org.apache.commons.logging

Class AndroidLogFactory

java.lang.Object

org.apache.commons.logging.AndroidLogFactory

Direct Known Subclasses:

AndroidLogFactoryImpl

public abstract class AndroidLogFactory
extends 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.

Author:

Nicolas Dos Santos

Field Summary

Fields

Modifier and Type	Field and Description
static String	DIAGNOSTICS_DEST_PROPERTY The name (org.apache.commons.logging.diagnostics.dest) of the property used to enable internal commons-logging diagnostic output, in order to get information on what logging implementations are being discovered, what classloaders they are loaded through, etc.
protected static Map<ClassLoader,AndroidLogFactory>	factories The previously constructed AndroidLogFactory instances, keyed by the ClassLoader with which it was created.
static String	FACTORY_DEFAULT The fully qualified class name of the fallback AndroidLogFactory implementation class to use, if no other can be found.
static String	FACTORY_PROPERTIES The name (android-commons-logging.properties) of the properties file to search for.
static String	FACTORY_PROPERTY The name (org.apache.commons.logging.LogFactory) of the property used to identify the AndroidLogFactory implementation class name.
static String	PRIORITY_KEY The name (priority) of the key in the config file used to specify the priority of that particular config file.

Constructor Summary

Constructors

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

Method Summary

Methods

Modifier and Type	Method and Description
protected static Object	createFactory(String factoryClass, ClassLoader classLoader)
abstract Object	getAttribute(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.
protected static ClassLoader	getClassLoader(Class<?> clazz) Safely get access to the classloader for the specified class.
static AndroidLogFactory	getFactory() Construct (if necessary) and return a AndroidLogFactory instance, using the following ordered lookup procedure to determine the name of the implementation class to be loaded.
abstract Log	getInstance(Class<?> clazz) Convenience method to derive a name from the specified class and call getInstance(String) with it.
abstract 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.
protected static boolean	isDiagnosticsEnabled()
protected static void	logRawDiagnostic(String msg)
protected static AndroidLogFactory	newFactory(String factoryClass, ClassLoader classLoader) Return a new instance of the specified AndroidLogFactory implementation class, loaded by the specified class loader.
static String	objectId(Object o) Returns a string that uniquely identifies the specified object, including its class.
abstract 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 AndroidLogFactory 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 AndroidLogFactory instances, after calling the instance method release() on each of them.
abstract void	removeAttribute(String name) Remove any configuration attribute associated with the specified name.
abstract 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

PRIORITY_KEY

public static final String PRIORITY_KEY

The name (priority) of the key in the config file used to specify the priority of that particular config file. The associated value is a floating-point number; higher values take priority over lower values.

See Also:

Constant Field Values

FACTORY_PROPERTY

public static final String FACTORY_PROPERTY

The name (org.apache.commons.logging.LogFactory) of the property used to identify the AndroidLogFactory implementation class name. This can be used as a system property, or as an entry in a configuration properties file.

See Also:

Constant Field Values

FACTORY_DEFAULT

public static final String FACTORY_DEFAULT

The fully qualified class name of the fallback AndroidLogFactory 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 (android-commons-logging.properties) of the properties file to search for.

See Also:

Constant Field Values

DIAGNOSTICS_DEST_PROPERTY

public static final String DIAGNOSTICS_DEST_PROPERTY

The name (org.apache.commons.logging.diagnostics.dest) of the property used to enable internal commons-logging diagnostic output, in order to get information on what logging implementations are being discovered, what classloaders they are loaded through, etc.

If a system property of this name is set then the value is assumed to be the name of a file. The special strings STDOUT or STDERR (case-sensitive) indicate output to System.out and System.err respectively.

Diagnostic logging should be used only to debug problematic configurations and should not be set in normal production use.

See Also:

Constant Field Values

factories

protected static Map<ClassLoader,AndroidLogFactory> factories

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

Constructor Detail

AndroidLogFactory

protected AndroidLogFactory()

Protected constructor that is not available for public use.

Method Detail

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.

getInstance

public abstract 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

getInstance

public abstract 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 AndroidLogFactory 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 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

getFactory

public static AndroidLogFactory getFactory()
                                    throws LogConfigurationException

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

• The org.apache.commons.logging.AndroidLogFactory system property.
• The JDK 1.3 Service Discovery mechanism
• Use the properties file android-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.AndroidLogFactoryImpl).

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

NOTE - In a multithreaded environment it is possible that two different instances will be returned for the same classloader environment.

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 AndroidLogFactory 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 AndroidLogFactory

releaseAll

public static void releaseAll()

Release any internal references to previously created AndroidLogFactory 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.

getClassLoader

protected static ClassLoader getClassLoader(Class<?> clazz)

Safely get access to the classloader for the specified class.

Theoretically, calling getClassLoader can throw a security exception, and so should be done under an AccessController in order to provide maximum flexibility. However in practice people don't appear to use security policies that forbid getClassLoader calls. So for the moment all code is written to call this method rather than Class.getClassLoader, so that we could put AccessController stuff in this method without any disruption later if we need to.

Even when using an AccessController, however, this method can still throw SecurityException. Commons-logging basically relies on the ability to access classloaders, ie a policy that forbids all classloader access will also prevent commons-logging from working: currently this method will throw an exception preventing the entire app from starting up. Maybe it would be good to detect this situation and just disable all commons-logging? Not high priority though - as stated above, security policies that prevent classloader access aren't common.

Note that returning an object fetched via an AccessController would technically be a security flaw anyway; untrusted code that has access to a trusted JCL library could use it to fetch the classloader for a class even when forbidden to do so directly.

Since:

1.1

newFactory

protected static AndroidLogFactory newFactory(String factoryClass,
                           ClassLoader classLoader)
                                       throws LogConfigurationException

Return a new instance of the specified AndroidLogFactory implementation class, loaded by the specified class loader.

Parameters:

factoryClass - Fully qualified name of the AndroidLogFactory implementation class

classLoader - ClassLoader from which to load this class

contextClassLoader - is the context that this new factory will manage logging for.

Throws:

LogConfigurationException - if a suitable instance cannot be created

Since:

1.1

createFactory

protected static Object createFactory(String factoryClass,
                   ClassLoader classLoader)

isDiagnosticsEnabled

protected static boolean isDiagnosticsEnabled()

logRawDiagnostic

protected static final void logRawDiagnostic(String msg)

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.