Using Log4J In Netbeans

Question

I am trying to use Log4J in Netbeans, however I am having a very hard time understanding the tutorials. Many of them say "do this" and assume I know what they are talking about. I do not. If you would, I'd like step-by-step instructions on where to find the correct libraries for Log4J, where to put them in a project, and an example program using Log4J.

Answer 1

log4j 2.x

Similar to below, but the name of the filename needs to be log4j2.properties. (Also note that old examples of log4j.properties configuration don't actually seem to do anything useful in Log4j 2, so make sure to copy your initial configuration from a tutorial dedicated to Log4j 2, and not the older v1.)

Thanks @bobulous

log4j 1.x

If you get log4j:WARN No appenders could be found for logger message, then it is most likely that you haven't included the log4j.properties file in your project. Here's a screenshot of how you should include it in NetBeans.

Answer 2

This very comprehensive working example for log4j2 has nearly everything, duplicated here incase the link breaks

To get a working example, create a new maven java application in netbeans (or any IDE)

New Project -> Maven -> Java Application

In your new maven project there is a pom.xml under 'project files' in netbeans, you need to add this dependency:

I tested this with log4j version 2.11.1, check for latest here

   ... 
   </properties>
   <dependencies>
       <dependency>
           <groupId>org.apache.logging.log4j</groupId>
           <artifactId>log4j-core</artifactId>
           <version>2.11.1</version>
       </dependency>
   </dependencies>
</project>

Create a src/main/resources/log4j2.properties (this exact path and name is required)

you can later customize the print layout using this as a reference

status = error
name = PropertiesConfig

filters = threshold
filter.threshold.type = ThresholdFilter
filter.threshold.level = debug

appenders = console
appender.console.type = Console
appender.console.name = STDOUT
appender.console.layout.type = PatternLayout
appender.console.layout.pattern = %d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

rootLogger.level = debug
rootLogger.appenderRefs = stdout
rootLogger.appenderRef.stdout.ref = STDOUT

Create a new class: Log4j2HelloWorldExample.java

package com.howtodoinjava.log4j2.examples;   

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;


public class Log4j2HelloWorldExample {

    private static final Logger LOGGER = LogManager.getLogger(Log4j2HelloWorldExample.class.getName());

    public static void main(String[] args) {
        LOGGER.debug("Debug Message Logged !!!");
        LOGGER.info("Info Message Logged !!!");
        LOGGER.error("Error Message Logged !!!", new NullPointerException("NullError"));
    }
}

When you run the class you will get his output:

 2016-06-16 13:41:27 DEBUG Log4j2HelloWorldExample:12 - Debug Message Logged !!!
 2016-06-16 13:41:27 INFO  Log4j2HelloWorldExample:13 - Info Message Logged !!!
 2016-06-16 13:41:27 ERROR Log4j2HelloWorldExample:14 - Error Message Logged !!!
 java.lang.NullPointerException: NullError
     at com.howtodoinjava.log4j2.examples.Log4j2HelloWorldExample.main(Log4j2HelloWorldExample.java:14)
    [classes/:?]

---

If the above example works stand alone, but not when you integrate it into your project there might be some dependency interference

Run mvn dependency:tree and exclude all interfering log4j dependencies, I needed to exclude these:

<exclusion>
    <!-- 
        [INFO] |  +- log4j:log4j:jar:1.2.17:compile
        [INFO] |  +- org.slf4j:slf4j-log4j12:jar:1.7.16:compile
    -->
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
</exclusion>
<exclusion>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
</exclusion>

To bridge existing slf4j code to my newly added log4j2, I had to include this dependency I found here

   <dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-slf4j-impl</artifactId>
      <version>2.9.0</version>
   </dependency>

I still saw this:

log4j:WARN No appenders could be found for logger
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

I also needed to ensure the log4j2.property file had my OS specific line endings, I was using Cygwin to create property files and running netbeans from windows and it failed to find appenders due to the property file all being read as a single line by Windows

Answer 3

http://www.tutorialspoint.com/log4j/log4j_sample_program.htm -

Download the jar from here: https://logging.apache.org/log4j/1.2/download.html

Add this file in your path:

log4j.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

# Here is the location output of the file!
log4j.appender.FILE.File=${log}/log.out

# Define the layout for file appender
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
log4j.appender.FILE.layout.conversionPattern=%m%n

Then run this:

log4jExample.java

import org.apache.log4j.Logger;

import java.io.*;
import java.sql.SQLException;
import java.util.*;

public class log4jExample{
  /* Get actual class name to be printed on */
  static Logger log = Logger.getLogger(
                      log4jExample.class.getName());

  public static void main(String[] args)
                throws IOException,SQLException{

     log.debug("Hello this is an debug message");
     log.info("Hello this is an info message");
  }
}