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How does Java Websocket implement online whiteboard function?

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Dec 17, 2023 pm 10:58 PM

javawebsocketwhiteboard

Java Websocket如何实现在线白板功能？

How does Java Websocket implement the online whiteboard function?

In the modern Internet era, people are paying more and more attention to the experience of real-time collaboration and interaction. Online whiteboard is a function implemented based on Websocket. It enables multiple users to collaborate in real-time to edit the same drawing board and complete operations such as drawing and annotation. It provides a convenient solution for online education, remote meetings, team collaboration and other scenarios.

1. Technical background
WebSocket is a new protocol provided by HTML5. It implements full-duplex communication on the same TCP connection, effectively solving the limitations of the request-response mode of the HTTP protocol. . WebSocket is based on an event-driven programming model and uses standardized APIs to make writing real-time communication applications simple and efficient.

2. Implementation steps

Introduce dependencies
Introduce Java WebSocket-related dependencies into the project's pom.xml file.

<dependency>
    <groupId>javax.websocket</groupId>
    <artifactId>javax.websocket-api</artifactId>
    <version>1.1</version>
</dependency>
<dependency>
    <groupId>org.glassfish.tyrus</groupId>
    <artifactId>tyrus-server</artifactId>
    <version>1.17</version>
</dependency>
<dependency>
    <groupId>org.glassfish.tyrus</groupId>
    <artifactId>tyrus-container-grizzly-server</artifactId>
    <version>1.17</version>
</dependency>

Create WebSocket endpoint
Create a class to implement the javax.websocket.Endpoint interface for handling WebSocket requests.

import java.io.IOException;
import javax.websocket.Endpoint;
import javax.websocket.EndpointConfig;
import javax.websocket.MessageHandler;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;

@ServerEndpoint(value = "/whiteboard")
public class WhiteboardEndpoint extends Endpoint {
    @Override
    public void onOpen(Session session, EndpointConfig config) {
        session.addMessageHandler(new MessageHandler.Whole<String>() {
            @Override
            public void onMessage(String message) {
                // 处理收到的消息
                System.out.println("Received message: " + message);
                // 广播消息给所有连接的客户端
                session.getOpenSessions().forEach(s -> {
                    try {
                        s.getBasicRemote().sendText(message);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                });
            }
        });
    }
}

Configure WebSocket container
Create a Servlet class to configure the WebSocket container and its related parameters.

import javax.servlet.annotation.WebServlet;
import org.glassfish.tyrus.server.Server;

@WebServlet(name = "WhiteboardServlet", urlPatterns = {"/whiteboard/*"})
public class WhiteboardServlet extends javax.servlet.http.HttpServlet {
    private static final long serialVersionUID = 1L;
    private static final int PORT = 8080;
    private static Server server;
    
    @Override
    public void init() {
        server = new Server("localhost", PORT, "/websocket", null, WhiteboardEndpoint.class);
        try {
            server.start();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    @Override
    public void destroy() {
        server.stop();
    }
}

Writing the front-end page
Add some JavaScript code to the HTML page to achieve connection and data interaction with the WebSocket server.

<!DOCTYPE html>
<html>
<head>
    <title>Online Whiteboard</title>
    <script type="text/javascript">
        var socket = new WebSocket("ws://localhost:8080/websocket/whiteboard");
        
        socket.onmessage = function(event) {
            // 收到消息时的处理逻辑
            console.log("Received message: ", event.data);
        };

        function send(message) {
            // 发送消息给服务器
            socket.send(message);
        }
    </script>
</head>
<body>
    <!-- 在这里放置绘图相关的HTML节点 -->
    <canvas id="canvas"></canvas>
    <button onclick="send('Hello, WebSocket!')">Send Message</button>
</body>
</html>

3. Function expansion
Based on the above foundation, we can further expand the functions of the online whiteboard.

Drawing operation
You can capture the user's mouse events through JavaScript, and then send the drawing command to the WebSocket server. The server broadcasts the command to all online users to draw and display the drawing content.
Marking and Annotation
Users can mark, annotate, annotate and other operations on the drawing board, and synchronize them to other online users in real time.
Handling connection and disconnection events
Add the processing of connection and disconnection events, which can record user connection and disconnection logs, and update the online user list in real time.

4. Summary
This article introduces how to use Java WebSocket to implement the online whiteboard function and how to interact with the front-end page. Through real-time collaboration and interaction, we can allow multiple users to collaboratively edit on the same drawing board, thereby improving collaboration efficiency and experience. I hope readers can use this article to have a certain understanding of Java WebSocket and be able to apply it to actual projects.

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