Michael Bolz created OLINGO-15:
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Summary: Content Type Handling hard coded in EntityProvider
Key: OLINGO-15
URL: https://issues.apache.org/jira/browse/OLINGO-15
Project: Olingo
Issue Type: Improvement
Components: odata2-core
Affects Versions: 0.0.0, 1.0.0
Reporter: Michael Bolz
Fix For: 1.0.0
Content Type Negotiation is done correctly (in most cases) but in the end the
content type which is set is hard coded in the response (see example for JSON
below).
After a review of the {{AcceptHeader}} content type process flow through the
{{Dispatcher}}, the {{RequestHandler}}, the {{Processor Implementation}}, the
{{EntityProvider}} and back it would be better to refactor the behavior were
the {{Content-Type Header}} of the response is set.
Suggested is to do the content negotiation at the {{RequestHandler}}, give the
result to the {{Dispatcher}} which simply pass through it to the {{Processor}}
implementation. The {{EntityProvider}} based classes *MUST NOT* set the
{{Content-Type Header}} of the {{ODataResponse}}. The only exception is when
the resulting {{Content-Type}} can only have one valid value, which is e.g. the
case for a {{$count}} request which only can be {{Content-Type: text/plain}}.
The {{Processor}} implementation returns with the {{ODataResponse}} back to the
{{RequestHandler}} which then checks if the {{Content-Type Header}} is set and
*only if it is not set* the {{RequestHandler}} set the header with the resulted
content type from the before done content negotiation. If the header is already
set (from the {{Processor}}) it is not changed.
With this solution the {{Content-Type}} handling and set for the response is
not spreaded through several layers of the library. It then is clear that it is
done by the {{RequestHandler}} and can be overwritten by the implementing
{{Processor}}.
In addition the {{EntityProvider}} does not have the {{Content-Type}} hard
coded which allows a better pre defined content negotiation in the library
(especially with parameters in the {{AcceptHeader}}).
Appendix:
JsonEntityProvider:
{code}
@Override
public ODataResponse writeFeed(final EdmEntitySet entitySet, final
List<Map<String, Object>> data, final EntityProviderWriteProperties properties)
throws EntityProviderException {
final EntityInfoAggregator entityInfo =
EntityInfoAggregator.create(entitySet, properties.getExpandSelectTree());
CircleStreamBuffer buffer = new CircleStreamBuffer();
try {
BufferedWriter writer = new BufferedWriter(new
OutputStreamWriter(buffer.getOutputStream(), DEFAULT_CHARSET));
new JsonFeedEntityProducer(properties).append(writer, entityInfo, data,
true);
writer.flush();
buffer.closeWrite();
----> return
ODataResponse.entity(buffer.getInputStream()).contentHeader(HttpContentType.APPLICATION_JSON).build();
} catch (EntityProviderException e) {
buffer.close();
throw e;
} catch (Exception e) {
buffer.close();
throw new
EntityProviderException(EntityProviderException.EXCEPTION_OCCURRED.addContent(e.getClass().getSimpleName()),
e);
}
}
{code}
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