Maven: The Definitive Guide

To round out our exploration of the assembly descriptor, we should touch briefly on two other sections: containerDescriptorHandlers and componentDescriptors. The containerDescriptorHandlers section refers to custom components that you use to extend the capabilities of the Assembly plugin. Specifically, these custom components allow you to define and handle special files which may need to be merged from the multiple constituents used to create your assembly. A good example of this might be a custom container-descriptor handler that merged web.xml files from constituent war or war-fragment files included in your assembly, in order to create the single web-application descriptor required for you to use the resulting assembly archive as a war file.

The componentDescriptors section allows you to reference external assembly-descriptor fragments and include them in the current descriptor. Component references can be any of the following:

Incidentally, when resolving a component descriptor, the Assembly plugin tries those different strategies in that exact order. The first one to succeed is used.

Component descriptors can contain many of the same content-oriented sections available in the assembly descriptor itself, with the exception of moduleSets, which is considered so specific to each project that it’s not a good candidate for reuse. Also included in a component descriptor is the containerDescriptorHandlers section, which we briefly discussed above. Component descriptors cannot contain formats, assembly id’s, or any configuration related to the base directory of the assembly archive, all of which are also considered unique to a particular assembly descriptor. While it may make sense to allow sharing of the formats section, this has not been implemented as of the 2.2-beta-2 Assembly-plugin release.