org.apache.juli.logging
Class LogFactory

java.lang.Object
  org.apache.juli.logging.LogFactory

public class LogFactory
extends Object

Modified LogFactory: removed all discovery, hardcode a specific implementation If you like a different logging implementation - use either the discovery-based commons-logging, or better - another implementation hardcoded to your favourite logging impl. Why ? Each application and deployment can choose a logging implementation - that involves configuration, installing the logger jar and optional plugins, etc. As part of this process - they can as well install the commons-logging implementation that corresponds to their logger of choice. This completely avoids any discovery problem, while still allowing the user to switch. 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 - and provides no plugin for other LogFactory implementation - 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 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:

$Id: LogFactory.java 1050504 2010-12-17 22:09:28Z markt $

Author:

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

Field Summary

static String	FACTORY_DEFAULT The fully qualified class name of the fallback LogFactory implementation class to use, if no other can be found.
static String	FACTORY_PROPERTIES The name of the properties file to search for.
static String	FACTORY_PROPERTY The name of the property used to identify the LogFactory implementation class name.
static String	HASHTABLE_IMPLEMENTATION_PROPERTY Setting this system property value allows the Hashtable used to store classloaders to be substituted by an alternative implementation.

Method Summary

Object	getAttribute(String name) Return the configuration attribute with the specified name (if any), or null if there is no such attribute.
String[]	getAttributeNames() Return an array containing the names of all currently defined configuration attributes.
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.
Log	getInstance(Class<?> clazz) Convenience method to derive a name from the specified class and call getInstance(String) with it.
Log	getInstance(String name) Construct (if necessary) and return a Log instance, using the factory's current set of configuration attributes.
static Log	getLog(Class<?> clazz) Convenience method to return a named logger, without the application having to care about factories.
static Log	getLog(String name) Convenience method to return a named logger, without the application having to care about factories.
static String	objectId(Object o) Returns a string that uniquely identifies the specified object, including its class.
void	release() Release any internal references to previously created Log instances returned by this factory.
static void	release(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.
void	removeAttribute(String name) Remove any configuration attribute associated with the specified name.
void	setAttribute(String name, 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 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 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 String FACTORY_PROPERTIES

The name of the properties file to search for.

See Also:

Constant Field Values

HASHTABLE_IMPLEMENTATION_PROPERTY

public static final String HASHTABLE_IMPLEMENTATION_PROPERTY

Setting this system property value allows the Hashtable used to store classloaders to be substituted by an alternative implementation.

Note: LogFactory will print:

 [ERROR] LogFactory: Load of custom hashtable failed
 

to system error and then continue using a standard Hashtable.

Usage: Set this property when Java is invoked and LogFactory will attempt to load a new instance of the given implementation class. For example, running the following ant scriptlet:

  <java classname="${test.runner}" fork="yes" failonerror="${test.failonerror}">
     ...
     <sysproperty 
        key="org.apache.commons.logging.LogFactory.HashtableImpl"
        value="org.apache.commons.logging.AltHashtable"/>
  </java>
 

will mean that LogFactory will load an instance of org.apache.commons.logging.AltHashtable.

A typical use case is to allow a custom Hashtable implementation using weak references to be substituted. This will allow classloaders to be garbage collected without the need to release them (on 1.3+ JVMs only, of course ;)

See Also:

Constant Field Values

Method Detail

getInstance

public Log getInstance(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 void release()

Release any internal references to previously created 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.

getAttribute

public 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 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.

removeAttribute

public 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 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

getInstance

public Log getInstance(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

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(Class<?> clazz)
                  throws LogConfigurationException

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)
                  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(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 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.

objectId

public static String objectId(Object o)

Returns a string that uniquely identifies the specified object, including its class.

The returned string is of form "classname@hashcode", ie is the same as the return value of the Object.toString() method, but works even when the specified object's class has overridden the toString method.

Parameters:

o - may be null.

Returns:

a string of form classname@hashcode, or "null" if param o is null.