I've following scenario:
ProjectA have two dependencies depA and dep2
I want to create two builds one with both dependencies and another one just have one dependency.
Now, my question is:
How can I achieve custom builds?
Can I create simply two POM files? If yes, then how should I be building projects using specific POM?
There are two ways you could create multiple output packages. One is to use the maven assembly plugin to create multiple archives. The other is to create a multi-module project and give each artifact it's own pom.xml. I would recommend the latter case as it embeds less assembly logic in your pom. In this case I would create at least three modules... one for the project artifact with no packaged dependencies and two others for that artifact plus the various dependency items.
Related
Under a common parent I have three Maven projects that are loosely related, and I must add the jars that all of these projects generate and their dependencies to a third party ear. For each of those three projects I have properly configurate de dependency:copy-dependencies goal.
In order to have things as automated as possible, I want to join all the jars in a single location.
An initial idea would be using an empty "joiner" project that depends on all of the previous three projects, and just use dependency:copy-dependencies on it. But I do not really like the idea of an empty project with its empty artifact, and I am wondering if there is a more standard way of doing this (ideally by copying the dependencies in a directory of the parent that does not need to be commited to version control) with the standard plugins.
I have a project which has multiple small utility classes which I want to package as separate jars, e.g. json-utils, xml-utils etc.
How can I manage this kind of build within a larger project?
Is the only way to do this by declaring each of these classes within a their own separate module? And does each one then need its own subfolder?
One of the basic concepts of Maven is one project (module), one artifact (jar, war, etc.):
Because a project is defined by a unique set of coordinates consisting of a group identifier, an artifact identifier, and a version [...]
So, "yes" to your last two questions.
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.
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
We are relatively new to Maven and now face a problem.
We have a Maven project (projectA) whose JAR is the dependency of several other projects. Some of the other projects are some custom web container while others are not, so some of projectA's dependency jars are provided in the case of the custom web container, but should be runtime scope in the case of other projects. We currently use exclusion list to filter out the provided jars in the case of the custom web container.
We are wondering if it would be better to use maven profiles. We know how to create the profiles with different dependencies (actually same dependencies different scope), and in both profiles, the built projectA jar is identical bit-wise. But what we don't know is, when we deploy/release the projectA jar artifact to a maven repository, what should the pom.xml look like? For these web container projects, the pom.xml should not include the provided jars, but for other projects, the pom.xml should include these jars.
We can use a different name for the jar in each profile and deploy each with a different pom.xml, but since these jars are identical bit-wise, it doesn't seem like a perfect solution. So we thought there's gotta be a better solution to this problem, only that we don't know since we are relatively new to Maven. Thanks.
The POM is the POM. You seem to be talking about managing transitive dependencies in other projects that reference "A". Your options in Maven are fairly limited:
You can use exclusions to remove transitive dependencies that you don't want.
You can declare dependencies in "A" as "provided", but this is only really correct if that jar actually is provided in A's target environment. It's primarily intended for Java EE api dependencies, like servlet-api, which are provided by containers and prohibited from being included in WAR files.
You can declare dependencies as optional, which is what people usually mean when they say "provided", and manually include those dependencies in the places where they're needed.
I'd personally choose the "optional" route because it's the job of each project to pull in the dependencies it needs, and if something is optional when using "A", it just means things that use "A" have to explicitly choose whether they'll use that optional part of it. This tends to be the best fit when building an artifact that has multiple, differing use cases.
For additional help in this area, you can also use the maven enforcer plugin to ban certain dependencies from builds so that you don't accidentally get jars that you don't want.