The Ultimate Guide to Java Method Server for Beginners

We’ll build a Java Method Server from scratch with real code, minimal theory, and plain English explanations. Perfect for beginners who want to see it working instead of reading endless jargon.

What is a Java Method Server

A Java Method Server is a Java program that executes methods on demand just like a REST API, but more flexible.

Instead of sending /api/add?a=5&b=3, you send:

{
  "methodName": "math.add",
  "params": { "a": 5, "b": 3 }
}

The server finds your Java method, runs it, and returns the result:

{
  "result": 8,
  "error": null
}

So basically:
Clients send a method name.
The server calls that method.
The response goes back fast.

This idea powers systems like Documentum, SOAP, and even RMI, but you’ll learn a simpler, modern way.

How a Java Method Server Works

Let’s keep it visual and code-oriented.

Step	Description	Code / Concept
1	Receive method request	JSON via /invoke
2	Find the right Java class	Use annotations or registry
3	Run the method	method.invoke()
4	Return the result	Send JSON back to client
5	Handle errors	Return "error" in response

Create a Spring Boot Project

You can use Spring Initializr
Choose:

• Project: Maven
• Dependencies: Spring Web, Lombok

Then open it in your IDE (like IntelliJ or VS Code).

Define a Request and Response Model

We’ll use simple Java classes for input/output.

// InvokeRequest.java
public class InvokeRequest {
    private String methodName;
    private Map<String, Object> params;

    // getters and setters
}

// InvokeResponse.java
public class InvokeResponse {
    private Object result;
    private String error;

    public InvokeResponse(Object result, String error) {
        this.result = result;
        this.error = error;
    }

    // getters
}

Create an Interface for Method Handlers

Each “method” will implement a common interface.

public interface MethodHandler {
    Object invoke(Map<String, Object> params) throws Exception;
}

We’ll annotate our method classes to register them automatically.

Add Custom Annotation

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface MethodService {
    String name();
}

Now we can tag each class with a readable method name.

Create a Simple Service

Let’s make a math service:

@MethodService(name = "math.add")
@Component
public class AddService implements MethodHandler {

    @Override
    public Object invoke(Map<String, Object> params) {
        int a = (Integer) params.get("a");
        int b = (Integer) params.get("b");
        return a + b;
    }
}

Easy! You can add more like math.subtract, user.getInfo, etc.

Build the Method Router

This is the heart of your Java Method Server it finds and calls the correct service.

@Service
public class MethodRouter {

    private final Map<String, MethodHandler> registry = new HashMap<>();

    @Autowired
    public MethodRouter(List<MethodHandler> handlers) {
        for (MethodHandler h : handlers) {
            MethodService ann = h.getClass().getAnnotation(MethodService.class);
            if (ann != null) {
                registry.put(ann.name(), h);
            }
        }
    }

    public Object dispatch(String name, Map<String, Object> params) throws Exception {
        MethodHandler handler = registry.get(name);
        if (handler == null) throw new IllegalArgumentException("No method: " + name);
        return handler.invoke(params);
    }
}

Now the router knows about all available methods.

Create the Controller (API Endpoint)

This will expose one POST endpoint /invoke to the outside world.

@RestController
public class ApiController {

    @Autowired
    private MethodRouter router;

    @PostMapping("/invoke")
    public ResponseEntity<InvokeResponse> invoke(@RequestBody InvokeRequest req) {
        try {
            Object result = router.dispatch(req.getMethodName(), req.getParams());
            return ResponseEntity.ok(new InvokeResponse(result, null));
        } 
        catch (Exception e) {
            return ResponseEntity
                    .status(HttpStatus.INTERNAL_SERVER_ERROR)
                    .body(new InvokeResponse(null, e.getMessage()));
        }
    }
}

Run the app → mvn spring-boot:run

Test It in Postman

Use:

POST http://localhost:8080/invoke
Content-Type: application/json

Body:

{
  "methodName": "math.add",
  "params": { "a": 10, "b": 20 }
}

Response:

{
  "result": 30,
  "error": null
}

You just built your first Java Method Server

Add More Methods

Example: Multiply numbers

@MethodService(name = "math.multiply")
@Component
public class MultiplyService implements MethodHandler {
    public Object invoke(Map<String, Object> params) {
        int a = (Integer) params.get("a");
        int b = (Integer) params.get("b");
        return a * b;
    }
}

Restart the server, call "math.multiply", and you’re good to go!

Add Error Handling and Validation

Add a validator before dispatching:

if (req.getMethodName() == null || req.getMethodName().isEmpty()) {
    throw new IllegalArgumentException("Missing method name!");
}

You can also catch specific exceptions in the router.

Add Thread Pool and Performance Boost

You don’t want your server to freeze on heavy tasks. Add async support:

@EnableAsync
@Configuration
public class AsyncConfig {
    @Bean
    public Executor taskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(5);
        executor.setMaxPoolSize(10);
        executor.initialize();
        return executor;
    }
}

In handlers:

@Async
public Object invoke(Map<String, Object> params) {
    // long-running task

Add Logging and Monitoring

Use SLF4J or Micrometer:

private static final Logger log = LoggerFactory.getLogger(MethodRouter.class);

log.info("Invoking method: {}", name);
long start = System.currentTimeMillis();
Object result = handler.invoke(params);
log.info("Completed in {}ms", System.currentTimeMillis() - start);

You can later plug this into Prometheus or Grafana dashboards.

Add Security (JWT Example)

You can easily protect /invoke:

@Bean
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
    http.csrf().disable()
        .authorizeHttpRequests()
        .anyRequest().authenticated()
        .and()
        .oauth2ResourceServer().jwt();
    return http.build();
}

Add Dynamic Method Loading

You can go further and load classes dynamically:

Class<?> clazz = Class.forName(className);
Method method = clazz.getMethod(methodName, paramTypes);
Object instance = clazz.getDeclaredConstructor().newInstance();
Object result = method.invoke(instance, args);

Final Thought

Building a Java Method Server may sound complex at first, but once you dive into the code, you realize it’s just about connecting requests to methods in a clean, scalable way. With just a few lines of Java and a simple structure, you can handle multiple operations, reuse logic, and make your backend smarter. The best part? It grows with your needs from a single test project to a full-blown enterprise service. So, keep experimenting, refactor often, and remember: every great server starts with a single method call.