Added a pluggable adapter implementation for parsing request bodies

[edwardUL99]

Converted the original Adapter implementation to a pluggable adapter implementation (with a narrow interface compared to the previous wide adapter interface). Won't merge this yet until J.J can compare the 2 adapter implementations in the next meeting.

The main classes involved with the adapter are as follows:

• RequestParser.java represents the target interface that parses a request body to a JsonObject
• RequestParserImpl.java represents the default implementation of the target interface
• APIRequest.java takes a RequestParser parameter to parse the request body for the getJsonBody method
• RequestParserAdapter.java represents the pluggable adapter that takes 2 delegate functions of type:
  • RequestParserDelegate.java (a functional interface that takes an Object representing the raw body to parse and returns JsonObject)
  • RequestTransformerDelegate.java (a functional interface that takes an APIRequest parameter and converts it to an Object that the RequestParserDelegate can parse, defaults to APIRequest.getBody)
• APIRequestFactory.java creates APIRequests from a HttpServletRequest
• RequestParserFactory.java takes APIRequests, examines their Content-Type and returns a RequestParser implementation suitable for parsing the body to JSON. This implementation can be the default JSON parser or a registered adapter
• RequestParsingConfig.java registers the adapters and their associated content types with the RequestParserFactory class. Uses the AdaptersConfigurer Spring Bean
• AdaptersConfigurer.java allows chaining of calls to register adapters to it. Used by RequestParsingConfig.java

[edwardUL99]

Vanilla adapter code contained within branch vanilla_adapter for comparison in the report