io.modelcontextprotocol.server

Class McpSyncServer

java.lang.Object

io.modelcontextprotocol.server.McpSyncServer

public class McpSyncServer
extends Object

A synchronous implementation of the Model Context Protocol (MCP) server that wraps McpAsyncServer to provide blocking operations. This class delegates all operations to an underlying async server instance while providing a simpler, synchronous API for scenarios where reactive programming is not required.

The MCP server enables AI models to expose tools, resources, and prompts through a standardized interface. Key features available through this synchronous API include:

• Tool registration and management for extending AI model capabilities
• Resource handling with URI-based addressing for providing context
• Prompt template management for standardized interactions
• Real-time client notifications for state changes
• Structured logging with configurable severity levels
• Support for client-side AI model sampling

While McpAsyncServer uses Project Reactor's Mono and Flux types for non-blocking operations, this class converts those into blocking calls, making it more suitable for:

• Traditional synchronous applications
• Simple scripting scenarios
• Testing and debugging
• Cases where reactive programming adds unnecessary complexity

The server supports runtime modification of its capabilities through methods like addTool(io.modelcontextprotocol.server.McpServerFeatures.SyncToolSpecification), addResource(io.modelcontextprotocol.server.McpServerFeatures.SyncResourceSpecification), and addPrompt(io.modelcontextprotocol.server.McpServerFeatures.SyncPromptSpecification), automatically notifying connected clients of changes when configured to do so.

Author:

Christian Tzolov, Dariusz Jędrzejczyk

See Also:

McpAsyncServer, McpSchema

Constructor Summary

Constructors

Constructor and Description
McpSyncServer(McpAsyncServer asyncServer) Creates a new synchronous server that wraps the provided async server.

Method Summary

Modifier and Type	Method and Description
void	addPrompt(McpServerFeatures.SyncPromptSpecification promptSpecification) Add a new prompt handler.
void	addResource(McpServerFeatures.SyncResourceSpecification resourceHandler) Add a new resource handler.
void	addResourceTemplate(McpServerFeatures.SyncResourceTemplateSpecification resourceHandler) Add a new resource template handler.
void	addTool(McpServerFeatures.SyncToolSpecification toolHandler) Add a new tool handler.
void	close() Close the server immediately.
void	closeGracefully() Close the server gracefully.
McpSchema.CreateMessageResult	createMessage(McpSchema.CreateMessageRequest createMessageRequest) Deprecated. This method will be removed in 0.9.0. Use McpSyncServerExchange.createMessage(McpSchema.CreateMessageRequest).
McpAsyncServer	getAsyncServer() Get the underlying async server instance.
McpSchema.ClientCapabilities	getClientCapabilities() Deprecated. This method will be removed in 0.9.0. Use McpSyncServerExchange.getClientCapabilities().
McpSchema.Implementation	getClientInfo() Deprecated. This method will be removed in 0.9.0. Use McpSyncServerExchange.getClientInfo().
McpSchema.ServerCapabilities	getServerCapabilities() Get the server capabilities that define the supported features and functionality.
McpSchema.Implementation	getServerInfo() Get the server implementation information.
void	loggingNotification(McpSchema.LoggingMessageNotification loggingMessageNotification) Send a logging message notification to all clients.
void	notifyPromptsListChanged() Notify clients that the list of available prompts has changed.
void	notifyResourcesListChanged() Notify clients that the list of available resources has changed.
void	notifyToolsListChanged() Notify clients that the list of available tools has changed.
void	removePrompt(String promptName) Remove a prompt handler.
void	removeResource(String resourceUri) Remove a resource handler.
void	removeResourceTemplate(String resourceUri) Remove a resource template handler.
void	removeTool(String toolName) Remove a tool handler.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

McpSyncServer

public McpSyncServer(McpAsyncServer asyncServer)

Creates a new synchronous server that wraps the provided async server.

Parameters:

asyncServer - The async server to wrap

Method Detail

addTool

public void addTool(McpServerFeatures.SyncToolSpecification toolHandler)

Add a new tool handler.

Parameters:

toolHandler - The tool handler to add

removeTool

public void removeTool(String toolName)

Remove a tool handler.

Parameters:

toolName - The name of the tool handler to remove

addResource

public void addResource(McpServerFeatures.SyncResourceSpecification resourceHandler)

Add a new resource handler.

Parameters:

resourceHandler - The resource handler to add

removeResource

public void removeResource(String resourceUri)

Remove a resource handler.

Parameters:

resourceUri - The URI of the resource handler to remove

addResourceTemplate

public void addResourceTemplate(McpServerFeatures.SyncResourceTemplateSpecification resourceHandler)

Add a new resource template handler.

Parameters:

resourceHandler - The resource handler to add

removeResourceTemplate

public void removeResourceTemplate(String resourceUri)

Remove a resource template handler.

Parameters:

resourceUri - The URI of the resource template handler to remove

addPrompt

public void addPrompt(McpServerFeatures.SyncPromptSpecification promptSpecification)

Add a new prompt handler.

Parameters:

promptSpecification - The prompt specification to add

removePrompt

public void removePrompt(String promptName)

Remove a prompt handler.

Parameters:

promptName - The name of the prompt handler to remove

notifyToolsListChanged

public void notifyToolsListChanged()

Notify clients that the list of available tools has changed.

getServerCapabilities

public McpSchema.ServerCapabilities getServerCapabilities()

Get the server capabilities that define the supported features and functionality.

Returns:

The server capabilities

getServerInfo

public McpSchema.Implementation getServerInfo()

Get the server implementation information.

Returns:

The server implementation details

getClientCapabilities

@Deprecated
public McpSchema.ClientCapabilities getClientCapabilities()

Deprecated. This method will be removed in 0.9.0. Use McpSyncServerExchange.getClientCapabilities().

Get the client capabilities that define the supported features and functionality.

Returns:

The client capabilities

getClientInfo

@Deprecated
public McpSchema.Implementation getClientInfo()

Deprecated. This method will be removed in 0.9.0. Use McpSyncServerExchange.getClientInfo().

Get the client implementation information.

Returns:

The client implementation details

notifyResourcesListChanged

public void notifyResourcesListChanged()

Notify clients that the list of available resources has changed.

notifyPromptsListChanged

public void notifyPromptsListChanged()

Notify clients that the list of available prompts has changed.

loggingNotification

public void loggingNotification(McpSchema.LoggingMessageNotification loggingMessageNotification)

Send a logging message notification to all clients.

Parameters:

loggingMessageNotification - The logging message notification to send

closeGracefully

public void closeGracefully()

Close the server gracefully.

close

public void close()

Close the server immediately.

getAsyncServer

public McpAsyncServer getAsyncServer()

Get the underlying async server instance.

Returns:

The wrapped async server

createMessage

@Deprecated
public McpSchema.CreateMessageResult createMessage(McpSchema.CreateMessageRequest createMessageRequest)

Deprecated. This method will be removed in 0.9.0. Use McpSyncServerExchange.createMessage(McpSchema.CreateMessageRequest).

Create a new message using the sampling capabilities of the client. The Model Context Protocol (MCP) provides a standardized way for servers to request LLM sampling ("completions" or "generations") from language models via clients.

This flow allows clients to maintain control over model access, selection, and permissions while enabling servers to leverage AI capabilities—with no server API keys necessary. Servers can request text or image-based interactions and optionally include context from MCP servers in their prompts.

Unlike its async counterpart, this method blocks until the message creation is complete, making it easier to use in synchronous code paths.

Parameters:

createMessageRequest - The request to create a new message

Returns:

The result of the message creation

Throws:

McpError - if the client has not been initialized or does not support sampling capabilities

McpError - if the client does not support the createMessage method

See Also:

McpSchema.CreateMessageRequest, McpSchema.CreateMessageResult, Sampling Specification