Apache Log4J Core framework tutorial

Apache Log4J Core framework tutorial Apache Log4j is a powerful Java log record framework that is widely used to develop and debug applications.LOG4J can help developers monitor the application status of the application in real time by recording log information and obtain key debugging information from them.This tutorial will introduce the basic concepts and usage of the Apache Log4j Core framework, and provide some Java code examples to help you get started quickly. 1. Installation and configuration log4j First, you need to download and install the log4j framework.You can get the latest log4j version from the Apache official website.After the installation is completed, add the LOG4J's jar file to your project and configure the log4j settings file (usually log4j2.xml or log4j2.properties) in the project's classpath.This configuration file will determine the log output format, target and level settings of log4j. 2. Create a logger Before using the log4j record log, you need to create a logger object.Logger is the core component of log4j, responsible for receiving and recording log information.You can obtain a Logger instance by calling the getlogger () method in the Logmanager class.Generally, the name of the logger should be associated with the package name or class name of your application in order to better organize and manage logs. import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; public class MyApp { private static final Logger logger = LogManager.getLogger(MyApp.class); } 3. Set the log level LOG4J provides multiple log levels, including Trace, Debug, Info, Warn, ERROR and FATAL.You can choose the appropriate log level as needed.By default, LOG4J will only output the info level and above log information.To change the log level, modify the relevant settings in the log4j configuration file. logger.trace("This is a TRACE level message."); logger.debug("This is a DEBUG level message."); logger.info("This is an INFO level message."); logger.warn("This is a WARN level message."); logger.error("This is an ERROR level message."); logger.fatal("This is a FATAL level message."); 4. Output log information LOG4J provides a variety of ways of output log information, which can be output to the console, files, databases and other goals.You can specify the goal of log information output by configured log4j settings.Here are some commonly used Appenders setting examples. Output to the console: <Console name="Console" target="SYSTEM_OUT"> <PatternLayout pattern="%d [%t] %-5level %logger{3.} - %msg%n"/> </Console> Output to file: <File name="File" fileName="application.log"> <PatternLayout pattern="%d [%t] %-5level %logger{3.} - %msg%n"/> </File> 5. Use log information formatting LOG4J provides the PatternLayout class to define the output format of and format logo information.You can use various placeholders and format options to define the output format.Here are some commonly used examples of placeholders: - %d: output log time - %T: Output thread name - %level: output log level - %Logger: The class name of the output log - %msg: Output log information main content <PatternLayout pattern="%d [%t] %-5level %logger{3.} - %msg%n"/> Through the above example code and configuration file, you can quickly understand and use the Apache Log4J Core framework.Through reasonable configuration and use of log4j, you can better monitor and manage your application and improve development and debug efficiency.I hope this tutorial will help you!