Java components (Maven)

This document describes the conventions and process used by the OME team for developing, maintaining and releasing its Java components using Maven as their build system.

The set of rules and procedures described below applies to all the following Java libraries.

Component name

GitHub URL


OME Common Java libary


OME Data model

org.openmicroscopy:ome-model org.openmicroscopy:ome-xml org.openmicroscopy:specification org.openmicroscopy:ome-model-doc





OME Stubs

org.openmicroscopy:ome-stubs org.openmicroscopy:lwf-stubs org.openmicroscopy:mipav-stubs

OME Metakit



Some of the historical monolithic Java projects, including Bio-Formats and OMERO, do not strictly comply with these guidelines yet. As the project evolves and components are migrated, any new Java repository should follow this set of rules.


Source code and build system

The source code of a Java library should be maintained under version control using Git and hosted on GitHub.

Maven should be used as the primary build system. The directory layout should follow the standard Maven layout i.e. in the case of a single-module project:


Additionally, the top-level pom.xml should be structured according to the Maven guidelines.

See also

Using Git


Java components use Semantic Versioning i.e. given a version number MAJOR.MINOR.PATCH, increment the:

  • MAJOR version when you make incompatible API changes,

  • MINOR version when you add functionality in a backwards-compatible manner, and

  • PATCH version when you make backwards-compatible bug fixes.

In between releases the version is bumped to the next SNAPSHOT version.

Code contributions should follow the guidelines highlighted in Code contributions.


All the release artifacts for the repositories listed above should be deployed to the Central Repository according to the process described in the next section.

Release process

Maintainer prerequisites

It is important to get familiar with the OSSRH guide and especially the Maven section for performing a release deployment.

To be able to maintain a Java component, a developer must:

  • have a GitHub account and have push rights to the GitHub source code repository

  • have a Sonatype account and be registered as a maintainer of the org.openmicroscopy repository (JIRA issues should be opened for each developer)

  • have a valid PGP key for signing the tags and the JARs

Release strategies

There are different strategies to release a Maven component. At the moment we are pushing 2 successive commits (or Pull Requests) to the master branch. The first commit/Pull Request bumps the version number to the release version and is used for generating the release while the second commit bumps the version to the next development cycle.

See also

A section describing approaches which OME might be considering.

Release preparation

The first step of the Java component release is to prepare a release candidate on the GitHub and Sonatype repositories.

The first operation to perform a Maven release is to bump the version out of SNAPSHOT either via editing the pom.xml manually or using the Maven versions plugin:

$ mvn versions:set -DnewVersion=x.y.z -DgenerateBackupPoms=false
$ git add -u .
$ git commit -m “Bump release version to x.y.z”

Additionally, a PGP-signed tag should be created for the released version e.g. using scc tag-release or more simply git tag -s:

$ scc tag-release -s x.y.z --prefix v

Push the master branch and the tag to your fork for validation by another member of the team:

$ git push <fork_name> master
$ git push <fork_name> vx.y.z

Once you have updated all the versions and ensured that your build passes without deployment you can perform the deployment by using the release profile with:

$ mvn clean deploy -P release
# Potentially add -D gpg.keyname=keyname if desired.

This will upload the artifacts to a staging Sonatype repository and perform all the validation steps. The uploaded artifacts can be examined at where xxxx is an number incremented for each release.

Release promotion

At the moment all Java components use the Nexus Staging Maven plugin with the autoReleaseAfterClose option set to false. A separate promotion step is necessary for releasing the component to the Sonatype releases repository. This promotion can happen either via the Sonatype UI using the Release button or using the release phase of the nexus-staging plugin:

$ mvn nexus-staging:release -P release

See the ‘Manually Releasing the Deployment to the Central Repository’ section of the Apache Maven guide for more instructions. You should be able to find the staged repository by visiting and searching for “org.openmicroscopy”.

The rsync to Central Maven and the update of Maven search usually happen within a couple of hours but the components are accessible beforehand.

Once the tag is validated, the master branch and the tag can also be pushed to the organization repository together:

$ git push origin vx.y.z
$ git push origin master

Next development version

Then finally restore the new development version using e.g. the Maven versions plugin again:

# Where w == z+1
$ mvn versions:set -DnewVersion=x.y.w-SNAPSHOT -DgenerateBackupPoms=false
$ git add -u .
$ git commit -m “Bump release version to x.y.w-SNAPSHOT”
$ git push origin master


At the moment, we use the service provided for public hosting of the Javadoc. For each release to Maven Central, the new Javadoc should be automatically deployed within 24h. It is possible to trigger the generation of the Javadoc by visiting the URL.