log4j tutorial

What is log4j

log4j is a reliable, fast and flexible logging framework (APIs) written in Java, which is

distributed under the Apache Software License.

log4j has been ported to the C, C++, C#, Perl, Python, Ruby, and Eiffel languages.

log4j is highly configurable through external configuration files at runtime. It views the

logging process in terms of levels of priorities and offers mechanisms to direct logging

information to a great variety of destinations.

Major Features Of Log4j

Log4j is a widely used framework and here are features of log4j :

ü  It is a thread-safe. It is optimized for speed

ü  It is based on a named logger hierarchy.

ü  It supports multiple outputs of appenders per logger.

ü  It supports internationalization.

ü  It is not restricted to a predefined set of facilities.

ü  Logging behavior can be set at runtime using a configuration file.

ü  It is designed to handle Java Exceptions from the start.

ü  It uses multiple levels, namely ALL, TRACE, DEBUG, INFO, WARN, ERROR and

FATAL.

ü  The format of the log output can be easily changed by extending the Layout class.

ü  The target of the log output as well as the writing strategy can be altered by implementations of the Appender interface.

ü  It is fail-stop. However, although it certainly strives to ensure delivery, log4j does not

guarantee that each log statement will be delivered to its destination.

Components of log4j

log4j has three main components:

loggers: Responsible for capturing logging information.

appenders: Responsible for publishing logging information to various preferred

destinations.

layouts: Responsible for formatting logging information in different styles.

Pros and Cons of Logging

Following are the Pros and Cons of Logging

Logging is an important component of software development. A well-written logging code offers quick debugging, easy maintenance, and structured storage of an application's runtime information. Logging does have its drawbacks also. It can slow down an application. If too verbose, it can cause scrolling blindness.

To alleviate these concerns, log4j is designed to be reliable, fast and extensible. Since logging is rarely the main focus of an application, the log4j API strives to be simple to understand and to use.

Purpose Of Logger Object

Logger Object − The top-level layer of log4j architecture is the Logger which provides the

Logger object.

The Logger object is responsible for capturing logging information and they are stored in a

namespace hierarchy.

Purpose of the Layout object

The layout layer of log4j architecture provides objects which are used to format logging

information in different styles. It provides support to appender objects before publishing

logging information.

Layout objects play an important role in publishing logging information in a way that is

human-readable and reusable.

Purpose of Appender object

The Appender object is responsible for publishing logging information to various preferred

destinations such as a database, file, console, UNIX Syslog, etc.

Purpose Of ObjectRenderer Object

The ObjectRenderer object is specialized in providing a String representation of different

objects passed to the logging framework.

This object is used by Layout objects to prepare the final logging information.

LogManager object

The LogManager object manages the logging framework. It is responsible for reading the

initial configuration parameters from a system-wide configuration file or a configuration

class.

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