I have come across npm(Node Package Manager) which is used to share the code between js developers. Since this can be achievable through the existing build tools from Apache.
What is the difference between npm(Node Package Manager) and Apache build tools(Ant, Maven, Groovy)?
npm is a package manager, designed to download code that other developers write and you want to share.
Ant and Maven are Java build tools designed to compile Java source code and turn it into a jar file that can be run. In a modern open source world we don't write all our own source code, so Maven pioneered the idea of also managing the jars that other developers write, which links with our code.
Lastly Groovy is a Java based programming language.
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I am currently starting my adventure with Maven, and I actually don't understand the idea behind using it to automate compilation of my source code. For the time being I am working on small projects with up to 15-20 classes, and 1 main method in the "app" class. Could someone please give me the explanation with examples, when it's necesarry (or recommended) to use build automatation tool to compile the source code and how could I benefit from using it regarding source code compilation?
Thank you very much in advance!
I was looking for different answers and I have a lot of work to do but since I've seen this question, as a Maven fanboy, I couldn't resist anymore and this below is my answer.
First of all, I agree with JF Meier which answered before me, but I think the answer can be improved.
IMO you have to consider Maven not just as a build tool, but as a multi-purpose tool which can help you to do very different things. The best 3, for me are:
Compiler. Obviously. Maven allows you to easily compile giant projects with a lot of submodules, even if some of these modules are interdependent one with each other.
Dependency and repository manager. Maven allows you to automatically download third party software and bind this downlaod to the build. This is immediately understandable if you think to framework or api dependencies from big corps (Apache found., Spark, Spring, Hibernate and so on ...) but it's really powerful in every enterprise context.
Example: you have a Maven project (let's say project A) which manages requests coming from a webservice and provides responses. This Maven project relys on another Maven project (let's say project B) which actually generates webservice jar and uploads it to a company repository. Well, when you have to add a field or a method to the webservice you just have to implements new software in project B, upload it the repo and change the version in Maven poms in both project A and B. Voilà: now EVERY developer of the company just have to "mvn clean install" project A to have the new version.
Sources and code automatic generator. Since Maven 2.x are available a lot of plugins (from Apache found. and others) which allow you to generate code and sources (tipically xml files) starting from little to none implementations.
Example 1: CXF plugin is commonly used to generate java classes from xml or xsd files.
Example 2: JAXWS plugin is commonly used to generate wsdl from SOAP webservice implementations or implementation starting from wsdl file.
Do you feel the power now?
-Andrea
The question is not very specific, but I will try to answer.
Usually, you want your source code to end up in a jar or war, so that you can use it as a library or run it somewhere (e.g. on an application server).
Maven not only compiles the classes you have and creates the final artifact (jar, war), but also handles your dependencies, e.g. the libraries your project depends upon.
Here I read about how to make a Groovy library .jar ... i.e. pretty much the same as making a Groovy (standalone) project. But I'm not clear what you do then with the resultant .jar...
Say I have two Eclipse "proper"/"standalone" projects (I'm using Groovy for everything) and I want them to share a third Gradle library project of mine as a dependency, which is merely a library of classes... how are my standalone projects expected to find the latest .jar version of the library which they're both using...?
My expectation would be that somehow these versions of the library .jar would have to under GRADLE_USER_HOME (i.e. same location as all other dependency .jars).
Then I would assume that in the build.gradle of both standalone projects you'd have a line like
compile 'mylibrary:mylibrarymodule:3.+'
... of course the first part of these compile directives normally involves a "domain name in reverse" ... and this is normally used by a repository like Maven. How does it work with something which doesn't need to be published?
NB at the time of writing I don't have a Maven account as such and have no idea whether "publication" for re-use of a local common library project like this is essential or not.
Naturally, when I distribute versions of my standalone projects they will need to be packaged up with the library .jar in question.
A link to a how-to for a case like this would be more than welcome: I haven't found it under gradle.org.
If you are developing by yourself, you can use maven-publish plugin to publish your artifacts to local maven repository(you don't have to install maven for this) and on your dependent project you can simply say use mavenLocal repository for dependencies.
If you are on a company, I suggest installing a repository manager and deploy your artifacts to this repository so others can use. You can use their respective plugins to deploy easily. (Gradle Artifactory Plugin, Gradle Nexus Plugin, these are just deployment plugins, you have to setup respository manager to. There are other repository management tools also.) Doing the above process from CI server is the preferred way.
To use latest version of a dependency, you can use Gradle Versions Plugin. If the versioning happen often, using snapshot versions also a possibility.
I am a total beginner at maven, I have read about it online but I am still confused how it can be used. I have eclipse Oxygen version installed and when I open projects I can see maven project option is already there. I was even able to create a maven project using YouTube tutorial. But now then I saw popular plugin called m2eclipse but I am not able to comprehend why is it actually used; when my application ran without it.
I am learning maven to get started with spring boot but I am finding it really overwhelming where to begin with, and many of the tutorial sites state to download maven (But maven already comes along with eclipse?)
Please explain.
Apache Maven is a build tool - a tool for compiling the source code of a project into a program that you can run (for example a jar file, or a war file that can be deployed on a Java EE application server). Besides automating all the tasks for building a project, it also gives you a standard way to organize your project and to keep track of dependencies (libraries that your project needs).
Why do you need such a tool?
When you write a small program that consists of one, or maybe a few source files, it's easy enough to compile it by hand on the command line, by directly using the Java compiler javac that comes with the JDK.
But when your project becomes more complex, and you have hundreds or even thousands of source files in multiple modules, it becomes really hard to keep track of everything and cumbersome to compile the files using javac. If your program needs libraries, it becomes even more complex, because you have to make sure that all the libraries are on the classpath, and some libraries need other libraries, which also have to be on the classpath.
A tool such as Maven helps you to compile all the source files in the right order and to keep track of all the libraries. Maven can automatically download libraries from the web and add them to your project, and downloading everything and building the whole project can be done with one simple command such as mvn clean package.
Spring Boot is part of the Spring Framework, which is a huge framework with tons of useful functionality for developing projects in Java. A Spring Boot project typically needs dozens of libraries, and it would be very hard to use if you'd have to keep track of all those libraries by hand - so that's why it uses Maven to manage all of this for you.
A Maven project is configured using a file named pom.xml - in that file, you describe your project and you put a list of libraries that your project needs. When you build your project, Maven will read the pom.xml file and figure out automatically what source files need to be compiled, and what libraries need to be downloaded.
m2eclipse comes preinstalled in Eclipse (at least when selecting "Eclipse for Java developers" or "Eclipse for Java EE developer"), thats why you were able to use Maven by default.
Still you probably want a command line Maven, because that's most likely how it will eventually run on the CI server, sometimes Eclipse Maven installation can produce different result than the command line install.
I have only little experience using maven with eclipse. One of the job descriptions which I received has "Workflow management using Maven" as a required skill. What does this mean ? What do they possibly expect?
I think they want you to correct them? :D
I'm not sure what they refer to. I would guess it relates to the developer workflow of creating and delivering software with eclipse (?) and maven.
So setting up a project from scratch is often done from an maven archetype (a project template if you like). A lot of open source frameworks offer archetypes to start with.
For existing projects you would check out the code from version control and import it into eclipse. the m2eclipse plugin is required to do that (but I think its quite common to have it)
Then there is building the software. Which is done through executing maven phases (which will then execute plugins). See maven-phases for more details. Maven phases have default plugins that execute (for example compile will run the compiler plugin).
So your workflow would look like this: you modify the files. compile them, test them, package them, deploy the artifacts into the maven repository. the maven install phase will store the artifacts in you local repository, the maven deploy phase will upload them into the company's repository.
From there the the files are installed. Yet you can use maven plugins to install the software into a application server. That depends on the traditions of the company.
I would not think of workflow as some strict step by step think like BPMN. Development is usually done with huge amounts of personal practices (are tests written in advance or while implementing, and so on).
Hope that will help :)
Now that Bazel (http://bazel.io/) has been opensourced, is there an incremental process by which I can gradually migrate (a large repository) from Maven to Bazel?
I work on Bazel. No, as far as we know there is no such process. I wish.
We have been running some migrations from other build systems to Bazel; the evidence isn't conclusive, but it's difficult to even envision how an incremental process would look like. There are some scenarios where we can envision one build system generating configuration files for another (like gyp), but then you still need to switch wholesale.
In the two years since Ulf responded, there's been a few efforts to assist with maven to bazel migration. In particular, the Bazel team is creating a tool to assist with this: https://github.com/bazelbuild/migration-tooling
The tool generates expansive WORKSPACE files from a set of pom files or maven coordinates. In the ideal case, you can pass the path to your maven project, and then it will generate a bzl file you can load into the WORKSPACE file.
More commentary on how to manage external dependencies can be found here: https://bazel.build/versions/master/docs/external.html
And another update (2018)...
There is a dedicated guide on migrating from Maven build tool to Bazel.
And on a general note, it’s best to have both build tools running in parallel until you have fully migrated your development team, CI system, and any other relevant integrations. You can run Maven and Bazel in the same repository.
https://docs.bazel.build/versions/master/migrate-maven.html
September 2019 update
Wix published a tool called Exodus to automatically migrate your Maven project to Bazel.
Additionally, rules_jvm_external has support for managing transitive Maven artifact dependencies.
May 2018 update
Here's another update using Jadep, a BUILD file generator for your Java projects.
There's a tutorial by the author who migrated google-java-format to Bazel: https://github.com/cgrushko/text/blob/master/migrating-gjf-to-bazel.md