Well here is an interesting experience i had since last couple of weeks structuring my maven multi module project.
When i decided to use maven for my build life cycle management i had couple of reason that i wished to choose maven.
a. Mostly development teams are divided so that each team can work on separate Module within the project like Team-A to work on User Management System, Team-B to work on Authorization System, Team-C to work on Document Management System...and so on. Each team has java developers, testers, UI experts etc.
So the maven Project structure should be such that each team can independently work on their respective modules. They must be able to code, compile, build, test, deploy their module without having to compile, test modules belonging to other teams.
And thus i came to conclusion that each development module of the maven multi-module project must represent a Functional Module
After some discussions on forums i found people suggesting me to follow layered approach were child modules must be layers like controller-layer,service-layer,dao-layer etc. I did not pay heed to this advice because this not solving my purpose of teams working on individual module. This way for large project the build and deployment time for each team during development increases which does impact the project time-lines. sometimes the build and deploy time is upto 30 minutes say if there are 10 to 11 modules in the project.
But i did pay heed to a suggestion that keeping DAO layer separate for each module is not a good idea as DAO is highly granular and reused by other modules. and so the dependency of one module on other would would any how become greater.
I found a solution to this problem by creating a common module and moving DAOs and DOMAIN to the common module which will be inherited as a dependency by each module. And this seems to be a more viable option. Now the Project Structure looks like this.
Now when i build the project and run the webapp on server, It complains 404, Resource Not Found. I found that this is because the WEB-INF/classes folder is missing, src/main/java is missing in web-app module. I searched and found couple of links that suggested it is Deployment Assembly issue in Eclipse. So i need to manually create these folders and add in the deployment assembly because maven does not do it.
But the bigger questions are
do i need to move the Controller classes like com.mycompany.usermgmtsys.controller.UserMgmtController etc.. to src/main/java Or maven should find the controllers from the module jars included as dependency in WEB-INF/lib.
I dont want to do this i.e. putting java file in web-app. i want all the controllers should be available to the web-app as dependency for example WEB-INF/lib/usermgmtsystem.jar. But then wouldnt the Tomcat be looking for controllers in classes folder.
I dont know what should i do ? Any suggestions would be appreciated.
Its the way the eclipse render maven based project. It generally creates two structure. One based on master pom (parent project) and others based on individual module pom. however doing changes in any structure will reflect in the other one. As a practice I do changes in individual module folder structures and is more easy to read too.
Personally I try to avoid multi-module projects as, if you're using the Maven Release Plugin, you are locked into releasing all your modules together.
While this may sound like a convenience the problem arises when you need to do bug fix release to one of the modules - you end up releasing all the modules, not just the module with the bug fix, incrementing their version even though they haven't changed.
You also take a hit if you're running CI with multi-module projects - you're build typically runs over all modules from you root pom but if you're working in a particular module, you end up taking the hit of building those that haven't changed, in effect losing some of the benefits that the modularization was meant to provide.
So, go with independent modules but, and this is the important bit, create a common 'dependency' pom used by each.
A 'dependency' pom is a pom that standardizes all the dependencies across your projects and is different in that those dependencies are specified in the dependencyManagement section rather than the dependencies section (it also sets up standard plugin config, etc). This allows your project poms to specify the dependency pom as their parent and then declare the dependencies they need minus the versions, which are picked up from the 'dependency' pom and thus standardized across your projects.
If you are still concerned about being able to built everything, this can be achieved with a simple batch-file.
This is a good question. There are many aspects that must be considered for a useful project layout. I'd like to try to answer one which you didn't mention. Is your app extensible by users? If it is, then consider creating a separate module for your public API layer (service interfaces, DTOs used by those services, and Exceptions thrown by the services).
In our app, we have several maven modules per functional area. The idea is that a group worked on a feature within just one functional area and this isolation kept them messing with sources being modified by another group. Each functional area is broken down further in maven sub-modules we call "api", "domain", and "service" - we don't lump services/controllers, domain, and exceptions into a single module. The api module contains those classes we want to expose to customers for their customizations. Our service layer is the implementation of those interfaces. Further, we do not allow one module's service to call another module's service as this would bypass our service orchestration layer where customer can attach extensions to our services. Using separate maven modules per functional area helps enforce this.
We have other modules (internal-api, web, adapter) but they don't really add to this topic.
I figured out the issue. Controllers are presentation-layer components. The dispatcher expects the presentation layer components in the WEB-INF/classes folder in the target rather than looking for it in the lib. I am not sure if this is valid only for maven based structuring in eclipse. So finally these are the changes i have made
a. Created a src/main/java source folder in web-app. It is not generated by default in web-app module.
b. Add packages and respective controllers in the src/main/java folder.
So the final structure that i have (i am not pasting exact eclipse snapshot, this is generalized view)
Related
I'm trying to understand the difference(s) between structuring a project with the Java Platform Module System (JPMS) versus structuring a project using multi-poms.
Is the main difference that the JPMS encapsulates the code while a multi-pom project separates project dependencies?
I've searched on google but I haven't found a good explanation on the differences, but rather I see the word module getting used interchangably.
The computing industry often recycles terms. Context is everything.
The two kinds of “module” you present are unrelated, orthogonal issues.
The Java Platform Module System (JPMS) is a way to identify to the Java compiler namespaces amongst all the classes and methods available at runtime.
Multi-module in Apache Maven is a way to conjoin into one project what could be handled as separate projects. Each module in the project has its own POM with its own dependency and build settings, yet all can be managed as one super-project when combined as a Maven multi-module. Each module results in producing an artifact, such as a JAR or WAR file.
Very simple apps in Java may use neither.
Ideally new Java apps would use the JPMS, but it is still technically optional. In a perfect world, JPMS would have been included in the original Java, but was in fact added only recently, in Java 9. JPMS is quite handy if your app will run as a standalone, with a JVM bundled, because you can include a JVM that has been stripped down to only the parts actually used by your particular app (see jlink, jpackage, and related tools enabled by JPMS).
Maven multi-module projects are generally only used for complicated projects such as an app that includes a piece of functionality which may be spun-off for use in other projects. Or a multi-module Maven project may be good for an app that combines both a frontend user-interface module along with a backend business-logic module where we want to manage each part separately yet combine them into a single deliverable, such as a Vaadin Flow web app.
I can see how you could become confused, as both have to do with arranging classes. To oversimplify, Maven modules are about compile-time (dependency management and build automation) while Java Platform Module System is about runtime.
I’ve read that Gradle is more adept at managing a multi-module project. You might consider switching from Maven to Gradle for your multi-module projects. Gradle obtains your dependencies from Maven repositories.
I am wanting to mavenize our projects but have a somewhat complex scenario. Need opinions on the best way to handle a situation in which classes from a web app are required by other apps that are built and deployed along side it.
My projects look like this:
Suite web app.
POS web app.
Membership app.
Two packages within the Suite app are used in the POS and Membership app, as well as in the server lib.
I am not really sure how to approach this. Should we designate/automate a regular build of the Suite app for the purpose of pushing the Suite jars to the repo to be used as a dependency, or should this all be taken care of in the top level pom for each build? There's also the issue of building the server lib.
Thoughts appreciated!
If there are interdependencies between your projects you either let your CI server take care of the logic (e.g. build your dependencies before your dependents, or if a dependency changes, rebuild the dependents) or you let maven do it using the reactor and using a multi module project. In there, POS and membership would have a maven dependency towards Suite (if i understand correctly your setup)
If you go with the latter, you need to have an aggregator pom that aggregates the three projects as <modules>s. This will be the pom where you will launch maven, so the reactor can do its job of determining the order
In a nutshell, what I am trying to do is build a bunch of libraries and applications, all Maven projects, all at once. From what I understand a way to accomplish this just in one command line run of mvn package would be to create a multimodule project that will list each module that I would like to build, throw them in the Maven reactor, and build.
Following examples in the Maven book it seems that normally a multimodule pom sits in a directory above the individual modules. However it is also normally the case that a parent pom sits in a directory above the modules, which raises the question, is it normally the case that a multimodule build should also be a parent? I think not; however I wonder why I am running into this funny design quirk.
So, I'm wondering the right way to set this up. I see the following conventions / requirements:
The multimodule pom must have knowledge of where the other modules live on disc. Since it is actually doing the build from source it can't simply rely on already installed versions (since it's installing them!)
The parent doesn't actually have to be a physical directory up although that would be preferable. I see this as the convention best to break.
Really the individual libraries/application shouldn't even need to know they are being built as part of a multimodule build.
How is this usually set up in a multimodule build? Is there a simpler way to manage building multiple Maven projects all at once?
I put all the individual modules within the root module. Some software has trouble with multiple layers of hierarchy.
To make a child module refer to it's parent on the same level:
<parent>
<groupId>com.domain</groupId>
<artifactId>xyz</artifactId>
<version>0.0.1-SNAPSHOT</version>
<relativePath>../xyz/pom.xml</relativePath>
</parent>
I suggest you do not put anything in the multimodule (e.g. properties) that individual modules need to inherit. If you do, you won't be able to build the other modules independently.
I would go so far as to say that this is the fuzzy part of the "conventions". The documentation, and common sense, both suggest that project aggregation ( aka multi-module builds ) and inheritance are two different mechanisms provided to handle different use cases.
At the same time, it seems that there is a de facto convention ( yeah, I know ) of combining both the project aggregation and inheritance parent roles into a single pom. In fact, both the element of the parent declaration and the module element of the project aggegration mechanism seem to steer the use toward this combination.
Personally, I find it very usefull to separate the parent pom out on a regular basis. And I also find it useful ot locate parent pom in a totally separation location in my source control, and thus my folder structure. However, it rarely seems useful to locate builds that are a part of the same multi-module build structure in source control / folder structure. Perhaps this is even a good measure of whether something should be included in the same aggregate build; if it seems to deserve collocation in the source folder structure, then perhaps its a strong candidate for aggregation.
The only thin I am sure of is that these things are worth sorting out a head of time. And it's probably better to error on the side of not creating monolithic build structures . . . it's very hard to deal with a huge lump of aggregated, parent child build modules that isn't really necessary. On the other hand, aggregating individual builds to run together is a functionality provide at higher levels, such as the CI build server. So, I guess I might suggest erroring on the side of more independence.
Like in most spring+hibernate enterprise cases, I want to separate Dao, Service, Web layers into different modules, so that I can reuse Dao layer simultaneously in front-end and admin web site. The issue is I found m2eclipse does not support this multi-module project very well, any solutions?
I'm using eclipse 3.7 and Sonatype m2eclipse, I have a typical multiple-module structure project, one abstract parent, 2 children modules(A and B). I can run "package" from the parent, but I can not get hint when I input a "dot" after any object like system.out, and it says "This compilation unit is not on the build path of a Java project." Moreover, I can not invoke methods in A from B after I set dependencies in A's pom.xml.
I found a very similar issue here Issues with maven project running in eclipse, not recognized as Java project, but which does not solve my problem. I heard m2eclipse has removed this support for multiple-module project, but the need is so common that I'm 100% sure that there must be some kind of solution.
Thanks.
I got it working by importing the whole project and sub-module as individual projects as well. I find in individual projects I can get prompt hint methods and debug, but I'm using the whole project's pom to build.
Multi-module is still supported in m2e, I don't know where you heard that was removed but that's utterly wrong.
You simply need to import your sub modules as existing maven projects.
Also take a look at http://www.sonatype.com/books/m2eclipse-book/reference/creating-sect-importing-projects.html#fig-creating-import-multi
What are the main possible reasons of breaking down a Maven project to sub-modules?
Are you looking something more than the benefits of Modularization? The sub-modules should ideally be representing a single concept/feature so that they are functionally cohesive.
Pom file inheritence
You can use the and sections of the root poms to keep consistent version numbers and configurations across all child projects. So if I have an aggregator project that lists 300 projects, all that use apache commons-io and I want to upgrade them all the the latest version of commons-io, I can just change the version in the dependencyManagement section of the root pom. None of the child projects need specify a version.
build profiles
In the above example, if I have 300 sub projects, an individual developer is probably not regularly working on all (or even many) of the 300 sub-projects. You can create a build profile that specifies only the modules you work on regularly, and if you have a continuous integration server that deploys artifacts to an artifact repository, you'll get all the changes the developers on your team make too, without having to build all 300 modules.
General organization/clarity
While waiting for an answer to my comment.
A reason to split a Java EE based maven project into sub modules is so you can build the JAR/RAR/WAR/EAR/whatever independently of eachother.
For regular Java apps, you might split out the functionality into separate JARs, again each of these could be a sub-module under the overall project and again you can build them independently, run separate goals/phases/reports etc.