Maven: The Complete Reference
Maven provides plugins that are used to create the most common archive types, most of which are consumable as dependencies of other projects. Some examples include the JAR, WAR, EJB, and EAR plugins. As discussed in Chapter 4, The Build Lifecycle these plugins correspond to different project packaging types each with a slightly different build process. While Maven has plugins and customized lifecycles to support standard packaging types, there are times when you’ll need to create an archive or directory with a custom layout. Such custom archives are called Maven Assemblies.
There are any number of reasons why you may want to build custom archives for your project. Perhaps the most common is the project distribution. The word ‘distribution’ means many different things to different people (and projects), depending on how the project is meant to be used. Essentially, these are archives that provide a convenient way for users to install or otherwise make use of the project’s releases. In some cases, this may mean bundling a web application with an application server like Jetty. In others, it could mean bundling API documentation alongside source and compiled binaries like jar files. Assemblies usually come in handy when you are building the final distribution of a product. For example, products like Nexus introduced in Repository Management with Nexus, are the product of large multi-module Maven products, and the final archive you download from Sonatype was created using a Maven Assembly.
In most cases, the Assembly plugin is ideally suited to the process of building project distributions. However, assemblies don’t have to be distribution archives; assemblies are intended to provide Maven users with the flexibility they need to produce customized archives of all kinds. Essentially, assemblies are intended to fill the gaps between the standard archive formats provided by project package types. Of course, you could write an entire Maven plugin simply to generate your own custom archive format, along with a new lifecycle mapping and artifact-handling configuration to tell Maven how to deploy it. But the Assembly plugin makes this unnecessary in most cases by providing generalized support for creating your own archive recipe without spending so much time writing Maven code.