Develop Reference

How can I make an existing maven project as a part of multi module maven project?

My goal is to turn an existing maven project (char-counter) into a module of my multi-module maven project. How can I do this? I use Eclipse 4.16.0.
Here is the structure of my projects.

You can include the sub-modules inside your parent maven project in following way.
Inside your multi-module-project pom.xml
<modules>
<module>char-counter</module>
</modules>
See here: Maven Multiple module

Assuming that you want to convert your char-counter project to multi-module-project.
You need to have following in your multi-module-project pom.
<groupId>com.parent</groupId>
<artifactId>multi-module-project</artifactId>
<version>1.0.0-SNAPSHOT</version>
<packaging>pom</packaging>
<modules>
<module>Anagram<module>
<module>Calculator<module>
</modules
And then in Anagram project's pom :
<parent>
<groupId>com.parent</groupId>
<artifactId>multi-module-project</artifactId>
<version>1.0.0-SNAPSHOT</version>
</parent>
<groupId>com.child</groupId>
<artifactId>Anagram</artifactId>
<version>1.0.0-SNAPSHOT</version>
<packaging>jar</packaging>
And in Calculator project's pom:
<parent>
<groupId>com.parent</groupId>
<artifactId>multi-module-project</artifactId>
<version>1.0.0-SNAPSHOT</version>
</parent>
<groupId>com.child</groupId>
<artifactId>Calcultor</artifactId>
<version>1.0.0-SNAPSHOT</version>
<packaging>jar</packaging>
Also you need to add dependency of one module to other,in which you want to use the code from other module and then you need to deploy the artifact(module) which has dependency included in it and has starting point to run (like main).

Imports cannot be resolved - Visual Studio Code for Java

I am working on a Java project which is managed by Maven.
The project actually is composed of three sub-projects:
- Backend
- Builder
- Frontend
Every single of those projects is Maven based and the Builder works as a bridge between Frontend and backend.
In fact the Builder is the parent project for all of them.
The pom.xml of the Builder is as follows:
...
<modules>
<module>Model</module>
</modules>
...
Whereas the Model has pom.xml like this:
...
<parent>
<groupId>...</groupId>
<artifactId>Builder</artifactId>
<version>1.0.0.0</version>
</parent>
<artifactId>Model</artifactId>
<build>
*Backend build directives*
</build>
...
The problem is that from Visual studio Code i can build every single module successfully without errors but the code editor gives me "import cannot be resolved.." wherever i have dependecies towards backend.
I came to think that this is a bug of the "Java Language Support by RedHat" which cannot find dependencies ...
Has this happened to anybody?
--- Edit 28/11/2019 ---
I forgot to clearify that all of the Builder's dependencies (so towards Backend and other Util libraries) are resolved correctly as I can see those Jars inside Frontend's resolved dependencies folder.

you could try like this:
in your parent project pom.xml:
<groupId>com.blackr</groupId>
<artifactId>cloudtest</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>pom</packaging>
in your child project pom.xml:
<artifactId>module</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<parent>
<groupId>com.blackr</groupId>
<artifactId>cloudtest</artifactId>
<version>0.0.1-SNAPSHOT</version>
<relativePath>../parent/pom.xml</relativePath> //Location of the parent project's pom.xml file
</parent>

Company Maven POM nested structure

Well I'm working on a company POM Maven structure. I want a structure like the example below. Now I have two questions!
Is this possible for a project to call the parent pom? (considering
that they are all installed in the local Maven repository).
If I adda License block to the Company POM, do I have to add to the
project POM a new License block?
All feedback, suggestions etc are welcome. Thank you in advance!
Company
Company POM
Contains organization information, not to much.
<groupId>org.company</groupId>
<artifactId>company</artifactId>
<version>1</version>
<modules>
<module>company-parent</module>
</modules>
Company Parent POM
Defines for all the projects basic dependencies/plugins (management).
<parent>
<groupId>org.company</groupId>
<artifactId>company</artifactId>
<version>1</version>
</parent>
<artifactId>company-parent</artifactId>
Project
Project POM
Project based organization information (developers etc).
<parent>
<groupId>org.company</groupId>
<artifactId>company-parent</artifactId>
<version>1</version>
</parent>
<groupId>org.company.project</groupId>
<artifactId>project</artifactId>
<version>1.0</version>
<modules>
<module>project-parent</module>
</modules>
Project Parent POM
Defines for the current project used dependencies/plugins (management).
<parent>
<groupId>org.company.project</groupId>
<artifactId>project</artifactId>
<version>1.0</version>
</parent>
<artifactId>project-parent</artifactId>
<modules>
<module>company-module-1</module>
<module>company-module-2</module>
<module>company-module-3</module>
</modules>
Project Module POM's
The modules with each his own buid, dependencies and stuff.
Module 1
<parent>
<groupId>org.company.project</groupId>
<artifactId>project-parent</artifactId>
<version>1.0</version>
</parent>
<artifactId>project-module-1</artifactId>
Module 2
<parent>
<groupId>org.company.project</groupId>
<artifactId>project-parent</artifactId>
<version>1.0</version>
</parent>
<artifactId>project-module-2</artifactId>
Module 3
<parent>
<groupId>org.company.project</groupId>
<artifactId>project-parent</artifactId>
<version>1.0</version>
</parent>
<artifactId>project-module-3</artifactId>

A Maven child project does not "call" a parent project. The POM is declarative, not imperative. Similar to Java class inheritance the child gets the parent's settings and can override them or add new ones. See Maven, POM Reference, 2.2.2. Inheritance.
So, no, you don't have to declare the parent project's licence settings in the child project once again if they are supposed to be the same there.

Maven module - How to use it as an external lib in an unrelated project

I have set-up a modular project in Maven with a parent project having more than one child projects.
The pom.xml of parent looks as follows -
<project ...>
<modelVersion>4.0.0</modelVersion>
<groupId>com.company</groupId>
<artifactId>parent-app</artifactId>
<version>${parent-application.version}</version>
<packaging>pom</packaging>
<dependencies>...</dependencies>
<properties>
<parent-application.version>1.0</parent-application.version>
</properties>
<modules>
<module>parent-model</module>
<module>parent-masters</module>
<module>parent-web</module>
</modules>
</project>
The pom.xml of child projects looks as follows -
<project ...>
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>com.company</groupId>
<artifactId>parent-app</artifactId>
<version>${parent-application.version}</version>
</parent>
<packaging>jar</packaging>
<artifactId>child-model</artifactId>
<dependencies>...</dependencies>
</project>
Now, I need to use one of the child projects as a lib in a separate unrelated project. The pom of the new project looks like below.
<project ...>
<modelVersion>4.0.0</modelVersion>
<groupId>com.company</groupId>
<artifactId>unrelated-app</artifactId>
<version>1.0</version>
<dependencies>
<dependency>
<groupId>com.company</groupId>
<artifactId>child-model</artifactId>
<version>1.0</version>
</dependency>
</dependencies>
</project>
I keep getting the below error
Illegal character in path at index 57: http://repo.maven.apache.org/maven2/com/company/parent-app/${parent-application.version}/parent-app-${parent-application.version}.pom
The reason seems that I am inheriting the version attribute in child-model from prent-app.
Is there a way to overcome this issue? OR do I need to provide the version for each child module in respective pom.xml and cannot inherit from common parent.
Thanks in advance.

There is a way to overcome this issue with relativePath but I would not recommend it (take a look at this answer)... You should always provide version for parent module. To update all versions of all modules (parent+children) you can use maven-version-plugin or maven-release-plugin.

Maven Multi Module Project breaking compile-time class resolution

I've been previously managing a 3-module project as 3 seperate maven projects. As this project has been moving forward, I decided I ought to take advantage of the dependency management of maven2 to streamline integration between these 3 evolving modules.
I defined a super-project that deploys as POM. Some shared dependencies are defined here, and the modules are defined in the POM in the order of dependency from the least dependent module to the most dependent module. Each module has a POM definition back to the parent, and where it applies there are dependencies from one module to the deployed artifact of another module. I'll include possibly worthwhile pom.xml lines at the end.
On to the problem, I setup this project yesterday and was able to get each module building and working on its own. I then come back today to work on one of the modules now that some fresh requirements have come in and all of sudden everything is breaking. I'm editing the projects in Eclipse, and each time I modify a file, it no longer can resolve any of the classes defined within the same project. That is to say if I have a class foo.bar.class1 and it has an object of foo.bar.class2, Eclipse (and the compiler at large) complains that it cannot resolve class foo.bar.class2... Now this is blowing my mind because this other class is in the same project and package. Similar issues are also present for classes not in the same package.
Is there something broken in my maven setup, or does anyone have any idea why these projects can't even resolve classes in the same package??
-::POMs::-
Parent -> /path/to/project/mainApp
<modelVersion>4.0.0</modelVersion>
<groupId>com.moremagic</groupId>
<artifactId>mainApp</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>pom</packaging>
<name>Main App</name>
<modules>
<module>Broker</module>
<module>Soap</module>
<module>UI</module>
</modules>
Broker -> /path/to/project/mainApp/Broker
<parent>
<artifactId>mainApp</artifactId>
<groupId>com.moremagic</groupId>
<version>0.0.1-SNAPSHOT</version>
<relativePath>../</relativePath>
</parent>
<modelVersion>4.0.0</modelVersion>
<groupId>com.moremagic</groupId>
<artifactId>Broker</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
Soap -> /path/to/project/mainApp/Soap
<parent>
<artifactId>mainApp</artifactId>
<groupId>com.moremagic</groupId>
<version>0.0.1-SNAPSHOT</version>
<relativePath>../</relativePath>
</parent>
<modelVersion>4.0.0</modelVersion>
<groupId>com.moremagic</groupId>
<artifactId>SOAP</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
...
<dependency>
<groupId>com.moremagic</groupId>
<artifactId>Broker</artifactId>
<version>1.0-SNAPSHOT</version>
<type>jar</type>
<scope>compile</scope>
</dependency>
...
UI -> /path/to/project/mainApp/UI
<parent>
<artifactId>mainApp</artifactId>
<groupId>com.moremagic</groupId>
<version>0.0.1-SNAPSHOT</version>
<relativePath>../</relativePath>
</parent>
<modelVersion>4.0.0</modelVersion>
<groupId>com.moremagic</groupId>
<artifactId>UI</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>
...
<dependency>
<groupId>com.moremagic</groupId>
<artifactId>SOAP</artifactId>
<version>1.0-SNAPSHOT</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>com.moremagic</groupId>
<artifactId>Broker</artifactId>
<version>1.0-SNAPSHOT</version>
<type>jar</type>
<scope>compile</scope>
</dependency>
...

It sounds like the problem is with your Eclipse setup and not Maven.
Does mvn compile work from the command-line within your projects? From both the parent project and each individual module (after doing mvn install for the dependencies)?
Are you using a Maven plugin for Eclipse, such as m2eclipse? Check that it is configured to load dependent projects from within Eclipse, rather than looking to the repository ("Enable Workspace Resolution"). What happens if you do Project > Clean to clean out all of the projects?