improve debug and return code for unfound writer
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Key: WINK-234
URL: https://issues.apache.org/jira/browse/WINK-234
Project: Wink
Issue Type: Improvement
Components: Common, Server
Affects Versions: 1.1
Reporter: Mike Rheinheimer
Fix For: 1.1
Recently a user got an NPE on the server side when he had inadvertently
forgotten to package the jettison provider with the DefectAsset sample. The
NPE:
java.lang.NullPointerException
at
org.apache.wink.common.internal.providers.entity.atom.AtomEntrySyndEntryProvider.writeTo(AtomEntrySyndEntryProvider.java:96)
This was due, of course, to not being able to find a provider to handler
DefectAsset to json data transformation. This problem could have been
prevented in one of two ways:
1) the isWriteable method in AtomEntrySyndEntryProvider could have checked for
a writer and returned false when one was not found, or
2) the writeTo method in AtomEntrySyndEntryProvider could have detected a null
return from providers.getMessageBodyWriter, and responded with some debug
output and a 500 response code.
As it is now, a user would have to inspect source code to determine the
possible cause of the NPE. In poking around at the various providers we have
in Wink, I see both strategies employed. Do we want to establish some
consistency on this? If so, which is the most appropriate? My understanding
is that we want isWriteable to be as fast as possible, so perhaps #2 makes the
most sense for performance. For usability, however, we should never even call
writeTo if isWriteable doesn't pass, so perhaps #1 is best.
Besides the isWriteable and writeTo problem, I did not see any such detection
or debug output in any of the isReadable and readFrom methods in the various
providers. I think we should do the same in these areas? Any opinions?
See the following provider that prompted the original user's question:
org.apache.wink.common.internal.providers.entity.atom.AtomEntrySyndEntryProvider
See this provider that detects null in the isWriteable method:
org.apache.wink.common.internal.providers.entity.app.CategoriesProvider
See this provider for an example of outputting debug and explicitly returning
500 http code:
org.apache.wink.common.internal.model.AnyContentHandler
I'll be glad to go through and adjust the providers once we reach a consensus
on this Jira.
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