springboot + websocket server receives messages & actively sends messages

1. Introduce maven configuration:

		<dependency>  
           <groupId>org.springframework.boot</groupId>  
           <artifactId>spring-boot-starter-websocket</artifactId>  
       </dependency> 

Two, config configuration:

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.server.standard.ServerEndpointExporter;

/**
 * WebSocket配置
 *
 * @author 
 * @version v1.0.0
 * @since 2021/5/17 16:00
 */
@Configuration
public class WebSocketConfig {

    @Bean
    public ServerEndpointExporter serverEndpointExporter() {
        return new ServerEndpointExporter();
    }

}

3. Message receiving and sending server:

import org.apache.commons.collections4.CollectionUtils;
import org.springframework.stereotype.Component;

import javax.websocket.*;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;

/**
 * websocket server服务
 *
 * @author 
 * @version v1.0.0
 * @since 2021/5/17 16:30
 */
@ServerEndpoint("/{userId}")
@Component
public class WebSocketServer {

    private static int onlineCount = 0;     // 统计在线人数，粗略统计，未涉及并发
    private static ConcurrentHashMap<String,WebSocketServer> webSocketMap = new ConcurrentHashMap<>();   // session管理map
    private Session session;    // 会话session
    private String userId="";   // 当前用户

    /**
     * 初始化连接
     *
     * @param session 会话session
     * @param userId 当前用户id
     */
    @OnOpen
    public void onOpen(Session session, @PathParam("userId") String userId) {
        this.session = session;
        this.userId=userId;

        // 保存各用户的会话session
        if(webSocketMap.containsKey(userId)){
            webSocketMap.remove(userId);
            webSocketMap.put(userId, this);
        }else{
            webSocketMap.put(userId, this);
            addOnlineCount();
        }

        try {
            sendMessage("connect success");
        } catch (IOException e) {
     
        }
    }

    /**
     * 连接关闭调用的方法
     */
    @OnClose
    public void onClose() {
        if(webSocketMap.containsKey(userId)){
            webSocketMap.remove(userId);
            subOnlineCount();
        }
    }

    /**
     * 收到客户端消息后调用的方法
     *
     * @param message 客户端发送过来的消息
     */
    @OnMessage
    public void onMessage(String message, Session session) {
    }

    /**
     * 异常处理
     * @param session
     * @param error
     */
    @OnError
    public void onError(Session session, Throwable error) {
        error.printStackTrace();
    }

    public void sendMessage(String message) throws IOException {
        this.session.getBasicRemote().sendText(message);
    }

    /**
     * 发送自定义消息
     *
     * @param message 消息体
     * */
    public void sendInfo(String message) throws IOException {

        List<String> keys = new ArrayList<>(webSocketMap.keySet());
        if (CollectionUtils.isNotEmpty(keys)) {
            for (String key : keys) {
                webSocketMap.get(key).sendMessage(message);
            }
        }
    }

    public static synchronized int getOnlineCount() {
        return onlineCount;
    }

    public static synchronized void addOnlineCount() {
        WebSocketServer.onlineCount++;
    }

    public static synchronized void subOnlineCount() {
        WebSocketServer.onlineCount--;
    }
}

Among them, the sendInfo(String message) method is the method exposed to other classes to actively send messages to the specified websocket, such as in class A through webSocketServer.sendInfo(msg); to actively send messages. In the code example, the message is sent to all users, or the message can be sent to the specified user according to actual needs