Package org.apache.commons.logging

Class 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:1.3.4

    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 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 Description
      protected LogFactory()
      Constructs a new instance.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      Object getAttribute​(String name)
      Gets 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)
      Gets a Log for the given class.
      org.apache.commons.logging.Log getInstance​(String name)
      Gets a (possibly new) Log instance, using the factory's current set of configuration attributes.
      static org.apache.commons.logging.Log getLog​(Class<?> clazz)
      Gets a named logger, without the application having to care about factories.
      static org.apache.commons.logging.Log getLog​(String name)
      Gets 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 obj)
      Returns a string that uniquely identifies the specified object, including its class.
      void release()
      Releases any internal references to previously created Log instances returned by this factory.
      static void release​(ClassLoader classLoader)
      Releases 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)
      Removes 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)  

    • 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

      • 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 hash table 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 hash tables don't allow null as a key.

    • Constructor Detail

      • LogFactory

        protected LogFactory()
        Constructs a new instance.

    • 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 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:
        org.apache.commons.logging.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
        Gets 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:
        org.apache.commons.logging.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
        Gets 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:
        org.apache.commons.logging.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 obj)
        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:
        obj - may be null.
        Returns:
        a string of form className@hashCode, or "null" if obj is null.
        Since:
        1.1

      • release

        public static void release​(ClassLoader classLoader)
        Releases 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)
        Gets 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
        Gets a Log for the given class.
        Parameters:
        clazz - Class for which a suitable Log name will be derived
        Returns:
        a name from the specified class.
        Throws:
        org.apache.commons.logging.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
        Gets a (possibly new) 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:
        org.apache.commons.logging.LogConfigurationException - if a suitable Log instance cannot be returned

      • release

        public void release()
        Releases 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)
        Removes 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