An experimental attempt at consuming and generating JSON requests and responses in context of the Play Framework for Java.

The route file provides two major endpoints:

• The palindrome testing page resource is given the route /palindrome
• The palindrome test API call resource is given the route /api/palindrome.json
  • It can be a helpful design practice to separate main page resource routes from AJAX API calls resource routes.
  • By adding the .json suffix to the resource, we leave the door open to permitting access via other formats, e.g. .xml. This pattern is even more useful when an API is publicly exposed.

Two simple models are used:

• PalindromeTestRequest handles the structure of the incoming palindrome test request; no logic is bound to this object, though accessors could certainly be used if desired.
• PalindromeTestResult handles the structure of the outgoing palindrome test result.
  • Objects of this model class include a helper method to retrieve a JSON node tree representation of themselves. This is for convenience and consistency, delegating the format to one location.
  • Note that other libraries not integrated with Play have more thoroughly integrated means of defining model structure mappings to XML and JSON. See the Jackson library as one such example.

The testPalindrome resource defines our primary point of logic for the application.

• The @BodyParser.Of annotation is used to declare what the expected content types will be for requests and responses.
• The JSON object is retrieved from the request's body (request().body().asJson()).
• The object is deserialized into a PalindromeTestRequest using the Play Framework wrapper function Json.fromJson.
  • This may throw other exceptions; the documentation is unclear.
• The PalindromeTestResult created returns a JSON tree that we can render directly as our output response.

The browser-based logic for the palindrome testing view is all inside the palindrome.js script.

• Note the module pattern being used.
  • Palindrome module dependencies to other loaded libraries are declared in the wrapping function call. This could be replaced with other dependency management libraries, e.g. RequireJS. This wrapper function is called immediately, creating a closure for the module.
  • Variable dependencies loaded by the page itself are loaded through the init function exposed in the module object Palindrome.
• The AJAX call is unfortunately not as clean as would be expected.
  • The built-in Play Framework JSON deserializer does not accept the standard JSON formatting of the jQuery AJAX call. It requires keys to be double-quote wrapped strings; therefore the output object is manually serialized here.