00-base.mdx

slug	/guides/rsocket-java/tutorial/base
title	Getting started
sidebar_label	Getting started

Application structure

In this step we will set up a minimal code required for both the server and the client.

The application will be composed of:

• Server side
• Client side
• Shared code

See resulting code on GitHub

Server side

We will set up a simple server to accept connections and respond to the client sending the user's name. The server will listen on TCP port 6565.

Below is the code for the ServerApplication class:

package io.rsocket.guide;

import io.rsocket.Payload;
import io.rsocket.RSocket;
import io.rsocket.SocketAcceptor;
import io.rsocket.core.RSocketServer;
import io.rsocket.transport.netty.server.TcpServerTransport;
import io.rsocket.util.DefaultPayload;
import reactor.core.publisher.Mono;

public class ServerApplication {

    public static void main(String[] args) {
        final var transport = TcpServerTransport.create(6565);

        final SocketAcceptor socketAcceptor = (setup, sendingSocket) -> Mono.just(new RSocket() {
            public Mono<Payload> requestResponse(Payload payload) {
                return Mono.just(DefaultPayload.create("Welcome to chat, " + payload.getDataUtf8()));
            }
        });

        RSocketServer.create()
                .acceptor(socketAcceptor)
                .bind(transport)
                .block()
                .onClose()
                .block();
    }
}

Lines 22-27 start an RSocket TCP server listening on localhost:6565.

The 2 parameters passed are:

• transport : An instance of a supported connection method. In this case it is at instance of TcpServerTransport created in Line 14.
• socketAcceptor: A callable which returns an RSocket instance wrapped in a Mono. This will be used to respond to the client's requests.

Lines 16-20 Define the RSocket service with a single requestResponse endpoint at *Lines 17-19.

The requestResponse method receives a single argument containing the payload. It is an instance of a Payload class which contains the data and metadata of the request. The data property is assumed to contain a UTF-8 encoded string of the username, so is retrieved using getDataUtf8.

Line 18 Takes the username from the Payload instance's data and returns it to the client with a "welcome" message.

A response is created using helper methods:

• DefaultPayload::create : This creates a payload which is the standard object which wraps all data transferred over RSocket. In our case, only the data property is set.
• Mono::just : All RSocket responses must be in the form of streams, either a Flux or a Mono.

In the example, only the requestResponse method of RSocket is overridden. In this class, we can override the methods which handle the 4 RSocket request types:

• requestResponse
• requestStream
• requestChannel
• fireAndForget

Check the RSocket for other methods which can be implemented.

Next we will look at a simple client which connects to this server.

Client side

The client will connect to the server, send a single response request and disconnect.

Below is the code for the ClientApplication class:

package io.rsocket.guide;

import io.rsocket.core.RSocketConnector;
import io.rsocket.transport.netty.client.TcpClientTransport;
import io.rsocket.util.DefaultPayload;

import java.time.Duration;

public class ClientApplication {

    public static void main(String[] args) {
        final var transport = TcpClientTransport.create("localhost", 6565);

        final var rSocket = RSocketConnector.create()
                .connect(transport)
                .block();

        final var payload = DefaultPayload.create("George");

        rSocket.requestResponse(payload)
                .doOnNext(response -> System.out.println(response.getDataUtf8()))
                .block(Duration.ofMinutes(1));
    }
}

Line 12 instantiates a TCP connection to localhost on port 6565, similar to the one in ServerApplication.

Lines 14-16 instantiates an RSocket client.

Line 18 Wraps the username "George" which the client will send to the server in a Payload using the DefaultPayload.create factory method

Finally, Line 20 sends the request to the server and prints (Line 21) the received response.

Since RSocket is reactive, and we want to wait for the request to finish before quitting, a call to block(Duration.ofMinutes(1)) is added to block for 1 minute.