Completed Error-handling system on server and client side.

[omzmarlon]

(Inspired by: http://stackoverflow.com/questions/30351481/play-framework-how-to-implement-proper-error-handling) (Stackable Trait Pattern: http://www.artima.com/scalazine/articles/stackable_trait_pattern.html) (Scala PartialFunctions: http://alvinalexander.com/scala/how-to-define-use-partial-functions-in-scala-syntax-examples)

Implementations:

• Overrode Play’s ErrorHandler class (see ManagementAppErrorPlayHandler and application.conf) so that we any exception thrown, we response with a meaningful JSON
• Used Scala’s Stackable Trace pattern so that ManagementAppErrorPlayHandler can find the proper handler for a thrown exception
• Used PartialFunction to define the type of error resolver. With PartialFunction we can easily compose/combine handlers. An error resolver (or handler) is a just a partial function that when turn a thrown exception to the proper play Result that should be sent as http response.
• Created a new DTO called ErrorMessageDTO. This is for server to send a formatted JSON message to front-end, and then our web app can display meaningful error message according to the JSON sent
• A custom exception or error message has these fields: exceptionCode(an unique exception code), status (http status code), code (exception title), message (detailed exception message)
• Implemented an error message formatter so that we can see meaningful message on terminal

Here’s how error-handling works:

• For a specific use case, define an custom exception to extend AbstractManagementAppException, and then when throwing the exception, define a unique MAExceptionCode (when looking at stack trace, we can easily find exactly where the exception was thrown using the exception code)
• After an exception is thrown, the ManagementAppErrorPlayHandler will catch the exception, and then through the stack of handler traits (BaseErrorHandler, CommonErrorHandler, AuthenticationErrorHandler, etc), it will find the a appropriate handler for the error
• The handler will turn the error to a proper play Result (see handler traits and MAErrorResults), and then send the Result response back to client

[omzmarlon]

Sample JSON responses and stack traces

[omzmarlon]