Log4Net- A Closer Look

Introduction

About Log4Net

Features of Log4Net.

License As Provided by Apache.

A Quick Example

• Open Visual Studio and create a new Console application project.


• Add to the project a reference to the \bin\net\2.0\release\log4net.dll assembly
  in the log4net distribution.


• Modify your Main() method like so:
  
  

   
  class Program 
  { 
  static void Main( string[] args )
   { 
  log4net.Config.BasicConfigurator.Configure();
              log4net.ILog logger = log4net.LogManager.GetLogger( typeof( Program ) ); 
  logger.Debug("Debug Example" );
  logger.Info( "Info Example" ); 
  logger.Warn( "Warning Example"); 
  logger.Error( "Error Example" ); 
  logger.Fatal( "Fatal Example" ); 
  Console.ReadLine();
              } } 

The Structure of log4net

Log4net is built using the layered approach, with five main components inside of
the framework.

Logger

Logger is the main component with which your application interacts. It is the basic
component that generates the log messages. Logger provides different methods to
log any message. The framework defines an interface called ILog which can be implemented
to create custom loggers of you own.

public interface ILog
        

        {

        void Debug(object message);
        

        void Info(object message);
        

        void Warn(object message);
        

        void Error(object message);

        void Fatal(ob /* There are overloads for all of the above methods which supports
        exceptions. Each overload in that case takes an addition parameter of type Exception
        like the one below.*/

        void Debug(object message, Exception ex);

        /* The Boolean properties are used to check the Logger's level (as we'll see Logging
        Levels in the next section) */

        bool isDebugEnabled;
        

        bool isInfoEnabled;
        

        // other boolean properties for each method }

Logging Levels

Appender

Appender is an object that persists your log messages someplace. Different
Appenders are available in the framework that relays the output to different
output streams. For e.g. log4net.Appender.ConsoleAppender appends logging events to the console. Framework contains almost all appenders you will need Easy to write your own Multiple appenders can be attached to each logger Each appender can receive logs from multiple loggers

List of Appenders

AdoNetAppender

AnsiColorTerminalAppender

AspNetTraceAppender

BufferingForwardingAppender

ColoredConsoleAppender

ConsoleAppender

DebugAppender

EventLogAppender

ForwardingAppender

FileAppender

LocalSyslogAppender

MemoryAppender

NetSendAppender

OutputDebugStringAppender

RemoteSyslogAppender

RemotingAppender

RollingFileAppender

SmtpAppender

SmtpPickupDirAppender

TelnetAppender

TraceAppender

UdpAppender

Layout

The Layout component is used to display the final formatted output to the user.
Output can be shown in multiple formats, depending upon the layout. Layout can be
linear or an XML file. Works with an appender. There is a list of different layouts
in the API documentation. You cannot use Multiple layouts cannot be used with an
appender. Inherit the log4net.Layout.LayoutSkeleton class, which implements the
ILayout interface to create your own layout. Commonly used layout is "Patternlayout".

Object Renderers

Log4net renders objects using their ToString() method If you want more control over
that, you can create and use your own renderer Derive from IObjectRenderer interface

Repository

Repository is the layer responsible for maintaining the organization of loggers
Implement a repository using the log4net.Repository.ILoggerRepository interface.
LogManager class can be used to automatically manage the repositories and the loggers.

Sample Application

• Getting Started


• Add a reference to log4net


• Add an XmlConfigurator attribute to your assembly


• Add an application configuration file


• Add a log4net using statement


• Get a static ILogmember for your class using LogManager.GetLogger()


• Use the static ILogmember to log

Configuration

Why Log4Net

• Open Source Works on all versions of .NET.




• The much improved logging of EntLib 2.0 and above is only available if your application
  is running on .NET 2.0 or greater.




• Simpler install
  
  
  
  • When using the Enterprise Library there are some services you really should install.
    This is as simple as running a bat file included with EntLib but it does complicate
    your deployment process.
  
  
  
  


• Faster than its alternatives Appender Buffering -
  
  
  • Buffering support with some appenders lets log4net queue up log entries and write
    them in a single go. If you are writing entries to the database then buffering is
    a good way to improve performance.
  
  
  
  


• More platforms - Enterprise Library does not support the .NET Compact Framework
  while log4net does.

Alternatives

1. Enterprise Library 3.1 Logging Application Block
   
   
   TheEnterprise Library 3.1 Logging Application Block from Microsoft Patterns & Practices
   is possibly a good choice if you are already using Enterprise Library. It is a bit
   heavy-weight Logging requires more code. Learn more from:
   http://msdn2.microsoft.com/en-us/aa480464.aspx.


2. NLog
   
   NLog API is similar to log4net Easy to configure BSD License .NET, C/C++ and COM
   interfaces Project hasn't been updated since its 1.0 release in Sept 2006 .
   


3. NET Logging Framework
   
   This is a lightweight but not as flexible as log4net. It has got a very little community
   support and more error prone. Moreover,it can also affect the overall performance
   

Best Practices

• Logging is only useful if you use it


• Two styles of logging


• Logging by software component


• Logging by functional area


• Log all exceptions, not just their message strings


• Use the format logging methods where appropriate


• Short circuit expensive logging with the various Is…Enabled properties


• Advice on Log Levels




• FATAL - For very serious errors that may crash the program


• ERROR - For errors that may corrupt data or cause improper program behaviour


• WARN - For errors that have been handled but that developers may want to track


• INFO - Non-verbose logging of program execution like startup of sub-systems, timings,
  remoting calls, etc.


• DEBUG – For verbose or low level debugging information mainly used to help the developer
  debug the system can be used in loops, for dumping data, detailed program flow,
  etc.