I forgot to say if you really want the size to be declared to the HTTP
container you can write a ContainerResponseFilter and adapt the
ContainerResponseWriter to buffer the bytes. You can choose to do this
per-resource method using a ResourceFilterFactory if you want to be
selective.
See the source code to
com.sun.jersey.api.container.filter.LoggingFilter for more details of
how to buffer.
Paul.
On Jan 5, 2011, at 11:22 AM, Paul Sandoz wrote:
> Hi Gary,
>
> The best practice i would advise is if you know the size before you
> do any serialization then this method can be used, otherwise return
> -1 and let the HTTP container do its thing (e.g. buffer or use
> chunked transfer encoding). A good example where getSize can return
> a non-negative integer is the serializing of byte[] or File.
>
> I would not recommend doing work in the getSize method and caching.
> Although the runtime will call getSize before writeTo it is not
> specified that getSize should be called just once or that writeTo
> will be called after getSize is called (and if so it is not stated
> that it will be on the same thread). For example, the application
> developer can inject Providers and from that obtain a
> MessageBodyWriter and do what ever it wants with it.
>
> The following is likely to be implementation specific to the HTTP
> container that is utilized. In the writeTo method you could buffer
> the serialization in byte[] then set the Content-Length header. You
> need to set this header before any bytes are written to the output
> stream, since when the first byte is written the headers are
> committed.
>
> Hth,
> Paul.
>
>
> On Jan 5, 2011, at 12:17 AM, Gary Moore wrote:
>
>> Right now, we're doing a lot of this in our MessageBodyWriter(s):
>>
>> @Override
>> public long getSize(PropValue value, Class<?> type, Type type1,
>> Annotation[] annotations, MediaType mediaType) {
>> //TODO: Do this
>> return -1L;
>> }
>>
>> The problem is that we're doing some objects->byte conversions in the
>> MessageBodyWriter.writeTo method. The docs for MessageBodyWriter say
>> getSize is called before writeTo, so to respond properly to getSize,
>> we have to do the objects->byte conversions twice, once to get the
>> size and another time to actually write it out.
>>
>> What is the Jersey lifecycle of MessageBodyWriters? Is it safe to do
>> the converting in the getSize method, then save the result for use in
>> the writeTo method?
>>
>> Thanks,
>> Gary
>>
>> --
>> Gary Moore
>> http://athena.fracturedatlas.org
>> http://www.gmoore.net
>