The technical principles of the Apache Log4J Web framework in the Java class library
Apache Log4j is a widely used log frame in the Java project.It provides a flexible and powerful log record function that can help developers easily track and debug applications.
The technical principle of Apache Log4j is based on the following key components:
1. Logger: Logger is the core component of the log record, which is responsible for output a log in a part of the application to a specific destination.Through the logger, you can control the level of the log to selectively output different levels of log information.
Here are a sample code to create a logger object:
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 myMethod() {
logger.info("This is an informational message");
logger.debug("This is a debug message");
logger.error("This is an error message");
}
}
2. Appender: Appender is a position used to specify log output, such as files, consoles or databases.LOG4J provides a variety of different types of APPENDER, which can choose the appropriate output method according to needs.
The following is an example code that output logs to files:
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.core.config.Configurator;
public class MyClass {
private static final Logger logger = LogManager.getLogger(MyClass.class);
public void myMethod() {
Configurator.initialize (null, "log4j2.xml"); // specify log4j configuration file
logger.info("This is an informational message");
}
}
3. Layout (layout): Layout is responsible for defining the format of log messages.LOG4J provides a variety of different types of layout, and developers can choose the appropriate layout method as needed.
The following is a code of the example layout:
<?xml version="1.0" encoding="UTF-8"?>
<Configuration>
<Appenders>
<Console name="console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} [%t] %-5level %logger{36} - %msg%n" />
</Console>
</Appenders>
<Loggers>
<Root level="info">
<AppenderRef ref="console" />
</Root>
</Loggers>
</Configuration>
By configured the XML file similar to the above, the log can be output to the console in a specific format.
4. Logger level: log4j to filter and control output logs according to the log level.It defines multiple levels, including (from high to low) Error, Warn, Info, Debug and Trace.By setting the level of Logger, log messages below the specified level can be filtered.
Here are a sample code setting Logger level:
import org.apache.logging.log4j.Level;
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 myMethod() {
Logger.SetLevel (level.info); // Set the log level as INFO, the log lower than the INFO level will not output
logger.info("This is an informational message");
Logger.debug ("this is a debug message"); // This log will not be output
}
}
In summary, Apache Log4j is a powerful and flexible log framework. It can easily perform logging and output control through core components such as Logger, APENDER, Layout, and Logger.Developers can choose appropriate components and configuration methods to achieve their log function according to specific needs.
