I have to make build architecture of my small project and I wonder how to proceed?
I have classes in one project for the so call core-part which can be used in other projects and api part in the first project which uses core-part.
So how to act?
To make multi-module Maven build and to produce 2 artifacts (which to upload to our company repo) and api-part have project dependency to core-part:
pom.xml
|
/core-part
|
/api-part(depends on core-part)
Create separate projects
Project1
/core-part
|
pom.xml
Project2
/api-part
|
pom.xml -> depends on project1's GAV artifact
Project3 ,...n depends on project1?
"Strong advice" : a project belongs in a multi-module build if release of that build requires release of that module, and vice versa. Multi-module projects should consist of things that must be released together.
An API should [practically] never depend on the release of its implementation, whereas the release of an API [nearly always] dictates the release of a new dependent implementation.
If you're not doing formal releases (why aren't you doing formal releases?) then this advice is still in force but less strong.
1. is the way if you'd like to build core-part and api-part within one build by building the aggregator/multi-module project (which has to have <packaging>pom).
There is actually a third artifact created (and installed and deployed to the repositories) then: The one for the aggregator project.
2. is the way if you'd like to handle (build, install, deploy) core-part and api-part individually. (An option you still have with 1. anyway.)
See:
POM Reference, Aggregation (or Multi-Module)
Maven: The Complete Reference, 3.6.2. Multi-module vs. Inheritance.
Related
I have a situation at the moment where I have:
Project A which is built into a fat jar using Maven assembly plugin.
Project B which uses the jar built in Project A. It is added to the project as a resource and launched in a separate process using a process builder.
I wonder if it's possible to achieve similar behaviour using just one Maven project. I.e build the jar containing only the classes and dependencies required for project A, and then build the rest of the project with the prebuilt jar.
Sorry if I'm not being very clear here.
This is against a few of Maven's core concepts:
One project, one model (POM). Two projects (A, B), two models (POMs).
There's one artifactId in a POM. What is a second artifact (jar) supposed to be named?
One project leads to one artifact. There is no additional "prebuilt jar" built within the very same project.
Dependencies are for the whole project (and possible sub-module projects). I'm not aware of how to "containing only the classes and dependencies required for project A".
Artifacts are stored:
in <project>/target temporarily
in the local Maven repository (default: ~/.m2/repository)
possibly in a remote Maven repository
... while resources are taken from <project>/src/main/resources during the build.
There might be some tricky solutions (which have possibly pitfalls, too) to achieve this if one thinks about it thoroughly. But I'd never ever recommend such.
I was trying to build Maven pom in something similar to the following hierarchical form:
root
+-- A-POM
+-- B-POM
+-- C-POM
+---D-POM
I was hoping that this could take care of my changed module problem. That is, if C is changed, then A must be rebuilt, etc.
But I ran into the issue that it seems the packaging at root is "pom," and after that I can't have A as packaging "war" then continue to drill in to have A include B, C as its modules. It seems to me that any POM which does not have "pom" in the then it can't have child modules. Is my understanding correct? Is there a way to do what I wanted to do?
In addition, I don't seem about to chain the "changed" mechanism in Maven (must due to my lack of knowledge). I like to have Maven detect a dependent project has changed and rebuild all the affected projects.
Thanks so much!
the reactor project (the root of the multimodule project) must have pom packaging. So your nested structure is invalid since A is not of type pom and I'm pretty sure you won't get it to work this way.
Second point is that Maven is a modularized build system and uses repository mechanisms to locate pre-built artifacts instead of checking out all modules from version control and building them in a monolithic way like in the old days ;) This means that Maven cannot know what to rebuild when you change something at your module since it simple does not have all the other module there at this time.
I think this is more a CI task than that should be handled by the build system itself. I know that your can achieve such a behavior with an appropriate build/CI Server like Jenkins that supports upstream and downstream projects. This means it is able to detect dependencies between the projects and trigger other builds as soon as a dependency has been built. This comes close to the behavior you are trying to achieve.
Btw. rebuilding other projects is only required for SNAPSHOT dependencies. Jenkins with the maven plugin supports this behavior but, depending on the number of SNAPSHOT dependencies of your project, this can cause long chains of project builds on the server. Some folks are of the opinion that in general SNAPSHOT versions are hell for CI tasks since these artifacts can change over time and are not reproducible. You could think over completely omitting SNAPSHOT versions and building final versions each time. This would also obviate your requirement to rebuild other modules as soon as a module changes. There are simply no changes until you upgrade dependency versions.
Very new to Maven, can someone please explain to me the difference between using maven modules vs just adding a dependency to your maven project to another maven project in your workspace? When would you use one over the other?
A dependency is a pre-built entity. You get the artifact for that dependency from Maven Central (or Nexus or the like.) It is common to use dependencies for code that belongs to other teams or projects. For example, suppose you need a CSV library in Android. You'd pull it as a dependency.
A Maven module gets built just like your project does. It is common to use Maven modules for components that the project owns. For example, maybe your project creates three jar files.
A dependency can be thought of as a lib/jar (aka Artifact in Maven parlance) that you need to use for building and/or running your code.
This artifact can either be built by your one of the modules of your multi module project or a third party pre-build library (for example log4j).
One of the concepts of maven is that each module is going to output a single artifact (say a jar). So in case of a complex project it is good idea to split your project to multiple modules. And these modules can be dependent on each other via declared dependencies.
See http://books.sonatype.com/mvnex-book/reference/multimodule-sect-intro.html for example of how a web app is split to parent and child modules and how they are linked.
One of the most confusing aspects of Maven is the fact that the parent pom can act as both a parent and as an aggregator.
99% of the functionality you think about in Maven is the parent pom aspect, where you inherit things like repositories, plugins, and most importantly, dependencies.
Dependencies are hard, tangible relationships between your libs that are evaluated during each build. If you think of your software as a meal, it's basically saying A requires ingredient B.
So let's say you're preparing lasagne. Then your dependency chain would look something like this:
lasagne
<- meatSauce
<- groundBeef
<- tomatoPaste
<- cheese
<- noodles
The key thing is, each of the above items (meatSause, groundBeef, cheese, etc) are individual builds that have their individual set of dependencies.
By contrast, the only section of your pom that pertains to aggregation is the modules section:
<modules>
<module>meatSauce</module>
<module>groundBeef</module>
<module>tomatoPaste</module>
<module>cheese</module>
<module>noodles</module>
</modules>
Aggregation simply tells your build engine that it should run these 5 builds in rapid succession:
groundBeef -> tomatoPaste -> cheese -> noodles -> meatSauce
The main benefit of aggregation is the convenience (just click build once) and ensuring the builds are in the correct order (e.g. you wouldn't want to build meatSauce before tomatoPaste).
Here's the thing though: even if you organize the libs as standalone projects without module aggregation, your build will still come out the same provided you build in the correct order.
Moreover, both Jenkins and Eclipse have mechanisms for triggering builds if a dependent project has changed (e.g. changing groundBeef will automatically trigger meatSauce).
Therefore if you're building out of Jenkins or Eclipse, there is no need for aggregation
It is my current impression that is impossible to do CI for a Maven 3 multi-module project well using Hudson (or Jenkins).
The situation seems to be that you have 2 realistic options of building a multi-module Maven 3 project with Hudson:
A freestyle project can also Build Maven projects, and with the incremental/recursive option it apparently should be able to deal with building only the necessary subtrees of the complete project tree.
A legacy, severly deprecated, with lots of warnings, Maven2/3 legacy build.
With the first option there is the significant disadvantage that your complete project looks like one big blob in Hudson, there is no visibility on the individual subprojects and there is no option for building individual subprojects and their dependees.
With the second option you have to basically swallow very little faith inducing warnings about legacy and "do not use" in order to find out that yes, it will build your multi-module project but the functionality of triggering subproject builds is completely broken and there is no intention of fixing this.
The only alternative I can figure out is to revert to Maven 2 for the build on the server, in which case the legacy plugin seems to work and even the individual sub-project builds can be triggered. But then I'm stuck on Maven 2.
I find my requirements to be rather conservative but I am completely stymied by the lack of Maven support in Hudson/Jenkins. Here's what I would expect:
ability to recognize multi-module projects and build them using Maven 3
ability to have "incremental" builds of such a multi-module project (i.e. only changed modules and its dependees)
ability to see the current status of the multi-module project and what sub-module has failed/succeeded/is unstable
The Maven project in question consists of about 84 Maven modules in a multi-module configuration with a common parent and a split into different subsystems. We are using Hudson 3.1.0.
Do I have any chance of achieving this?
Yes, it is impossible to do it well with the current Maven 2/3 project type.
I have done it well enough using a matrix / multi-configuration project type, and adding a "Module" axis manually. The configuration of the matrix job is a pain, and you have to remember to update your axis any time you add, remove or rename a module. But once configuration is complete, this solution works well for building. You can see the build and test results for each module separately, or integrated under the matrix job.
My colleague has been working on implementing Maven 3 multi-module functionality in Jenkins.
https://github.com/adamcin/maven-plugin
Not sure what the upstream acceptance status is.
The entire java project has an ant build; however couple of module(s) have maven build too.
My new module (maven built, say A) has dependency over an existing module(or simply a folder?, say B) which is being built using ant which just packages the src into jar and drops it inside the project.
Maven build for module A fails (unable to locate moduleB files); Options -
1. Package module B using maven, push to m2_repo
I do not want to go with this option.
Please let me know what are the other options available for the same.
If you have control over the source of all your modules, and if you decided that Maven is your way to go forward, then I recommend to to go all-in as soon as possible. If you do not then you will have continuous problems for the two build strategies to play along. And not only during build time but also at deploy time when it is time to collect all your runtime dependencies. Unless you build one uber-JAR as your only deployable artifact.
If your modules will (almost) always release in sync, then consider using a multi-module project setup.
When I say "all-in" then I do not mean that you have to give up Ant completely. You can use the maven-antrun-plugin to kick of your existing ant builds.
You should also consider running your own repository server, e.g. Nexus, to take full advantage of your maven builds.