I do the same. Usually getSize() is unimplemented. I also try to avoid
buffering as I want large data sets to perform well and not have huge
amounts of things in memory, if I'm making sense...
Paul Sandoz wrote:
> Hi Reto,
>
> My approach has been to only implement get size iff it is known in
> advanced (e.g. File size). I consider it more of a hint to the HTTP
> container to know whether it can use a Content-Length with that value
> instead of:
>
> 1) using chunked transfer encoding;
>
> 2) buffering the content to determine the length; or
>
> 3) closing the connection after the response entity has been written.
>
> I think the HTTP container should determine the best strategy of one of
> the three above and the writers do not need to be involved in such details.
>
> If getSize returns a value > -1 then that value should be equal to the
> value that is number of bytes that are written to the OutputStream of
> the writeTo method for the same parameter values passed to both methods.
>
> Paul.
>
> On Jan 29, 2009, at 9:41 AM, Reto Bachmann-Gmür wrote:
>
>> Hello
>>
>> I'm wondering what the best practice to write MBWs is. In my experience
>> the getSize and the writeTo method often have very similar code, or the
>> getSize-method looks similar to this:
>>
>> @Override
>> public long getSize(GraphNode node, Class<?> clazz, Type t,
>> Annotation[] as,
>> MediaType m) {
>> ByteArrayOutputStream baos = new ByteArrayOutputStream();
>> try {
>> writeTo(node, clazz, t, as, m, null, baos);
>> } catch (IOException ex) {
>> throw new RuntimeException(ex);
>> } catch (WebApplicationException ex) {
>> throw new RuntimeException(ex);
>> }
>> return baos.size();
>> }
>>
>> One optimization might be to cache the resulting object- bytes mapping
>> (in a ThreadLocal weak reference of a WeakHashMap) so that when the
>> implementation invokes writeTo, the already computed bytes can be
>> written to the OutputStream.
>>
>> Another approach could be to return an estimate of the size or -1 in the
>> getSize method, and set the exact Content-Length to the headers-map when
>> writeTo is invoked.
>>
>> Another issue is when the rendering of the object could change between
>> invocation of getSize and writeTo. The class GraphNode represents a node
>> in a graph (which is occasionally modified), the writers for different
>> media-types expand the neighborhood of the node to different depths so
>> that it would be awkward to do this expansion in the resource method and
>> return a value-object. I think in such a scenario the writeTo method
>> must either write the bytes pre-computed on invocation of getSize or
>> (re)set the Content-Length header.
>>
>> Cheers,
>> Reto
>>
>>
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--
Bill Burke
JBoss, a division of Red Hat
http://bill.burkecentral.com