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How to add dependencies which are in different directory and build them together with main project

I'm new to using IntelliJ. I have a project named X which has 5 dependencies a, b, c, d, e. These dependencies are linked as follows:
a->b->c
while c, d and e are independent.
Currently, when I'm seeing the project structure under
File->Project Structure->Project Settings->Modules, these dependencies source are pointed to .m2 directory. Since they are just imported and not built yet, so their output is not available in .m2 directory, hence not available for main project.
I want to know, in IntelliJ, how to import all dependencies with main project and build the main project, so that it also builds the dependencies first? Any guide or article which I can refer?

Can you show your pom.xml?
It sounds like your dependencies are sub module of your project.
You can add dependency from your modules like you add all the other dependencies, so you should add something like that in your pom.xml:
<dependency>
<groupId>com.example</groupId>
<artifactId>a</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>com.example</groupId>
<artifactId>d</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>com.example</groupId>
<artifactId>e</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>

Spring boot multi module maven projects without repository

I have multiple spring boot projects, every project is independent and has its own CICD pipeline.
These projects need some common classes, I have created a separate project with common classes.
Parent
pom.xml (with packaging)
lib-project
pom.xml
project-1
pom.xml
project-2
pom.xml
I can build project easily from the parent directory, it builds all the projects
parent$ mvn clean package
it generates all the jar files and put them in their respective target folder of projects
My problem is I can't initiate this at the parent level, this has to be initiated from within each project from its own pipeline.
and
I cannot use any local or remote repository, to put the dependent jar in m2 using mvn clean install and then refer to it as dependency
I want to build it from the relavent project directory
parent/project-1$ mvn clean package
it shows following error:
Could not resolve dependencies for project com.test.multiple:project-1:jar:0.0.1-SNAPSHOT: Could not find artifact com.test.multiple:lib-project:jar:0.0.1-SNAPSHOT
My expectation stepwise on compilation of project-1
Check if there is a dependency for project-1
Go to ../lib-project
Compile and build it in target folder (or anywhere relative to our project)
Add this generated jar to "project-1" dependency
Compile and build the "project-1" jar file.
Parent Pom Configurations
<project ...>
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.4.3</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.test.multiple</groupId>
<artifactId>parent</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>pom</packaging>
<modules>
<module>lib-project</module>
<module>project-1</module>
</modules>
</project>
** Lib project pom **
<project ...>
<parent>
<groupId>com.test.multiple</groupId>
<artifactId>parent</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<groupId>com.test.multiple</groupId>
<artifactId>lib-project</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>lib-project</name>
<properties>
<java.version>11</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
</project>
Project-1 pom
<project ...>
<parent>
<groupId>com.test.multiple</groupId>
<artifactId>parent</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<groupId>com.test.multiple</groupId>
<artifactId>project-1</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>project-1</name>
<properties>
<java.version>11</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>com.test.multiple</groupId>
<artifactId>lib-project</artifactId>
<version>${project.version}</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>

I have multiple spring boot projects, every project is independent and has its own CICD pipeline.
These projects need some common classes, I have created a separate project with common classes.
Congratulations, your projects are not independent any more!
Given the definitions above, here are the dependencies:
lib-project depends on parent;
project-1 depends on parent;
project-1 depends on lib-project.
Please check Introduction to the POM and Guide to Working with Multiple Modules for the discussion on the dependencies in Maven projects.
I cannot use any local or remote repository, to put the dependent jar in m2 using mvn clean install and then refer to it as dependency
Given this limitation, and dependencies listed above, the POMs and source files of all the projects have to be present on the disk for build purposes. The build process has to start from the parent folder. The build process has to build all modules at once.
Also, please consider using mvn clean verify instead of mvn clean install to avoid populating the local repository with the artifacts you are building.

A maven project isn't designed to build its dependencies on demand. However, jenkins can be configured to build downstream projects when changes are pushed to an upstream dependency.
I have also worked around this by using the -pl option on a parent pom in the relevant jenkinsfile to build a subset of the child projects
Jenkinsfile
clone parent project
mvn clean package -pl core,deployable

Maven child module in parent pom as dependency

I'm trying to create a maven spring-boot project with multiple modules. I have created a parent module with packaging type pom and many children submodules with packaging type jar.
So my parent's pom.xml looks like:
<groupId>Creator</groupId>
<artifactId>DPAI</artifactId>
<packaging>pom</packaging>
<version>1.0-SNAPSHOT</version>
<modules>
<module>starter</module>
<module>DatabaseApi</module>
...
</modules>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.2.4.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
</dependencies>
One of submodules: starter contains only starting class annotated with #SpringBootApplicatoion and in its pom.xml there is a section with other child artifacts like:
<parent>
<artifactId>DPAI</artifactId>
<groupId>Creator</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<artifactId>starter</artifactId>
<packaging>jar</packaging>
<dependencies>
<dependency>
<groupId>Creator</groupId>
<artifactId>DatabaseApi</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
...
</dependencies>
So I'm trying to do some refactoring and move Main.class and all dependencies to my parent's pom, but it doesn't compile with error with message that my dependencies referencing itself.
In my opinion, the problem is that my parent pom contains section with it's own submodules. Parent of that submoduls is the same pom, where I try to add described dependencies

The parent.pom can't contain any java code, only Maven specifics e.g. See: https://howtodoinjava.com/maven/maven-parent-child-pom-example/#parent-content
Maybe tell us, what you want to achieve.

In a Maven multi module project you usually have a parent Pom (with packaging Pom) and several modules at the same level as you already set your project up.
Build the modules without dependecies on your code first, the the dependent modules: In your parent Pom change the order of the modules to
<modules>
<module>DatabaseApi</module>
<module>starter</module>
...
</modules>

So I'm trying to do some refactoring and move Main.class and all
dependencies to my parent's pom
I dont think this is possible. Your parent pom is actually of type pom, meaning you're not actually supposed to have any java code in it. Its meant to hold the versions of jars used in your child modules. You can relate this to the spring-boot-parent module. When we declare the spring-boot-parent module in a spring boot project, your adding your project as a child of the spring-boot-parent. And the parent will manage the versions of all of your dependencies.
I think the best way forward would be to maintain all your service related code in your spring-boot module. Filters, controllers,etc. The other stuff like your jdbc, integration layers can be maintained in other child modules and then referred to the spring module as jar references similar to your example.

So I'm trying to do some refactoring and move Main.class and all
dependencies to my parent's pom,
I'm not 100% sure if Maven would support something like the following in the parent POM itself:
<dependencies>
<dependency>
<groupId>${project.groupId}</groupId>
<artifactId>DatabaseApi</artifactId>
<version>${project.version}</version>
</dependency>
...
</dependencies>
But for sure it won't support Java classes in a Module with pom-packaging (such as parent modules or multi-module modules). The compiler:compile goal etc. are not bound to any phase for pom-packaging by default. In other words: Maven does not compile Java classes for pom-modules by default.
My recommendation:
Keep the SpringBootApplication in a Java-based module. For Spring MVC/ WebFlux application I usually create a "-web" module with:
SpringBootApplication
web service controllers
http/ web filters
global configs such as: security, swagger, async
application.yml
...
It's also the module where I configure the Spring Boot Plugin to create an executable JAR.

How to create an aggregate fat jar from super pom file?

I have an aggregate maven module that is a multi module maven project consisting of a super POM. This aggregate module consists of several sub maven projects. In the super POM of the aggregate module, I have included the jar dependencies that are common for the sub-projects. In the POM file of each sub-project, I have included the jars that are only specific to these projects.
The super POM looks like this:
<?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.testproject</groupId>
<artifactId>testproject</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>pom</packaging>
<modules>
<module>../../Projects/ProjectA</module>
<module>../../Projects/ProjectB</module>
<module>../../Projects/ProjectC</module>
</modules>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
<dependency>
<groupId>org.swinglabs.swingx</groupId>
<artifactId>swingx-core</artifactId>
<version>1.6.3</version>
</dependency>
<dependency>
<groupId>org.jdesktop</groupId>
<artifactId>swing-layout</artifactId>
<version>1.0.3</version>
</dependency>
</dependencies>
</project>
An important note is that my aggregate module contains no source code, but just the super POM. Hence there is no main class as well and therefore I cannot use the Maven Assembly Plugin. My main class is in one of the sub-projects.
How can I create a jar file out of the super POM of the aggregate module?
The reason why I would like to get a jar from the POM file is that I would like to continue using ant for the build process.
My expectation is that the final jar from the super POM contains all the dependent jars like junit, swingx-core, swing-layout etc as one fat jar
that I can include in the ant build process.
Is this possible with maven? Am I missing something?
I have tried to change the packaging from pom to jar but I get a compile error on mvn-install saying "packaging with jar is invalid. Aggregator projects require 'pom' as packaging".
mvn-install and mvn-compile work fine when I use packaging as pom.

Can't use classes from different Maven modules

Need to create a multi module maven project which consist of a registration module and main project. The problem is that it's impossible to use classes declared in different modules.
e.g.: I have a ParentClaz in my parent's src/main/java dir and ChildClaz in child's src/main/java dir. Right now it's not possible to use neither ParentClaz in ChildClaz nor vice versa.
The project's structure looks like this:
+-- AdminPortal <- parent root
+-- registration <- child root
-- pom.xml <- child pom
-- pom.xml <- parent pom
my AdminPortal POM:
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifactId>AdminPortal</artifactId>
<packaging>pom</packaging>
<version>1.0-SNAPSHOT</version>
<name>AdminPortal</name>
<url>http://maven.apache.org</url>
<modules>
<module>registration</module>
</modules>
Here's child POM:
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>com.example</groupId>
<artifactId>AdminPortal</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<groupId>com.example.AdminPortal</groupId>
<artifactId>registration</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>
<name>registration</name>
<url>http://maven.apache.org</url>
How can this problem be solved?

Your parent pom has packaging type pom, this is not jar. This is special aggregator module. All java code should be located in jar modules.
Module with packaging type pom cant generate artifacts like jar, war or ear.
Maven by Example - The Simple Parent Project
The parent project doesn’t create a JAR or a WAR like our previous projects; instead, it is simply a POM that refers to other Maven projects.
To use Classes from one module in other module use maven dependency.
Typical project looks like this:
* administration project (pom)
* registration (jar)
* portal (war)

Child can use parent dependencies, try to add this to parent
<dependencies>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.14</version>
</dependency>
</dependencies>
and make this class in child
import org.apache.log4j.Logger;
public class Test {
public static void main(String[] args) {
Logger.getLogger(Test.class);
}
}
and you will see that it compiles.