Aggregation Server

This system aggregates and distributes weather data in JSON format using a RESTful API. It allows multiple clients to simultaneously GET data from the server.

Start

Start on port 4567 by default but allow a command-line argument to set the port.

RESTful API

Using HTTPServer to create a server that listens on a port.

HttpServer server = HttpServer.create(new InetSocketAddress(port), 0);

Using HTTPHandler to handle GET and PUT requests.

Synchronization

Using ReadWriteLock to synchronize access to the weather data file.

private static final ReadWriteLock rwLock = new ReentrantReadWriteLock();

Allow multiple clients to read the data at the same time.

rwLock.readLock().lock();

When we reach the code

rwLock.writeLock().lock();

allows only one client to write the data at a time.

Lamport Clock

Using AtomicInteger to implement the Lamport Clock.

Update the Lamport Clock in the JSON if it's older than the current clock.

lamportClock.updateAndGet(localClock ->
  Math.max(receivedClock, localClock) + 1
);

Put the Lamport Clock in the JSON.

weatherData.put("lamport_clock", lamportClock.get());

JSON

Using Gson to convert txt to JSON.

Gson gson = new Gson();
String json = gson.toJson(*data*);

Delete JSON

If the client does not send a request for 30 seconds, the server will delete the JSON file.

Get the current time and store it in lastCommunicationTime.

lastCommunicationTime = System.currentTimeMillis();