LogFactory (OPS4J Pax Logging

java.lang.Object
- org.apache.commons.logging.LogFactory

```
public class LogFactory
extends Object
```
Factory for creating Log instances, with discovery and configuration features similar to that employed by standard Java APIs such as JAXP.
This is an adaptation of the Jakarta Commons Logging API for OSGi usage.
This is the only class from org.apache.commons.logging package that is adjusted. Other commons-logging classes are simply repackaged from original jar.
There's no need for discovery code that's constituting most of original version's functionality.
Original org.apache.commons.logging.LogFactory is abstract. In pax-logging-api, this class is concrete. All public methods and fields are preserved. Unnecessary private and protected methods and fields are removed.
pax-logging-api used source from commons-logging:commons-logging:1.3.0

Author:

Niclas Hedhman (responsible for the OSGi adaptation.), Craig R. McClanahan, Costin Manolache, Richard A. Sitze, Grzegorz Grzybek (adjustments and code cleanup)

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 class loaders they are loaded through, etc.
`protected static Hashtable<ClassLoader,LogFactory>`	`factories` The previously constructed `LogFactory` instances, keyed by the `ClassLoader` with which it was created.
`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 (`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 LogFactory implementation class name.
`static String`	`HASHTABLE_IMPLEMENTATION_PROPERTY` Setting this system property (`org.apache.commons.logging.LogFactory.HashtableImpl`) value allows the `Hashtable` used to store class loaders to be substituted by an alternative implementation.
`protected static LogFactory`	`nullClassLoaderFactory` Deprecated. since 1.1.2
`static String`	`PRIORITY_KEY` The name (`priority`) of the key in the configuration file used to specify the priority of that particular configuration file.
`protected static String`	`SERVICE_ID` JDK 1.3+ 'Service Provider' specification.
`static String`	`TCCL_KEY` The name (`use_tccl`) of the key in the configuration file used to specify whether logging classes should be loaded via the thread context class loader (TCCL), or not.

Constructor Summary

Constructors
Modifier Constructor and Description

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

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

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`Object`	`getAttribute(String name)` Return the configuration attribute with the specified name (if any), or `null` if there is no such attribute.
`String[]`	`getAttributeNames()` Gets an array containing the names of all currently defined configuration attributes.
`protected static ClassLoader`	`getClassLoader(Class<?> clazz)` Safely get access to the class loader for the specified class.
`static LogFactory`	`getFactory()` Opposite to original `LogFactory.getFactory`, simply preinstantiated factory is returned.
`org.apache.commons.logging.Log`	`getInstance(Class<?> clazz)` Convenience method to derive a name from the specified class and call `getInstance(String)` with it.
`org.apache.commons.logging.Log`	`getInstance(String name)` Constructs (if necessary) and return a `Log` instance, using the factory's current set of configuration attributes.
`static org.apache.commons.logging.Log`	`getLog(Class<?> clazz)` Convenience method to return a named logger, without the application having to care about factories.
`static org.apache.commons.logging.Log`	`getLog(String name)` Convenience method to return a named logger, without the application having to care about factories.
`protected static void`	`handleThrowable(Throwable t)` Checks whether the supplied Throwable is one that needs to be re-thrown and ignores all others.
`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)` Sets the configuration attribute with the specified name.
`static void`	`setPaxLoggingManager(PaxLoggingManager manager)`

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 configuration file used to specify the priority of that particular configuration file. The associated value is a floating-point number; higher values take priority over lower values.
    
    See Also:
    
    Constant Field Values
  - TCCL_KEY
```
public static final String TCCL_KEY
```
    The name (use_tccl) of the key in the configuration file used to specify whether logging classes should be loaded via the thread context class loader (TCCL), or not. By default, the TCCL is used.
    
    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 LogFactory 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 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 (commons-logging.properties) of the properties file to search for.
    
    See Also:
    
    Constant Field Values
  - SERVICE_ID
```
protected static final String SERVICE_ID
```
    JDK 1.3+ 'Service Provider' specification.
    
    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 class loaders 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
  - HASHTABLE_IMPLEMENTATION_PROPERTY
```
public static final String HASHTABLE_IMPLEMENTATION_PROPERTY
```
    Setting this system property (org.apache.commons.logging.LogFactory.HashtableImpl) value allows the Hashtable used to store class loaders 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 class loaders to be garbage collected without the need to release them (on 1.3+ JVMs only, of course ;).
    See Also:
    
    Constant Field Values
  - factories
```
protected static Hashtable<ClassLoader,LogFactory> factories
```
    The previously constructed LogFactory instances, keyed by the ClassLoader with which it was created.
  - nullClassLoaderFactory
```
@Deprecated
protected static volatile LogFactory nullClassLoaderFactory
```
    Deprecated. since 1.1.2
    Previously constructed LogFactory instance as in the factories map, but for the case where getClassLoader returns null. This can happen when:
    - using JDK1.1 and the calling code is loaded via the system class loader (very common)
    - using JDK1.2+ and the calling code is loaded via the boot class loader (only likely for embedded systems work).
    Note that factories is a Hashtable (not a HashMap), and hashtables don't allow null as a key.
- Constructor Detail
  - LogFactory
```
protected LogFactory()
```
    Protected constructor that is not available for public use.
- Method Detail
  - setPaxLoggingManager
```
public static void setPaxLoggingManager(PaxLoggingManager manager)
```
  - getClassLoader
```
protected static ClassLoader getClassLoader(Class<?> clazz)
```
    Safely get access to the class loader 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 class loaders. A policy that forbids all class loader 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 class loader 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 class loader for a class even when forbidden to do so directly.
    
    Parameters:
    
    clazz - Class.
    
    Returns:
    
    a ClassLoader.
    
    Since:
    
    1.1
  - getFactory
```
public static LogFactory getFactory()
                             throws org.apache.commons.logging.LogConfigurationException
```
    Opposite to original LogFactory.getFactory, simply preinstantiated factory is returned. No discovery is performed at all. Constructs (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.
    
    NOTE - In a multi-threaded environment it is possible that two different instances will be returned for the same class loader environment.
    Returns:
    
    a LogFactory.
    
    Throws:
    
    LogConfigurationException - if the implementation class is not available or cannot be instantiated.
  - getLog
```
public static org.apache.commons.logging.Log getLog(Class<?> clazz)
                                             throws org.apache.commons.logging.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
    
    Returns:
    
    a named logger.
    
    Throws:
    
    LogConfigurationException - if a suitable Log instance cannot be returned
  - getLog
```
public static org.apache.commons.logging.Log getLog(String name)
                                             throws org.apache.commons.logging.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)
    
    Returns:
    
    a named logger.
    
    Throws:
    
    LogConfigurationException - if a suitable Log instance cannot be returned
  - handleThrowable
```
protected static void handleThrowable(Throwable t)
```
    Checks whether the supplied Throwable is one that needs to be re-thrown and ignores all others. The following errors are re-thrown:
    - ThreadDeath
    - VirtualMachineError
    Parameters:
    
    t - the Throwable to check
  - 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", that is, 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.
    
    Since:
    
    1.1
  - 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.
  - 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
    
    Returns:
    
    the configuration attribute with the specified name.
  - getAttributeNames
```
public String[] getAttributeNames()
```
    Gets an array containing the names of all currently defined configuration attributes. If there are no such attributes, a zero length array is returned.
    
    Returns:
    
    an array containing the names of all currently defined configuration attributes
  - getInstance
```
public org.apache.commons.logging.Log getInstance(Class<?> clazz)
                                           throws org.apache.commons.logging.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
    
    Returns:
    
    a name from the specified class.
    
    Throws:
    
    LogConfigurationException - if a suitable Log instance cannot be returned
  - getInstance
```
public org.apache.commons.logging.Log getInstance(String name)
                                           throws org.apache.commons.logging.LogConfigurationException
```
    Constructs (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.
    
    In pax-logging, loggers are obtained from current or fallback PaxLoggingManager
    
    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)
    
    Returns:
    
    a Log instance.
    
    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.
  - 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)
```
    Sets 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

Class LogFactory

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

PRIORITY_KEY

TCCL_KEY

FACTORY_PROPERTY

FACTORY_DEFAULT

FACTORY_PROPERTIES

SERVICE_ID

DIAGNOSTICS_DEST_PROPERTY

HASHTABLE_IMPLEMENTATION_PROPERTY

factories

nullClassLoaderFactory

Constructor Detail

LogFactory

Method Detail

setPaxLoggingManager

getClassLoader

getFactory

getLog

getLog

handleThrowable

objectId

release

releaseAll

getAttribute

getAttributeNames

getInstance

getInstance

release

removeAttribute

setAttribute