21. GeoMesa Blob Store¶
The GeoMesa Blob Store is found in geomesa-blobstore in the source distribution.
The GeoMesaIndexedBlobStore is an interface that describes the
function of a GeoMesa BlobStore, which is to store and retrieve files
that have spatio-temporal data associated with them. A GeoMesa Blobstore
is created by combining a geotools data store and a backing blob store
which will contain the blobs separated from the geo index. The
BlobStore interface can be used to implement compatibility with
other databases or distributed file systems.
During ingest of a file into a GeoMesa BlobStore, a pluggable system of
FileHandlers examines the files (and associated maps of
parameters) and creates SimpleFeatures which are the written to a
GeoMesa data store while the blobs are persisted using a class that
implements the BlobStore interface.
File retrieval is a two-step process. First a query is made to the
GeoMesa FeatureStore. The returned SimpleFeatures will contain
a URI field. That URI points to the desired file stored in Accumulo, and
can be retrieved by the GeoMesaIndexedBlobStore API or by the REST
interface.
21.1. FileHandler Interface¶
The FileHandler interface is designed to allow file handling in the
Blobstore to be pluggable. Implementors should implement
org.locationtech.geomesa.blob.api.handlers.FileHandler or extend the
abstract implementation
org.locationtech.geomesa.blob.api.handlers.AbstractFileHandler. The
class WKTFileHandler serves as an example of that latter approach.
FileHandler implementations are loaded at runtime by the Java
ServiceLoader. As such, available implementations should have their
classname registered in
META-INF/services/org.locationtech.geomesa.blob.api.FileHandler.
21.2. BlobStore Interface¶
The BlobStore interface is designed to allow the backing blob store
of a GeoMesaIndexedBlobStore to be pluggable. Implementors should
implement org.locationtech.geomesa.blob.api.BlobStore interface. The
AccumuloBlobStoreImpl serves as an example implementation of a
BlobStore .
As of this time the BlobStore interface does not yet use the Service
Provider Interface.
21.3. Provided File Handlers¶
The BlobStore API contains by default the WKTFileHandler and
ByteArrayHandler handlers. The WKTFileHandler allows users to
ingest any file by associating a WKT geometry to a file. Similarly the
ByteArrayHandler allows users to ingest arbitrary byte arrays
accompanied with spatio-temporal attributes.
Along with these included handlers, the GeoMesa BlobStore has two sub modules of additional handlers in the geomesa-blobstore-handlers module.
21.3.1. GeoMesa-BlobStore-EXIF¶
The EXIF module contains the MetadataFileHandler which can parse
EXIF metadata to retrieve geolocation information. This enables ingest
of large collections of geotagged images into a GeoMesa BlobStore.
21.3.2. GeoMesa-BlobStore-GDAL¶
The GDAL module contains the GDALFileHandler which utilizes GDAL to
extract geolocation information and time from raster/imagery files
supported by GDAL 2.0.0. For a complete list of GDAL supported file
formats please refer to: GDAL formats list.
To utilize this handler the user must have compiled GDAL Java bindings and have placed relevant JNI libraries in the LD_LIBRARY_PATH environment variable. To build GDAL and the JNI libraries, follow the instructions here: GDAL JNI build instructions.
21.4. GeoMesa-BlobStore-Accumulo¶
The BlobStore-Accumulo module contains concrete implementations of the
GeoMesaIndexedBlobStore interface for Accumulo as well as an
implementation of the BlobStore interface for Accumulo, the
AccumuloBlobStoreImpl class. The GeoMesaAccumuloBlobStore
utilizes a GeoMesa Accumulo DataStore as well as the
AccumuloBlobStoreImpl for the Blob persistance layer.
File retrieval is a two-step process. First a query is made to the
GeoMesa FeatureStore. The returned SimpleFeatures will contain
a URI field. That URI points to the desired file stored in Accumulo, and
can be retrieved by the GeoMesaIndexedBlobStore API or by the REST
interface.
21.5. REST API¶
The GeoMesa BlobStore comes with a RESTful web interface servlet that can be used in place of more direct programmatic access via the Java and Scala classes. As of now the the BlobStore only provides an interface to an Accumulo backed DataStore and BlobStore. Once the servlet is deployed the RESTful api for the Blobstore can be easily utilized via cURL.
DataStores are managed by assigning them to aliases, this allows users to connect to multiple blobstores. To Register a GeoMesa Blob Store to an alias (in this case myBlobStore):
curl -d 'accumulo.instance.id=myCloud' -d 'accumulo.zookeepers=zoo1,zoo2,zoo3' -d 'accumulo.catalog=myBlobStore' -d 'accumulo.user=user' -d 'accumulo.password=password' http://localhost:8080/geoserver/geomesa/blobstore/ds/myBlobStore
Other Blob Store commands:
- DELETE /ds/:alias - Delete a previously registered GeoMesa data store
- GET /ds/:alias - Display a registered GeoMesa data store
- GET /ds/ - Display all registered BlobStores
To ingest a file:
curl -X POST -F file=@filename.whatever http://localhost:8080/geoserver/geomesa/blobstore/blob/:alias
To GET a file with the original filename preserved via id, run:
curl -JO http://localhost:8080/geoserver/geomesa/blobstore/blob/:alias/some-id/
The Blobstore servlet also has optional GZip support which can be used
by adding the --compressed cURL parameter.
curl --compressed -JO http://localhost:8080/geoserver/geomesa/blobstore/blob/:alias/some-id
To DELETE a file from the blobstore, you must do so by id:
curl -X "DELETE" http://localhost:8080/geoserver/geomesa/blobstore/blob/:alias/some-id
21.6. Servlet Configuration Options¶
File upload constraints for the BlobstoreServlet can be configured with
the following system properties:
org.locationtech.geomesa.blob.api.maxFileSizeMB (defaults to 50MB)
org.locationtech.geomesa.blob.api.maxRequestSizeMB (defaults to 100MB)
The expected unit for these properties is in MB, so setting
org.locationtech.geomesa.blob.api.maxFileSizeMB=10 will result in a
10MB maxFileSize.