Module io.modelcontextprotocol.sdk.mcp
Package io.modelcontextprotocol.client.transport

Class HttpClientSseClientTransport

java.lang.Object
io.modelcontextprotocol.client.transport.HttpClientSseClientTransport
All Implemented Interfaces:
ClientMcpTransport, McpClientTransport, McpTransport
public class HttpClientSseClientTransport extends Object implements McpClientTransport
Server-Sent Events (SSE) implementation of the McpTransport that follows the MCP HTTP with SSE transport specification, using Java's HttpClient.

This transport implementation establishes a bidirectional communication channel between client and server using SSE for server-to-client messages and HTTP POST requests for client-to-server messages. The transport:

  • Establishes an SSE connection to receive server messages
  • Handles endpoint discovery through SSE events
  • Manages message serialization/deserialization using Jackson
  • Provides graceful connection termination

The transport supports two types of SSE events:

  • 'endpoint' - Contains the URL for sending client messages
  • 'message' - Contains JSON-RPC message payload
Author:
Christian Tzolov
See Also:

  • Field Details

    • objectMapper

      protected com.fasterxml.jackson.databind.ObjectMapper objectMapper
      JSON object mapper for message serialization/deserialization

  • Constructor Details

    • HttpClientSseClientTransport

      public HttpClientSseClientTransport(String baseUri)
      Creates a new transport instance with default HTTP client and object mapper.
      Parameters:
      baseUri - the base URI of the MCP server

    • HttpClientSseClientTransport

      public HttpClientSseClientTransport(HttpClient.Builder clientBuilder, String baseUri, com.fasterxml.jackson.databind.ObjectMapper objectMapper)
      Creates a new transport instance with custom HTTP client builder and object mapper.
      Parameters:
      clientBuilder - the HTTP client builder to use
      baseUri - the base URI of the MCP server
      objectMapper - the object mapper for JSON serialization/deserialization
      Throws:
      IllegalArgumentException - if objectMapper or clientBuilder is null

  • Method Details

    • connect

      public reactor.core.publisher.Mono<Void> connect(Function<reactor.core.publisher.Mono<McpSchema.JSONRPCMessage>,reactor.core.publisher.Mono<McpSchema.JSONRPCMessage>> handler)
      Establishes the SSE connection with the server and sets up message handling.

      This method:

      • Initiates the SSE connection
      • Handles endpoint discovery events
      • Processes incoming JSON-RPC messages
      Specified by:
      connect in interface McpClientTransport
      Specified by:
      connect in interface McpTransport
      Parameters:
      handler - the function to process received JSON-RPC messages
      Returns:
      a Mono that completes when the connection is established

    • sendMessage

      public reactor.core.publisher.Mono<Void> sendMessage(McpSchema.JSONRPCMessage message)
      Sends a JSON-RPC message to the server.

      This method waits for the message endpoint to be discovered before sending the message. The message is serialized to JSON and sent as an HTTP POST request.

      Specified by:
      sendMessage in interface McpTransport
      Parameters:
      message - the JSON-RPC message to send
      Returns:
      a Mono that completes when the message is sent
      Throws:
      McpError - if the message endpoint is not available or the wait times out

    • closeGracefully

      public reactor.core.publisher.Mono<Void> closeGracefully()
      Gracefully closes the transport connection.

      Sets the closing flag and cancels any pending connection future. This prevents new messages from being sent and allows ongoing operations to complete.

      Specified by:
      closeGracefully in interface McpTransport
      Returns:
      a Mono that completes when the closing process is initiated

    • unmarshalFrom

      public <T> T unmarshalFrom(Object data, com.fasterxml.jackson.core.type.TypeReference<T> typeRef)
      Unmarshals data to the specified type using the configured object mapper.
      Specified by:
      unmarshalFrom in interface McpTransport
      Type Parameters:
      T - the target type
      Parameters:
      data - the data to unmarshal
      typeRef - the type reference for the target type
      Returns:
      the unmarshalled object