Why do I need a Repository Manager?

Maven Repository managers serve two purposes: they act as highly configurable proxies between your organization and the public Maven repositories and they also provide an organization with a deployment destination for your own generated artifacts.

Proxying a Maven repository brings a number of benefits. Proxying speeds up builds throughout your organization by installing a local cache for all artifacts from the Central Maven repository. If a developer in your organization needs to download version 2.5 of the Spring Framework and you are using a Maven Repository Manager, the dependencies (and the dependency’s dependencies) only need to be downloaded from the remote repository once. With a high-speed connection to the Internet this might seem like a minor concern, but if you are constantly asking your developers to download hundreds of megabytes of third-party dependencies, the real cost savings are going to be the time it takes Maven to check for new versions of dependencies and to download dependencies. Serving Maven dependencies from a local repository can save you hundreds of requests over HTTP, and, in very large multi-project builds, this can shave minutes from a build.

If your project is relying on a number of SNAPSHOT dependencies, Maven will need to check for updated version of these snapshots. Depending on the configuration of your remote repositories, Maven will check for SNAPSHOT updates periodically, or it might be checking for SNAPSHOT updates on every build. When Maven checks for a snapshot update it needs to interrogate the remote repository for the latest version of the SNAPSHOT dependency. Depending on your connection to the public Internet and the load on the central Maven repository, a SNAPSHOT update can add seconds to your project’s build for each SNAPSHOT update. When you host a local repository proxy with a repository manager, your repository manager is going to check for SNAPSHOT updates on a regular schedule, and your applications will be able to interact with a local repository. If you develop software with a lot of SNAPSHOT dependencies, using a local repository manager can often shave minutes from a large multi-module project build, your 5-10 second SNAPSHOT update checks against the public central repository are going to execute in hundreds of milliseconds (or less).

In addition to the simple savings in time and bandwidth, a repository manager provides an organization with control over what is downloaded by Maven. You can include or exclude specific artifacts from the public repository, and having this level of control over what is downloaded from the central Maven repository is a prerequisite for organizations which need strict control over what dependencies are used throughout an organization. An organization which wants to standardize on a specific version of a dependency like Hibernate or Spring can enforce this standardization by only providing access to a specific version of an artifact in a repository manager. Other organizations might be concerned with making sure that every external dependency has a license compatible with the legal standards of that organization. If a corporation is producing a application which is distributed, they might want to make sure that no one inadvertently adds a dependency on a third-party library which is covered under a copy-left license like the GPL. Repository managers provide for the level of control that an organization needs to make sure that overall architecture and policy can be enforced.

Aside from the benefits of mediating access to remote repositories, a repository manager also provides something essential to full adoption of Maven. Unless you expect every member of your organization to download and build every single internal project, you will want to provide a mechanism for developers and departments to share both SNAPSHOT and releases for internal project artifacts. A Maven repository manager provides your organization with such a deployment target. Once you install a Maven repository manager, you can start using Maven to deploy snapshots and releases to a custom repository managed by the repository manager. Over time, this central deployment point for internal projects becomes the fabric for collaboration between different development teams.

The List of Repository Managers

The Following is a list of the known Maven repository managers and listed in alphabetical order: