What is a log4j category?

log4j. Category class figures at the core of the package. Categories are named entities. In a naming scheme familiar to Java developers, a category is said to be a parent of another category if its name, followed by a dot, is a prefix of the child category name.

What is logger in 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.

What are the different log levels in log4j?

Five standard log4j levels

DEBUG Level. This log4j level helps developer to debug application.
INFO Level. This log4j level gives the progress and chosen state information.
WARN Level. This log4j level gives a warning about an unexpected event to the user.
ERROR Level.
FATAL Level.
ALL Level.
OFF Level.
TRACE Level.

What is logger category?

Logger is a subclass of Category, i.e. it extends Category. In other words, a logger is a category. Thus, all operations that can be performed on a category can be performed on a logger. Internally, whenever log4j is asked to produce a Category object, it will instead produce a Logger object.

What is log4j and why it is used?

log4j is a tool to help the programmer output log statements to a variety of output targets. In case of problems with an application, it is helpful to enable logging so that the problem can be located. With log4j it is possible to enable logging at runtime without modifying the application binary.

Is Log4j thread safe?

Is log4j thread-safe? Yes, log4j is thread-safe. Log4j components are designed to be used in heavily multithreaded systems.

What does logger debug mean?

If you want to print the value of a variable at any given point, you might call Logger. debug . This combination of a configurable logging level and logging statements within your program allow you full control over how your application will log its activity.

What is logger level?

What Is a Logging Level. A log level or log severity is a piece of information telling how important a given log message is. It is a simple, yet very powerful way of distinguishing log events from each other. If the log levels are used properly in your application all you need is to look at the severity first.

How is a logger defined in log4j.xml?

In log4j a logger is associated with a package or sometimes with a particular class. Package/class of a logger is defined by the attribute “name”. A logger logs messages in its package and also in all the child packages and their classes.

What are the three main components of Log4j?

The main components of Log4j:: logger: this is what we use in the application to issue messages. category: the source of the log message, i.e. package or realm. Besides those three components, there is a terminology called level. Logger is an object that is responsible for issuing log messages.

Is there way to log levels in Log4j?

The org.apache.log4j.Level levels. You can also define your custom levels by sub-classing the Level class. 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.

How is a logger defined in a package?

Package/class of a logger is defined by the attribute “name”. A logger logs messages in its package and also in all the child packages and their classes. The only exception is the root logger that logs messages for the all classes in the application. A logger also has level and may have one or many appenders (logging destinations) attached to it.