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[jsr339-experts] Re: Example 3: Why current ReaderInterceptors are cool.

  • From: Sergey Beryozkin <sberyozkin@...>
  • To: <jsr339-experts@...>
  • Subject: [jsr339-experts] Re: Example 3: Why current ReaderInterceptors are cool.
  • Date: Fri, 27 Apr 2012 17:23:46 +0100

Hi Bill
On 27/04/12 17:02, Bill Burke wrote:


On 4/27/12 4:35 AM, Sergey Beryozkin wrote:
Hi Bill

It's a good example,

On 26/04/12 23:23, Bill Burke wrote:
Here's "Example 3" where a ClientResponseFilter and a ReaderInterceptor
work beautifully together. This also shows why you might want to allow a
ReaderInterceptor the ability to return a java.lang.Object.

-- Example 3: Client-side Caching --

Flow:

0. Application code calls:
Response response = target.request().get();

1. ClientRequestFilter find that the request URL is cached, but the
cache may have expired
2. ClientRequestFilter adds If-None-Match, If-Modified-Since headers and
does a conditional GET
3. ClientResponseFilter processes the response.
4. ClientResponseFilter finds that cached entity is still valid.
5. ClientResponseFilter updates cache entry with any new Cache-Control
metadata
6. ClientResponseFilter sets the response InputStream to the raw
representation of the resource (a gzipped XML document in this case)
6. ClientResponseFilter adds Content-Type header and changes Response
code to 200.
7. ClientResponseFilter adds the cache entry to the its context's
property map so that the ReaderInterceptor can reference it.
7. Application code calls:

Foo foo = response.getEntity(Foo.class);

8. Caching ReaderInterceptor pulls the cache entry from context property
map
9. Caching ReaderInterceptor asks the cache entry if it has ever
unmarshalled Foo.class. If it has, it returns it. Done. *THIS IS AN
EXAMPLE OF a READER INTERCEPTOR CHANGING THE ENTITY*. In this case, it
totally bypasses the MBR.
10. Caching ReaderInterceptor just proceeds to the next
ReaderInterceptor
11. GZIP ReaderInterceptor sees that the cached InputStream is gzip
encoded by seeing a Content-Encoding header. It wraps the InputStream.
12. MBR unmarshalls the GZIPPED XML Document.


Why steps 8-11 can not be made before response.getEntity() ?


You can't do step #9 because before resposne.getEntity() because you
don't know the Java type.

What if at step 7 (actually has to be 8), we have
response.getEntity(InputStream.class) ?


Its a special case for the caching interceptor. In that case, it would
create/return an InputStream pointing to the raw representation bytes of
the cache entry.

Yes, I can see the caching example is convincing.
So at the moment, on the client side we have filters per/post processing the data before the control is returned to the application.
Next we have Reader interceptors involved between the Response.getEntity() & MBR. Filters & ReaderInterceptors communicate with each other by passing the properties around.

In the follow up email I thought that composite MBR (delegating to individual MBRs) can act effectively as Reader interceptors. May be that option is too limiting, given I did not implement a client side caching handler myself :-), but seems it might work with the exception handling being at the composite MBR level, though this option may be a bit 'coarse-grained'.

I'm not entirely appreciating the original Marek's concerns as I haven't started implementing, but I think it's worth exploring the possibility of minimizing the number of handlers. If the current approach of having both the filters and Reader interceptors wins then I'll be happy with that too :-)

Cheers, Sergey






[jsr339-experts] HEADS-UP, IMPORTANT: Problems with JAX-RS interceptors

Marek Potociar 04/26/2012

[jsr339-experts] Re: HEADS-UP, IMPORTANT: Problems with JAX-RS interceptors

Sergey Beryozkin 04/26/2012

[jsr339-experts] Re: HEADS-UP, IMPORTANT: Problems with JAX-RS interceptors

Bill Burke 04/26/2012

[jsr339-experts] Example 3: Why current ReaderInterceptors are cool.

Bill Burke 04/26/2012

[jsr339-experts] Re: Example 3: Why current ReaderInterceptors are cool.

Sergey Beryozkin 04/27/2012

[jsr339-experts] Re: Example 3: Why current ReaderInterceptors are cool.

Sergey Beryozkin 04/27/2012

[jsr339-experts] Re: Example 3: Why current ReaderInterceptors are cool.

Bill Burke 04/27/2012

[jsr339-experts] Re: Example 3: Why current ReaderInterceptors are cool.

Sergey Beryozkin 04/27/2012

[jsr339-experts] Re: Example 3: Why current ReaderInterceptors are cool.

Bill Burke 04/27/2012

[jsr339-experts] Re: Example 3: Why current ReaderInterceptors are cool.

Marek Potociar 04/27/2012

[jsr339-experts] Re: HEADS-UP, IMPORTANT: Problems with JAX-RS interceptors

Bill Burke 04/26/2012

[jsr339-experts] Re: [jax-rs-spec users] Re: HEADS-UP, IMPORTANT: Problems with JAX-RS interceptors

Marek Potociar 04/27/2012

[jsr339-experts] Re: [jax-rs-spec users] Re: HEADS-UP, IMPORTANT: Problems with JAX-RS interceptors

Bill Burke 04/27/2012
 
 
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