springboot 使用websocket技术主动给前端发送消息的实现

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

package com.spark.common.config; 
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.server.standard.ServerEndpointExporter;
 

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

package com.spark.common.utils.websocket; 
import com.alibaba.fastJSON.jsON;
import com.alibaba.fastjson.JSONObject;
import com.spark.common.utils.StringUtils;
import lombok.extern.slf4j.Slf4j;
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.concurrent.ConcurrentHashMap;
 

@ServerEndpoint("/socketServer/{userId}")
@Component
@Slf4j
public class WebSocketServer { 
    
    private static int onlineCount = 0;
    
    private static ConcurrentHashMap<String, WebSocketServer> webSocketMap = new ConcurrentHashMap<>();
    
    private Session session;
    
    private String userId = "";
 
    
    @OnOpen
    public void onOpen(Session session, @PathParam("userId") String userId) {
        this.session = session;
        this.userId = userId;
        if (webSocketMap.containsKey(userId)) {
            webSocketMap.remove(userId);
            webSocketMap.put(userId, this);
            //加入set中
        } else {
            webSocketMap.put(userId, this);
            //加入set中
            addOnlineCount();
            //在线数加1
        }
 
        log.info("用户连接:" + userId + ",当前在线人数为:" + getOnlineCount());
 
        try {
            sendMessage("连接成功");
        } catch (IOException e) {
            log.error("用户:" + userId + ",网络异常!");
        }
    } 
 
    
    @OnClose
    public void onClose() {
        if (webSocketMap.containsKey(userId)) {
            webSocketMap.remove(userId);
            //从set中删除
            subOnlineCount();
        }
        log.info("用户退出:" + userId + ",当前在线人数为:" + getOnlineCount());
    } 
 
    
    @OnMessage
    public void onMessage(String message, Session session) {
        log.info("用户消息:" + userId + ",报文:" + message);
        //可以群发消息
        //消息保存到数据库、Redis
        if (StringUtils.isNotBlank(message)) {
            try {
                //解析发送的报文
                JSONObject jsonObject = JSON.parseObject(message);
                //追加发送人(防止串改)
                jsonObject.put("fromUserId", this.userId);
                String toUserId = jsonObject.getString("toUserId");
                //传送给对应toUserId用户的websocket
                if (StringUtils.isNotBlank(toUserId) && webSocketMap.containsKey(toUserId)) {
                    webSocketMap.get(toUserId).sendMessage(jsonObject.toJSONString());
                } else {
                    log.error("请求的userId:" + toUserId + "不在该服务器上");
                    //否则不在这个服务器上，发送到Mysql或者redis
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
 
    
    @OnError
    public void onError(Session session, Throwable error) {
        log.error("用户错误:" + this.userId + ",原因:" + error.getMessage());
        error.printStackTrace();
    }
 
    
    public void sendMessage(String message) throws IOException {
        this.session.getBasicRemote().sendText(message);
    } 
 
    
    public static void sendInfo(String message, @PathParam("userId") String userId) throws IOException {
        log.info("发送消息到:" + userId + "，报文:" + message);
        if (StringUtils.isNotBlank(userId) && webSocketMap.containsKey(userId)) {
            webSocketMap.get(userId).sendMessage(message);
        } else {
            log.error("用户" + userId + ",不在线！");
        }
    }
 
    
    public static synchronized int getOnlineCount() {
        return onlineCount;
    }
 
    
    public static synchronized void addOnlineCount() {
        WebSocketServer.onlineCount++;
    }
 
    
    public static synchronized void subOnlineCount() {
        WebSocketServer.onlineCount--;
    } 
}

package com.charles.socket; 
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint; 
@ServerEndpoint(value = "/helloSocket")
public class TestSocket { 
    
    @OnOpen
    public void open(Session session) {        
        System.out.println("开始建立了链接...");
        System.out.println("当前session的id是：" + session.getId());
    }
    
    
    @OnMessage
    public void message(Session session, String data) {        
        System.out.println("开始处理消息...");
        System.out.println("当前session的id是：" + session.getId());
        System.out.println("从前端页面传过来的数据是：" + data);
    }
}

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "Http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Charles-WebSocket</title> 
<script type="text/javascript">    
    var websocket = null;
    var target = "ws://localhost:8080/websocket/helloSocket";    
    function buildConnection() {
        
        if('WebSocket' in window) {
            websocket = new WebSocket(target);        
        } else if('MozWebSocket' in window) {
            websocket = MozWebSocket(target);
        } else {
            window.alert("浏览器不支持WebSocket");
        }
    }
    
    // 往后台服务器发送消息.
    function sendMessage() {        
        var sendmsg = document.getElementById("sendMsg").value;
        console.log("发送的消息：" + sendmsg);        
        // 发送至后台服务器中.
        websocket.send(sendmsg);
    }
    
</script>
</head>
<body>
    
    <button onclick="buildConnection();">开始建立链接</button>
    <hr>
    <input id="sendMsg" /> <button onclick="sendMessage();">消息发送</button> 
</body>
</html>