Differences to Log4j

The following fundamental differences exist between Log4Qt and Log4j:

• As a JAVA package Log4j does not have to manage object ownership and lifetime in the same way then it is required in C++. For details on how object ownership is handled see Object ownership.
• The package uses itself for its internal logging similar to Log4j 1.3. For details see Logging within the package.
• The configuration using system properties was replaced with a combination of environment variables and application settings. For details see Environment Variables.
• Custom levels are not supported.
• Multiple Logger Repositories are not supported

The following classes have been changed:

• AppenderSkeleton
  • The procedure of checking, if logging is possible, originally used by WriterAppender was generalised and is used in AppenderSkeleton and derived classes (checkEntryConditions()).
  • The doAppend() member function will check the entry conditions by calling the sub-class specific checkEntryConditions(). If successful the sub-class specific append() function is called.

• Configurator
  • Configure functions return a boolean indicating, if the configuration was successful.
  • Configure errors are accessible over ConfiguratorHelper::configureError().
  • Watching for configuration file changes is a function performed centrally by the ConfiguratorHelper. The class provides signals to notify on configuration change and errors.
  • The class PropertyConfigurator was extended to be able to read configuration data from a QSettings object.

• Level
  • A new value Level::NULL_INT was introduced to indicate there is no level set.

• Logger
  • The method isEnabledFor() does also take the repository threshold into account.
  • Several overloaded convenience member function are available to log messages with arguments of different types.
  • Two macros, LOG4QT_DECLARE_STATIC_LOGGER and LOG4QT_DECLARE_QCLASS_LOGGER, allows retrieving and caching of a pointer to a logger object.

• LogManager
  • A QtMessage handler can be installed via setHandleQtMessages(), to redirect all messages created by calls to qDebug(), qWarning(), qCritical() and qFatal() to a logger. The logger is named Qt and can be accessed using qtLogger().
  • The initialisation procedure is available over a public method (startup()).
  • The LogManager provides access to the logger used internally by the package (logLogger()) and to its default initialisation procedure (configureLogLogger()).

• WriterAppender
  • The class will call handleIoErrors() after all I/O operations. Sub-classes should re-implement the function to handle errors.

The following classes have been added:

• An additional appender class, DebugAppender, was added. The class appends logging events to the platform specific debug output.
• Various helper class have been introduced:
  • ClassLogger: The class ClassLogger provides logging for a QObject derived class.
  • ConfiguratorHelper: The class ConfiguratorHelper provides a configuration file watch and last error for configurator classes.
  • DateTime: The class DateTime provides extended functionality for QDateTime.
  • LogError: The class LogError represents an error.
  • Factory: The class Factory provides factories for Appender, Filter and Layout objects.
  • InitialisationHelper: The class InitialisationHelper performs static initialisation tasks.
  • LogObject: The class LogObject is the common base class for many classes in the package.
  • LogObjectPtr: The class LogObjectPtr implements automatic reference counting for LogObject objects.
  • PatternFormatter: The class PatternFormatter formats a logging event based on a pattern string.
  • Properties: The class Properties implements a JAVA property hash.