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From "Philip Mundt (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SLING-8047) Rendered/exported JSON requested via SlingRequestProcessor is not written to output stream
Date Mon, 22 Oct 2018 13:21:00 GMT
Philip Mundt created SLING-8047:
-----------------------------------

             Summary: Rendered/exported JSON requested via SlingRequestProcessor is not written
to output stream
                 Key: SLING-8047
                 URL: https://issues.apache.org/jira/browse/SLING-8047
             Project: Sling
          Issue Type: Bug
          Components: Feature Model, Servlets
            Reporter: Philip Mundt


While trying to facilitate the {{SlingRequestProcessor}} to get a rendered or exported JSON
representation of a resource, we ran into the problem of the response always being empty.
The HTML rendering worked without any issue.

(See example code of [Get the rendered HTML for an AEM resource, component or page|http://www.nateyolles.com/blog/2015/10/get-rendered-html-for-an-aem-resource-or-component]
or [https://stackoverflow.com/a/34218708])

Main, observed difference seem to be the method calls to print writer:
h4. JsonRenderer

{{org.apache.sling.servlets.get.impl.helpers.JsonRenderer#render}} uses {{#write}} method
of response's print writer.
h4. ExportServlet (via JacksonExporter)

{{org.apache.sling.models.impl.ExportServlet#doGet}} uses {{#write}} method of response's
print writer.
h4. HTMLRenderer

{{org.apache.sling.servlets.get.impl.helpers.HtmlRenderer#render}} uses {{#print}} and {{#println}}
methods of response's print writer.
h3. Further observations

When the print writer's {{autoFlush}} property is set to true and one uses the {{#println}}
method instead of {{#write}}, the {{JsonRenderer}} will flush the print writer's buffer to
the output stream. Due to wrapping the response in {{org.apache.sling.scripting.core.impl.helper.OnDemandWriterResponse}}
(where {{autoFlush=false}}) this does not work for the {{ExportServlet}}.

When adding implicit {{#flush()}} calls to both classes, both request scenarios will work.
According to the servlet specification, it should not be necessary to flush the print writer,
as the container must immediately flush all remaining content to the client upon "termination
of the service method of the servlet".

Please find two test cases for (where implicit {{#flush()}} calls were added):
 * JsonRenderer (tbd)
 * ExportServlet (tbd)



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