Java: log4j initialization error

Question

I'm new in using the log4j package and I don't see the error: This is a very simple and straightforward code sample:

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

public class TestLogger {

    private static Logger logger;

    public static void main(String[] args) {

        logger = LogManager.getLogger(TestLogger.class);
        logger.info("Hello");

    }
}

When I try to compile I get this error:

Exception in thread "main" java.lang.NullPointerException at org.apache.logging.log4j.LogManager.getLogger(LogManager.java:129) at my.package.logging.TestLogger.main(TestLogger.java:15)

I am wondering what on earth it's all supposed to mean ...

Could you help here?

Which version of log4jare you using? Also post your .properties or .xml file — betomontejo
– betomontejo, Commented Oct 6, 2012 at 22:25
please read the logging.apache.org/log4j/1.2/manual.html Next you will face missing Appenders. — Simulant
– Simulant, Commented Oct 6, 2012 at 22:26
I am using version 2.0-beta1 without a xml, i.e. it should handle it by default. — John Rumpel
– John Rumpel, Commented Oct 6, 2012 at 22:46

SixDoubleFiveTreeTwoOne · Accepted Answer · 2012-10-16 15:51:58Z

3

I solved this problem by avoiding multiple copies on the classpath of the log4j2 jars.

The NPE occurs at Line 129 of LogManager. (return statement = Line 129)

/**
 * Return a Logger with the specified name.
 *
 * @param name The logger name.
 * @return The Logger.
 */
public static Logger getLogger(String name) {

    return factory.getContext(LogManager.class.getName(), null, false).getLogger(name);
}

The Problem seems to be, that the factory (LoggerContextFactory) is null = not initialized. Initialization takes place in a static initializer block in the class LogManager.

My assumption is, that initialization failes when there is more than one LogManager on the classpath.

In my project (a webapplication developed with eclipse) i had the jars in my WEB-INF/lib and referenced by a dependency to another project. Making ALL references point to the same jars solved that issue in my case.

edited Oct 16, 2012 at 15:51

answered Oct 14, 2012 at 0:45

SixDoubleFiveTreeTwoOne

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Comments

betomontejo · Accepted Answer · 2012-10-06 23:15:08Z

2

You're most probably missing one of the dependencies. This is easy reproducible if you only include in your classpath the log4j-api-2.0-beta1.jar file.

If you downloaded the binary distribution, include also the log4j-core-2.0-beta1.jar in your classpath. If your using Maven, put this in your pom.xml:

  <dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-api</artifactId>
    <version>2.0-beta1</version>
  </dependency>
  <dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.0-beta1</version>
  </dependency>

answered Oct 6, 2012 at 23:15

betomontejo

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1 Comment

John Rumpel Over a year ago

Your are absolutely right. This error occurs when missing to add log4j-core to the referenced libraries! Now when I implemented my first basic xml, I am able to log. Thanks a lot!

DNA · Accepted Answer · 2012-10-06 22:47:18Z

1

The following works for me (updated: now the same as your original posting, but showing the imports)

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

public class TestLogger
{
    private static Logger logger;

    public static void main(String[] args) {
        logger = LogManager.getLogger(TestLogger.class);
        logger.info("Hello");
    }
}

provided that you have created a log4j configuration, otherwise you'll get the dreaded error:

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

edited Oct 6, 2012 at 22:47

answered Oct 6, 2012 at 22:20

DNA

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8 Comments

John Rumpel Over a year ago

This code is direcly adopted from logging.apache.org/log4j/2.x/manual/api.html. Logger hasn't a function like this anymore. Probably in log4j.v1

DNA Over a year ago

OK - but I have just tried both versions (Logger and LogManager) and both versions work for me.

John Rumpel Over a year ago

ok. I added the imports. Since I am using the log4j-api2.0-beta1 package, there is another package reference org.apache.logging.log4j instead of org.apache.log4j as in the log4j12 package

DNA Over a year ago

Ah, that might explain it - I am using 1.2.16

John Rumpel Over a year ago

Anyways, i tried to use 1.2 and got a java.lang.NullPointerException at org.apache.logging.log4j.LogManager.getContext(LogManager.java:203)

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