Recently I came across with the term 'artifact' in related to maven build tool...
Can someone please explain what it's meant by 'artifact' in software industry and specifically in maven.
Maven organizes it's build in projects.
An artifact in maven is a resource generated by a maven project. Each maven project can have exactly one artifact like a jar, war, ear, etc.
The project's configuration file "pom.xml" describes how the artifact is build, how unit tests are run, etc.
Commonly a software project build with maven consists of many maven-projects that build artifacts (e.g. jars) that constitute the product.
E.g.
Root-Project // produces no artifact, simply triggers the build of the other projects
App-Project // The application, that uses the libraries
Lib1-Project // A project that creates a library (jar)
Lib2-Project // Another library
Doc-Project // A project that generates the user documentation from some resources
Maven artifacts are not limited to java resources. You can generate whatever resource you need. E.g. documentation, project-site, zip-archives, native-libraries, etc.
Related
In a Tycho build OSGi dependencies are usually specified in the MANIFEST.MF of the respective modules (e.g., Eclipse plugins). As far as I understand, Tycho identifies those dependencies, resolves them and adds them to the maven build model at build time (sorry for the wayback machine link; the Tycho site seems to undergo some changes right at the moment).
Is it possible to reference such a derived dependency in other maven plugins? For example, if I want to copy particular dependencies with maven-dependency-plugin how would I get to know which groupId, artifactId and version I would have to provide?
Tycho has its own dependency resolution mechanism which is different from Maven's. Tycho loads dependencies defined in the Manifest from p2 repositories and not from Maven repositories (at least usually*). Maven artifacts and p2 bundles have different meta-data structures so you can't always map them to each other. For example bundles don't have the concept of group/artifact ID.
Regular Maven plugins can only handle regular Maven dependencies. p2 artifacts are not visible to them.
Depending on what you are trying to achieve, you could try to convert p2 bundles to Maven dependencies first, and then process them with Maven plugins. For your specific example this might help, if you don't mind splitting the build into multiple steps: Use dependencies from Eclipse p2 repository in a regular Maven build?
* You can configure Tycho with pomDependencies=consider to include Maven artifacts. Those would be visible to regular Maven plugins, but I would not recommend doing that, it makes building/deploying harder the more complex the build gets
Ive been working off the guides which mention to start by doing
gradle init
on the project. So this creates build.grade. However, the rest of the gradle file is very thinly padded. Im quite new to doing these conversions, but broadly speaking, what would be the next step to get things in harmony?
The Gradle docs lists the following features of the Maven POM conversion:
Uses effective POM and effective settings (support for POM inheritance, dependency management, properties)
Supports both single module and multimodule projects
Supports custom module names (that differ from directory names)
Generates general metadata - id, description and version
Applies maven, java and war plugins (as needed)
Supports packaging war projects as jars if needed
Generates dependencies (both external and inter-module)
Generates download repositories (inc. local Maven repository)
Adjusts Java compiler settings
Supports packaging of sources and tests
Supports TestNG runner
Generates global exclusions from Maven enforcer plugin settings
This means, every required functionality beyond these features must be added manually, either by searching and applying plugins equivalent to the ones used in Maven or by implementing the functionality on your own.
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.
Typically, a maven built jar artifact will have it's pom included under META-INF. I recently noticed that the Spring jars don't have this. So, that causes me to wonder about the purpose of that pom.
It seems like maven retrieves the pom directly from the repository when it's doing things that require knowledge of the artifacts meta-data, e.g. when determining dependencies.
So, what's the embedded one for?
The Maven docs suggest two reasons for the pom in this location.
1) Merely for reference, as a convenience. As the docs say, it makes the artifact "self describing"
2) You can get at this information from within your application using Java. This enables the arfiact to auto-report it's version within the application.
http://maven.apache.org/guides/getting-started/index.html
The pom you will find in the repository is not necessarily the one used to build the artifact. It is aimed at the users of the artifact and can be customized when building your artifact.
The one included inside the artifact IS the one used to produce the artifact.
There are options to not have it included in the artifact.
I want to create a maven project, which has to depend on a non maven project which in turn depends on 2 other non maven projects. I do not have ownership of any of the other projects and it would not be possible for me to change anything in those projects let alone the structure to conform to the maven structure.
I asked if I could just get jars -- but was told that because of multiple levels of dependency, it would be "difficult" -- although I haven't understood why.
Is this possible or should I just abandon the use of maven to create my project and go with a regular project with jars in the lib folder?
Inxsible
If you can go with a regular project build that means you must have access to the other project's jar files?
It doesn't really matter how the other project builds them, you can still gain more control over your own build process by loading the jars you depend on into a Maven repository.
I'd suggest using one of the following repository managers:
Nexus
Artifactory
Archiva
They'll give you management screens to uploading 3rd party jars, they'll also a more efficient way to use other Maven repositories like Maven Central.
Once you've got your Maven build process working, you could encourage the other projects to automatically publish their versions into your Maven repo.
They could use the ANT tasks provided by the Maven or Apache ivy projects. Worst case you just continue to load their libraries until they see the light :-)