What is Log4J?
This tutorial is going to explain about Apache Log4J.
- Apache Log4J is logging framework provided by Apache Software Foundation.
- Log4j is a Java logging framework used in Java programming and Java applications to debug any error/exception in the logs.
- Log4j has various built-in types of logging debug levels, see below low to high order.
Log4J Logging Levels:
| Logging Levels | Description |
| OFF | The highest possible rank and is intended to turn off logging.
|
| FATAL | Severe errors that cause premature termination to lead the application to abort. |
| ERROR | Error will allow the application to continue running (unexpected conditions/ runtime errors).
|
| WARN | Runtime situation that is undesirable or unexpected, almost error condition. |
| INFO | Info will be immediately visible to console. |
| DEBUG | Detailed information on the flow through the system, all are written to logs, this level is very useful to debug the program/application.
|
| TRACE | More detailed information and those are written to logs, more than debug level. |
| ALL | All logging levels, including custom levels.
|
Step 1
In Eclipse create a Java Project (File > New > Java Project)
Step 2
1 . Create a class file > java
/**
*/
package com.rrmaha.test;
import org.apache.log4j.Logger;
/**
* @author rrmaha.com
*/
public class LogTest {
static final Logger logger = Logger.getRootLogger();
public static void main(String[] args) {
logger.debug(“Test debug message”);
logger.info(“Test info message”);
logger.warn(“Test warn message”);
logger.error(“Test error message”);
logger.fatal(“Test fatal message”);
}
}
2. Create a file properties file > properties
# Define the root logger with appender file
log = /usr/home/log4j
log4j.rootLogger = debug, FILE
# Define the file appender
log4j.appender.FILE=org.apache.log4j.FileAppender
log4j.appender.FILE.File=${log}/log.out
# number of log files to keep before deleting the oldest one
log4j.appender.MaxBackupIndex=25
log4j.appender.MaxFileSize=1KB
log4j.appender=org.apache.log4j.RollingFileAppender
log4j.appender.file=jpe.log
# Define the layout for file appender
# Log message layout: date-time [thread] priority category – message lineTerminator
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
log4j.appender.FILE.layout.conversionPattern=%d{dd MMM yyyy HH:mm:ss} [%t] %-5p %c – %m%n
3. Create a folder
/usr/home/log4j
4. Create output file name(log file name)
log.out
5. Add log4j jar file > log4j-1.2.16.jar
Step 3
Step 4
Open a file > \usr\home\log4j\ log.out
04 May 2017 19:59:27 [main] DEBUG root – Test debug message
04 May 2017 19:59:27 [main] INFO root – Test info message
04 May 2017 19:59:27 [main] WARN root – Test warn message
04 May 2017 19:59:27 [main] ERROR root – Test error message
04 May 2017 19:59:27 [main] FATAL root – Test fatal message