Understand the technical principles and usage of Apache Log4J Web framework in the Java class library
Apache Log4j is a log record framework for the Java platform. It provides a variety of features of rich features and can help developers to effectively record and manage applications of applications.This article will introduce the technical principles and usage methods of Apache Log4J, and provide some Java code examples to explain related concepts.
1. Technical principle:
1. Logger: Apache Log4j uses the logger object to perform log records.Each logger has a unique name to identify different log recorders.
2. Log Level: Apache Log4J defines a set of log levels to distinguish the importance of logs.Common log levels include Trace, Debug, Info, Warn, ERROR and FATAL.Different logs represent different degrees of severity. Developers can choose the log record at a appropriate level according to the needs.
3. Appender and Layout: Appender in Apache Log4j is responsible for output log messages to the specified place, such as console, files or databases.Layout is responsible for the output of the format log message in order to better organize and display log information.
4. Configuration file: Apache Log4j uses a configuration file to define the behavior of log records.The configuration file can specify the log level, the configuration of APPENDER and Layout, and other related settings.The configuration file can be a .properties file or a .xml file.
2. How to use:
1. Introduce log4j library: First of all, you need to introduce the log4j library in the project.You can use Maven to introduce by adding the following dependencies to the pom.xml file:
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-api</artifactId>
<version>2.14.0</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>2.14.0</version>
</dependency>
2. Create a logger object: In Java code, you can create a logger object by calling the logmanager.getLogger () method.It is necessary to pass a unique name in order to identify during the logging process.
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class MyClass {
private static final Logger logger = LogManager.getLogger(MyClass.class);
public void doSomething() {
// Logging example
logger.info ("Log Message");
}
}
3. Configure log4j: Create a log4j2.xml file in the project resource directory, and define the configuration information of the log record in the file.The following is a simple configuration example:
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
<Appenders>
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSS} [%level] %msg%n"/>
</Console>
</Appenders>
<Loggers>
<Root level="info">
<AppenderRef ref="Console"/>
</Root>
</Loggers>
</Configuration>
The above configuration outputs the log message to the console and sets the log level to INFO.Can be configured more detailed according to demand, such as output logs to files, databases or other places.
4. Record log: In the Java code, you can record the log message by calling different methods of the logger object.For example:
Logger.trace ("This is a trace -level log message"););
Logger.debug ("This is a log message of Debug"););
Logger.info ("This is an info -level log message");
logger.warn ("This is a narn -level log message");
Logger.error ("This is a log -level log message");
Logger.Fatal ("This is a Fatal -level log message");
According to the log level set in the configuration file, the log message with higher levels above or equal to the configuration level will be recorded.
Summarize:
Apache Log4j is a powerful Java log record framework. It has flexible configuration and rich characteristics, which can help developers effectively manage the logs of the application.This article introduces the technical principles and usage methods of log4j, and provides some example code, hoping to help readers better understand and use the log4j framework.
