org.apache.juli.logging

Class 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 arround 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: $Revision: 899141 $ $Date: 2010-01-14 11:12:25 +0100 (Thu, 14 Jan 2010) $

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

Field Summary
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.
static StringHASHTABLE_IMPLEMENTATION_PROPERTY

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

Method Summary
ObjectgetAttribute(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 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.
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.

LoggetInstance(Class clazz)
Convenience method to derive a name from the specified class and call getInstance(String) with it.
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 StringobjectId(Object o)
Returns a string that uniquely identifies the specified object, including its class.
voidrelease()
Release any internal references to previously created Log instances returned by this factory.
static voidrelease(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 voidreleaseAll()
Release any internal references to previously created LogFactory instances, after calling the instance method release() on each of them.
voidremoveAttribute(String name)
Remove any configuration attribute associated with the specified name.
voidsetAttribute(String name, Object value)
Set the configuration attribute with the specified name.

Field Detail

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.

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 scriplet:

  <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 ;)

Method Detail

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.

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 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

getInstance

public 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

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

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 overidden the toString method.

Parameters: o may be null.

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

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.

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.

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

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