Repository

II. Repository

Another concept in Maven is that of a repository. The repository holds the artifacts on which your project depends. There are two kinds of repository: local and remote. Both of them can be declaratively set. Unless specified otherwise, the local repository is created in a special directory called ".m2/repository". In Windows, this directory is created in C:\Documents and Settings\Administrator. For example, if your project depends on commons-logging version 1.0.4, you can specify the dependency in pom.xml and when maven is executed, it will copy the appropriate commons-logging jar file from the remote repository to the local repository and then use it to build your project's artifact like JARs, WARs, EARs etc. 

The maven repository folder has subfolders for each library. For instance, there is a sub folder for commons-logging. Beneath the commons-logging folder there is another subfolder called jars. This jars folder has the commons logging jar files suffixed by version number. 

The role of the repository is immediately obvious. Instead of each project having its own copies of third party libraries, the repository helps developers across projects to share the libraries. Each project can also in turn generate its artifacts and publish it into the remote repository. The process of publishing a jar into the repository is called "install" in Maven lingo. This install process helps organizations to share internal artifacts across projects in a standard manner. This also holds the basis for continuous integration among inter-dependent projects. 

Figure shows the  pom.xml, repository and plugins. The grey colored rectangles are provided by you. The blue colored rectangles are provided by Maven. The orange colored rectangle shaded is the output - the real deployment artifact obtained for your project. Custom plug-ins  are optional. The rest of the inputs are mandatory.