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Java how to use methods from another module in Intellij

I have added two projects as modules in empty intellij project.
Then I added in pom of module B following dependency to first project(module A):
<dependency>
<groupId>Tests</groupId>
<artifactId>Group</artifactId>
<version>1.0-SNAPSHOT</version>
<scope>compile</scope>
</dependency>
This allows me to import classes from module A into module B.
But I can't see any method from that module (it looks like classes are empty or they have only private fields/methods).
What am I missing? What should I do to see all public methods/fields from A module?
Thanks
Kamil

If you are adding one of them as a dependency, you can avoid to join them as modules. For local purposes, you can build(mvn clean package) one of them and add that as a dependency to another one. You can check relevant .class file to see the access levels of the class members.
For multi-module projects, please, see: https://www.jetbrains.com/help/idea/creating-and-managing-modules.html

Third party API can't see class in multi module Maven project

I have a multi module maven project, and in the dao module, I added the JSON-IO dependency. When I try to deserialize my object, it gives me:
Exception in thread "main" com.cedarsoftware.util.io.JsonIoException: Class listed in #type [hu.kleatech.projekt.model.Employee] is not found
The class name is correct, the Employee is public, and the dao has the module as dependency. What could have gone wrong?
Edit: Since this is an old question and have been answered long ago, I'm deleting the github repository that I made specifically for this question. The solution to the problem is in the accepted answer, the exact code is not relevant.

Please try adding an empty constructor to Employee class.
Edit: Actually, while adding an empty constructor solves the problem, it is not necessarily required. Json-IO "will make a valiant effort to instantiate passed in Class, including calling all of its constructors until successful. The order they tried are public with the fewest arguments first to private with the most arguments."
(copied from MetaUtils.java javadoc)
Also, when calling a multi-argument constructor, the library fills the arguments with nulls and defaults for primitives. Then any exceptions thrown during the constructor call is ignored. In your case, a NullPointerException was thrown, because the constructor is not null-safe. So either modify the constructor so that it can handle nulls, or add an empty constructor.

Maven dependency configuration is hierarchical from <parent> element not from <modules> element.
It means that in the project's pom.xml file where you have dependency on "JSON-IO dependency" you do not have dependency on your dao project or where that class is.
<modules> stands only to define what projects to build. Order of modules definition does not matter, since Maven detects order by required dependencies
So, you can define dependency in <parent> pom.xml either in
<dependencies> element. then all children will have it.
or in <dependencyManagement> - then children who need it can include it in their <dependencies> without common configurations like version, scope etc...
look at quite similar answer here:
How to minimize maven pom.xml

As per your project and modules Pom your main Pom should have modules in following order ....
<modules>
<module>core</module>
<module>controller</module>
<module>service</module>
<module>dao</module>
</modules>
service depends on core so core should be build before service
dao depends on service and core both so dao should be after core and service.
Employee class is available in core and it should be available in core jar.
You should add depencyManagent in main Pom and then add all the module as dependencies in dependencyManagement so whoever adds your main Pom as dependency will be able to access all your jars.
Once you change order build your project again and then update your maven project.
If this code is being used in another project then make sure that you have uploaded jars to repository (mvn deploy) so whoever uses it can download it when they are building their project.
One way to verify whether this jar is downloaded in the main project where it is used or not is check in project explorer there would be a Maven Dependencies section where you can see all dependency jars and check if core is present or not.
I am not sure what controller module is doing in main Pom as I couldn’t find a module by that name in your project so you should either remove it or add a module (folder) for it.

Maven Plugin: accessing resources accross multiple modules

I'm currently writing a custom maven plugin for generating a XML file in a multi-module maven project.
My maven structure is pretty standard: one parent project and a module by project components in the parent project folder:
-- Parent
-- module A
-- module B
-- module C
I need to list, by module, a set of classes flagged by a custom annotation.
I already wrote a set of custom annotations and an annocation processor to create a XML file at compile time in the corresponding module output directory (${project.build.outputDirectory}) .
Now i need to merge each module XML into one file, but i don't know how to access each modules from within my maven plugin except having each path set as parameters (i don't like this method).
Any idea on how to do this ?
Does maven plugins can traverse project modules ?
Thank you in advance.

To get the list list of all projects you can use:
List<MavenProject> projectList = MavenSession.getProjectDependencyGraph().getSortedProjects()
If one of your goals is correctly executed you will get everything you need. Every MavenProject contains a getBaseDir() etc.

After some researches, it seems that MavenProject.getCollectedProjects() will return the list of projects beeing manipulated by a goal execution in a multi-module project.

Maven Assembly: config files best practice

I have a multi-module maven project, including a seperate assembly-project. As i develop and run my application from eclipse (during development), i have specific configuration-files (e.g. log4j or other property-files) in my main-module (which contains the main-class). These files contain development-time-specific information. The assembly-project contains each of the config-files for production. The assembled product then should use these configs instead. This is my current setup:
MainModule/src/main/resources
+configA.properties
+log4j.properties
Module1/src/main/resources
+configB.properties
AssemblyProj/src/main/resources
+configA.properties
+configB.properties
+log4j.properties
And the generated project has this structure:
libs/
+MainModule.jar
+Module1.jar
configs/
+configA.properties
+configB.properties
+log4j.properties
the config-directory overlays the config-files in each *.jar because of the classpath, i.e.
java -cp configs/;libs/* My.Main.Class
Now the problem that i have, is that there are still all dev-configs included in each jar. Also i have kind of a bad feeling about using that overlay-classpath-method. Is there any practice on how to do this in a better manner?

Extract these resources into classifier-based dependencies for each of the mentioned modules. Then define <profiles/> that trigger their usage. In your assembly use the classifiers as necessary.

How to use a single checkstyle suppression file in Maven for all modules

I have a project that consists of several Maven modules which are all children of a parent module.
I have the parent set up to use checkstyle and the child modules all inherit this behaviour correctly. I would like all the child modules to use the parents suppression file defined in its plugin.
I define a property checkstyle.suppression which is used in the checkstyle plugin
<properties>
<checkstyle.suppressions>${basedir}\src\checkstyle\suppressions.xml</checkstyle.suppressions>
</properties>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-checkstyle-plugin</artifactId>
<version>2.2</version>
<configuration>
<configLocation>config/sun_checks.xml</configLocation>
<suppressionsLocation>${checkstyle.suppressions}</suppressionsLocation>
<suppressionsFileExpression>${checkstyle.suppressions}</suppressionsFileExpression>
</configuration>
</plugin>
</plugins>
Which works fine for the parent but all the child modules try to find the file in their basedir which does make sense.
I am sure there must be a simple solution I am missing but is there a way to define this location so that all the child modules will use the parent location without hard coding it?

The answers above are dangerous. I maintain that each project should be self contained, so referring to files external to it is going to break a build sooner or later. Checkstyle can take a url for the file but that means you can't build offline. A better approach is to package your file (can also add pmd.xml) into a jar and then add that jar to the classpath of the checkstyle (or pmd) plugin. I have an example of it here and more about overridding a plugin classpath here

The plugin's documentation mentions a similar use case here:
http://maven.apache.org/plugins/maven-checkstyle-plugin/examples/multi-module-config.html

Have you tried defining the property like this in the parent pom or redefining it in the childrens?
<properties>
<checkstyle.suppressions>${parent.project.basedir}\src\checkstyle\suppressions.xml</checkstyle.suppressions>
</properties>

If the parent isn't going to run checkstyle, you might just be able to rewrite it to
<properties>
<checkstyle.suppressions>..\..\src\checkstyle\suppressions.xml</checkstyle.suppressions>
</properties>
Or something like this. Or you could put something in settings.xml to point everything to an system wide config directory.
While it might not be recommended, you can have use a boot-strap or set-up project or task put a copy of the suppressions.xml file to a location specified by a property in settings.xml and then always refer to it by that locations.