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mvn checkstyle plugin: google_checks no reached

maven checkstyle plugin is telling me that it's using sun_checks.xml by default:
INFO] There are 5 errors reported by Checkstyle 8.29 with sun_checks.xml ruleset.
I mean, I've not located any sun_checks.xml into my project in order to tell checkstyle plugin to use this file.
So, I guess, plugin has available this file by default.
According to documentation, plugin has available two check rulesets by default: sun_checks.xml and google_checks.xml.
I've tried to change it:
<reporting>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-checkstyle-plugin</artifactId>
<version>${checkstyle-plugin.version}</version>
<configuration>
<configLocation>google_checks.xml</configLocation>
</configuration>
</plugin>
</plugins>
</reporting>
After performing mvn checkstyle:check goal, it's telling me that it's using sun_checks.xml instead of google_checks.xml:
$ mvn checkstyle:check
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< net.gencat.clt.arxius:backend >--------------------
[INFO] Building backend 0.0.1-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-checkstyle-plugin:3.1.1:check (default-cli) # backend ---
[INFO] There are 4 errors reported by Checkstyle 8.29 with sun_checks.xml ruleset.
[ERROR] src/main/java/net/gencat/clt/arxius/backend/BackendApplication.java:[1] (javadoc) JavadocPackage: Missing package-info.java file.
[ERROR] src/main/java/net/gencat/clt/arxius/backend/BackendApplication.java:[6,1] (design) HideUtilityClassConstructor: Utility classes should not have a public or default constructor.
[ERROR] src/main/java/net/gencat/clt/arxius/backend/BackendApplication.java:[9,1] (whitespace) FileTabCharacter: File contains tab characters (this is the first instance).
[ERROR] src/main/java/net/gencat/clt/arxius/backend/BackendApplication.java:[9,9] (javadoc) MissingJavadocMethod: Missing a Javadoc comment.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.265 s
[INFO] Finished at: 2020-10-21T10:45:52+02:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:3.1.1:check (default-cli) on project backend: You have 4 Checkstyle violations. -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException
Any ideas?

You are using the google_checks.xml under <reporting> tag. You can keep it like this but repoting tag as maven.apache.org says: A plugin is actually not a report plugin in itself. But one (or several) of its goals or Mojos may be specialized to be invoked by maven-site-plugin, typically during the site build life cycle.
if you want to use mvn checkstyle:check goal you need to also have:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-checkstyle-plugin</artifactId>
<version>2.17</version>
<executions>
<execution>
<id>checkstyle</id>
<phase>validate</phase>
<goals>
<goal>check</goal>
</goals>
</execution>
</executions>
<configuration>
<configLocation>google_checks.xml</configLocation>
</configuration>
</plugin>
</plugins>
</build>

The parameters 'mainClass' for goal org.codehaus.mojo:exec-maven-plugin:1.6.0:java are missing or invalid

I want to set main class in pom.xml to run exec:java I checked lots of resources but still have the same error.
I tried putting it in under execution tag.
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2.1</version>
<executions>
<execution>
<goals>
<goal>java</goal>
</goals>
<configuration>
<mainClass>com.mertilovski.app.Game</mainClass>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
My main class in under app directory.
TicTacToe/TicTacToe-Game/src/main/java/com/mertilovski/app
pom.xml is in TicTacToe directory.
That is where I run
mvn exec:java -Dexec.mainClass="com.mertilovski.app.Game"
I tried making an package com.mertilovski.app; declaration on top.
mvn exec:java -Dexec.mainClass="src.main.java.com.mertilovski.app.com.mertilovski.app.Game
"
Result is :
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------
------------
[INFO] Building TicTacToe-Game 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------
------------
[INFO]
[INFO] >>> exec-maven-plugin:1.2.1:java (default-cli) > validate #
TicTacToe-Game >>>
[INFO]
[INFO] <<< exec-maven-plugin:1.2.1:java (default-cli) < validate #
TicTacToe-Game <<<
[INFO]
[INFO] --- exec-maven-plugin:1.2.1:java (default-cli) # TicTacToe-
Game ---
[WARNING]
java.lang.ClassNotFoundException: com.mertilovski.app.Game
at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:285)
at java.lang.Thread.run(Thread.java:748)
[INFO] ------------------------------------------------------------
------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------
------------
[INFO] Total time: 0.639 s
[INFO] Finished at: 2019-03-26T01:30:18+03:00
[INFO] Final Memory: 8M/106M
[INFO] ------------------------------------------------------------
------------
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-
plugin:1.2.1:java (default-cli) on project TicTacToe-Game: An
exception occured while executing the Java class.
com.mertilovski.app.Game -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven
with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug
logging.
[ERROR]
[ERROR] For more information about the errors and possible
solutions, please read the following articles:
[ERROR] [Help 1]
http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

Your XML structure seems incorrect as configuration node should be outside executions (docs):
<executions>
<execution>
<goals>
<goal>java</goal>
</goals>
</execution>
</executions>
<configuration>
<mainClass>com.mertilovski.app.Game</mainClass>
</configuration>

Firstly I declared a package com.mertilovski.app in top of my Game.java file.
Than I ran the
mvn exec:java -Dexec.mainClass="com.mertilovski.app.Game"
pom.xml looks like this (remaining part is same)
<configuration>
<mainClass>com.mertilovski.app.Game</mainClass>
</configuration>
When I run find . -type f -name "Game.class" I get :
./src/main/java/com/mertilovski/app/com/mertilovski/app/Game.class
./target/classes/com/mertilovski/app/Game.class

Error: unknown option: -M while using module option of maven-jdeps-plugin

I found the module attribute on the official documentation of the maven-jdeps-plugin which states that
Show module containing the package
Type: boolean
Since: JDK 1.9.0
Required: No
User Property: jdeps.module
Default: false
Trying to make use of it with the current minimal pom.xml as follows:-
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.7.0</version>
<configuration>
<source>9</source>
<target>9</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jdeps-plugin</artifactId>
<version>3.1.0</version>
<configuration>
<apiOnly>false</apiOnly>
<failOnWarning>true</failOnWarning>
<module>true</module>
</configuration>
<executions>
<execution>
<goals>
<goal>jdkinternals</goal> <!-- verify main classes -->
<goal>test-jdkinternals</goal> <!-- verify test classes -->
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
The build of my project(named sparkjdk9) on executing
mvn clean install
results into these logs:-
[INFO] --- maven-jdeps-plugin:3.1.0:jdkinternals (default) # sparkjdk9 ---
[INFO]
Error: unknown option: -M
Usage: jdeps <options> <path ...>]
use -h, -?, -help, or --help for a list of possible options
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.649 s
[INFO] Finished at: ...
[INFO] Final Memory: 13M/44M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-jdeps-plugin:3.1.0:jdkinternals (default) on project sparkjdk9:
[ERROR] Exit code: 2
[ERROR] Command line was: /bin/sh -c '/Library/Java/JavaVirtualMachines/jdk-9.jdk/Contents/Home/bin/jdeps' '-M' '.../sparkjdk9/target/classes'
Looking further for similar flag in jdeps tool, I could see the error is justified since there is no such flag -M in its usage.
Q. What is the use of this attribute and how can it be used?

See https://github.com/apache/maven-plugins/blob/trunk/maven-jdeps-plugin/src/main/java/org/apache/maven/plugin/jdeps/AbstractJDepsMojo.java#L322
The -M used to be the module parameter, but it seems like it has been renamed to -m/--module in the meantime.
Update : This should be resolved with 3.1.1 release of the Maven JDeps Plugin as followed by the tracker](See https://github.com/apache/maven-plugins/blob/trunk/maven-jdeps-plugin/src/main/java/org/apache/maven/plugin/jdeps/AbstractJDepsMojo.java#L322
The -M used to be the module parameter, but it seems like it has been renamed to -m/--module in the meantime.
Update : This should be resolved with 3.1.1 release of the Maven JDeps Plugin as followed by the tracker.

Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile

Given the below pom.xml:
<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.myApp</groupId>
<artifactId>malloc</artifactId>
<version>0.0.1</version>
<packaging>war</packaging>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
</properties>
<repositories>
<repository>
<id>project</id>
<url>file:///${basedir}/lib</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>com.myApp</groupId>
<artifactId>myApp.core</artifactId>
<version>1.0.0</version>
</dependency>
... //other dependencies
</dependencies>
<build>
<sourceDirectory>src</sourceDirectory>
<resources>
<resource>
<directory>src</directory>
<excludes>
<exclude>**/*.java</exclude>
</excludes>
</resource>
</resources>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>2.4</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
</manifest>
<addMavenDescriptor>false</addMavenDescriptor>
</archive>
<webResources>
<webResource>
<directory>${project.build.directory}/WebContent/WEB-INF</directory>
<includes>
<include>web.xml</include>
</includes>
<targetPath>WEB-INF</targetPath>
<filtering>true</filtering>
</webResource>
</webResources>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.10</version>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>package</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<outputDirectory>${project.build.directory}/WebContent/WEB-INF/lib</outputDirectory>
<includeScope>runtime</includeScope>
<overWriteReleases>false</overWriteReleases>
<overWriteSnapshots>false</overWriteSnapshots>
<overWriteIfNewer>true</overWriteIfNewer>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
And the following project structure:
I expect the maven-dependency-plugin would copy all the dependencies to the WebContent/WEB-INF/lib but when I run
mvn clean install
The following error is generated:
[INFO] Scanning for projects...
[INFO]
[INFO] Using the builder org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder with a thread count of 1
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building api-malloc 0.0.1
[INFO] ------------------------------------------------------------------------
[WARNING] The POM for com.oracle:ojdbc6:jar:10.2.0.4.0 is missing, no dependency information available
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) # api-malloc ---
[INFO] Deleting C:\Development\malloc\target
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) # api-malloc ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 1 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) # api-malloc ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 8 source files to C:\Development\malloc\target\classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /C:/Development/malloc/src/com/myApp/api/malloc/dto/RegionTypeDTO.java:[3,34] package com.myApp.api.core.dto does not exist
[ERROR] /C:/Development/malloc/src/com/myApp/api/malloc/dto/RegionTypeDTO.java:[5,39] cannot find symbol
symbol: class IDTO
[INFO] 26 errors
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.209 s
[INFO] Finished at: 2015-11-26T15:33:40-05:00
[INFO] Final Memory: 21M/227M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project malloc: Compilation failure: Compilation failure:
[ERROR] /C:/Development/malloc/src/com/myApp/api/malloc/dto/RegionTypeDTO.java:[3,34] package com.myApp.api.core.dto does not exist
[ERROR] /C:/Development/malloc/src/com/myApp/api/malloc/dto/RegionTypeDTO.java:[5,39] cannot find symbol
[ERROR] symbol: class IDTO
[ERROR] location: class com.myApp.api.malloc.controllers.TestController
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException
I noticed the WEB-INF/lib folder is always empty, maven dependencies are not copied over.
I am suspecting the copy-dependencies plugin didn't get run before the compile stage but I can't really figure out - anything that I missed?

The copy-dependencies goal indeed will never be executed if the compilation fails because its binding is to the package phase, which comes after the compile phase (to which by default is linked the Maven Compiler Plugin).
If you want it to run before the compile phase, you need to change the phase value of the execution of the copy-dependencies goal. Changing to process-resources should be fine and should also make sense.
<phase>package</phase>
For a full description of phases, you can check official documentation, here.
You should also fix the compilation errors the build output is pointing at. I see the sourceDirectory element is overriding what Maven uses by default for Java source code (src\main\java), hence I suppose your code is directly under the src folder.
Updated: the package X does not exist error occurs when the code is referring to a package not resolved by the Java compiler, hence it is not able to see that package in the classpath, which means in the declared dependencies: does myApp.core contain that package and class? If yes, then the repositories element (the lib folder) is probably not properly providing the myApp dependency.
You can try to install the dependency locally in your .m2 maven cache using the Maven Install Plugin as specified here.
You could execute from the command line as following:
mvn org.apache.maven.plugins:maven-install-plugin:2.5.2:install-file
-Dfile=lib\myApp.core-1.0.0.jar \
-DgroupId=com.myApp \
-DartifactId=myApp.core \
-Dversion=1.0.0 \
-Dpackaging=jar \
Side note: Maven prefers lower case groupid and artifactid tokens. Moreover, instead of using Camel Case (i.e. myApp), Maven convention is also use a dash for separating tokens (i.e. myapp-core).

exec-maven-plugin error, even on working example

EDIT5 Updated /
I'm using Maven 3.3.3.
I just create new project and added compile and exec plugin, as examples on web.
I tried to execute, but I got error
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2.1:java (default-cli) on project QNAProject: An exception occured while executing the Java class. com.jadex.qna.QNAProject.App -> [Help 1]<br>
[ERROR] <br>
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.<br>
[ERROR] Re-run Maven using the -X switch to enable full debug logging.<br>
[ERROR] <br>
[ERROR] For more information about the errors and possible solutions, please read the following articles:<br>
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException<br>
I tried exec-maven-plugin version 1.2.1 and 1.4.0, but got same error. Here is my pom.xml
<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.jadex.qna</groupId>
<artifactId>QNAProject</artifactId>
<version>0.1</version>
<packaging>jar</packaging>
<name>QNAProject</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<source>1.6</source>
<target>1.6</target>
</configuration>
</plugin>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2.1</version>
<executions>
<execution>
<goals>
<goal>java</goal>
</goals>
</execution>
</executions>
<configuration>
<executable>maven</executable>
<mainClass>com.jadex.qna.QNAProject.App</mainClass>
</configuration>
</plugin>
</plugins>
</build>
</project>
I even tried a working example project from several sites,
such as
http://examples.javacodegeeks.com/enterprise-java/maven/create-java-project-with-maven-example/
http://www.mkyong.com/maven/how-to-create-a-java-project-with-maven/
but I got same error.
I unzipped maven at C:\apache-maven-3.3.3 and created environment variable MAVEN_HOME as same path.
What is the problem?
====================================
EDIT: Here is the result
Well.. I set MAVEN_HOME, not M2_HOME because tutorial what I found said to set it only...
Of course, echo %MAVEN_HOME% shows
C:\apache-maven-3.3.3
is it wrong?
I added %MAVEN_HOME%\bin to PATH variable, but it did not work too.
And, I'm using eclipse
=====================================
EDIT2: Here is full log. I used goal 'clean exec:java -e -X'
It was too long, so I uploaded to my blog here.
And note that I changed repository folder from C:\Users.....m2 to new local repository folder C:\apache-maven-localrepository
https://arincblossom.wordpress.com/2015/06/15/error-logs/
=======================================
EDIT3: I changed maven-compiler-plugin setting like this
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<verbose>true</verbose>
<fork>true</fork>
<executable>${env.JAVA_HOME}/bin/javac</executable>
<compilerVersion>1.5</compilerVersion>
<!-- <source>1.8</source>
<target>1.8</target> -->
</configuration>
</plugin>
It prevented me from having error from mvn -e compile exec:java but I can't run with mvn exec:java -Dexec.mainClass="com.jadex.qna.QNAProject.App"
=================================
EDIT4: OK, I'll try from the bottom, and post again. Thanks for your sincere helps.
======================================
EDIT5
I reset all the sequences... re-installed eclipse, maven.. and re-created projects... but nothing worked...
I changed eclipse settings to fix JDK path to installed jdk path, not JRE path. then I found that 'mvn -e clean compile exec:java' is working, but I want to just 'mvn clean exec:java' work. It does not work at all.
You can check full source here
https://github.com/arincblossom/MavenTestProject
This is current console message for 'mvn -e clean exec:java'
[WARNING]
[WARNING] Some problems were encountered while building the effective settings
[WARNING] expected START_TAG or END_TAG not TEXT (position: TEXT seen ...ore artifacts.\n |\n | Default: ${user.home}/.m2/repository\n <l... #53:5) # C:\apache-maven-3.3.3\conf\settings.xml, line 53, column 5
[WARNING] expected START_TAG or END_TAG not TEXT (position: TEXT seen ...ore artifacts.\n |\n | Default: ${user.home}/.m2/repository\n <l... #53:5) # C:\apache-maven-3.3.3\conf\settings.xml, line 53, column 5
[WARNING]
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building MavenTestProject 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) # MavenTestProject ---
[INFO] Deleting C:\Users\bonavision_laptop\Desktop\Project\JadeX\MavenTestProject\MavenTestProject\target
[INFO]
[INFO] --- exec-maven-plugin:1.4.0:java (default-cli) # MavenTestProject ---
[WARNING]
java.lang.ClassNotFoundException: com.jadex.qna.MavenTestProject.App
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:281)
at java.lang.Thread.run(Thread.java:745)
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.900 s
[INFO] Finished at: 2015-06-15T17:42:19+09:00
[INFO] Final Memory: 8M/153M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.4.0:java (default-cli) on project MavenTestProject: An exception occured while executing the Java class. com.jadex.qna.MavenTestProject.App -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

This issue happens, when it is not compatible with eclipse too.
Try this
mvn clean install eclipse:eclipse
Vote up, if it works to help fellow members

The error log which you posted says the following:
java.lang.ClassNotFoundException com.jadex.qna.QNAProject.App
So it clear what the root source of the error is. You are trying to execute the main() method of a class whose class file Maven cannot find. As this SO article discusses, you can try explicitly compiling first, then executing after the class file has been generated:
mvn -e compile exec:java
mvn exec:java -Dexec.mainClass="com.jadex.qna.QNAProject.App"

I ran into this same problem, it was caused by a port conflict.
my tomcat server tried to start on port 8080 but i already had a binding for it.
netstat -anto will show you port bindings 0.0.0.0:8080 or similar and it's PID this will help you determin what process is already running the port bidning, either change it in your timcat server or whatever process is using the bidning. Could be caused by an IIS, SKype or similar.