } return new LogConfigurationException(e); } } }); if (result instanceof LogConfigurationException) throw (LogConfigurationException)result; return (LogFactory)result; } private static InputStream getResourceAsStream(final ClassLoader loader, final String name) { return (InputStream)AccessController.doPrivileged( new PrivilegedAction() { public Object run() { if (loader != null) { return loader.getResourceAsStream(name); } else { return ClassLoader.getSystemResourceAsStream(name); } } }); } }


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