39

My code is very simple using apache-log4j-2.0.2:

import org.apache.log4j.BasicConfigurator;
import org.apache.log4j.Logger;

public class Log4jtest {
  static Logger log =Logger.getLogger(Log4jtest.class);
  public static void main(String[] args) {
    BasicConfigurator.configure();
        log.debug("This is debug message");
  }

}

But I'm getting exception like:

Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.ClassCastException: org.apache.logging.slf4j.SLF4JLoggerContext cannot be          cast to org.apache.logging.log4j.core.LoggerContext``
at org.apache.log4j.Logger.getLogger(Logger.java:41)
at Log4jtest.<clinit>(Log4jtest.java:11)

Why is the exception coming from a simple program?

Robert
  • 5,218
  • 1
  • 18
  • 35
user3334466
  • 391
  • 1
  • 3
  • 3
  • 1
    please check your log4j cconfiguration file. – Vineet Kasat Sep 17 '14 at 13:24
  • I had a similar issue. I think I was telling SLF4J to log with a certain binding and then telling log4j to send logging message to SLF4J, which wasn't properly configured, due to the .jars that were included in the classpath. In my case I had a jar like this, that when remove, resolved the issue (by letting log4j log using it's own framework, instead of trying to use the SLFJ framework) log4j-to-slf4j-2.0.2.jar – atom88 Apr 03 '19 at 18:34

2 Answers2

78

Remove below jar's from class path and it should fix the issue -

log4j-to-slf4j-2.0.2.jar
log4j-to-slf4j-2.0.2-sources.jar
log4j-slf4j-impl-2.0.2.jar
log4j-slf4j-impl-2.0.2-sources.jar

I was able to replicate and fix the issue after downloading apache-log4j-2.0.2 from http://www.apache.org/dyn/closer.cgi/logging/log4j/2.0.2/apache-log4j-2.0.2-bin.zip.

TheCodingFrog
  • 3,248
  • 3
  • 20
  • 27
  • 2
    Also, please do remember to accept your answers (all of them) if they have given you satisfactory answers (by clicking on the tick mark on the left of the answers), it would be helpful to the community – TheCodingFrog Jun 27 '15 at 16:11
  • 4
    This works as cool but may I know the exact reason how its happened – Chandra Shekhar Aug 04 '16 at 10:00
  • This worked for me too. I excluded the sources and tests jar supplied within the official Log4J Package. Then added the flume-ng-sdk jar to remove ClassNotFoundException. Then finally removed these 2 JARs for this ClassCastException. This answer should be accepted. – Navin Israni Jun 26 '17 at 16:38
  • This solution is not good if you *want* log4j to forward log events to slf4j via `log4j-to-slf4j`. – Christoffer Hammarström Apr 12 '19 at 10:20
  • 1
    not a good answer but degrading log4j2 version from 2.11.x to 2.8.x worked for me. – prayagupa Jun 29 '19 at 20:06
  • I don't have these jars but still get error. – Philip Rego Jan 21 '21 at 23:29
9

I was using Maven. I found that declaring my log4j/slf4j dependencies at the top of the <dependencies> list (before Spring Boot, which used logback) fixed the issue.

To @TheCodingFrog's credit, adding exclusions to my Spring Boot dependencies also solved the problem. Like so:

<dependencies>
    <dependency>
        <groupId>...</groupId>
        <artifactId>...</artifactId>
        <exclusions>
            <exclusion>
                <groupId>log4j</groupId>
                <artifactId>*</artifactId>
            </exclusion>
            <exclusion>
                <groupId>org.slf4j</groupId>
                <artifactId>*</artifactId>
            </exclusion>
            <exclusion>
                <groupId>org.apache.logging.log4j</groupId>
                <artifactId>*</artifactId>
            </exclusion>
        </exclusions>
    </dependency>
</dependencies>

NOTE: If you care about which logging framework is actually used, one perhaps important difference is that with @TheCodingFrog's method, slf4j retained logback as the binding:

SLF4J: Actual binding is of type [ch.qos.logback.classic.util.ContextSelectorStaticBinder]

whereas, with the method I used, slf4j/log4j was used:

SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory]

In case anyone's interested, the log4j/slf4j dependencies I used are:

<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.7</version>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.7.7</version>
</dependency>
Hau
  • 413
  • 4
  • 12