Develop Reference

What is maven release plugin and what does github to do with it?

What exactly is maven release plugin? What is its purpose? I found it in the middle of a tutorial but don't understand what it is useful for. Also, the teacher is showing us how to create tags on GitHub. What do the maven release plugin and GitHub have in common?

Fundamentally, "releasing a project" means that you have a version of your project that is stable and that you wish to release to the public ("publishing" could be a good synonym).
The maven release plugin helps you with several tasks that need to be done in order to release a project:
Make sure that the project uses no SNAPSHOT-dependencies (as SNAPSHOT-dependencies are considered unreleased and thus not necessarily stable)
Create a tag in your source control management system (in your case GitHub) so that you can come back to the released version e. g. if you need to fix a bug in an older release
Remove the -SNAPSHOT suffix from the project version in your pom.xml
Build the project
Deploy the project to your release repository (usually Maven Central).
Bump the version string in your pom.xml and add -SNAPSHOT again
Note that you can do all of these steps manually (e. g. you can simply edit your pom.xml and remove the -SNAPSHOT suffix and then run mvn deploy to deploy the project to Maven Central), but the release plugin helps with that as it automates those tasks and makes sure that you don't forget anything.
To answer what GitHub has to do with it: Again, the release plugin automatically creates a tag in your SCM so-that you can check it out some time later if you need to. It does not matter what your SCM is, it can be GitHub, Bitbucket, GitLab or whatever else. It's just that most people use GitHub as their SCM host.

Using maven-release-plugin in Eclipse

I recently tried to use maven-release-plugin since it is apparently the recommended way of building and packages releases in the Maven universe.
However I wanted to use this within Eclipse, as the rest of my development workflow is Eclipse based. I normally run Maven commands via the m2eclipse plugin provided as part of Eclipse Juno (4.2)
I noticed a few oddities when I tried to run "release:prepare" within Eclipse:
Some extra files were created in the root project directory - "pom.xml.releaseBackup" and "release.properties". Do they really belong there? Have I got the release directories set up correctly? I wouldn't really consider these temporary artifacts as part of my source code tree......
The pom.xml gets manually overwritten with the updated release number. Eclipse warns you and is happy to reload the updated version - but is this generally safe?
The prepare ultimately fails giving the error [ERROR] Failed to execute goal org.apache.maven.plugins:maven-release-plugin:2.0:prepare (default-cli) on project clisk: Failed to invoke Maven build. Error configuring command-line. Reason: Maven executable not found at: C:\Users\Mike\git\clisk\EMBEDDED\bin\mvn.bat -> [Help 1] - presumably because I am using the built-in Maven excetable provided by m2eclipse rather than the command line. I guess I could install command line maven as well.... but is that sensible or will it just cause more problems?
Given these kind of issues, Is there a way to get maven-release-plugin to work smoothly within Eclipse, or should I just give up and continue to do releases manually?

I have been using release plugin, but only from command line.
Re. 1. The backup files that release plugin creates are needed if something goes wrong in time of preparing the release. You can always rollback the prepared release using release:rollback command. When you do release:perform they will be deleted.
Re. 2. The plugin changes the version number from snapshot version for example: 0.0.1-SNAPSHOT: to release version: 0.0.1. Then after release:perform release version is moved to the maven repository and release plugin changes version again to 0.0.2-SNAPSHOT. Now you can use you full released (tested) version in your testing or production enviornment and snapshot version for developping purposes.
Re. 3. I don't know what is causing the problem, but I don't see the problem by using release plugin from command line.

Also mvn 3.3.3 installs a mvn.cmd file, instead of a mvn.bat file in Windows.
You should copy mvn.cmd to mvn.bat

Well i know this link is OLD , but to help some on who reffers this link for the issue 3.
Install maven separately on to local Box and give the path of the installation under Windows->Preferences--> maven--> Installation. Also you have to define the same in the run configuration within the Eclipse.
Attached is a link that explains the same.
http://maven.40175.n5.nabble.com/Build-Failure-prepare-release-td510949.html

You might be able to overcome the error you mention by installing command line Maven and configure Eclipse to use that rather than the embedded one by choosing Window -> Preferences -> Maven -> Installations, but I agree with the advice of making your releases outside Eclipse.

Version Number Management - how do you do it?

I have a Maven project that needs to be versioned. I have chosen to use the versions-maven-plugin as my versioning plugin but am unsure if that's the best option.
I have read the documentation that such plugin actually modifies the POM and I don't really like that approach. I have worked on projects where they had separate build.properties file that got modified manually.
What I want to achieve is to have my CI generating the artifact for me ready to be deployed and update the version number automatically.
So, any suggestions? How have you done before?
Thank you

I'd get the version number from the one source that matters: that's the source code management system (Subverson, Mercurial, or Git), not Maven.
I'd say that Maven might be out of synch unless your Maven plug-in is getting it from SCM.

Use the Release Plugin. You want to perform automatic deployment and batch release. The Versions Plugin is designed for something else.

We have found MAVEN-RELEASE-PLUGIN super useful and can not imagine releasing and managing version with it.

Eclipse won't believe I have Maven 2.2.1

I have a project (built from an AppFuse template) that requires Maven 2.2.1. So I upgraded to this (from 2.1.0) and set my path and my M2_HOME and MAVEN_HOME env variables.
Then I ran mvn eclipse:eclipseand imported the project into Eclipse (Galileo).
However, in the problems list for the project (and at the top of the pom.xml GUI editor) it says:
Unable to build project
'/export/people/clegg/data/Workspace/funcserve/pom.xml;
it requires Maven version 2.2.1
This persists whether I set Eclipse to use its Embedded Maven implementation, or the external 2.2.1 installation, in the Preferences -> Maven -> Installations dialog.
I've tried closing and reopening the project, reindexing the repository, cleaning the project, restarting the IDE, logging out and back in again, everything I can think of! But Eclipse still won't believe I have Maven 2.2.1.
I just did a plugin update so I have the latest version of Maven Integration for Eclipse -- 0.9.8.200905041414.
Does anyone know how to convince Eclipse I really do have the right version of Maven? It's like it's recorded the previous version somewhere else and won't pay any attention to my changes :-(

Eclipse allows you to specify an external Maven installation. But there's a catch. :(
Have a look at Windows > Preferences > Maven > Installations.
You will see a message like this:
Note: Embedded runtime is always used for dependency resolution, but does
not use global settings when it is used to launch Maven.
To learn more, visit the maven web page.
Translating to English, it means that Eclipse will continue to employ its internal Maven instance in order to perform some tasks.
When you "Run As > maven install" it will run your pom.xml script employing the external Maven instance you specified but when Eclipse performs some of its internal stuff, it will continue to use the embedded Maven instance, whatever version it is.
(edited)
As far as I know, when you install M2Eclipse you are implicitly defining which "internal Maven instance" you will have, which is exactly that one packaged by the plugin.
In the plugin configuration, you can add external Maven instances by telling where they are installed.

If you are using a recent m2eclipse version, you can try this too:
<prerequisites>
<maven>>=2.2.1</maven>
</prerequisites>
Notice the greater than in >=2.2.1. It works fine for me.

A common source of trouble (of this kind) is if you change global preferences and don't remember or know that you have enabled some project specific settings. At least it's a chance that the global setting is now set to use the external maven but the project setting is still set to 'embedded'.

M2Eclipse uses an embedded maven instance, not the maven instance you have installed on your system.

Have you tried switching workspaces?
You can still reference the same project in the new workspace. This would provide about as much of a reset as you can do in terms of eclipses internal settings.

Try creating your eclipse project with mvn project:m2eclipse or use the maven import option under import project.

Using m2eclipse, my fallback in these situations is to do Maven > Update Dependencies and then Maven > Update Project Configuration. The first is just me being supersticious, but the second will rewrite .project and .classpath.
As Pascal says about, m2eclipse can also be pointed at an external instance. I've done this in the past, though not at 2.2.1.
Dan

I got the same issue. Resolved it by restarting the system because every time you change the 'Path' in environment variables you should restart the system or else if would not pick the changes.

How to keep updated libraries in MAVEN?

On the development shop I work for, we have an internal MAVEN repository, to keep our libraries (proprietary & open-souce). A common problem that we face is that, sometimes, the open-source libraries in our local MAVEN repository gets obsolete. Is there an automatic way to keep all the open-source libraries I use in my MAVEN repository always updated? What do you suggest to resolve this issue?

Archiva has been mentioned, but nexus seems more popular. Both have been designed to solve problems like the one you're having

Assuming you:
Don't want to download everything
Don't want to run another server
process
Only want to track a limited number
of projects
You might want to create a separate pom.xml file with dependencies like this:
<dependency>
<groupId>org.openfoo</groupId>
<artifactId>jfoo</artifactId>
<version>[1.0.0,2.0.0)</version>
</dependency>
This will tell maven to use jfoo 1.0.0 up to jfoo 2.0.0 so when jfoo releases version 1.2.17, you'll be fetching that in the next build assuming your settings are set to check versions each time.
This pom doesn't have to actually build anything. Just list those things you want to track.
Running:
cd the-path-to-the-project; mvn -q -B -U package
Via cron once a day will update all the dependencies in that pom and only report when there is a problem
BTW, this is a hack. If the number of developers is > 3 and you have the resources to run nexus, don't bother with the hack.

Take a look at Apache Archiva, a repository manager for Maven.