Non socket based Java Server [closed]

You need sockets. They serve as the end-points to the connection. Although, you can use alternatives to the blocking Socket and ServerSocket implementations.

NIO (New IO) uses channels. It allows for non-blocking I/O:

class Server {
     public static void main(String[] args) throws Exception {
          ServerSocketChannel ssc = ServerSocketChannel.open();
          ssc.configureBlocking(false);

          while(true) {
               SocketChannel sc = ssc.accept();

               if(sc != null) {
                    //handle channel
               }
          }
     }
}

Using a Selector (optional, but recommended)

You could use a Selector to switch between reading/writing/accepting to allow blocking only when theres nothing to do (to remove excess CPU usage)

class Server {
     private static Selector selector;
     public static void main(String[] args) throws Exception {
          ServerSocketChannel ssc = ServerSocketChannel.open();
          ssc.configureBlocking(false);
          Selector selector = Selector.open();
          ssc.register(selector, SelectionKey.OP_ACCEPT);

          while(true) {
               selector.select();

               while(selector.iterator().hasNext()) {
                    SelectionKey key = selector.iterator().next();

                    if(key.isAcceptable()) {
                         accept(key);
                    }
               }
          }
     }

     private static void accept(SelectionKey key) throws Exception {
          ServerSocketChannel channel = (ServerSocketChannel) key.channel();
          SocketChannel sc = channel.accept();
          sc.register(selector, OP_READ);
     }
}

SelectionKey supports accepting via isAcceptable(), reading via isReadable() and writing via isWritable(), so you can handle all 3 on the same thread.

This is a basic example of accepting a connection using NIO. I highly suggest looking into it a bit more to get a better understanding of how things work.