The Plug-in API

The metadata extraction plug-in API allows you to create plug-ins for both metadata extraction (reading metadata from files) and metadata injection (inserting metadata into content item fields). Both processes are managed by the MetadataService class, which delegates the actual work to type-specific plug-ins.

Metadata extraction is performed by implementations of the StreamMetadataExtractor interface. Metadata injection is performed by implementations of the ContentMetadataInjector interface.

The plug-in API uses the Service Provider facility as described in the JAR file specification for discovery of plug-ins (see

A plug-in, then, usually consists of a single JAR file containing:

  • One or more implementation classes

  • A service provider (Spi) class for each implementation

Each service provider class is responsible for instantiating the corresponding implementation class.

Metadata Extraction and Storage Plug-ins

The Content Store also supports plug-in implementations of the Storage interface, which allows developers to add support for different file storage back ends. Third-party implementations of Storage should ideally provide a storage-specific StorageMetadataExtractor implementation in order to enable the use of metadata stored outside the data stream itself (usually file attributes such as size, last modification date and so on).