How Does RPC Work? A Step‑by‑Step Java Implementation with Netty and Zookeeper

Introduction

This article explains the principles of Remote Procedure Call (RPC) and walks through a simple Java implementation using Spring, Netty, and Zookeeper.

What a basic RPC call involves

Modern RPC frameworks such as Dubbo rely on interface‑based remote method invocation. The client needs only the interface definition; at runtime a dynamic proxy (e.g., JDK Proxy) creates a proxy object that forwards calls to the server. The call traverses network communication, requiring serialization, deserialization, and codec handling. Service registration and discovery are typically managed by a registry (e.g., Zookeeper), which stores service metadata and enables clients to locate providers.

Basic implementation

Server (provider)

Define a service interface

public interface HelloService { String sayHello(String somebody); }

Implement the interface

public class HelloServiceImpl implements HelloService { public String sayHello(String somebody) { return "hello " + somebody + "!"; } }

Register the service in Spring configuration and publish its metadata to Zookeeper using a custom StormServiceNamespaceHandler and ProviderFactoryBean.

Start a Netty server that listens on a configured port, adds a decoder, encoder, and a business‑logic handler ( NettyServerInvokeHandler) to the pipeline.

Client (consumer)

Generate a JDK dynamic proxy for the service interface.

Obtain the list of provider nodes from Zookeeper and select one according to a load‑balancing strategy.

Send a StormRequest containing the target method, arguments, and provider info through a Netty client.

Receive a StormResponse, extract the result, and return it to the caller.

Testing

Server main class loads storm-server.xml and publishes the service. Client main class loads storm-client.xml, retrieves the HelloService bean, and invokes sayHello("World").

Result

Server console shows “service published completed”. Client prints “hello World”. Screenshots of the server, client, and Zookeeper node tree are shown below.

Conclusion

The article provides a concise overview of the RPC workflow and a runnable example that demonstrates service registration, discovery, network communication, and remote method invocation.