project-name/
├── pom.xml
└── src/
    ├── main/java/com/example/McpServerApp.java
    └── test/java/com/example/McpServerAppTest.java

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.example</groupId>
  <artifactId>mcp-server-demo</artifactId>
  <version>0.1.0</version>

  <properties>
    <maven.compiler.release>17</maven.compiler.release>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>io.modelcontextprotocol.sdk</groupId>
        <artifactId>mcp-bom</artifactId>
        <version>2.0.1</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
      <dependency>
        <groupId>org.junit</groupId>
        <artifactId>junit-bom</artifactId>
        <version>6.1.3</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>

  <dependencies>
    <dependency>
      <groupId>io.modelcontextprotocol.sdk</groupId>
      <artifactId>mcp</artifactId>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-simple</artifactId>
      <version>2.0.17</version>
      <scope>runtime</scope>
    </dependency>
    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter</artifactId>
      <scope>test</scope>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-shade-plugin</artifactId>
        <version>3.6.2</version>
        <executions>
          <execution>
            <phase>package</phase>
            <goals>
              <goal>shade</goal>
            </goals>
            <configuration>
              <createDependencyReducedPom>false</createDependencyReducedPom>
              <transformers>
                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                  <mainClass>com.example.McpServerApp</mainClass>
                </transformer>
              </transformers>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

package com.example;

import java.util.List;
import java.util.Map;

import io.modelcontextprotocol.json.McpJsonDefaults;
import io.modelcontextprotocol.server.McpServer;
import io.modelcontextprotocol.server.McpServerFeatures.SyncToolSpecification;
import io.modelcontextprotocol.server.transport.StdioServerTransportProvider;
import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
import io.modelcontextprotocol.spec.McpSchema.ServerCapabilities;
import io.modelcontextprotocol.spec.McpSchema.Tool;

public final class McpServerApp {

    static SyncToolSpecification divideTool() {
        Tool tool = Tool.builder("divide", Map.of(
                        "type", "object",
                        "properties", Map.of(
                                "a", Map.of("type", "number", "description", "Dividend"),
                                "b", Map.of("type", "number", "description", "Divisor")),
                        "required", List.of("a", "b")))
                .description("Divide a by b.")
                .build();

        return SyncToolSpecification.builder()
                .tool(tool)
                .callHandler((exchange, request) -> {
                    double a = ((Number) request.arguments().get("a")).doubleValue();
                    double b = ((Number) request.arguments().get("b")).doubleValue();
                    if (b == 0) {
                        return CallToolResult.builder().addTextContent("b must not be zero.").isError(true).build();
                    }
                    return CallToolResult.builder().addTextContent(String.valueOf(a / b)).build();
                })
                .build();
    }

    public static void main(String[] args) {
        McpServer.sync(new StdioServerTransportProvider(McpJsonDefaults.getMapper()))
                .serverInfo("demo", "0.1.0")
                .capabilities(ServerCapabilities.builder().tools(false).build())
                .tools(divideTool())
                .build();
    }
}

package com.example;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.nio.file.Path;
import java.util.Map;

import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;

import io.modelcontextprotocol.client.McpClient;
import io.modelcontextprotocol.client.McpSyncClient;
import io.modelcontextprotocol.client.transport.ServerParameters;
import io.modelcontextprotocol.client.transport.StdioClientTransport;
import io.modelcontextprotocol.json.McpJsonDefaults;
import io.modelcontextprotocol.spec.McpSchema.CallToolRequest;
import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
import io.modelcontextprotocol.spec.McpSchema.TextContent;

class McpServerAppTest {

    private static McpSyncClient client;

    @BeforeAll
    static void startServer() {
        String java = Path.of(System.getProperty("java.home"), "bin", "java").toString();
        ServerParameters server = ServerParameters.builder(java)
                .args("-cp", System.getProperty("java.class.path"), McpServerApp.class.getName())
                .build();
        client = McpClient.sync(new StdioClientTransport(server, McpJsonDefaults.getMapper())).build();
        client.initialize();
    }

    @AfterAll
    static void stopServer() {
        client.close();
    }

    @Test
    void divide() {
        CallToolResult result = client.callTool(
                CallToolRequest.builder("divide").arguments(Map.of("a", 6, "b", 3)).build());
        assertEquals("2.0", ((TextContent) result.content().get(0)).text());
    }

    @Test
    void divideByZero() {
        CallToolResult result = client.callTool(
                CallToolRequest.builder("divide").arguments(Map.of("a", 1, "b", 0)).build());
        assertTrue(result.isError());
        assertTrue(((TextContent) result.content().get(0)).text().contains("must not be zero"));
    }
}

{
  "servers": {
    "demo": {
      "type": "stdio",
      "command": "java",
      "args": ["-jar", "/absolute/path/to/project/target/mcp-server-demo-0.1.0.jar"]
    }
  }
}