Add a null logger implementation
--------------------------------
Key: LOG4NET-326
URL: https://issues.apache.org/jira/browse/LOG4NET-326
Project: Log4net
Issue Type: Improvement
Components: Core
Reporter: Carl Raymond
Priority: Minor
Please consider adding a null logger implementation to log4net. This would be
an implementation of ILog where all logging method do nothing and all
IsXxxEnabled methods return false. This supports Dependency Injection and unit
testing patterns. By providing a do-nothing implementation of ILog, it is
easier to move creation of a real logger via LogManager.GetLogger(...) outside
of the logging class, and into the DI container configuration. Because this
class is inherently thread-safe, a singleton is appropriate. Note that this
class would never be returned by LogManager.GetLogger(). It exists to serve as
a default value for a read/write property of type ILog.
Use case: A client project with class Thing that (optionally) logs has a
property of type ILog, where the default value of the property is the null
logger. The property can be set to another logger by the DI container in
production, or set to a mock ILog by a testing framework.
Code:
public class Thing
{
private ILog _myLogger = log4net.NullLogger.Instance;
public ILog MyLogger
{
get { return _messageLogger; }
set { _messageLogger = value; }
}
public SomeMethod()
{
// do some work...
MyLogger.Info("message");
}
}
The advantage of using a null logger as the property's default value is that
the logging class does not need to wrap all calls to the logger with null
checks.
In a unit testing situation, it is not necessary to activate log4net at all.
When the test at hand tests logging behavior, the test code would set the
property to a mock ILog implementation, which would then verify that the
appropriate method was called. Other tests not involving logging do not need
to set a value on the property.
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