Apache log4j API log level and its use

Apache Log4j is a Java log practical tool that provides a wide range of logs and is very popular.It allows developers to record log messages at various levels in applications.This article will introduce the log level in the Apache Log4j API and their usage methods, and provide the corresponding Java code example. ## 1. Logue Overview Apache Log4J defines seven different logs, and is: trace from low to high according to severity: trace, Debug (debug), INFO (information), warn (warning), error) And off (closed log records).By selecting the appropriate log level, you can control the log output of the application, while filtering and analyzing log messages as needed. ## 2. Log level example code Below is a simple Java example code, demonstrating how to set and use different log levels with Apache Log4J API. import org.apache.log4j.Level; import org.apache.log4j.Logger; public class LogLevelExample { // Get the log recorder private static final Logger logger = Logger.getLogger(LogLevelExample.class); public static void main(String[] args) { // Set the log level as DEBUG logger.setLevel(Level.DEBUG); // Print different levels of log messages 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."); } } In the above example, we first obtain a log recorder object through the `logger.getLogger ()`, and then use the `setLevel ()` method to set the log level as Debug.Next, we print different levels of log messages using the `Logger` object.By running this sample code, you can see that log messages at different levels are output on the console. ## 3. Use a log level to filter By setting a proper log level, you can flexibly control the log output of the application.For example, you can set the log level to WARN so that only the log message of the warning level and above.This can reduce the number of log output, and it is easier to filter and view interesting log messages. Here are a sample code that uses logs to filter in log level: import org.apache.log4j.Level; import org.apache.log4j.Logger; public class LogFilterExample { // Get the log recorder private static final Logger logger = Logger.getLogger(LogFilterExample.class); public static void main(String[] args) { // Set the log level as warn logger.setLevel(Level.WARN); // Print different levels of log messages 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."); } } In the above example, we set the log level to Warn, which means that only the log messages of Warn, ERROR and FATAL levels will be output.By running this sample code, you can see that there are log messages only warning levels and above to output on the console. ## in conclusion The log level of Apache Log4j API provides fine log control functions, allowing developers to flexibly manage the output of log messages according to actual needs.By selecting the appropriate log level, you can reduce logging and quickly position and solve problems.I hope this article can help you better understand the log level and how to use the Apache Log4j API.