Langchain4j Mcp Server Patterns

package com.example.mcp;

import dev.langchain4j.mcp.*;
import dev.langchain4j.mcp.transport.*;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

import java.util.List;

// Helper imports
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.Map;

/**
 * Template for creating MCP servers with LangChain4j.
 *
 * This template provides a starting point for building MCP servers with:
 * - Tool providers
 * - Resource providers
 * - Prompt providers
 * - Spring Boot integration
 * - Configuration management
 */
@SpringBootApplication
public class MCPServerTemplate {

    public static void main(String[] args) {
        SpringApplication.run(MCPServerTemplate.class, args);
    }

    /**
     * Configure and build the main MCP server instance.
     */
    @Bean
    public MCPServer mcpServer(
            List<ToolProvider> toolProviders,
            List<ResourceListProvider> resourceProviders,
            List<PromptListProvider> promptProviders) {

        return MCPServer.builder()
            .server(new StdioServer.Builder())
            .addToolProvider(toolProviders)
            .addResourceProvider(resourceProviders)
            .addPromptProvider(promptProviders)
            .enableLogging(true)
            .build();
    }

    /**
     * Configure MCP clients for connecting to external MCP servers.
     */
    @Bean
    public McpClient mcpClient() {
        StdioMcpTransport transport = new StdioMcpTransport.Builder()
            .command(List.of("npm", "exec", "@modelcontextprotocol/server-everything@0.6.2"))
            .logEvents(true)
            .build();

        return new DefaultMcpClient.Builder()
            .key("template-client")
            .transport(transport)
            .cacheToolList(true)
            .build();
    }

    /**
     * Configure MCP tool provider for AI services integration.
     */
    @Bean
    public McpToolProvider mcpToolProvider(McpClient mcpClient) {
        return McpToolProvider.builder()
            .mcpClients(mcpClient)
            .failIfOneServerFails(false)
            .build();
    }
}

/**
 * Example tool provider implementing a simple calculator.
 */
class CalculatorToolProvider implements ToolProvider {

    @Override
    public List<ToolSpecification> listTools() {
        return List.of(
            ToolSpecification.builder()
                .name("add")
                .description("Add two numbers")
                .inputSchema(Map.of(
                    "type", "object",
                    "properties", Map.of(
                        "a", Map.of("type", "number", "description", "First number"),
                        "b", Map.of("type", "number", "description", "Second number")
                    ),
                    "required", List.of("a", "b")
                ))
                .build(),
            ToolSpecification.builder()
                .name("multiply")
                .description("Multiply two numbers")
                .inputSchema(Map.of(
                    "type", "object",
                    "properties", Map.of(
                        "a", Map.of("type", "number", "description", "First number"),
                        "b", Map.of("type", "number", "description", "Second number")
                    ),
                    "required", List.of("a", "b")
                ))
                .build()
        );
    }

    @Override
    public String executeTool(String name, String arguments) {
        try {
            // Parse JSON arguments
            ObjectMapper mapper = new ObjectMapper();
            JsonNode argsNode = mapper.readTree(arguments);
            double a = argsNode.get("a").asDouble();
            double b = argsNode.get("b").asDouble();

            switch (name) {
                case "add":
                    return String.valueOf(a + b);