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Logback throwing ConcurrentModificationException on exiting program inside docker container

My application is throwing ConcurrentModificationException when it is trying to exit the program.It is using a standard Logback configuration. This works fine when running as a standalone java application but throws the exception when trying to run inside a docker container. The stack trace is as below:
Exception in thread "Logback shutdown hook [default]" java.util.ConcurrentModificationException
at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1043)
at java.base/java.util.ArrayList$Itr.next(ArrayList.java:997)
at ch.qos.logback.classic.LoggerContext.fireOnReset(LoggerContext.java:323)
at ch.qos.logback.classic.LoggerContext.reset(LoggerContext.java:226)
at ch.qos.logback.classic.LoggerContext.stop(LoggerContext.java:348)
at ch.qos.logback.core.hook.ShutdownHookBase.stop(ShutdownHookBase.java:39)
at ch.qos.logback.core.hook.DelayingShutdownHook.run(DelayingShutdownHook.java:57)
at java.base/java.lang.Thread.run(Thread.java:834)
I am using a standard Logback configuration file through logback-spring.xml
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<!--See https://docs.spring.io/spring-boot/docs/current/reference/html/howto-logging.html -->
<shutdownHook
class="ch.qos.logback.core.hook.DelayingShutdownHook"/>
<include resource="org/springframework/boot/logging/logback/defaults.xml"/>
<appender name="CONSOLE_JSON" class="ch.qos.logback.core.ConsoleAppender">
<encoder class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
<layout class="ch.qos.logback.contrib.json.classic.JsonLayout">
<jsonFormatter class="ch.qos.logback.contrib.jackson.JacksonJsonFormatter">
<!-- <prettyPrint>true</prettyPrint> -->
</jsonFormatter>
<timestampFormat>yyyy-MM-dd'T'HH:mm:ss.SSSXXX</timestampFormat>
<includeContextName>false</includeContextName>
<appendLineSeparator>true</appendLineSeparator>
</layout>
<charset>UTF-8</charset>
</encoder>
</appender>
<appender name="ASYNCSTDOUT" class="ch.qos.logback.classic.AsyncAppender">
<queueSize>5000</queueSize> <!-- Default is 256 -->
<discardingThreshold>0</discardingThreshold> <!-- Instruction to drop events
once the buffer reaches the max capacity. Default value is 20%.
20 means drop lower event when has 20% capacity remaining -->
<neverBlock>true</neverBlock><!-- default false. Setting it to true to
cause the Appender not block the application and just drop the messages -->
<maxFlushTime>5000</maxFlushTime> <!-- The default maximum queue flush time allowed during appender stop. If
the worker takes longer than this time it will exit, discarding any remaining
cartItems in the queue -->
<appender-ref ref="CONSOLE_JSON"/>
</appender>
<logger name="org.springframework.web" level="INFO"/>
<root level="INFO">
<appender-ref ref="ASYNCSTDOUT"/>
</root>
</configuration>
The artifacts I am using in my pom are as below:
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.5.8</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-autoconfigure</artifactId>
<version>2.5.8</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-core</artifactId>
<version>1.2.3</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.3</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-access</artifactId>
<version>1.2.3</version>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-sleuth</artifactId>
<version>2.1.0.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
<version>5.3.14</version>
</dependency>
<dependency>
<groupId>net.logstash.logback</groupId>
<artifactId>logstash-logback-encoder</artifactId>
<version>6.6</version>
</dependency>
<dependency>
<groupId>ch.qos.logback.contrib</groupId>
<artifactId>logback-jackson</artifactId>
<version>0.1.5</version>
</dependency>
<dependency>
<groupId>ch.qos.logback.contrib</groupId>
<artifactId>logback-json-classic</artifactId>
<version>0.1.5</version>
</dependency>
</dependencies>

How to make log4j2 create different logging files with Spring Boot and Maven

I am a beginner and have a problem with setting log4j2 in my Spring Boot application. I've tried to do it myself for about a week now, read many hints, posts and tutorials and still didn't find solution. Could anyone pls help me with that? I would like to create different files for different log levels like error.log, warn.log and so on.
pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.6.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.assessment.ww</groupId>
<artifactId>Assessment_Exercise</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>Assessment_Exercise</name>
<description>Spring Boot Project</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-log4j2</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
log4j2.xml
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
<Appenders>
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{yyyy-MMM-dd HH:mm:ss} [%t] %-5level %logger{36} - %msg%n"/>
</Console>
<File name="File" target="logs/app.log">
<PatternLayout pattern="%d{yyyy-MMM-dd HH:mm:ss} [%t] %-5level %logger{36} - %msg%n"/>
</File>
</Appenders>
<Loggers>
<!-- Log everything -->
<Logger name="com.assessment.ww.Assessment_Exercise" level="debug" additivity="false">
<AppenderRef ref="Console"/>
<AppenderRef ref="File"/>
</Logger>
<!-- Log everything in Spring Boot -->
<Logger name="org.springframework.boot" level="debug" additivity="false">
<AppenderRef ref="Console"/>
<AppenderRef ref="File"/>
</Logger>
<!-- Log everything in Spring Core -->
<Logger name="org.springframework.core" level="debug" additivity="false">
<AppenderRef ref="Console"/>
<AppenderRef ref="File"/>
</Logger>
<Root level="all">
<AppenderRef ref="Console"/>
<AppenderRef ref="File"/>
</Root>
</Loggers>
</Configuration>
starting class
package com.assessment.ww.Assessment_Exercise;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
#SpringBootApplication
public class AssessmentExerciseApplication {
private static final Logger logger = LogManager.getLogger(AssessmentExerciseApplication.class);
public static void main(String[] args) {
SpringApplication.run(AssessmentExerciseApplication.class, args);
logger.info("Starting SB app");
}
}
I also have such a warning - maybe it will help:
enter image description here
It prints my logger.info message (but why without formatting?) but do not create any files.
enter image description here
Thank You in advance for any advices.

Finally, I've found a solution. The problem was Logback - even that I disabled it in spring-boot-starter-web dependency in pom.xml, it was still active in spring-boot-starter-data-jpa and spring-boot-starter-actuator.
So now my pom.xml looks like this:
...
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
...

Logback, Eclipse, and Maven

I'm having a problem with getting eclipse to recognize links in logging output. I have a standard maven project with classes in src/main folder and classes in a src/test folder. If I use the logging strategy outlined here:
How do I get Logback to work nicely with Eclipse?
The links work for java files in src/main but do NOT work for files in src/test. How do I get the links for files in src/test to work?
This is my pom file:
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.mycompany.myproject</groupId>
<artifactId>MyProject</artifactId>
<version>0.0.1-SNAPSHOT</version>
<dependencies>
<!-- JUNIT https://mvnrepository.com/artifact/junit/junit -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<!-- JUNIT-TOOLBOX https://mvnrepository.com/artifact/com.googlecode.junit-toolbox/junit-toolbox -->
<dependency>
<groupId>com.googlecode.junit-toolbox</groupId>
<artifactId>junit-toolbox</artifactId>
<version>2.4</version>
<scope>test</scope>
</dependency>
<!-- SLF4J LOGBACK CLASSIC https://mvnrepository.com/artifact/ch.qos.logback/logback-classic -->
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.3</version>
</dependency>
<!-- HTTPCLIENT https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient -->
<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpclient</artifactId>
<version>4.5.6</version>
</dependency>
<!-- ORG.JSON https://mvnrepository.com/artifact/org.json/json -->
<dependency>
<groupId>org.json</groupId>
<artifactId>json</artifactId>
<version>20180130</version>
</dependency>
</dependencies>
</project>
This is my logback.xml file:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<appender name="STDOUT"
class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level (%file:%line\) - %message%n</pattern>
</encoder>
</appender>
<root level="info">
<appender-ref ref="STDOUT" />
</root>
</configuration>
This is the version of Eclipse I'm using:
Spring Tool Suite
Version: 3.9.4.RELEASE
Build Id: 201804120921
Platform: Eclipse Oxygen.3a (4.7.3a)
Copyright (c) 2007 - 2018 Pivotal Software, Inc.
All rights reserved. Visit http://spring.io/tools/sts

Logback Kafka Appender Not Writing Logs to Topic

I am trying to do a simple test of Logback Kafka Appender. Following is what I have in my logback.xml which I have placed in src/main/resources:
<?xml version="1.0" encoding="UTF-8"?>
<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
<encoder> <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<!-- This is the kafkaAppender -->
<appender name="kafkaAppender"
class="com.github.danielwegener.logback.kafka.KafkaAppender">
<encoder>
<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
</pattern>
</encoder>
<topic>test</topic>
<keyingStrategy
class="com.github.danielwegener.logback.kafka.keying.NoKeyKeyingStrategy" />
<deliveryStrategy
class="com.github.danielwegener.logback.kafka.delivery.AsynchronousDeliveryStrategy" />
<!-- Optional parameter to use a fixed partition -->
<!-- <partition>0</partition> -->
<!-- Optional parameter to include log timestamps into the kafka message -->
<!-- <appendTimestamp>true</appendTimestamp> -->
<!-- each <producerConfig> translates to regular kafka-client config (format:
key=value) -->
<!-- producer configs are documented here: https://kafka.apache.org/documentation.html#newproducerconfigs -->
<!-- bootstrap.servers is the only mandatory producerConfig -->
<producerConfig>bootstrap.servers=localhost:9092</producerConfig>
<!-- this is the fallback appender if kafka is not available. -->
<!-- <appender-ref ref="STDOUT" /> -->
</appender>
<logger name="com.my.package" level="info" additivity="false">
<appender-ref ref="kafkaAppender" />
</logger>
<root level="info">
<appender-ref ref="kafkaAppender" />
</root>
I have started a Kafka server on Windows with a separate Zookeeper. I have created a test topic as well.
Started Zookeeper on Windows with : zkServer.cmd
Started Kafka Server on Windows with : kafka-server-start.bat config\server.properties
Created a topic : kafka-topics.bat --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic test
Started a consumer on Windows with : kafka-console-consumer.bat --bootstrap-server localhost:9092 --topic test --from-beginning
In my Java class all I have is a logger inside a method.
private static final Logger logger =
LoggerFactory.getLogger(FormController.class);
logger.debug("DEBUG :: Inside do post method");
logger.info("INFO :: Inside do post method");
My imports are:
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
My pom.xml is as follows:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.my.package</groupId>
<artifactId>SampleIGApp</artifactId>
<packaging>war</packaging>
<version>0.0.1-SNAPSHOT</version>
<name>SampleIGApp Maven Webapp</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/log4j/log4j -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.21</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-simple -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.21</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.apache.kafka/kafka-clients -->
<dependency>
<groupId>org.apache.kafka</groupId>
<artifactId>kafka-clients</artifactId>
<version>1.0.1</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.github.danielwegener/logback-kafka-appender -->
<dependency>
<groupId>com.github.danielwegener</groupId>
<artifactId>logback-kafka-appender</artifactId>
<version>0.2.0-RC1</version>
</dependency>
</dependencies>
<build>
<finalName>MyApp</finalName>
</build>
Can someone please tell me as to what am I doing wrong? Even if I comment out STDOUT appender-name, then also logs keep getting written to console, which in my case is Tomcat's catalina.out. I would appreciate any help. Thank you.

The documentation says you need to add logback-classic as dependency:
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.3</version>
<scope>runtime</scope>
</dependency>
logback-kafka-appender

WildFly 8 and Log4j 2’s log4j-web module

I am working on a web application that is running on WildFly and that is using SLF4J and Log4j 2 as logging system. On the Apache pages about Log4j 2 I read about the advantages of using the log4j-web module in a web application (Using Log4j 2 in Web Applications), so I added it and since then WildFly refuses the deployment (that is why I have commented it out in the listing below).
So, here is my question: is it advisable to use the log4j-web module with WildFly and if so, how do I set it up to work with WindFly?
Here are relevant listings:
webapp\WEB-INF\classes\log4j2.xml
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
<Appenders>
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
</Console>
<File name="File" fileName="myFile.log">
<PatternLayout pattern="%d{yyy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
</File>
</Appenders>
<Loggers>
<Root level="DEBUG">
<AppenderRef ref="Console"/>
<AppenderRef ref="File"/>
</Root>
</Loggers>
</Configuration>
webapp\WEB-INF\jboss-deployment-structure.xml
<?xml version="1.0" encoding="UTF-8"?>
<jboss-deployment-structure>
<deployment>
<exclude-subsystems>
<subsystem name="logging"/>
</exclude-subsystems>
</deployment>
</jboss-deployment-structure>
Parent pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
*snip*
<properties>
<java.version>1.8</java.version>
<slf4j.version>1.7.10</slf4j.version>
<log4j.version>2.1</log4j.version>
<maven.plugin.compiler.version>3.2</maven.plugin.compiler.version>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencyManagement>
<dependencies>
<!-- SLF4J -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>${slf4j.version}</version>
</dependency>
<!-- Apache Log4j API -->
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-api</artifactId>
<version>${log4j.version}</version>
</dependency>
<!-- Apache Log4j SLF4J Binding -->
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-slf4j-impl</artifactId>
<version>${log4j.version}</version>
</dependency>
<!-- Apache Log4j Core -->
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>${log4j.version}</version>
</dependency>
</dependencies>
</dependencyManagement>
*snip*
</project>
Backend pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
*snip*
<dependencies>
<!-- SLF4J -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
</dependency>
<!-- Apache Log4j API -->
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-api</artifactId>
</dependency>
<!-- Apache Log4j SLF4J Binding -->
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-slf4j-impl</artifactId>
</dependency>
<!-- Apache Log4j Core -->
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
</dependency>
</dependencies>
</project>
WebApp pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
*snip*
<properties>
<servlet.version>3.1.0</servlet.version>
<maven.plugin.war.version>2.6</maven.plugin.war.version>
<maven.plugin.wildfly.version>1.0.2.Final</maven.plugin.wildfly.version>
</properties>
<dependencyManagement>
<dependencies>
<!-- Backend dependency -->
<dependency>
*snip*
</dependency>
<!-- Apache Log4j Web -->
<!--<dependency>-->
<!--<groupId>org.apache.logging.log4j</groupId>-->
<!--<artifactId>log4j-web</artifactId>-->
<!--<version>${log4j.version}</version>-->
<!--<scope>runtime</scope>-->
<!--</dependency>-->
<!-- Java Servlet API -->
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>${servlet.version}</version>
<scope>provided</scope>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<!-- Backend dependency -->
<dependency>
*snip*
</dependency>
<!-- Apache Log4j Web -->
<!--<dependency>-->
<!--<groupId>org.apache.logging.log4j</groupId>-->
<!--<artifactId>log4j-web</artifactId>-->
<!--</dependency>-->
<!-- Java Servlet API -->
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
</dependency>
</dependencies>
<build>
<pluginManagement>
<plugins>
<!-- Maven WAR Plugin -->
<plugin>
<artifactId>maven-war-plugin</artifactId>
<version>${maven.plugin.war.version}</version>
</plugin>
<!-- WildFly Maven Plugin -->
<plugin>
<groupId>org.wildfly.plugins</groupId>
<artifactId>wildfly-maven-plugin</artifactId>
<version>${maven.plugin.wildfly.version}</version>
<configuration>
<!-- Server credentials from Maven's settings.xml -->
<id>WildFlyServer</id>
</configuration>
</plugin>
</plugins>
</pluginManagement>
<plugins>
<!-- WildFly Maven Plugin -->
<plugin>
<groupId>org.wildfly.plugins</groupId>
<artifactId>wildfly-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>

This is a common bug with wildfly 8.x, and there is a fix only for wildfly 9.x
Log4j2 2.1 onward will have deployment error with wildFly 8.x.
Log4j2 2.0.2 does not have this error but have other blocker bug (LOG4J2-832)