Building an Internet Chat System with Netty, WebSocket, and Spring Integration

0. Introduction

The goal is to build an Internet chat system, comparable to the web version of WeChat, using Netty as the core framework and WebSocket as the application‑layer protocol. Only essential features such as one‑to‑one chat, group chat, and file transfer are implemented, and the project is integrated with Spring to be open‑source and extensible.

About Netty

Netty is a Java client/server framework that abstracts low‑level network operations and provides an easy‑to‑use API.

About WebSocket

WebSocket solves the limitation of HTTP where only the client can initiate communication; it uses an HTTP handshake to upgrade the connection and then enables lightweight, efficient, bidirectional text transmission.

1. Technical Preparation

IDE: MyEclipse 2016

JDK: 1.8.0_121

Browsers: Google Chrome, 360 Browser (speed mode)

Key technologies: Netty 4, WebSocket + HTTP, Spring MVC + Spring, jQuery, Bootstrap 3 + bootstrap‑fileinput, Maven 3.5, Tomcat 8.0

2. Overall Design

2.1 Design Idea

Tomcat runs on port 8080 handling HTTP requests such as login and user information, while a separate thread runs a Netty WebSocket server on port 3333 for real‑time message exchange. After a user logs in, the browser keeps a Session (30‑minute timeout). Tomcat returns user data and stores the user's WebSocket connection for later messaging. When a user sends a message, the server looks up the recipient’s connection and forwards the message. On logout, both the Session and the WebSocket connection are released to avoid memory leaks.

2.2 System Architecture

The system follows a B/S model and adopts an MVC‑like layering: View, Controller, Service, Model, and Data Access.

2.3 Project Structure

Backend and frontend directory structures are illustrated in the following images.

2.4 System Modules

Login module – uses a simple Session mechanism for authentication and releases the WebSocket connection on logout.

Chat management module – core functionality built with Netty, supporting single and batch text/file messages and emojis.

Other modules (friend management, chat history, registration) are not implemented but can be added.

2.5 User State Diagram

2.6 User Interface

Sample chat UI screenshots:

3. Core Code

The following Java class shows how to start and gracefully shut down the Netty WebSocket server. The full source is available in the repository.

/**
 * 描述: Netty WebSocket服务器
 *      使用独立的线程启动
 * @author Kanarien
 * @version 1.0
 * @date 2018年5月18日 上午11:22:51
 */
public class WebSocketServer implements Runnable{

    /**
     * 描述：启动Netty Websocket服务器
     */
    public void build() {
        // 略，详细请看源码
    }

    /**
     * 描述：关闭Netty Websocket服务器，主要是释放连接
     *     连接包括：服务器连接serverChannel，
     *     客户端TCP处理连接bossGroup，
     *     客户端I/O操作连接workerGroup
     *
     *     若只使用
     *         bossGroupFuture = bossGroup.shutdownGracefully();
     *         workerGroupFuture = workerGroup.shutdownGracefully();
     *     会造成内存泄漏。
     */
    public void close(){
        serverChannelFuture.channel().close();
        Future
bossGroupFuture = bossGroup.shutdownGracefully();
        Future
workerGroupFuture = workerGroup.shutdownGracefully();

        try {
            bossGroupFuture.await();
            workerGroupFuture.await();
        } catch (InterruptedException ignore) {
            ignore.printStackTrace();
        }
    }

}

4. Demonstration

4.1 Login

Login URLs:

http://localhost:8080/WebSocket/login or http://localhost:8080/WebSocket/

There are nine preset users (Member001‑Member009) each with password equal to the numeric suffix.

4.2 Chat Demo

After logging in, users can exchange messages, files, and emojis in real time.

5. Source Code Download

Download link: https://pan.baidu.com/s/1uLyUXvQKWL09URNsLEOdHw?pwd=654k

Extraction code: 654k