Why Nexus?
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 internally generated artifacts.
Proxying a Maven repository brings a number of benefits. For starters, you are going to speed 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 Nexus, 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.
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 specifically include or exclude certain artifacts from the public repository. Having control over what is downloaded from the central Maven repository is often a prerequisite for using Maven in most organizations which need to maintain very strict control over what dependencies are used throughout the 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 the GPL license. 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. Nexus provides your organization with such a deployment target. Once you install Nexus, you can start using Maven to deploy snapshots and releases to a custom repository managed by Nexus.
