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execute jar error could not find or load main class

sorry for another "could not find or load main class" question.
I'm new to Java. I searched for a while but couldn't find the reason.
My project is a very simple one created with maven.
mvn archetype:generate -DgroupId=mycompany -DartifactId=faker -DinteractiveMode=false
pom.xml(default, not change)
<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>mycompany</groupId>
<artifactId>faker</artifactId>
<packaging>jar</packaging>
<version>1.0-SNAPSHOT</version>
<name>faker</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
</project>
and source code(default, not change)
package mycompany;
public class App {
public static void main( String[] args ) {
System.out.println( "Hello World!" );
}
}
I build jar file with jar command.
~$ jar cvfm MyCompany.jar manifest.txt src/main/java/mycompany/App.java
# added manifest
# adding: src/main/java/mycompany/App.java(in = 705) (out= 352)(deflated 50%)
manifest.txt
~$ cat manifest.txt
Main-Class: mycompany.App
# (has an empty new line here)
but whenever I executed it, it give me following error:
~$ java -jar MyCompany.jar
Error: Could not find or load main class mycompany.App
Where is wrong ?
openjdk version "1.8.0_181"
Apache Maven 3.5.2
Thanks #ohlec and #Kayaman, to be more specific, here's the way to solve it.
# get App.class
~$ cd src/main/java/mycompany/ && javac App.java
# back to faker folder
~$ jar cvfm MyCompany.jar manifest.txt -C src/main/java mycompany/App.class
~$ java -jar MyCompany.jar
# Hello World!

Your jar should have a directory structure that mirrors the package structure; in your case, src/main/java is included, although that is not a package prefix. Use -C to specify the root directory:
jar cvfm MyCompany.jar manifest.txt -C target mycompany/App.class
Edit: Also, as Kayaman pointed out, you need to include the .class file, not the .java file.

Dependency error in eclipse project making use of Maven

I am using Eclipse Mars to run my Java project. I am making use of Maven in it. But while trying to compile my package I am getting the following error.
Failed to execute goal on project apex-check: Could not resolve dependencies for project org.fundacionjala.enforce.sonarqube:apex-check:jar:1.0: Failed to collect dependencies at org.fundacionjala.enforce.sonarqube:apex-squid:jar:1.0: Failed to read artifact descriptor for org.fundacionjala.enforce.sonarqube:apex-squid:jar:1.0: Could not transfer artifact org.fundacionjala.enforce.sonarqube:apex-squid:pom:1.0 from/to central (https://repo.maven.apache.org/maven2): Failed to authenticate with proxy -> [Help 1].
I am able to find that my pom.xml has a bug in its dependency. But don't know how to resolve it. I have given below my pom.xml file
<?xml version="1.0" encoding="UTF-8"?>
<!-- ~ Copyright (c) Fundacion Jala. All rights reserved. ~ Licensed under the MIT license. See LICENSE file in the project root for full license information. -->
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.fundacionjala.enforce.sonarqube</groupId>
<artifactId>apex</artifactId>
<version>1.0b${build.number}</version>
</parent>
<artifactId>apex-check</artifactId>
<name>Apex :: Checks</name>
<dependencies>
<dependency>
<groupId>${project.groupId}</groupId>
<artifactId>apex-squid</artifactId>
<version>${project.version}</version>
</dependency>
</dependencies>
</project>
I have written 'apex-check' and 'apex-squid' as two separate projects.
Can anyone explain how to correct my pom.xml?

You need to have:
org.fundacionjala.enforce.sonarqube:apex-check:jar:1.0
org.fundacionjala.enforce.sonarqube:apex-squid:jar:1.0
jar files available in your local .m2/repository folder. If they are not present maven will try to download from central repository and as an expected result it will fail on firewall or it will not find the artifact. i.e. if:
apex-check requires apex-squid project as dependency first you need to install squid project files by using mvn install on squid project folder.
But it seems more like you want to create a multi module maven project, take a look at this question. Create a parent project similar to this project, add check and squid as module and run mvn clean install on parent.
**edit: I just see you already have parent, so make sure parent has your projects as modules, which helps reactive build order and eclipse imports

Locally installed jar not seen by maven

I have source code for a framework, let's call it my-framework. It provides various packages, including com.not_telling.framework.db.
I have a pom.xml file for this framework:
<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.not_telling</groupId>
<artifactId>my-famework</artifactId>
<packaging>jar</packaging>
<version>0.0.1-SNAPSHOT</version>
<name>my-framework Maven Library</name>
<url>http://maven.apache.org</url>
<!-- more things here... -->
</project>
I can compile this and install it to my local repository cache, using this command:
mvn install
End of the install log:
[INFO] Installing C:\Users\MyUserName\my-framework\backend\target\my-framework.jar to C:\Users\MyUserName\.m2\repository\com\not_telling\my-famework\0.0.1-SNAPSHOT\my-famework-0.0.1-SNAPSHOT.jar
[INFO] Installing C:\Users\MyUserName\my-framework\backend\pom.xml to C:\Users\MyUserName\.m2\repository\com\not_telling\my-famework\0.0.1-SNAPSHOT\my-famework-0.0.1-SNAPSHOT.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
Then I have another project, that tries to use this as a dependency:
<dependency>
<groupId>com.not_telling</groupId>
<artifactId>my-famework</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
The compilation phase of this project fails with this message:
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project my-project: Compilation failure: Compilation failure:
[ERROR] /C:/Users/MyUserName/workspace/my-project/backend/src/main/java/com/not_telling/some_example.java:[13,17] package com.not_telling.framework.db does not exist
Why is that? Maybe because the jar is in the repository cache, but not in a local repository?
This question is a follow up of absolute maven pomderived entry added to classpath - I realized that instead of doing magic with relative source directory references, I need to make a separate module, but I'm facing this problem.

It was bleeding from numerous wounds. These needed to be fixed:
move source files from under src/ to under src/main/java, in both the framework and the application project
change the group and the artifact id to match the package name E.g. for a package that is named "com.not_telling.framework" I had to use groupId=com.not_telling and name=framework.
The dependency scope was wrong in the application's pom file. I had to remove test
Now it works from command line I can do "mvn install" for the framework, and then "mvn package" for the applications.
The only problem left is that the application cannot be compiled from eclipse, I had to remove all linked source folders / build paths in the application project to the framework.

maven external jar dependency

I am trying to use a jar given by my teacher in my code. So I placed the jar in a lib directory in my project and ran this command :
mvn install:install-file -Dfile=lib/IDLogger.jar -DgroupId=IDLogger -DartifactId=IDLogger -Dversion=1.0 -Dpackaging=jar
Everything is fine.
Then I add the dependency to the pom :
<dependency>
<groupId>IDLogger</groupId>
<artifactId>IDLogger</artifactId>
<version>1.0</version>
<scope>compile</scope>
</dependency>
But then when I try to use the jar, the compilation fails and tells me that the symbol(the class) can't be found. I even tried adding an import statement :
import IDLogger.IDLogger;
but it tells me that there is no such package.
How can I use this jar in my code in maven?
This is the code :
IDLogger logger = IDLogger.getInstance();
...
logger.logID(id);
I get the symbol IDLogger not found error
This is as much as I know about this custom jar...

Try to add your lib in system scope :
1. add in your project :
Your Project/lib
+IDLogger.jar
2. in your pom :
<dependency>
<groupId>IDLogger</groupId>
<artifactId>IDLogger</artifactId>
<version>1.0</version>
<scope>system</scope>
<systemPath>${project.basedir}/lib/IDLogger.jar</systemPath>
</dependency>

Out-of-tree build with maven. Is it possible?

I start learning packaging for several distros (currently Cygwin and Debian).
They have requirement to build system to allow out-of-tree build (synonym out-of-source build):
http://wiki.debian.org/UpstreamGuide#Out-of-Tree_Builds
To work-around "dumb" build system for example cygport recommend use lndir (from xutils project):
lndir ${S} ${B}
cd {B}
...build-commands...
I read mvn(1) man page but doesn't found anything appropriated. Next I just try:
$ mvn archetype:generate -DgroupId=com.mycompany.app -DartifactId=my-app -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false
...
$ pwd
/maven/simple
$ ls
my-app
$ mvn -f my-app/pom.xml compile
...
[INFO] --- maven-compiler-plugin:2.0.2:compile (default-compile) # my-app ---
[INFO] Compiling 1 source file to /maven/simple/my-app/target/classes
As you can see target directory created in source root hierarchy while I look for a way to avoid this.
Is it possible out-of-tree build with maven? And how?

You could do like this to get it in your current working directory:
<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.stackoverflow</groupId>
<artifactId>Q13173063</artifactId>
<version>1.0-SNAPSHOT</version>
<name>${project.artifactId}-${project.version}</name>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<buildDir>${user.dir}</buildDir>
</properties>
<build>
<directory>${buildDir}</directory>
</build>
</project>
Then you can issue
mvn -f my-app/pom.xml compile
And it will give you your classes in the current working directory.
And easily change to another output directory:
mvn -f my-app/pom.xml -DbuildDir=/tmp/build compile

It might be as simple as having a
<build>
<directory>/your/build/directory</directory>
</build>
in your pom.xml. /your/build/directory need not be in the source tree and can be parameterized using the usual ${...} syntax.
Cheers,