Log4j log level setting: how to accurately record the running status of the application

log4j log level setting guide: how to accurately record program running information

Overview:
In the software development process, it is very important to accurately record program running information , able to quickly locate and solve problems. In Java development, log4j is a popular logging tool that is flexible and configurable. This article will introduce the log level settings of log4j, including how to choose the appropriate level and how to configure and use it specifically.

1. Introduction to log levels:
log4j provides seven log levels, from low to high in severity: TRACE, DEBUG, INFO, WARN, ERROR, FATAL and OFF. These levels are used to determine which logs will be logged. Different levels are suitable for different scenarios, as follows:

1. TRACE: The lowest level, used for the most detailed logging, usually used to track problems and troubleshoot bugs. This level is generally not used in a production environment.
2. DEBUG: Used for debugging programs, outputting detailed information to track the execution flow and status of the program. Likewise, DEBUG level should be disabled in production environments.
3. INFO: used for general program running information. For example, record program start and end information, success or failure of key operations, etc.
4. WARN: Warning level, used for non-fatal exceptions and errors, indicating that some abnormal conditions have occurred during program operation, but will not cause program termination or interruption.
5. ERROR: Error level, used to record fatal exceptions and errors, indicating that an unrecoverable error occurred during program operation, causing the program to be interrupted or terminated.
6. FATAL: The highest level, indicating a serious error that can cause the application to crash. This level is generally not used in a production environment.
7. OFF: The highest level, turns off all logging.

2. Select the appropriate log level:
Selecting the appropriate log level can be decided according to the actual needs and the complexity of the program:

1. Debugging phase: In During the development and debugging phases of the program, you can use the TRACE or DEBUG levels. In this way, the execution flow of the program and the values ​​of variables can be recorded in detail, making it easier to locate problems.
2. Testing phase: During the testing phase of the program, the INFO level can be used. This can record the success or failure information of key operations, as well as some necessary running information.
3. Formal environment: In a formal environment, it is generally recommended to use WARN, ERROR and FATAL levels. This can record abnormal conditions and error information to help detect and solve problems in a timely manner.

3. Configure the log level of log4j:
Before using log4j to record logs, appropriate configuration is required. The following is a simple log4j.properties configuration file example:

# 设置根日志级别为INFO
log4j.rootLogger=INFO, console
log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

# 设置特定包的日志级别为DEBUG
log4j.logger.com.example=DEBUG

In the above configuration example, the root log level is set to INFO, which means that only logs above the INFO level are output. The log level of the specific package com.example is set to DEBUG, which means that logs above the DEBUG level are output.

4. Use log4j to record logs:
It is very simple to use log4j to record logs in the program. You only need to import the relevant dependency packages of log4j and add appropriate logging statements in the program. For example, the sample code for using log4j to record logs in Java code is as follows:

import org.apache.log4j.Logger;

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

    public void myMethod() {
        logger.info("This is an info message");
        logger.debug("This is a debug message");
        logger.warn("This is a warning message");
        logger.error("This is an error message");
        logger.fatal("This is a fatal message");
    }
}

In the above sample code, we first import the Logger class and create a static Logger object, and then use different methods in the myMethod method. Log at the log level. According to the log4j configuration, only logs with a log level higher than or equal to the level set in the configuration will be output.

Summary:
Accurately recording program running information is very important for the software development process. Using the log4j log level setting can flexibly manage and control the output of the log. When selecting the log level, you need to make a judgment based on actual needs and the complexity of the program. Through proper configuration and use of log4j logging statements, developers can easily record and track the execution flow and status of the program, helping to improve the maintainability and debuggability of the program.

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