Archiva Developer's Documentation
These documents cover the architecture of Archiva and how to work with it. Information for users and plugin developers can be found instead in the main Archiva documentation.
Note: This documentation is far from complete, and mostly covers new improvements relevant to developers as they are made, and may not cover older topics such as the archiva-model or archiva-repository-layer libraries that are still in use and particularly coupled to certain repository types and the web interfaces.
Overview
Archiva is built as a layered application. It is intended to provide a platform for dealing with repositories of varied types, and so is built as a series of modular libraries that aim to be able to be used independently (such as embedded scenarios, from the CLI, or within the Archiva web application).
Central to the redesign of Archiva is the concept of a metadata content repository. Archiva separates the physical storage of a repository from the representation it works on, allowing it to store information about the repository in an extensible format that any plugin can operate on or add to, without all subsystems needing to know about each other. The metadata is not specific to any repository type - for instance, the Maven 2 portions can be completely optional. More information on the metadata format and how it is persisted is present in the section below.
This structure allows metadata repositories to be physically separated from the repository they represent and remotely updated. However, it is also possible to link the repository storage via the API so that the metadata can operate "live" on a repository, detecting changes. This also allows plugins that wish to operate directly on a repository (for example, Maven snapshot purging).
Similarly, the resolution strategy for resources in the repository is abstracted from the storage and metadata to allow multiple strategies. This facilitates features such as repository proxying, repository grouping, and on the fly format conversion. These are described in the Repository API documents.
On top of the metadata repository, components can be built to provide the services available in the application. These are described as plugins, though at this time there is no formal plugin registration mechanism or interface - they are loaded by the presence of the JAR in the application classpath, with the appropriate Spring or Plexus manifest and implementation of a core interface that they can "plug in" to. At present, these plugins interact either due to a user request (the repository resolution extension points), a distinct scheduled task, or as part of a repository scanning operation (the Archiva 1.0+ 'consumer' mechanism). In the future, an event mechanism is envisaged as the main means of triggering plugin operations, further decoupling them from the core interfaces. Plugins generally interact directly with the metadata repository to retrieve information, or store their own.
Some examples of current plugins are:
- Maven 2 storage repository type
- Repository statistics
- File-based metadata content repository persistence
Finally, we look to the web application layers. At present, there is a single web application that serves both a WebDAV and Struts 2-based application, and operates directly on the metadata repository and some of the legacy APIs. Future development plans to better decouple these from the underlying plugins and legacy APIs, to allow applications to be much more componentised in their deployment.