Log4j Interview Questions and Answers

What is log4j?

Log4j is a simple, flexible and fast java based logging framework. It is thread safe and supports internationalization.
See more at: Log4j overview.

What are the components of log4j?

1. Logger: It is used to log the messages.
2. Appender: It is used to publish the logging information to the destination like file, database, console etc.
3. Layout: It is used to format logging information in different styles.
See more at: Log4j overview.

Explain Logger class?

Logger class provides the methods for logging process. We can use the getLogger() method to get the Logger object.
Syntax: public static Logger getLogger(String name);
Where name is the fully qualified class name.
See more at: Logger class.
What is purpose of ALL log level?
ALL − All levels including custom levels.

What is purpose of DEBUG log level?

DEBUG − Designates fine-grained informational events that are most useful to debug an application.

What is purpose of ERROR log level?

ERROR − Designates error events that might still allow the application to continue running.

What is purpose of FATAL log level?

FATAL − Designates very severe error events that will presumably lead the application to abort.

What is purpose of INFO log level?

INFO − Designates informational messages that highlight the progress of the application at coarse-grained level.

What is purpose of OFF log level?

OFF − The highest possible rank and is intended to turn off logging.

What is purpose of TRACE log level?

TRACE − Designates finer-grained informational events than the DEBUG.

What is purpose of WARN log level?

WARN − Designates potentially harmful situations.

How do Levels Works?

A log request of level p in a logger with level q is enabled if p >= q. This rule is at the heart of log4j. It assumes that levels are ordered. For the standard levels, we have ALL < DEBUG < INFO < WARN < ERROR < FATAL < OFF. 
See more at: Logging levels in log4j.

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