Develop Reference

Implement project with maven in another maven project

I have created a Java project with maven that I want to implement in other maven project.
The child project is not a spring project, is a Java project created from scratch migrated to maven to manage the dependencies.
I can generate the jar with mvn install. So far so good.
Then I try to implement this jar to other project that is built with maven and spring.
For that I added that jar to my local maven repo with the following command:
mvn install:install-file -Dfile=/Users/.../target/app-0.0.1-SNAPSHOT.jar -DgroupId=com.mycompany.childapp -DartifactId=childapp -Dversion=0.0.1-SNAPSHOT -Dpackaging=jar
Then I am able to see that in the repo folder in .m2, the jar file is correct.
And this in the parent project pom.xml:
<dependency>
<groupId>com.mycompany.childapp</groupId>
<artifactId>childapp</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
And also, in the plugin section:
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
At least for eclipse everything is good, as I can develop and implement the classes inside the library without any issue. I can build the parent app with mvn clean package But when I run the app and try to execute the section of the code that uses the child library I get ClassNotFoundException for the classes that are in the child project.
In the parent project, in the libraries imported by maven I see that my library has a folder icon instead of the one the other have.
How could this be fixed?

mvn clean package creates jar for parent project but it does not include child jar.
You should use SpringBoot
mvn bootRun to run your project locally
mvn bootJar to build fat jar which will include all required dependencies.
To run this fat jar call java -jar parent.jar

Finally it was that the library was like... 'corrupted'.. or something like that.. It was a Java Project (created with eclipse wizard) than then I converted to maven (with eclipse wizard).
I started a new project as maven project from the beggining and everything was working at the first attempt....
So I just have to run mvn clean install to generate the jar and installed in the .m2 repo
Then in the main app pom.xml I have to declare as any other dependency:
<dependency>
<groupId>com.mycompany</groupId>
<artifactId>mylibrary</artifactId>
<version>0.0.1</version>
</dependency>

As per the comments, you want to create a project with maven which will create a jar file. That jar file will be used in another project. If my understanding is correct. You have to do the followings.
Create a simple maven project with simple type archetype.
Run the pom.xml with the command like mvn clean install or mvn clean package.
Use the jar file from the simple project upload into your nexus/artifactory repository and use the maven definition in another maven project.
If you do not have nexus or artifactory, you can use the jar file locally in another maven project.
To add a jar file locally in another project, you have to add the following dependency structure in pom.xml.
<dependency>
<groupId>your group id</groupId>
<artifactId>name of the application</artifactId>
<version>some version</version>
<scope>system</scope>
<systemPath>your location/jar-file-name.jar</systemPath>
</dependency>
Hope it answers your question.

Why maven is not finding a package located in another module/project?

I'm trying to compile a multi-module maven project. I have problems to compile a new module I added. This problem arises because the new module is trying to import a pair of packages which exist in another module.
This is the pom.xml of the new module:
Here is the view in the eclipse's project explorer, where i highlighted the 2 packages I'm importing from the class ServicioJMS of the new module:
And here's the error showed in the command line after doing a mvn clean package
As you can see below I added the module in the parent pom.xml:
So, I don't know what I'm doing wrong here ¿Any ideas?
NOTE: Eclipse has no problem resolving the dependencies related to the discussed imports.

I had a similar problem. Go to the library on which you are depending (under your ~/.m2/repository directory or in the ./target directory of the library) and find the compiled library jar. Use jar -tf to list it and check that the missing classes are listed directly in the jar.
If you are using the spring boot maven plugin or similar in the library on which you are depending then it constructs a jar with a radically different structure and the classes, while being in there, will be hidden within the structure rather than being directly in the jar by name. Eclipse understands this, but the spring boot loader won't unpack the spring boot maven plugin structure of a library within a dependency, it will only do that for the runnable jar being executed.
If this is true for you then you can remove the offending build plugin from the pom of your library making it just a library, not a runnable spring boot jar.

A few things:
1) Don't put a version or group if you have a parent, let them be picked up from the parent.
2) When importing a dependency from a module under the same parent use ${project.version}
here's an example:
<parent>
<artifactId>parent</artifactId>
<groupId>com.essexboy</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<artifactId>web</artifactId>
<dependencies>
<dependency>
<groupId>com.essexboy</groupId>
<artifactId>library</artifactId>
<version>${project.version}</version>
</dependency>
</dependencies>

Use install instead of package because IntegradorTransformador artifact (jar) was created but not exists in m2 repository and IntegradorTransformadorReproceso project can't found the artifact
mvn clean install

How to organize local dependencies with Maven?

in my company, I have a Java project:
common: This contains classes that are used for several projects
GUI: This project contains a GUI for common
Without Maven, I add common to the class path, I can build the project. But how to setup the POM.xml and the Eclipse workspace when I want to build the GUI with Maven?
I also want to package the app into a JAR later, so I tried to setup the gui as .jar package
But then how to assign a Maven type to the common project?
Ideally, I could import "common" to the Maven project?
UPDATE:
Ok, it seems the mvn package command is able to resolve the "common" project when I add as local dependency see this under GUI. Still a bit confused about whether to use "pom", "maven-plugin" or "module" - anyone can add some links/clarifications, when to use what approach?

Declare common as usual maven dependency in GUI.
If it isn't maven project, add it to local repository as shown there How to add local jar files in maven project?

I would follow this steps
Create a local maven repository to store your custom jars. Which nothing but a proper directory structure with pom files in it.
Create your sub projects(common, gui) and package them as jar.
Install the local jars to local mvn repository.
Use the jars as dependency from your project.
Example:
Create a master project on ${master_project} location and your subprojects on ${master_project}/${common} and ${master_project}/${gui} location.
Create mvn repository in: ${master_project}/local-maven-repo
Specify your local repository location in your subprojects pom.xml located in ${master_project}/${gui}/pom.xml
<repository>
<id>local-maven-repo</id>
<url>file:///${project.parent.basedir}/local-maven-repo</url>
</repository>
Install your jars in local mvn repository
mvn install:install-file
-Dfile=<path-to-file>
-DgroupId=<group-id>
-DartifactId=<artifact-id>
-Dversion=<version>
-Dpackaging=<packaging>
-DgeneratePom=true
Where: <path-to-file> the path to the file to load
<group-id> the group that the file should be registered under
<artifact-id> the artifact name for the file
<version> the version of the file
<packaging> the packaging of the file e.g. jar
Finally use them as regular dependency
<dependency>
<groupId>org.company</groupId>
<artifactId>common</artifactId>
<version>0.9.0-SNAPSHOT</version>
</dependency>
Reference for this answer.
Here's further resources for Maven multiple module projects

install the maven plugin in your eclipse using the following link.
This will enable maven in your eclipse. Then right click on your project and click Configure and you will see Convert to Maven Project option. This will convert your existing project to a maven project. You can configure your project to be build as a .jar, .war etc. while converting from the wizard. The following is the tutorial on how to do it... link

how to add jar dependency in maven?

When I run
mvn compile
I get package com.ibm.icu.util does not exist. So I downloaded the ICU4J jar and installed it into the local repository. I confirmed it's in .m2/repository/com/ibm/icu/icu4j/3.4.4/icu4j-3.4.4.jar. Inside that jar file is the missing class file com/ibm/icu/util/Calendar.class. Then I added the following into the dependencies section of pom.xml:
<dependency>
<groupId>com.ibm.icu</groupId>
<artifactId>icu4j</artifactId>
<version>3.4.4</version>
</dependency>
But when I run mvn compile again, I get the same error. What am I doing wrong?

You should avoid adding dependencies manually.
If you don't know a groupId and artifactId of the dependency you need, search for it at http://mvnrepository.com/. Usually, groupId matches the package names in the jar file.
For your case, the dependency is already there: http://mvnrepository.com/search?q=com.ibm.icu
So, go to http://mvnrepository.com/artifact/com.ibm.icu/icu4j and get the version of the dependency you need, e.g. 55.1: http://mvnrepository.com/artifact/com.ibm.icu/icu4j/55.1
Grab maven dependency xml and put it to your pom.xml file:
<dependency>
<groupId>com.ibm.icu</groupId>
<artifactId>icu4j</artifactId>
<version>55.1</version>
</dependency>
If you didn't find your dependency try to find it in google. Sometimes the dependency may be found in some corporate public repositories, not in a central. In this case you need to add the third-party repository to repositories section of your pom.xml.
If you're unable to find your dependency in the public repository then you have three options:
A. Install jar to internal repository server (e.g. nexus)
B. Put the JAR file in your project sources and declare project maven repository :
<repositories>
<repository>
<id>my-local-repo</id>
<url>file://${basedir}/my-repo</url>
</repository>
</repositories>
Important: You should keep the maven repository layout in your local repository.
C. [Bad Practice] Use maven install plugin to install your custom jar to local repository on your machine. But it's a badIt's not recommended.
mvn org.apache.maven.plugins:maven-install-plugin:2.5.2:install-file -Dfile=path-to-your-artifact-jar -DpomFile=path-to-pom
D. [Bad Practice] Use system dependency with absolute path to the JAR file, although it's a bad practice and should be avoided.
<dependency>
<groupId>test</groupId>
<artifactId>test</artifactId>
<version>X.Y.Z</version>
<scope>system</scope>
<systemPath>${user.home}/jars/my.jar</systemPath>
</dependency>

You should not be manually installing things into the maven repository directory. That directory is maintained by maven itself.
The way dependencies work is that when you run mvn compile or some other goal, it will connect to the maven central repository and download the needed dependencies and their dependencies.
If you manually install a jar file, it may not have it's dependencies. That icu artifact will likely have other things it depends on. Maven will automatically resolve these dependencies.
I would recommend using mvn clean install this will clean the target directory and rebuild everything.
If it fails to download, then you likely need to change the maven configuration. For example, if you are behind a proxy server you need to configure maven with the proxy credentials.
Also, if you manually copied anything into the .m2/repository/ directory you should delete it and let maven put it in there correctly instead.
The beauty of maven is that you don't need to worry about things like downloading jars. It just handles that for you. Let it do it's job.

If you have an internal artifactory like JFrog maybe you should check that the jar is there. Do not download manually to .m2 because it's at least strange. At most you can upload the jar in that artifactory manually.

Rebuild java project from compiled one

There is a java project built with Maven. I have project sources, need to improve something and then rebuild the project.
The problem is one of Maven dependencies is now lost (seems like it was only in developer's local repo). But there is a compiled project (.ear). I suppose it has code from that Maven dependency.
Is there a way to build a project using old project's compiled files?

Extract the required jar from old ear, and in new pom add that jar as dependency,
<dependency>
<groupId>GroupId</groupId>
<artifactId>ArtifactId</artifactId>
<version>VersionNo</version>
<scope>system</scope>
<systemPath>path/to/the/jar</systemPath>
</dependency>

You can use the compiled jar's and put them into library folder and rebuild path.