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What is Central?

When you develop software you depend on open source, and these external libraries are likely available on a central repository we call Central.

Central is a highly-available cluster of machines in North America and Europe. Central serves billions of requests a year from millions of developers all over the world. If you want to make it easy for millions of developers to use your software, you put it on Central. Once it’s there all they need to do is add a set of simple coordinates. It couldn’t be easier.

Central Changed the Game

Central changed the way that open source Java libraries were distributed, quickly becoming the distribution mechanism of choice for most open source Java projects.

First, let’s go back in time to 2002: before Central was invented. Before Central, developers had to scrounge the internet for the software they needed hitting ten or more web sites and manually figuring out dependencies wasn’t uncommon. Back then builds didn’t just know how to download dependencies.

This was before the advent of automatic dependency management. At the time, your state-of-the-art build was Apache Ant, and you were likely working on systems with four or five external dependencies - all of which were checked into source control. It was a very manual process, and it was error prone - so error prone, you avoided messing with your project’s dependencies. Once they were set, that was it. Builds were brittle.

Fast forward to today, and you’ll notice two big differences:

First, managing your dependencies is much easier. Whether you use a tool like Gradle or Maven, your builds download dependencies for you. No more wandering around the web fishing for the Download link. That logic is built in.

Second, your applications likely have more external dependencies. Back in 2002 you were likely depending on Struts and maybe some Commons libraries. Today, you’ve got ten Spring dependencies on top of several Hibernate and a few JRuby jars. It isn’t uncommon for your Java web application to have thirty or more dependencies.

In the time between 2002 and today, open source Java has taken off and your applications consume more open source as a result. Central established a common coordinate space for Open Source Java. Hibernate isn’t just Hibernate, Spring isn’t just Spring, these two libraries have coordinates: a groupId, artifactId, and version number that locate them in a repository. Your build can go to a repository and download an artifact along with a file that describes that artifacts dependencies.

Central also made it easier for open source developers to distribute software and to depend on other open source libraries. This led to a renaissance of open source Java innovation. The presence of an efficient “exchange” for open source artifacts reduced the startup cost for someone interested in publishing a new open source library. As an open source project, before Central you had to convince people to show up at a web site, download an artifact, and then manually manage dependencies. After Central, all you needed to do to attract new users was to give them a simple XML snippet containing a coordinate.

If Java developers didn’t have a system this efficient, if we were still managing all of this by hand we wouldn’t have as much choice. Not only did Central make it easier to download dependencies, it created an environment that facilitated publishing. Put simply, there wouldn’t be as much open source Java available today were it not for the Central repository.