public interface DataFilter
data providers
before passing it to data loaders.DataProvider,
DataLoader| Modifier and Type | Method and Description |
|---|---|
DataSource |
filter(DataSource original)
Filter the data source.
|
DataSource filter(DataSource original) throws IOException
Filtering is often based on suffix. For example a gzip compressed file will have an original name of the form base.ext.gz when the corresponding uncompressed file will have a filtered name base.ext.
A filter must never open
the DataSource by itself, regardless of the fact it will return
the original instance or a filtered instance. The rationale is that it
is the upper layer that will decide to open (or not) the returned
value and that a DataSource can be opened only once; this is the
core principle of lazy-opening provided by DataSource.
Beware that as the data providers manager
will attempt to pile all filters in a stack as long as their implementation
of this method returns a value different from the original parameter.
This implies that the filter, must perform some checks to see if it must
be applied or not. If for example there is a need for a deciphering filter
to be applied once to all data, then the filter should for example check
for a suffix in the name and create a new
filtered DataSource instance only if the suffix is present,
removing the suffix from the filtered instance. Failing to do so and simply
creating a filtered instance with one deciphering layer without changing the
name would result in an infinite stack of deciphering filters being built, until
a stack overflow or memory exhaustion exception occurs.
original - original data sourceoriginal if this filter
does not apply to this data sourceIOException - if filtered stream cannot be createdCopyright © 2002-2023 CS GROUP. All rights reserved.