try {
XMLInputSource is = fEntityResolver.resolveEntity(
new XMLResourceIdentifierImpl(publicId,systemId,baseUri,null));
if(is==null) return null;
LSInput di = new DOMInputImpl();
di.setBaseURI(is.getBaseSystemId());
di.setByteStream(is.getByteStream());
di.setCharacterStream(is.getCharacterStream());
di.setEncoding(is.getEncoding());
di.setPublicId(is.getPublicId());
di.setSystemId(is.getSystemId());
return di;
} catch( IOException e ) {
// erors thrown by the callback is not supposed to be
// reported to users.