Hello!

I would like to see a method

public void ShapefileDataStore.modifyFeatureType(AttributeType[]
removedTypes, AttributeType[] addedTypes, Object[] defaultAddedValues)
throws IOException;

for modifying current ShapefileDataStore schema.

There is a unimplemented stuff updateSchema(FeatureType) that can just
delegate real work to the underlying method by analyzing passed FeatureType
with current schema.

The developer may call ShapefileDataStore.updateSchema(FeatureType) or
modifyFeatureType(...) directly from ShapefileDataStore. The last method
gives more freedom to manipulate by attribute types without creating
FeatureType (etc.).

The ShapefileDataStore has to perform schema modifications internally
because of read/write lock object is inside of it. The approach is usual:
read from current datastore, modify features on the fly to conform changes,
write into temporary. Then lock current datastore to rewrite files from
temporary one, unlock. 

I have implemented the method, also tests. Any comments or suggestions
(for/against this proposal).
If there are no points against I can commit to geotools 2.2.x branch and to
trunk.

Regards, Vitali.

P.S. the difficulty to perform this operation outside of ShapefileDataStore
- there is no possibility to get lock. Because of the requirement is schema
modification of the current shapefile, not a creation of new shapefile.
Without lock it is dangerous in multi-threading environment like UDIG and
led to exceptions like "java.io.IOException: Shp has extra record"...


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