org.apache.commons.logging

Class LogFactory

java.lang.Object

org.apache.commons.logging.LogFactory

public abstract class LogFactory
extends java.lang.Object

Factory for creating 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: 1.21 $ $Date: 2003/03/30 23:42:36 $

Author:

Craig R. McClanahan, Costin Manolache, Richard A. Sitze

Field Summary

Fields

Modifier and Type	Field and Description
protected static java.util.Hashtable	factories The previously constructed LogFactory instances, keyed by the ClassLoader with which it was created.
static java.lang.String	FACTORY_DEFAULT The fully qualified class name of the fallback LogFactory implementation class to use, if no other can be found.
static java.lang.String	FACTORY_PROPERTIES The name of the properties file to search for.
static java.lang.String	FACTORY_PROPERTY The name of the property used to identify the LogFactory implementation class name.
protected static java.lang.String	SERVICE_ID JDK1.3+ 'Service Provider' specification ( http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html )

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	LogFactory() Protected constructor that is not available for public use.

Method Summary

Methods

Modifier and Type	Method and Description
abstract java.lang.Object	getAttribute(java.lang.String name) Return the configuration attribute with the specified name (if any), or null if there is no such attribute.
abstract java.lang.String[]	getAttributeNames() Return an array containing the names of all currently defined configuration attributes.
protected static java.lang.ClassLoader	getContextClassLoader() Return the thread context class loader if available.
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.
abstract Log	getInstance(java.lang.Class clazz) Convenience method to derive a name from the specified class and call getInstance(String) with it.
abstract Log	getInstance(java.lang.String name) Construct (if necessary) and return a Log instance, using the factory's current set of configuration attributes.
static Log	getLog(java.lang.Class clazz) Convenience method to return a named logger, without the application having to care about factories.
static Log	getLog(java.lang.String name) Convenience method to return a named logger, without the application having to care about factories.
protected static LogFactory	newFactory(java.lang.String factoryClass, java.lang.ClassLoader classLoader) Return a new instance of the specified LogFactory implementation class, loaded by the specified class loader.
abstract void	release() Release any internal references to previously created Log instances returned by this factory.
static void	release(java.lang.ClassLoader classLoader) Release any internal references to previously created LogFactory instances that have been associated with the specified class loader (if any), after calling the instance method release() on each of them.
static void	releaseAll() Release any internal references to previously created LogFactory instances, after calling the instance method release() on each of them.
abstract void	removeAttribute(java.lang.String name) Remove any configuration attribute associated with the specified name.
abstract void	setAttribute(java.lang.String name, java.lang.Object value) Set the configuration attribute with the specified name.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

FACTORY_PROPERTY

public static final java.lang.String FACTORY_PROPERTY

The name of the property used to identify the LogFactory implementation class name.

See Also:

Constant Field Values

FACTORY_DEFAULT

public static final java.lang.String FACTORY_DEFAULT

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

See Also:

Constant Field Values

FACTORY_PROPERTIES

public static final java.lang.String FACTORY_PROPERTIES

The name of the properties file to search for.

See Also:

Constant Field Values

SERVICE_ID

protected static final java.lang.String SERVICE_ID

JDK1.3+ 'Service Provider' specification ( http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html )

See Also:

Constant Field Values

factories

protected static java.util.Hashtable factories

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

Constructor Detail

LogFactory

protected LogFactory()

Protected constructor that is not available for public use.

Method Detail

getAttribute

public abstract java.lang.Object getAttribute(java.lang.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 java.lang.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.

getInstance

public abstract Log getInstance(java.lang.Class clazz)
                         throws LogConfigurationException

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(java.lang.String name)
                         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.

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

release

public abstract void release()

Release any internal references to previously created Log instances returned by this factory. This is useful 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(java.lang.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(java.lang.String name,
                java.lang.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

getFactory

public static LogFactory getFactory()
                             throws LogConfigurationException

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.

Throws:

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

getLog

public static Log getLog(java.lang.Class clazz)
                  throws LogConfigurationException

Convenience method to return a named logger, without the application having to care about factories.

Parameters:

clazz - Class for which a log name will be derived

Throws:

LogConfigurationException - if a suitable Log instance cannot be returned

getLog

public static Log getLog(java.lang.String name)
                  throws LogConfigurationException

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

release

public static void release(java.lang.ClassLoader classLoader)

Release any internal references to previously created 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 LogFactory instances, after calling the instance method release() on each of them. This is useful 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.

getContextClassLoader

protected static java.lang.ClassLoader getContextClassLoader()
                                                      throws LogConfigurationException

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.

newFactory

protected static LogFactory newFactory(java.lang.String factoryClass,
                    java.lang.ClassLoader classLoader)
                                throws LogConfigurationException

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