RSocket Support

The RSocket Spring Integration module (spring-integration-rsocket) allows for executions of RSocket application protocol.

You need to include this dependency into your project:

compile "org.springframework.integration:spring-integration-rsocket:6.0.0-SNAPSHOT"

This module is available starting with version 5.2 and is based on the Spring Messaging foundation with its RSocket component implementations, such as RSocketRequester, RSocketMessageHandler and RSocketStrategies. See Spring Framework RSocket Support for more information about the RSocket protocol, terminology and components.

Before starting an integration flow processing via channel adapters, we need to establish an RSocket connection between server and client. For this purpose, Spring Integration RSocket support provides the ServerRSocketConnector and ClientRSocketConnector implementations of the AbstractRSocketConnector.

The ServerRSocketConnector exposes a listener on the host and port according to provided io.rsocket.transport.ServerTransport for accepting connections from clients. An internal RSocketServer instance can be customized with the setServerConfigurer(), as well as other options that can be configured, e.g. RSocketStrategies and MimeType for payload data and headers metadata. When a setupRoute is provided from the client requester (see ClientRSocketConnector below), a connected client is stored as a RSocketRequester under the key determined by the clientRSocketKeyStrategy BiFunction<Map<String, Object>, DataBuffer, Object>. By default, a connection data is used for the key as a converted value to string with UTF-8 charset. Such an RSocketRequester registry can be used in the application logic to determine a particular client connection for interaction with it, or for publishing the same message to all connected clients. When a connection is established from the client, an RSocketConnectedEvent is emitted from the ServerRSocketConnector. This is similar to what is provided by the @ConnectMapping annotation in Spring Messaging module. The mapping pattern * means accept all the client routes. The RSocketConnectedEvent can be used to distinguish different routes via DestinationPatternsMessageCondition.LOOKUP_DESTINATION_HEADER header.

A typical server configuration might look like this:

public RSocketStrategies rsocketStrategies() {
    return RSocketStrategies.builder()
        .dataBufferFactory(new DefaultDataBufferFactory(true))

public ServerRSocketConnector serverRSocketConnector() {
    ServerRSocketConnector serverRSocketConnector = new ServerRSocketConnector("localhost", 0);
    serverRSocketConnector.setMetadataMimeType(new MimeType("message", "x.rsocket.routing.v0"));
    serverRSocketConnector.setServerConfigurer((server) -> server.payloadDecoder(PayloadDecoder.ZERO_COPY));
    serverRSocketConnector.setClientRSocketKeyStrategy((headers, data) -> ""
                                    + headers.get(DestinationPatternsMessageCondition.LOOKUP_DESTINATION_HEADER));
    return serverRSocketConnector;

public void onApplicationEvent(RSocketConnectedEvent event) {

All the options, including RSocketStrategies bean and @EventListener for RSocketConnectedEvent, are optional. See ServerRSocketConnector JavaDocs for more information.

Starting with version 5.2.1, the ServerRSocketMessageHandler is extracted to a public, top-level class for possible connection with an existing RSocket server. When a ServerRSocketConnector is supplied with an external instance of ServerRSocketMessageHandler, it doesn’t create an RSocket server internally and just delegates all the handling logic to the provided instance. In addition, the ServerRSocketMessageHandler can be configured with a messageMappingCompatible flag to handle also @MessageMapping for an RSocket controller, fully replacing the functionality provided by the standard RSocketMessageHandler. This can be useful in mixed configurations, when classic @MessageMapping methods are present in the same application along with RSocket channel adapters and an externally configured RSocket server is present in the application.

The ClientRSocketConnector serves as a holder for RSocketRequester based on the RSocket connected via the provided ClientTransport. The RSocketConnector can be customized with the provided RSocketConnectorConfigurer. The setupRoute (with optional templates variables) and setupData with metadata can be also configured on this component.

A typical client configuration might look like this:

public RSocketStrategies rsocketStrategies() {
    return RSocketStrategies.builder()
        .dataBufferFactory(new DefaultDataBufferFactory(true))

public ClientRSocketConnector clientRSocketConnector() {
    ClientRSocketConnector clientRSocketConnector =
            new ClientRSocketConnector("localhost", serverRSocketConnector().getBoundPort().block());
    return clientRSocketConnector;

Most of these options (including RSocketStrategies bean) are optional. Note how we connect to the locally started RSocket server on the arbitrary port. See ServerRSocketConnector.clientRSocketKeyStrategy for setupData use cases. Also see ClientRSocketConnector and its AbstractRSocketConnector superclass JavaDocs for more information.

Both ClientRSocketConnector and ServerRSocketConnector are responsible for mapping inbound channel adapters to their path configuration for routing incoming RSocket requests. See the next section for more information.

RSocket Inbound Gateway

The RSocketInboundGateway is responsible for receiving RSocket requests and producing responses (if any). It requires an array of path mapping which could be as patterns similar to MVC request mapping or @MessageMapping semantics. In addition, (since version 5.2.2), a set of interaction models (see RSocketInteractionModel) can be configured on the RSocketInboundGateway to restrict RSocket requests to this endpoint by the particular frame type. By default, all the interaction models are supported. Such a bean, according its IntegrationRSocketEndpoint implementation (extension of a ReactiveMessageHandler), is auto detected either by the ServerRSocketConnector or ClientRSocketConnector for a routing logic in the internal IntegrationRSocketMessageHandler for incoming requests. An AbstractRSocketConnector can be provided to the RSocketInboundGateway for explicit endpoint registration. This way, the auto-detection option is disabled on that AbstractRSocketConnector. The RSocketStrategies can also be injected into the RSocketInboundGateway or they are obtained from the provided AbstractRSocketConnector overriding any explicit injection. Decoders are used from those RSocketStrategies to decode a request payload according to the provided requestElementType. If an RSocketPayloadReturnValueHandler.RESPONSE_HEADER header is not provided in incoming the Message, the RSocketInboundGateway treats a request as a fireAndForget RSocket interaction model. In this case, an RSocketInboundGateway performs a plain send operation into the outputChannel. Otherwise, a MonoProcessor value from the RSocketPayloadReturnValueHandler.RESPONSE_HEADER header is used for sending a reply to the RSocket. For this purpose, an RSocketInboundGateway performs a sendAndReceiveMessageReactive operation on the outputChannel. The payload of the message to send downstream is always a Flux according to MessagingRSocket logic. When in a fireAndForget RSocket interaction model, the message has a plain converted payload. The reply payload could be a plain object or a Publisher - the RSocketInboundGateway converts both of them properly into an RSocket response according to the encoders provided in the RSocketStrategies.

Starting with version 5.3, a decodeFluxAsUnit option (default false) is added to the RSocketInboundGateway. By default, incoming Flux is transformed the way that each its event is decoded separately. This is an exact behavior present currently with @MessageMapping semantics. To restore a previous behavior or decode the whole Flux as single unit according application requirements, the decodeFluxAsUnit has to be set to true. However the target decoding logic depends on the Decoder selected, e.g. a StringDecoder requires a new line separator (by default) to be present in the stream to indicate a byte buffer end.

See Configuring RSocket Endpoints with Java for samples how to configure an RSocketInboundGateway endpoint and deal with payloads downstream.

RSocket Outbound Gateway

The RSocketOutboundGateway is an AbstractReplyProducingMessageHandler to perform requests into RSocket and produce replies based on the RSocket replies (if any). A low level RSocket protocol interaction is delegated into an RSocketRequester resolved from the provided ClientRSocketConnector or from the RSocketRequesterMethodArgumentResolver.RSOCKET_REQUESTER_HEADER header in the request message on the server side. A target RSocketRequester on the server side can be resolved from an RSocketConnectedEvent or using ServerRSocketConnector.getClientRSocketRequester() API according some business key selected for connect request mappings via ServerRSocketConnector.setClientRSocketKeyStrategy(). See ServerRSocketConnector JavaDocs for more information.

The route to send request has to be configured explicitly (together with path variables) or via a SpEL expression which is evaluated against request message.

The RSocket interaction model can be provided via RSocketInteractionModel option or respective expression setting. By default, a requestResponse is used for common gateway use-cases.

When request message payload is a Publisher, a publisherElementType option can be provided to encode its elements according an RSocketStrategies supplied in the target RSocketRequester. An expression for this option can evaluate to a ParameterizedTypeReference. See the JavaDocs for more information about data and its type.

An RSocket request can also be enhanced with a metadata. For this purpose a metadataExpression against request message can be configured on the RSocketOutboundGateway. Such an expression must evaluate to a Map<Object, MimeType>.

When interactionModel is not fireAndForget, an expectedResponseType must be supplied. It is a String.class by default. An expression for this option can evaluate to a ParameterizedTypeReference. See the RSocketRequester.RetrieveSpec.retrieveMono() and RSocketRequester.RetrieveSpec.retrieveFlux() JavaDocs for more information about reply data and its type.

A reply payload from the RSocketOutboundGateway is a Mono (even for a fireAndForget interaction model it is Mono<Void>) always making this component as async. Such a Mono is subscribed before producing into the outputChannel for regular channels or processed on demand by the FluxMessageChannel. A Flux response for the requestStream or requestChannel interaction model is also wrapped into a reply Mono. It can be flattened downstream by the FluxMessageChannel with a passthrough service activator:

@ServiceActivator(inputChannel = "rsocketReplyChannel", outputChannel ="fluxMessageChannel")
public Flux<?> flattenRSocketResponse(Flux<?> payload) {
    return payload;

Or subscribed explicitly in the target application logic.

The expected response type can also be configured (or evaluated via expression) to void treating this gateway as an outbound channel adapter. However, the outputChannel still has to be configured (even if it just a NullChannel) to initiate a subscription to the returned Mono.

See Configuring RSocket Endpoints with Java for samples how to configure an RSocketOutboundGateway endpoint a deal with payloads downstream.

RSocket Namespace Support

Spring Integration provides an rsocket namespace and the corresponding schema definition. To include it in your configuration, add the following namespace declaration in your application context configuration file:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns=""


To configure Spring Integration RSocket inbound channel adapters with XML, you need to use an appropriate inbound-gateway components from the int-rsocket namespace. The following example shows how to configure it:

<int-rsocket:inbound-gateway id="inboundGateway"

A ClientRSocketConnector and ServerRSocketConnector should be configured as generic <bean> definitions.


<int-rsocket:outbound-gateway id="outboundGateway"
                              metadata-expression="{'metadata': new org.springframework.util.MimeType('*')}"/>

See spring-integration-rsocket.xsd for description for all those XML attributes.

Configuring RSocket Endpoints with Java

The following example shows how to configure an RSocket inbound endpoint with Java:

public RSocketInboundGateway rsocketInboundGatewayRequestReply() {
    RSocketInboundGateway rsocketInboundGateway = new RSocketInboundGateway("echo");
    return rsocketInboundGateway;

@Transformer(inputChannel = "requestReplyChannel")
public Mono<String> echoTransformation(Flux<String> payload) {

A ClientRSocketConnector or ServerRSocketConnector is assumed in this configuration with meaning for auto-detection of such an endpoint on the “echo” path. Pay attention to the @Transformer signature with its fully reactive processing of the RSocket requests and producing reactive replies.

The following example shows how to configure a RSocket inbound gateway with the Java DSL:

public IntegrationFlow rsocketUpperCaseFlow() {
    return IntegrationFlow
        .<Flux<String>, Mono<String>>transform((flux) ->

A ClientRSocketConnector or ServerRSocketConnector is assumed in this configuration with meaning for auto-detection of such an endpoint on the “/uppercase” path and expected interaction model as “request channel”.

The following example shows how to configure a RSocket outbound gateway with Java:

@ServiceActivator(inputChannel = "requestChannel", outputChannel = "replyChannel")
public RSocketOutboundGateway rsocketOutboundGateway() {
    RSocketOutboundGateway rsocketOutboundGateway =
            new RSocketOutboundGateway(
                    new FunctionExpression<Message<?>>((m) ->
            new FunctionExpression<Message<?>>((m) -> m.getHeaders().get("rsocket_interaction_model")));
    return rsocketOutboundGateway;

The setClientRSocketConnector() is required only for the client side. On the server side, the RSocketRequesterMethodArgumentResolver.RSOCKET_REQUESTER_HEADER header with an RSocketRequester value must be supplied in the request message.

The following example shows how to configure a RSocket outbound gateway with the Java DSL:

public IntegrationFlow rsocketUpperCaseRequestFlow(ClientRSocketConnector clientRSocketConnector) {
    return IntegrationFlow

See IntegrationFlow as a Gateway for more information how to use a mentioned Function interface in the beginning of the flow above.