Maven's build process is driven by three key concepts: the build lifecycle, mojos, and the lifecycle mappings. If you're not familiar with these concepts, you can read up on them in Maven, The Definitive Guide, especially Chapter 1 and Chapter 10.
Maven's basic unit of work during the build is the Mojo (Maven POJO). Mojos are contained in plugins that group them together with similar functions. Additionally, Maven supplies a standard set of scaffolds - called build lifecycles - that provide an abstract, structured progression of the types of activities (lifecycle phases) typically found in a build. The standard build for a particular type of project is defined when the appropriate mojos are bound to the appropriate lifecycle phases using a lifecycle mapping.
Obviously, this is only a starting point; individual projects can further fine-tune their own builds by binding or reconfiguring mojos in their own POMs. However, the default build for a particular type of project - specified by the packaging element in the POM - is defined by its lifecycle mapping.
Maven provides mappings for many common project packagings out-of-the-box. But what if we have a custom project type? Maybe something that produces a particular type of artifact that only our internal systems know how to use? If we're building a large number of these projects, it may make sense to teach Maven to support a custom project packaging. This is a relatively easy task, if you know a few tricks.
The Custom Lifecyle Mapping
In many cases, we're interested in building a project artifact that is loosely based on the
jar archive layout, with some critical details such as files added to
META-INF/ that turn it into more than a run-of-the-mill classpath entry.