Introduction to the Logging Application Block

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The Enterprise Library Logging Application Block simplifies the implementation of common logging functions. Developers can use the Logging Block to write information to a variety of locations:

  • The event log
  • An e-mail message
  • A database
  • A message queue
  • A text file
  • A WMI event
  • Custom locations using application block extension points

The application block provides a consistent interface for logging information to any destination. Your application code does not specify the destination for the information. Configuration settings determine whether the application block writes the logging information and the location for that information. This means that operators as well as developers can modify logging behavior without changing application code.

The Logging Application Block helps with application development in a number of ways:

  • It helps maintain consistent logging practices, both within an application and across the enterprise.
  • It eases the learning curve for developers by using a consistent architectural model.
  • It provides implementations that you can use to solve common application logging tasks.
  • It is extensible, supporting custom implementations of components that format and write event information.

Common Scenarios

Developers frequently write applications that require logging functionality. Typically, these applications format and log information in response to application events. For example, developers often write code to log information in response to unexpected conditions, such as an application exception, or failure to connect to a database. Developers also write code to trace application flow through components during the execution of an application use case or scenario.

Applications need to write information either locally or over the network. In some cases, you may have to collate events from multiple sources into a single location.

The Logging Application Block simplifies application development by providing a small set of easy-to-use classes and methods that encapsulate many of the most common logging scenarios. These scenarios include:

  • Populating and logging event information.
  • Including context information in the event.
  • Tracing application activities.

Each task is handled in a consistent manner, abstracting the application code from the specific logging providers.

For more information about the scenarios that the Logging Application Block can help you with, see Scenarios and Goals.

Example Application Code

The following code shows how to populate and raise an event in your application**.** The LogEntry object has a priority of 2 and belongs to both the Trace and UI Events categories.

LogEntry logEntry = new LogEntry();
logEntry.EventId = 100;
logEntry.Priority = 2;
logEntry.Message = "Informational message";
logEntry.Categories.Add("Trace");
logEntry.Categories.Add("UI Events");

Logger.Write(logEntry);

'Usage
Dim logEntry As LogEntry = New LogEntry()
logEntry.EventId = 100
logEntry.Priority = 2
logEntry.Message = "Informational message"
logEntry.Categories.Add("Trace")
logEntry.Categories.Add("UI Events")

Logger.Write(logEntry)

Audience Requirements

This guide is intended for software architects, software developers, and policy makers. To benefit fully from this guide, you should understand the following technologies:

  • Microsoft Visual Studio 2005 development system
  • Microsoft .NET Framework 2.0

Highlights of This Release

The Enterprise Library 3.1 — May 2007 release of the Logging Application Block includes the following new features:

  • The RollingFlatFileTraceListener class. This class allows you to control the size and age of a text log file. It either overwrites the existing file or creates a new file depending on criteria that you configure. For more information, see Rolling Flat File Trace Listener in the Logging Application Block Properties section.
  • Integration with WCF. You can now integrate the Logging Application Block with applications that use WCF. For more information, see WCF Integration in Design of the Logging Application Block and Entering Configuration Information.
  • An enhanced version of the TimeStampToken class.****Earlier releases of the Logging Application Block only allowed timestamps to be logged in UTC time. In this release, the timestamp token now supports a local: prefix that indicates that the timestamp should be displayed in local time. For more information see Trace Listener Properties in Logging Application Block Properties.
  • The ReflectedPropertyToken class. This release of the Logging Application Block supports a new formatting token that allows you to log custom properties on custom classes that either derive from the LogEntry class or modify it.****For more information, see Extending and Modifying the Logging Application Block.

System Requirements

To use the Logging Application Block, you need the following:

  • Microsoft Windows XP Professional, Windows Server 2003, or Windows Vista operating system

  • Microsoft .NET Framework 2.0.

  • Microsoft Visual Studio 2005 development system (any of the following editions):

    Microsoft Visual Studio 2005 Standard Edition

    Microsoft Visual Studio 2005 Professional Edition

    Microsoft Visual Studio 2005 Team Edition for Software Developers

    Microsoft Visual Studio 2005 Team Edition for Software Testers

    Microsoft Visual Studio 2005 Team Edition for Software Architects

    Microsoft Visual Studio 2005 Team Suite

  • Stores to maintain log messages. If you are using the MsmqTraceListener trace listener to store log messages, you need a message queue. If you are using the DatabaseTraceListener trace listener to store log messages, you need a database server. If you are using the EmailTraceListener trace listener to store log messages, you need an SMTP server.

Logging Application Block Dependencies

The Logging Application Block depends on other code included in the Enterprise Library:

  • Core library functionality. The Enterprise Library Core provides services such as instrumentation and configuration, and is a shared dependency of all Enterprise Library application blocks. The core library functionality is contained in the assembly Microsoft.Practices.EnterpriseLibrary.Common.dll.
  • The ObjectBuilder subsystem. The ObjectBuilder subsystem performs all the repetitive and necessary tasks for creating and disposing of object instances, while still providing a high level of flexibility. Enterprise Library uses the ObjectBuilder subsystem for tasks such as injecting configuration into block classes and connecting instrumentation classes to application blocks. The ObjectBuilder subsystem is contained in the assembly Microsoft.Practices.ObjectBuilder.dll.

Depending on the specific functionality you require from the Logging Application Block, you may also require the Data Access Application Block, which the Logging Application Block uses for the database trace listener. You can also use the Logging Application Block with the Exception Handling Application Block to log formatted exception information. In this case, it is the Exception Handling Application Block that depends on the Logging Application Block. For more information, see the Exception Handling Application Block documentation.

The recommended way to modify the configuration settings for the Logging Application Block is to use the Enterprise Library Configuration Console.

Logging Application Block Documentation

In addition to the introduction, the documentation contains the following topics:

  • Developing Applications with the Logging Application Block. This topic explains how to download and install the Logging Application Block so that you can use it in your applications. It also explains how to add application code to the application block where required. This topic includes two subtopics. The first subtopic, Configuration, describes how to configure the application block to perform common tasks. The second subtopic, Key Scenarios, demonstrates how to use the application block to perform the most common logging operations.
  • Design of the Logging Application Block. This topic explains the decisions that went into designing the application block and the rationale behind those decisions.
  • Extending and Modifying the Logging Application Block. This topic explains how to extend the application block by creating your own custom trace listeners and how to modify the source code.
  • Deployment and Operations. This topic explains how to deploy and update the application block's assemblies and also contains information about configuration.
  • QuickStarts. This topic explains how to install and configure the QuickStart applications. This section contains a series of walkthroughs that demonstrate how to incorporate common logging operations in an application.

More Information

For more information, see the following patterns & practices guides:

Retired Content

This content is outdated and is no longer being maintained. It is provided as a courtesy for individuals who are still using these technologies. This page may contain URLs that were valid when originally published, but now link to sites or pages that no longer exist.
The latest Enterprise Library information can be found at the Enterprise Library site.