/**
* Load a {@link Dataset} or {@link View} for the given {@link URI}.
*
* <p>URIs must begin with {@code dataset:} or {@code view:}. The remainder of the URI is
* implementation specific, depending on the dataset scheme.
*
* <p>If you use a dataset URI, {@code load} returns the unfiltered dataset. If you use a view
* URI, {@code load} returns a {@code View} configured to read a subset of the dataset.
*
* @param uri a {@code Dataset} or {@code View} URI
* @param type a Java class that represents an entity in the dataset
* @param <E> the type used for readers and writers created by this {@code Dataset}
* @param <V> the type of {@code View} expected
* @return a {@code View} for the given URI
* @throws DatasetNotFoundException if there is no dataset for the given URI
* @throws NullPointerException if any arguments are {@code null}
* @throws IllegalArgumentException if {@code uri} is not a dataset or view URI
*/
@SuppressWarnings("unchecked")
public static <E, V extends View<E>> V load(URI uri, Class<E> type) {
boolean isView = URIBuilder.VIEW_SCHEME.equals(uri.getScheme());
Preconditions.checkArgument(
isView || URIBuilder.DATASET_SCHEME.equals(uri.getScheme()),
"Not a dataset or view URI: " + uri);
Preconditions.checkNotNull(
type,
"The entity type can't be null, use Object.class to have the type"
+ " determined by the schema.");
Pair<DatasetRepository, Map<String, String>> pair =
Registration.lookupDatasetUri(URI.create(uri.getRawSchemeSpecificPart()));
DatasetRepository repo = pair.first();
Map<String, String> uriOptions = pair.second();
Dataset<E> dataset =
repo.load(
uriOptions.get(URIBuilder.NAMESPACE_OPTION),
uriOptions.get(URIBuilder.DATASET_NAME_OPTION),
type);
if (isView) {
return Datasets.<E, V>view(dataset, uriOptions);
} else {
// if the URI isn't a view URI, only load the dataset
return (V) dataset;
}
}
