org.semanticdesktop.aperture.accessor
Interface DataAccessor

All Known Implementing Classes:

AbstractJavaMailCrawler, FileAccessor, HttpAccessor, ImapCrawler, MboxCrawler, OutlookAccessor

public interface DataAccessor

A DataAccessor provides access to physical resources by creating DataObjects representing the resource, based on a url and optionally previous acces data and other parameters.

Method Summary

DataObject	getDataObject(String url, DataSource source, Map params, RDFContainerFactory containerFactory) Get a DataObject for the specified url.
DataObject	getDataObjectIfModified(String url, DataSource source, AccessData accessData, Map params, RDFContainerFactory containerFactory) Get a DataObject for the specified url.

Method Detail

getDataObject

DataObject getDataObject(String url,
                         DataSource source,
                         Map params,
                         RDFContainerFactory containerFactory)
                         throws UrlNotFoundException,
                                IOException

Get a DataObject for the specified url.

The resulting DataObject's ID may differ from the specified url due to normalization schemes, following of redirected URLs, etc. It is required though to provide a URI through which this DataAccessor can later on also access the same resource, i.e. the URI should also be a URL.

Specific DataAccessor implementations may accept additional parameters through the params Map, e.g. to speed up this method with ready-made datastructures it can reuse. See the documentation of these implementations for information on the type of parameters they accept. However, implementations should not rely on the contents of this Map to work properly.

Parameters:

url - The url of the requested resource.

source - The DataSource to be registered as the source of the DataObject (optional).

params - Additional parameters facilitating access to the physical resource (optional).

containerFactory - An RDFContainerFactory that delivers the RDFContainer to which the metadata of the DataObject should be added. The provided RDFContainer can later be retrieved as the DataObject's metadata container.

Returns:

A DataObject for the specified URI.

Throws:

UrlNotFoundException - When the specified url did not point to an existing resource.

IOException - When any kind of I/O error occurs.

getDataObjectIfModified

DataObject getDataObjectIfModified(String url,
                                   DataSource source,
                                   AccessData accessData,
                                   Map params,
                                   RDFContainerFactory containerFactory)
                                   throws UrlNotFoundException,
                                          IOException

Get a DataObject for the specified url.

The resulting DataObject's ID may differ from the specified url due to normalization schemes, following of redirected URLs, etc. It is required though to provide a URI through which this DataAccessor can later on also access the same resource, i.e. the URI should also be a URL.

The optionally passed AccessData can be used to let the DataAccessor store information about the created DataSource. The next time it is invoked with the same URL, it can then use this information to determine whether the resource has changed or not. The DataAccessor should return null when the resource has not changed. This facilitates fast incremental crawling of DataSources. When no AccessData is specified, no change detection takes place and an AccessData is always returned.

Specific DataAccessor implementations may accept additional parameters through the params Map, e.g. to speed up this method with ready-made datastructures it can reuse. See the documentation of these implementations for information on the type of parameters they accept. However, implementations should not rely on the contents of this Map to work properly.

Parameters:

url - The url of the requested resource.

source - The DataSource to be registered as the source of the DataObject (optional).

accessData - Any access data obtained during the previous access to this DataObject (optional).

params - Additional parameters facilitating access to the physical resource (optional).

containerFactory - An RDFContainerFactory that delivers the RDFContainer to which the metadata of the DataObject should be added. The provided RDFContainer can later be retrieved as the DataObject's metadata container.

Returns:

A DataObject for the specified URI, or null when the binary resource has not been modified since the last access.

Throws:

UrlNotFoundException - When the specified url did not point to an existing resource.

IOException - When any kind of I/O error occurs.