org.apache.commons.logging

Class LogFactory

public abstract class LogFactory extends Object

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.

Version: $Revision: 1.27 $ $Date: 2004/06/06 21:15:12 $

Author: Craig R. McClanahan Costin Manolache Richard A. Sitze

Field Summary
protected static Hashtablefactories
The previously constructed LogFactory instances, keyed by the ClassLoader with which it was created.
static StringFACTORY_DEFAULT
The fully qualified class name of the fallback LogFactory implementation class to use, if no other can be found.
static StringFACTORY_PROPERTIES
The name of the properties file to search for.
static StringFACTORY_PROPERTY
The name of the property used to identify the LogFactory implementation class name.
protected static StringSERVICE_ID
Constructor Summary
protected LogFactory()
Protected constructor that is not available for public use.
Method Summary
static voidcacheFactory(ClassLoader classLoader, LogFactory factory)
abstract ObjectgetAttribute(String name)
Return the configuration attribute with the specified name (if any), or null if there is no such attribute.
abstract String[]getAttributeNames()
Return an array containing the names of all currently defined configuration attributes.
static LogFactorygetCachedFactory(ClassLoader contextClassLoader)
Check cached factories (keyed by contextClassLoader)
protected static ClassLoadergetContextClassLoader()
Return the thread context class loader if available.
static LogFactorygetFactory()

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.
abstract LoggetInstance(Class clazz)
Convenience method to derive a name from the specified class and call getInstance(String) with it.
abstract LoggetInstance(String name)

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.

static LoggetLog(Class clazz)
Convenience method to return a named logger, without the application having to care about factories.
static LoggetLog(String name)
Convenience method to return a named logger, without the application having to care about factories.
static InputStreamgetResourceAsStream(ClassLoader loader, String name)
protected static LogFactorynewFactory(String factoryClass, ClassLoader classLoader)
Return a new instance of the specified LogFactory implementation class, loaded by the specified class loader.
abstract voidrelease()
Release any internal references to previously created {@link Log} instances returned by this factory.
static voidrelease(ClassLoader classLoader)
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.
static voidreleaseAll()
Release any internal references to previously created {@link LogFactory} instances, after calling the instance method release() on each of them.
abstract voidremoveAttribute(String name)
Remove any configuration attribute associated with the specified name.
abstract voidsetAttribute(String name, Object value)
Set the configuration attribute with the specified name.

Field Detail

factories

protected static Hashtable factories
The previously constructed LogFactory instances, keyed by the ClassLoader with which it was created.

FACTORY_DEFAULT

public static final String FACTORY_DEFAULT
The fully qualified class name of the fallback LogFactory implementation class to use, if no other can be found.

FACTORY_PROPERTIES

public static final String FACTORY_PROPERTIES
The name of the properties file to search for.

FACTORY_PROPERTY

public static final String FACTORY_PROPERTY
The name of the property used to identify the LogFactory implementation class name.

SERVICE_ID

protected static final String SERVICE_ID
JDK1.3+ 'Service Provider' specification.

Constructor Detail

LogFactory

protected LogFactory()
Protected constructor that is not available for public use.

Method Detail

cacheFactory

private static void cacheFactory(ClassLoader classLoader, LogFactory factory)

getAttribute

public abstract Object getAttribute(String name)
Return the configuration attribute with the specified name (if any), or null if there is no such attribute.

Parameters: name Name of the attribute to return

getAttributeNames

public abstract String[] getAttributeNames()
Return an array containing the names of all currently defined configuration attributes. If there are no such attributes, a zero length array is returned.

getCachedFactory

private static LogFactory getCachedFactory(ClassLoader contextClassLoader)
Check cached factories (keyed by contextClassLoader)

getContextClassLoader

protected static ClassLoader getContextClassLoader()
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.

Throws: LogConfigurationException if a suitable class loader cannot be identified.

getFactory

public static LogFactory getFactory()

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.

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.

Throws: LogConfigurationException if the implementation class is not available or cannot be instantiated.

getInstance

public abstract Log getInstance(Class clazz)
Convenience method to derive a name from the specified class and call getInstance(String) with it.

Parameters: clazz Class for which a suitable Log name will be derived

Throws: LogConfigurationException if a suitable Log instance cannot be returned

getInstance

public abstract Log getInstance(String name)

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.

Parameters: 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)

Throws: LogConfigurationException if a suitable Log instance cannot be returned

getLog

public static Log getLog(Class clazz)
Convenience method to return a named logger, without the application having to care about factories.

Parameters: clazz Class from which a log name will be derived

Throws: LogConfigurationException if a suitable Log instance cannot be returned

getLog

public static Log getLog(String name)
Convenience method to return a named logger, without the application having to care about factories.

Parameters: 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)

Throws: LogConfigurationException if a suitable Log instance cannot be returned

getResourceAsStream

private static InputStream getResourceAsStream(ClassLoader loader, String name)

newFactory

protected static LogFactory newFactory(String factoryClass, ClassLoader classLoader)
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.

Parameters: factoryClass Fully qualified name of the LogFactory implementation class classLoader ClassLoader from which to load this class

Throws: LogConfigurationException if a suitable instance cannot be created

release

public abstract void release()
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.

release

public static void release(ClassLoader classLoader)
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.

Parameters: classLoader ClassLoader for which to release the LogFactory

releaseAll

public static void releaseAll()
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.

removeAttribute

public abstract void removeAttribute(String name)
Remove any configuration attribute associated with the specified name. If there is no such attribute, no action is taken.

Parameters: name Name of the attribute to remove

setAttribute

public abstract void setAttribute(String name, Object value)
Set the configuration attribute with the specified name. Calling this with a null value is equivalent to calling removeAttribute(name).

Parameters: name Name of the attribute to set value Value of the attribute to set, or null to remove any setting for this attribute

Copyright 2002-2004 The Apache Software Foundation.