Develop Reference

build plugin in multi-module maven project

I have a multi-module maven project that I am attempting to build.
The project structure is, generally:
Parent project (pom)
Sub Module 1
Sub Module 1A
Sub Module 1B
Sub Module 2
Sub Module 3
Inside of the parent project POM, I have the net.revel.code.formatter plugin defined in my build section to format the JAVA code inside of all of the sub-projects.
One of the attributes that I have to define in the plugin is the location of the configuration file. The file is located in a resource directory inside of Sub Module 3
I have the location attribute specified as ${project.parent.basedir}/submodule3/src/main/resources/eclipse/formatter.xml
The problem that I am running into is that when Sub Module 1A (as an example) is building, it seems that the ${project.parent.basedir} is resolving to the parent directory for Sub Module 1A (which is Sub Module 1) instead of the root of the project (where the property is actually defined).
Could someone help me sort out how to resolve this?

What happens to a dependency defined in a root project in a subproject in gradle?

I have a gradle project with several subprojects. I have defined several dependencies with version numbers in the root project but not all subprojects use all of these dependencies.
root
- build.gradle
- compile 'math:math:1.0.0'
- settings.gradle
- include 'messages'
- include 'message-handler'
\ messages
- build.gradle
- //no math
\ message-handler
- build.gradle
- compile 'math:math'
Will my artifact of the messages project contain a dependency on the math library?
In other words, if I make a separate project that depends on the messages artifact from a nexus repository, would my dependency tree show the math library for this new project?

Yes - your messages project artifact will contain a dependency on the math library.
According to Gradle Documentation:
For most multi-project builds, there is some configuration which is
common to all projects. In our sample, we will define this common
configuration in the root project, using a technique called
configuration injection. Here, the root project is like a container
and the subprojects method iterates over the elements of this
container - the projects in this instance - and injects the specified
configuration
In other words, every configuration which is included in the root project will hold for all the sub-projects.

How to create a maven archetype with both inherited and aggregated modules?

I am using mvn archetype:create-from-project within a manually created project
This project has both inherited and aggregated modules.
However when creating a new project based on this fresh archetype, the aggregated module pom file always finds itself injected with <parent>..</parent> attribute thus inheriting rather than being aggregated, which screws up the build order.
How can I prevent this aggregated module to be injected with <parent> tag?

It's actually not possible.
There's an open request for it on their JIRA from November 2011:
As mentioned in ARCHETYPE-110, the current implementation overwrites parent information if there are no existing parent definition inside the body of the pom.xml. So if we don't want such declaration we haven't no alternatives.
Source: https://jira.codehaus.org/browse/ARCHETYPE-393

Maven modules and Spring test resources

I have a Maven project made up of several modules. Some of the modules depend on the other modules for example Module C <- Module B <- Module A. Module C depends on Module B which depends on Module A.
In each module, I have Spring config files in main/resources and test/resources, those under test are for unit testing, while the those under main are for release/production. Each config file is self contained - Module B contained only its Spring config (file names are like so foo-B.xml, foo-A.xml)
However, when I need to test Module C, I need to reference Module B's Spring config under test/resources, but what is included is Module B's main/resources config file. This presents a problem because the production file has references to JNDI datasources where test one does not.
How can I get Maven or Spring to reference the test configuration file from the module dependency?

Maven separates the source classes & resources from the test classes & resources. You may configure Module B to create a test jar using the maven-jar-plugin test-jar goal. Then, you may have Module C reference Module B's test code as a dependency.
<dependency>
<groupId>com.myCompany</groupId>
<artifactId>moduleB</artifactId>
<version>${project.version}</version>
<classifier>tests</classifier>
<scope>test</scope>
</dependency>
Alternately, you can create a regular Maven project including only the test code you'd like to share, then include that as a test dependency where needed. This idea is described in the maven jar plugin's usage docs.

I'm not sure this can be done. Maven deliberately does not include test resources in artifacts. If I were in your place, I would duplicate the test resources in module C. Presumably, you're not testing the same things in both modules, so hopefully it won't cause a bad case of copy&paste/dual-maintenance.
As an aside, I try to avoid having "production" data sources and "test" data sources. Use the same JNDI name for both, but have the JNDI provider configured to point to test or production based on the circumstance. For example, all of our web servers have the same data sources defined, but the JDBC urls are different for dev/qa/prod. For your unit tests, use something like simple-jndi to simulate a JNDI environment.

maven - separate modules for interfaces and implementation with Spring

We are working on Mavenizing our java project and we would like to setup a clean separation between interfaces and implementations for each module.
In order to do so, we want to split each module into two sub-modules one for interfaces and data objects used by them and another for implementations.
For example:
+commons
+commons-api
+commons-impl
The POMs of the modules will be configured such that no module depends on the impl sub-modules. This way no code from one module will be able to "see" implementation details of another module.
What we are having trouble with, is where to put our spring XMLs.
In our project we automatically import spring XML files using wildcard import like
<import resource="classpath*:**/*-beans.xml"/>
This way the location of Spring XMLs doesn't really matter at runtime, as all the modules get loaded into the same class loader and, the strict one way dependency rules in the POMs don't apply.
However, during development we want the IDE - we use Intellij IDEA - to recognize implementation classes referenced from the spring XMLs.
We also want IDEA to recognize beans defined in other modules.
If we put the spring XMLs in API sub-modules - they won't "see" the implementation classes in the impl sub-modules.
If we put them in the impl sub-modules, their beans won't be "seen" from other modules.
It is probably possible to configure the IDEA project to recognize spring XMLs from modules on which there is no dependency, but we prefer for our POMs to hold all the project structure information and not rely on IDEA project files.
We considered creating a third sub-module just to hold Spring XMLs (and perhaps hibernate xmls as well). For example:
+commons
+commons-api
+commons-impl
+commons-config
The external modules will depend on both commons-api and commons-config and commons-config will depend on both commons-api and commons-impl, with the dependency on commons-impl marked as "provided" (to prevent transitive resolution).
This however seems like a complex and awkward solution and we feel that there must be a better - simpler way to achieve interface/impl separation with Maven and Spring.

What you need is a runtime dependency scope:
runtime - This scope indicates that the dependency is not required for compilation, but is for execution. It is in the runtime and test classpaths, but not the compile classpath.
(https://maven.apache.org/guides/introduction/introduction-to-dependency-mechanism.html)
Define a runtime dependency from one impl module to another impl module where you use the impl classes in the *-beans.xml config. Intellij will correctly recognize this in spring configuration files, but won't auto complete them in code (but it will do that in test code).
Also if anyone used the classes in the code, compilation through maven would fail, because the runtime dependency is not on a compile class path.

You can achieve decoupling of api and impl like this:
+ commons (pom)
+ pom.xml <--- serves as a parent aggregator (see below)
+ commons-api (jar) <--- contains models, interfaces and abstract classes only
+ commons-impl (jar) <--- depends on commons-api
+ commons-config (jar) <--- depends on commons-impl only (no need to depend on commons-api as it is brought in transitively)
+ external-project (war or jar) <--- has commons-config as a dependency
Parent aggregator pom (specify build order):
<modules>
<module>commons-api</module>
<module>commons-impl</module>
<module>commons-config</module>
</modules>
The config module can be omitted if it only contains spring application context configuration. The app configuration xml should be in the classpath and folder structure of the module that contains the artifact that you are deploying. So if you are building a war artifact, the app context should be in there.
The only configuration that should be in your commons module would be in a test package of your impl module.

In short you want Idea to override maven dependency graph but avoid keeping this configuration in idea project files?
One option is to group implementation dependencies in a maven profile. This profile would not be enabled by default but you should be able to mark it as active under idea.

Two ideas come to mind:
You will have one (or more) modules where all the modules (api+impl) are dependencies, you could place your spring configuration files there.
Place the spring configuration files in the api modules and declare a dependency on the impl module with scope provided this way the implementations will be known, while there is no dependency of the api for the deployment.

commons-impl at runtime scope in external modules
commons (pom dependencyManagement) =>
+commons-api (compile)
+commons-impl (compile)
+commons-config (compile)
commons-impl (pom dependencies) =>
+commons-api (compile)
+commons-config (compile)
external modules (pom dependencies) =>
+commons-impl (runtime)
+commons-api (compile)
+commons-config (compile)

keep modules number as little as possible;
This speeds up project build time and simplifies its layout.
keep modules structure as plain as possible: single root + all sub modules in the same folder, e. g.:
pom.xml
commons-api/
commons-runtime/
module-a-api/
module-a-runtime/
...
This simplifies navigation across the project, when modules number is really high (>50)
provide runtime-scoped dependencies to the runtime modules only when they are required;
This keeps your architecture clear. Use mocks instead of explicit dependency to another runtime module.
keep your api spring contexts in api modules, define your public beans as abstract bean + interface;
keep your implementation contexts in runtime modules, override api beans with your implementations via spring profiles (use <beans profile="default").
Result: simple, transparent layout and design; full ide support; no explicit dependencies on runtime module internals.