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How to find package name once Maven dependency is added

I'm attempting to use the socket.io implementation for Java. I need 2 dependencies: 1) Engine.IO Java Server and 2) Socket.IO Server Java. I'm struggling to import the actual Java packages once the dependencies have been added to my pom.xml. Looking at the javadocs for Engine.IO Java Server, it looks like the package name to import should be io.socket.engineio.server. However, this results in an error (details below). For other dependencies that I add, what's the best way to find the package name to actually import the dependency in my Java source code?
I'm not using an IDE like IntelliJ/Eclipse. I'm just using a more simple text editor (VSCode) and a terminal. Also, I've ensured the dependencies are actually downloaded and installed in my ~/.m2/repository directory. Here are my files/terminal output.
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>
<groupId>com.mycompany.app</groupId>
<artifactId>game-server</artifactId>
<version>1.0-SNAPSHOT</version>
<name>game-server</name>
<!-- FIXME change it to the project's website -->
<url>http://www.example.com</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>io.socket</groupId>
<artifactId>engine.io-server</artifactId>
<version>6.1.0</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>io.socket</groupId>
<artifactId>socket.io-server</artifactId>
<version>4.0.1</version>
<scope>compile</scope>
</dependency>
</dependencies>
<build>
<pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
<plugins>
<!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
<plugin>
<artifactId>maven-clean-plugin</artifactId>
<version>3.1.0</version>
</plugin>
<!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>3.0.2</version>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
</plugin>
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.22.1</version>
</plugin>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>3.0.2</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<classpathPrefix>lib/</classpathPrefix>
<mainClass>com.mycompany.app.App</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<artifactId>maven-install-plugin</artifactId>
<version>2.5.2</version>
</plugin>
<plugin>
<artifactId>maven-deploy-plugin</artifactId>
<version>2.8.2</version>
</plugin>
<plugin>
<artifactId>maven-project-info-reports-plugin</artifactId>
<version>3.0.0</version>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
App.java
package com.mycompany.app;
import io.socket.engineio.server;
public class App
{
public static void main( String[] args )
{
System.out.println( "Hello World!" );
}
}
Terminal Output
$ mvn compile
[INFO] Scanning for projects...
[INFO]
[INFO] -------------------< com.mycompany.app:game-server >--------------------
[INFO] Building game-server 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:3.0.2:resources (default-resources) # game-server ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /home/josh/Repos/game/game-server/src/main/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.8.0:compile (default-compile) # game-server ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /home/josh/Repos/game/game-server/target/classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /home/josh/Repos/game/game-server/src/main/java/com/mycompany/app/App.java:[3,26] package io.socket.engineio does not exis

Maven build failure classNotFoundException

It's my first time trying out maven and I can't understand why I keep getting classnotfoundexception every time I am trying to build. This is the error I am receiving:
[INFO] Scanning for projects...
[INFO]
[INFO] ---------------------------< owmapi:owmapi >----------------------------
[INFO] Building OwmAPICase 0.0.1-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- exec-maven-plugin:3.0.0:java (default-cli) # owmapi ---
[WARNING]
java.lang.ClassNotFoundException: owmapi.Main
at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:435)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:589)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:246)
at java.base/java.lang.Thread.run(Thread.java:832)
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.582 s
[INFO] Finished at: 2021-02-28T14:09:17+01:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:3.0.0:java (default-cli) on project owmapi: An exception occured while executing the Java class. owmapi.Main -> [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
And this 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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>owmapi</groupId> <!-- case.se.ctk -->
<artifactId>owmapi</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>OwmAPICase</name>
<properties>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
</properties>
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>3.0.0</version>
<configuration>
<mainClass>owmapi.Main</mainClass>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/net.aksingh/owm-japis -->
<dependency>
<groupId>net.aksingh</groupId>
<artifactId>owm-japis</artifactId>
<version>2.5.3.0</version>
</dependency>
</dependencies>
</project>
Everything works fine if i simply run the project as a java application in eclipse but for some reason it won't work with maven. I guess the problem lies in mainClass in my pom but I've tried several solutions to no avail.

I think your main class have some dependencies on the jar mentioned in the pom.xml. You're simply creating a target jar which doesn't have those dependencies included. You need to create the uber/fat jar which include all the relevant dependencies. You can use this following plugin maven-assembly-plugin for creating the target jar.
Assumption: Main.java class is under package owmapi.
<build>
<finalName>owmapi</finalName>
<plugins>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<mainClass>owmapi.Main</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
</plugin>
</plugins>
</build>

What causes "an unknown compilation problem occurred"?

When trying to compile my project using Maven, I get the following error: An unknown compilation problem occurred.
I tried running the following command to get more details on the error, but I still can't figure it out: mvn -e -X clean install
This is the log I got:
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] An unknown compilation problem occurred
[INFO] 1 error
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO]
[INFO] app ................................................ SUCCESS [ 2.033 s]
[INFO] models ............................................. SUCCESS [ 4.418 s]
[INFO] authorization-db ................................... SUCCESS [ 1.654 s]
[INFO] test-utils ......................................... SUCCESS [ 0.721 s]
[INFO] clients ............................................ SUCCESS [ 7.412 s]
[INFO] data-access ........................................ FAILURE [ 3.289 s]
[INFO] templating ......................................... SKIPPED
[INFO] guice-vertx ........................................ SKIPPED
[INFO] routing ............................................ SKIPPED
[INFO] frontend-tests ..................................... SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 19.756 s
[INFO] Finished at: 2019-06-18T11:00:07+01:00
[INFO] Final Memory: 53M/190M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project data-access: Compilation failure
[ERROR] An unknown compilation problem occurred
[ERROR] -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project data-access: Compilation failure
An unknown compilation problem occurred
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:212)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:307)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:863)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:288)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:199)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
at org.codehaus.classworlds.Launcher.main(Launcher.java:47)
Caused by: org.apache.maven.plugin.compiler.CompilationFailureException: Compilation failure
An unknown compilation problem occurred
at org.apache.maven.plugin.compiler.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:858)
at org.apache.maven.plugin.compiler.CompilerMojo.execute(CompilerMojo.java:129)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:207)
... 21 more
[ERROR]
[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
[ERROR]
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR] mvn <goals> -rf :data-access
EDIT: This is the pom.xml file of the data-access module:
<?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>com.some.app</groupId>
<artifactId>app</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<artifactId>data-access</artifactId>
<packaging>jar</packaging>
<dependencies>
<dependency>
<groupId>com.some.app</groupId>
<artifactId>authorization-db</artifactId>
</dependency>
<dependency>
<groupId>com.englishtown.vertx</groupId>
<artifactId>vertx-guice</artifactId>
</dependency>
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-core</artifactId>
</dependency>
<dependency>
<groupId>io.vertx</groupId>
<artifactId>vertx-core</artifactId>
</dependency>
<dependency>
<groupId>io.vertx</groupId>
<artifactId>vertx-web</artifactId>
</dependency>
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
</dependency>
<dependency>
<groupId>io.vertx</groupId>
<artifactId>testtools</artifactId>
</dependency>
<dependency>
<groupId>io.vertx</groupId>
<artifactId>vertx-unit</artifactId>
</dependency>
<dependency>
<groupId>io.vertx</groupId>
<artifactId>vertx-codetrans</artifactId>
</dependency>
<dependency>
<groupId>io.vertx</groupId>
<artifactId>vertx-rx-java</artifactId>
</dependency>
<dependency>
<groupId>com.some.app</groupId>
<artifactId>clients</artifactId>
<version>${project.version}</version>
</dependency>
<dependency>
<groupId>com.some.app</groupId>
<artifactId>models</artifactId>
<version>${project.version}</version>
</dependency>
<dependency>
<groupId>com.some.app</groupId>
<artifactId>test-utils</artifactId>
<version>${project.version}</version>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-csv</artifactId>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.dataformat</groupId>
<artifactId>jackson-dataformat-yaml</artifactId>
</dependency>
<dependency>
<groupId>com.google.zxing</groupId>
<artifactId>core</artifactId>
</dependency>
<dependency>
<groupId>com.google.zxing</groupId>
<artifactId>javase</artifactId>
</dependency>
<dependency>
<groupId>com.itextpdf</groupId>
<artifactId>itextpdf</artifactId>
</dependency>
<dependency>
<groupId>org.apache.poi</groupId>
<artifactId>poi-ooxml</artifactId>
<version>3.17</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-deploy-plugin</artifactId>
<configuration>
<skip>true</skip>
</configuration>
</plugin>
</plugins>
</build>
</project>
EDIT 2: Maven compiler plugin configuration on root pom.xml:
...
<properties>
<maven-compiler-plugin.version>3.1</maven-compiler-plugin.version>
<java.version>11</java.version>
</properties>
...
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>${maven-compiler-plugin.version}</version>
<configuration>
<source>${java.version}</source>
<target>${java.version}</target>
</configuration>
</plugin>
...
To note that this compilation problem started happening after I migrated the Java version in the project from 1.8 to 11.

I was facing same issue. I was able to get rid of this issue after removing
<compilerArgument>-Werror</compilerArgument>
line from maven compiler plugin configuration in pom.xml file.
maven-compiler-plugin configuration before removing above line:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<encoding>UTF-8</encoding>
<source>1.8</source>
<target>1.8</target>
<compilerArgument>-Werror</compilerArgument>
</configuration>
</plugin>
maven-compiler-plugin configuration after removing above line:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<encoding>UTF-8</encoding>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>

You are using old version of maven plugin (3.1) to compile your code. To compile java 11 code using maven please use maven plugin with below configuration:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
<configuration>
<release>11</release>
</configuration>
</plugin>

Follow steps are given below,
1) Run as Maven clean
2) Go to Project(top bar in eclipse) and clean it
3) Run as Maven install
(Sometimes need to clean twice in eclipse before run mvn install)
Hope this will help.

You are using the maven compiler plugin and it is a fight to use correct version compatibility between maven, JDK, and this plug-in.
In my case, reason of the issue was, I was using jdk-8u291-windows-x64 instead of jdk-8u211-windows-x64.

Could not find goal 'devmode' in plugin org.codehaus.mojo

I am a beginner in GWT and Maven. I created a new GWT Application project in Eclipse. Then, I converted that project into Maven Project by right-click on Project name => Configure => Convert to Maven Project and I saw that a pom file was generated for that project. Next, I run as project as Maven build but it was not compiled since a goal was not specified there. Actually, I don't understand what exactly have I to write under that goal section, therefore, I wrote package under that and then again I built maven and it compiled successfully.
After that, I tried to run this maven project in Command Prompt on the SuperDevMode using the 2nd step mentioned on Run the GWT Project under the Setting up a new project section. But while following these steps on Command Prompt, I got an error that devmode could not be found. Here is my Command prompt log:
C:\Users\TEST>cd eclipse-workspace/MyWebApp
C:\Users\TEST\eclipse-workspace\MyWebApp>mvn war:exploded
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building MavenApp 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-war-plugin:3.1.0:exploded (default-cli) # abcdef ---
[INFO] Exploding webapp
[INFO] Assembling webapp [abcdef] in [C:\Users\TEST\eclipse-workspace\MyWebApp\target\abcdef-0.0.1-SNAPSHOT]
[INFO] Processing war project
[INFO] Webapp assembled in [63 msecs]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.920 s
[INFO] Finished at: 2017-08-30T11:24:53+05:30
[INFO] Final Memory: 12M/107M
[INFO] ------------------------------------------------------------------------
C:\Users\TEST\eclipse-workspace\MyWebApp>mvn gwt:devmode
[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.301 s
[INFO] Finished at: 2017-08-30T11:25:02+05:30
[INFO] Final Memory: 8M/107M
[INFO] ------------------------------------------------------------------------
[ERROR] Could not find goal 'devmode' in plugin org.codehaus.mojo:gwt-maven-plugin:2.8.1 among available goals clean, compile, compile-report, css, debug, eclipse, eclipseTest, generateAsync, help, i18n, mergewebxml, resources, run, run-codeserver, source-jar, test -> [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/MojoNotFoundException
Here is my pom.xml 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>MyWebApp</groupId>
<artifactId>abcdef</artifactId>
<version>0.0.1-SNAPSHOT</version>
<build>
<sourceDirectory>src</sourceDirectory>
<testSourceDirectory>test</testSourceDirectory>
<resources>
<resource>
<directory>src</directory>
<excludes>
<exclude>**/*.java</exclude>
</excludes>
</resource>
</resources>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
<name>MavenApp</name>
<description>It is a maven app</description>
</project>
I searched a lot to resolve this error but found no solution for that issue. Please help me to fix this issue as I am very confused on how to fix it.
Edit: After further study, I used mvn gwt:run as an alternative to the command mvn gwt:devmode, but still I got another error on command prompt as given below:
[ERROR] Failed to execute goal org.codehaus.mojo:gwt-maven-plugin:2.8.1:run (default-cli) on project MyWebApp: The parameters 'runTarget' for goal org.codehaus.mojo:gwt-maven-plugin:2.8.1:run are missing or invalid

Without any more information than gwt:devmode, Maven will try to find an appropriate plugin, based on its default settings. It happens that a gwt-maven-plugin exists with org.codehaus.mojo as groupId, fitting in Maven built-in plugin resolution.
But this is not the plugin you're looking for.
You are probably trying to use this one, so just add this to your pom.xml, in the <plugins> section:
<plugin>
<groupId>net.ltgt.gwt.maven</groupId>
<artifactId>gwt-maven-plugin</artifactId>
<version>1.0-rc-8</version>
<extensions>true</extensions>
<configuration>
<moduleName>com.example.app.App</moduleName>
</configuration>
</plugin>
Adapting the moduleName if needed.

Well, I was able to solve this issue by copying some dependencies, plugin, and configuration from the pom.xml file (which is generated in the project created by the webAppCreator using maven) to the pom.xml file of my project created in the Eclipse. So, this is my pom.xml file created finally:
<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>MyPersonalProject</groupId>
<artifactId>MyPersonalProject</artifactId>
<version>0.0.1-SNAPSHOT</version>
<properties>
<!-- Setting maven.compiler.source to something different to 1.8
needs that you configure the sourceLevel in gwt-maven-plugin since
GWT compiler 2.8 requires 1.8 (see gwt-maven-plugin block below) -->
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
<!-- Don't let your Mac use a crazy non-standard encoding -->
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
</properties>
<dependencyManagement>
<dependencies>
<!-- ensure all GWT deps use the same version (unless overridden) -->
<dependency>
<groupId>com.google.gwt</groupId>
<artifactId>gwt</artifactId>
<version>2.8.1</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>com.google.gwt</groupId>
<artifactId>gwt-servlet</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>com.google.gwt</groupId>
<artifactId>gwt-user</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>com.google.gwt</groupId>
<artifactId>gwt-dev</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<outputDirectory>${project.build.directory}/${project.build.finalName}/WEB-INF/classes</outputDirectory>
<sourceDirectory>src</sourceDirectory>
<testSourceDirectory>test</testSourceDirectory>
<resources>
<resource>
<directory>src</directory>
<excludes>
<exclude>**/*.java</exclude>
</excludes>
</resource>
</resources>
<plugins>
<plugin>
<groupId>net.ltgt.gwt.maven</groupId>
<artifactId>gwt-maven-plugin</artifactId>
<version>1.0-rc-6</version>
<executions>
<execution>
<goals>
<goal>import-sources</goal>
<goal>compile</goal>
<goal>import-test-sources</goal>
<goal>test</goal>
</goals>
</execution>
</executions>
<configuration>
<moduleName>mypackage.MyPersonalproject</moduleName>
<failOnError>true</failOnError>
<!-- GWT compiler 2.8 requires 1.8, hence define sourceLevel here if you use
a different source language for java compilation -->
<sourceLevel>1.8</sourceLevel>
<!-- Compiler configuration -->
<compilerArgs>
<!-- Ask GWT to create the Story of Your Compile (SOYC) (gwt:compile) -->
<arg>-compileReport</arg>
<arg>-XcompilerMetrics</arg>
</compilerArgs>
<!-- DevMode configuration -->
<warDir>${project.build.directory}/${project.build.finalName}</warDir>
<classpathScope>compile+runtime</classpathScope>
<!-- URL(s) that should be opened by DevMode (gwt:devmode). -->
<startupUrls>
<startupUrl>MyPersonalProject.html</startupUrl>
</startupUrls>
</configuration>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
When I run this application using maven in the Command Prompt, it ran successfully except showing 2 or 3 warnings in the Command Prompt log. Also, I noticed that the SNAPSHOT generated in the version is different for the pom.xml created by Eclipse as compared to the one created by the maven project on command prompt.

Error running project in eclipse wtih maven "Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile" [duplicate]

This question already has answers here:
How to set specific Java version to Maven?
(28 answers)
Closed 8 years ago.
I'm learning google app engine programs with eclipse and maven but I've been stuck on this error since 2 days. I've looked everywhere on the internet but couldn't get a solution to my problem.
Here's the console output
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building helloworld 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] >>> appengine-maven-plugin:1.9.4:devserver (default-cli) > package # helloworld >>>
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) # helloworld ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /Users/AdioJack/Developer/Scalable Apps (Udacity)/ud859-master/Lesson_2/000_Hello_Endpoints/src/main/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) # helloworld ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 3 source files to /Users/AdioJack/Developer/Scalable Apps (Udacity)/ud859-master/Lesson_2/000_Hello_Endpoints/target/helloworld-1.0-SNAPSHOT/WEB-INF/classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.462 s
[INFO] Finished at: 2014-09-10T12:34:38+05:30
[INFO] Final Memory: 6M/81M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project helloworld: Fatal error compiling: invalid target release: 1.7 -> [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
and here's the 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>
<packaging>war</packaging>
<version>1.0-SNAPSHOT</version>
<groupId>com.google.training.helloworld</groupId>
<artifactId>helloworld</artifactId>
<properties>
<appengine.app.version>1</appengine.app.version>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<prerequisites>
<maven>3.1.0</maven>
</prerequisites>
<dependencies>
<!-- Compile/runtime dependencies -->
<dependency>
<groupId>com.google.appengine</groupId>
<artifactId>appengine-api-1.0-sdk</artifactId>
<version>1.9.4</version>
</dependency>
<dependency>
<groupId>com.google.appengine</groupId>
<artifactId>appengine-endpoints</artifactId>
<version>1.9.4</version>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>2.5</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>javax.inject</groupId>
<artifactId>javax.inject</artifactId>
<version>1</version>
</dependency>
<!-- Test Dependencies -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>com.google.appengine</groupId>
<artifactId>appengine-testing</artifactId>
<version>1.9.4</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>com.google.appengine</groupId>
<artifactId>appengine-api-stubs</artifactId>
<version>1.9.4</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<!-- for hot reload of the web application-->
<outputDirectory>${project.build.directory}/${project.build.finalName}/WEB-INF/classes</outputDirectory>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<version>3.1</version>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.7</source>
<target>1.7</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>2.4</version>
<configuration>
<webXml>${project.build.directory}/generated-sources/appengine-endpoints/WEB-INF/web.xml</webXml>
<webResources>
<resource>
<!-- this is relative to the pom.xml directory -->
<directory>${project.build.directory}/generated-sources/appengine-endpoints</directory>
<!-- the list has a default value of ** -->
<includes>
<include>WEB-INF/*.discovery</include>
<include>WEB-INF/*.api</include>
</includes>
</resource>
</webResources>
</configuration>
</plugin>
<plugin>
<groupId>com.google.appengine</groupId>
<artifactId>appengine-maven-plugin</artifactId>
<version>1.9.4</version>
<configuration>
<enableJarClasses>false</enableJarClasses>
<!-- Comment in the below snippet to bind to all IPs instead of just localhost -->
<!-- address>0.0.0.0</address>
<port>8080</port -->
<!-- Comment in the below snippet to enable local debugging with a remove debugger
like those included with Eclipse or IntelliJ -->
<!-- jvmFlags>
<jvmFlag>-agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n</jvmFlag>
</jvmFlags -->
</configuration>
<executions>
<execution>
<goals>
<goal>endpoints_get_discovery_doc</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>
Here's java & maven version information
Apache Maven 3.2.3 (33f8c3e1027c3ddde99d3cdebad2656a31e8fdf4; 2014-08-12T02:28:10+05:30)
Maven home: /usr/local/Cellar/maven/3.2.3/libexec
Java version: 1.8.0_20, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.8.0_20.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.10", arch: "x86_64", family: "mac"
This question is different from
How to set specific java version to Maven
I've only 1 version of java installed i.e. JDK 8
This is the command I ran in terminal to make maven is using latest java version
export JAVA_HOME=$(/usr/libexec/java_home)

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project helloworld: Fatal error compiling: invalid target release: 1.7 -> [Help 1]
If you look at the error, its complaining about an JDK7. Make sure you are using correct version of Java to be able to compile the application. You need atleast jdk1.7 (or higher).
As the question is tagged for eclipse, you can also set the available java compilers in the 'installeded JREs' option inside eclipse
Apart from that, you can also set the compliance level inside the pom of the project as below
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<configuration>
<source>1.7</source> <!-- or 1.8 -->
<target>1.7</target> <!-- or 1.8 -->
</configuration>
</plugin>

You have to install java 7 for the compile to work, however, java 8 and newer should also work