Yash DWP solution for dissertation.

Setup and Build

Java 11

You will need to have the Java 8 JDK (or higher) installed. Check by typing the following into the command line:

$ java -version
java version "11.0.10" 2021-01-19 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.10+8-LTS-162)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.10+8-LTS-162, mixed mode)

$ javac -version
javac 11.0.10
Maven 3.6.3.

If these are not found or show a version lower than 1.8 then download and install the latest Java 8 JDK from Oracle.

Once installed, the directory containing java should have been added to your PATH environment variable, so that the above java and javac commands will work from the command line.

Building and starting the server from the command line

cd path/to/this/dir
mvnw package            (./mvnw - if using bash)
mvnw spring-boot:run    (Use Control-C or task-manager to stop)

Browse to http://localhost:8080/swagger-ui/ expand the controller and "Try it out".

Running in an IDE

This project uses Lombok to insert getters, setters and other boiler plate code during runtime. As a consequence the raw code will show compilation errors in an IDE such as Eclipse, IntelliJ or Netbeans.

To avoid this use the Lombok plugin. Go to https://projectlombok.org/ and select the installation instructions for your IDE from the "Install" menu.

Notes on Implementation

Assumptions

When finding users who are listed as living in London, I have assumed:

• That all users returned by https://bpdts-test-app.herokuapp.com/city/London/users are required, even if their coordinates appear to associate them with other places called London outside the UK.

When finding users who are currently within 50 miles of London, I have assumed:

• The latitude and longitude fields found in the data returned by the onward ReST service indicate the user's current position.
• That "London" in this case is the capital of Great Britain.
• That users should be within 50 miles of the centre of London (51.507222, -0.1275) as given by Wikipedia.
• That this is 50 miles as the crow flies calculated using the Haversine formula.
• That users that fall into both categories should appear only once in the response.

If the coordinates are not the user's position, then perhaps the ip_address could be used to determine an approximate location. This assumes the ip_address is associated with a current connection to a system by the user, and that a product such as Maxmind's GeoIP2 meets requirements.

Spring-Webflux

I have chosen to use Spring-Webflux and Spring-Boot to solve this test. In a high volume service, Webflux should stream the results from the onward ReST source without blocking and using less threads and memory.

A more traditional Spring-MVC application would have required broadly similar code, with occurrences of Flux<User> being replaced by List<User>. However, a single server thread would be entirely consumed from the moment the request was received until the entire response was returned.

JSON Streaming [disabled]

Spring-Webflux supports JSON streaming but the Swagger-UI does not. As the application/stream+json was appearing as the default MediaType in the UI and as the default resulted in the Swagger-UI displaying an error, I have disabled JSON streaming.

Streaming can be re-enabled by adding MediaType.APPLICATION_STREAM_JSON_VALUE to the "produces" parameter on the services annotation:

@GetMapping(path = "/londonusers", produces = {
            APPLICATION_JSON_VALUE,
            APPLICATION_STREAM_JSON_VALUE })
ResponseEntity<Flux<User>> londonUsers() {
    ...