Exception Handling Section

[AustinSeto]

Create section in guide to handle exceptions

Addresses #49

[griffinhadfield]

• src/main/java/io/openliberty/guides/rest/exceptions should be created in the start directory with a .gitkeep in it.
• Add file hotspots for GenericExceptionMapper.java and NotFoundExceptionMapper.java
• Consider adding hotspots for toResponse() and ErrorResponse in the excerpt from the Exception Handling section below:

When JAX-RS sees any Throwable, it will search for a matching ExceptionMapper interface that has been marked with the @Provider annotation. It will pass the Throwable to the toResponse() method to construct a response using the ErrorResponse class.

[AustinSeto]

@griffinhadfield changes made, hotspots added

[griffinhadfield]

Feedback has been addressed, LGTM.

[andymc12]

Suggested (via slack) describing how to set a Response in a WebApplicationException (or subclass) - and minor changes in wording.

[andymc12]

I would rephrase this section. I'm not sure that the client will always receive an empty response or an HTML error page. And ideally, the client would receive the error response in the same MediaType (MIME type) that they would receive a normal response in (i.e. it could be text, xml, etc.).

Maybe something like this:

Most application developers will want to ensure that when an exception occurs in the application (such as the client requesting a resource that does not exist or posting an invalid resource, etc.) that it is handled consistently and in a way that allows the client to fully understand the failure (i.e. bad input, server outage, etc.). This can be accomplished using the exception handling mechanisms in JAX-RS such as sending a Response via a WebApplicationException (or subclass) or by using ExceptionMapper providers.

[andymc12]

Suggested change

	This will be handled using an `ExceptionMapper` which maps exceptions to responses and builds appropriate JSON payloads.
	The following example uses an `ExceptionMapper` which maps exceptions to responses and builds appropriate JSON payloads.

[andymc12]

We discussed in slack that it might be better to use a different exception type here - ideally an application-specific, business exception (like WidgetNotFoundException) since NotFoundException is a subclass of WebApplicationException - and it could hold it's own Response object (and thus doesn't need to be mapped).

[andymc12]

Just a couple tweaks - otherwise, looks good. Thanks!

[andymc12]

Suggested change

	NotFoundExceptionMapper.java
	PropertyNotFoundExceptionMapper.java

[andymc12]

Suggested change

	`src/main/java/io/openliberty/guides/rest/exceptions/NotFoundExceptionMapper.java`
	`src/main/java/io/openliberty/guides/rest/exceptions/PropertyNotFoundExceptionMapper.java`

[andymc12]

Looks good! Thanks @AustinSeto!