Log4j log level setting strategy: Efficiently grasp program exceptions

log4j is a powerful logging tool that can help developers effectively grasp program exceptions. When using log4j, it is very important to set the log level appropriately. This article will introduce the log4j log level setting strategy and provide specific code examples.

1. The five log levels of log4j

log4j provides five log levels, namely TRACE, DEBUG, INFO, WARN and ERROR. These levels represent different levels of importance of logs. Developers can choose the appropriate level for log recording based on specific needs.

1. TRACE: The lowest level log, used to record the most detailed debugging information. This level is not recommended in production environments.
2. DEBUG: Used to record debugging information, usually only used in development and testing environments.
3. INFO: Used to record the running information of the program, such as startup information and important operation tips.
4. WARN: Used to record warning information. It will not cause program errors, but may cause some potential problems.
5. ERROR: Used to record error information, indicating that a recoverable error has occurred in the program, but will not cause the program to crash.

2. Set the log level reasonably

In actual development, we should set the log level reasonably according to the needs of the software and the operating environment. Generally speaking, we recommend using the DEBUG level in development and testing environments to record detailed debugging information, and using the INFO level in production environments to record program running information and important tips. Warnings and error messages, whether in development, testing or production environments, should be recorded and processed in a timely manner.

3. Log4j configuration file example

The following is an example of a simple log4j configuration file, which contains five log level settings.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

    <appender name="consoleAppender" class="org.apache.log4j.ConsoleAppender">
        <param name="Target" value="System.out" />
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%d [%t] %-5p %c{1} - %m%n" />
        </layout>
    </appender>

    <logger name="com.example">
        <level value="DEBUG" />
    </logger>

    <root>
        <level value="INFO" />
        <appender-ref ref="consoleAppender" />
    </root>

</log4j:configuration>

In the above example, we used ConsoleAppender as the output target of the log and set the format of the log. In the logger element, we specify that the classes under the com.example package use the DEBUG level for logging. In the root element, we specify the default log level as INFO and output the log to the consoleAppender.

4. Using log4j in the code

Using log4j in the code is very simple. You only need to introduce the log4j class where the log needs to be recorded, and use the corresponding log level for logging. Can. The following is a specific example:

import org.apache.log4j.Logger;

public class ExampleClass {
    private static final Logger logger = Logger.getLogger(ExampleClass.class);

    public void doSomething(){
        logger.debug("这是一个调试信息");
        logger.info("这是一个运行信息");
        logger.warn("这是一个警告信息");
        logger.error("这是一个错误信息");
        //...其他代码
    }
}

In the above example, we obtained a logger instance through the Logger.getLogger method. Then, we can record the corresponding level of log information by calling different log level methods.

5. Summary

The setting of log4j log level is very important, which can help us clearly understand the running status and abnormal situations of the program. By setting log levels appropriately, we can flexibly control log output in development, testing, and production environments. When using log4j, developers can choose the appropriate log level for log recording based on specific needs, and flexibly control the log output method through the log4j configuration file.

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