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Spring Boot中使用WebSocket总结（二）：向指定用户发送WebSocket消息并处理对方不在线的情况

在上一篇文章（ www.zifangsky.cn/1355.html ）中我介绍了在Spring项目中使用WebSocket的几种实现方式。但是，上篇文章中只介绍了服务端采用广播模式给所有客户端发送消息，然而我们有时需要服务端给指定用户的客户端发送消息（比如：发送Web通知、实时打印用户任务的日志、两个用户点对点聊天等）。

关于服务端如何给指定用户的客户端发送消息，一般可以通过以下三种方案来实现：

方案一 ：WebSocket使用“Java提供的@ServerEndpoint注解”实现或者使用“Spring低层级API”实现，在建立连接时从 HttpSession 中获取用户登录后的用户名，然后把“ 用户名+该WebSocket连接 ”存储到 ConcurrentHashMap 。给指定用户发送消息，只需要根据接收者的用户名获取对方已经建立的WebSocket连接，接着给他发送消息即可。
方案二 ：在页面的监听路径前面动态添加当前登录的“ 用户ID/用户名 ”，这样给指定用户发送消息，只需要发送广播消息到监听了前面那个路径的客户端即可。
方案三 ：这种方案类似于方案一。使用Spring的高级API实现WebSocket，然后自定义 HandshakeHandler 类并重写 determineUser 方法，其目的是为了在建立连接时使用用户登录后的用户名作为此次WebSocket的凭证，最后我们就可以使用 messagingTemplate.convertAndSendToUser 方法给指定用户发送消息了。

注：本篇文章的完整源码可以参考： github.com/zifangsky/W…

使用SimpMessagingTemplate发送消息

使用 org.springframework.messaging.simp.SimpMessagingTemplate 类可以在服务端的任意地方给客户端发送消息。此外，在我们配置Spring支持STOMP后 SimpMessagingTemplate 类就会被自动装配到Spring的上下文中，因此我们只需要在想要使用的地方使用 @Autowired 注解注入SimpMessagingTemplate即可使用。

需要说明的是， SimpMessagingTemplate 类有两个重要的方法，它们分别是：

public void convertAndSend(D destination, Object payload) ：给监听了路径 destination 的所有客户端发送消息 payload
public void convertAndSendToUser(String user, String destination, Object payload) ：给监听了路径 destination 的用户 user 发送消息 payload

一个简单示例：

package cn.zifangsky.stompwebsocket.controller;

import cn.zifangsky.stompwebsocket.model.websocket.Greeting;
import cn.zifangsky.stompwebsocket.model.websocket.HelloMessage;
import cn.zifangsky.stompwebsocket.service.RedisService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.messaging.simp.SimpMessagingTemplate;
import org.springframework.messaging.simp.user.SimpUserRegistry;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.annotation.Resource;

/**
 * 测试{@link org.springframework.messaging.simp.SimpMessagingTemplate}类的基本用法
 * @author zifangsky
 * @date 2018/10/10
 * @since 1.0.0
 */
@Controller
@RequestMapping(("/wsTemplate"))
public class MessageTemplateController {
    private final Logger logger = LoggerFactory.getLogger(getClass());

    @Autowired
    private SimpMessagingTemplate messagingTemplate;

    @Autowired
    private SimpUserRegistry userRegistry;

    @Resource(name = "redisServiceImpl")
    private RedisService redisService;

    /**
     * 简单测试SimpMessagingTemplate的用法
     */
    @PostMapping("/greeting")
    @ResponseBody
    public String greeting(@RequestBody Greeting greeting) {
        this.messagingTemplate.convertAndSend("/topic/greeting", new HelloMessage("Hello," + greeting.getName() + "!"));

        return "ok";
    }

}
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很显然，这里发送的地址是上篇文章中最后那个示例监听的地址，在客户端页面建立连接后，我们使用 Postman 请求一下上面这个方法，效果如下：

Spring Boot中使用WebSocket总结（二）：向指定用户发送WebSocket消息并处理对方不在线的情况

然后我们可以发现页面中也收到消息了：

向指定用户发送WebSocket消息并处理对方不在线的情况

给指定用户发送消息：

如果接收者在线，则直接发送消息；
否则将消息存储到redis，等用户上线后主动拉取未读消息。

（1）自定义HandshakeInterceptor，用于禁止未登录用户连接WebSocket：

package cn.zifangsky.stompwebsocket.interceptor.websocket;

import cn.zifangsky.stompwebsocket.common.Constants;
import cn.zifangsky.stompwebsocket.common.SpringContextUtils;
import cn.zifangsky.stompwebsocket.model.User;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.stereotype.Component;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.server.HandshakeInterceptor;

import javax.servlet.http.HttpSession;
import java.text.MessageFormat;
import java.util.Map;

/**
 * 自定义{@link org.springframework.web.socket.server.HandshakeInterceptor}，实现“需要登录才允许连接WebSocket”
 *
 * @author zifangsky
 * @date 2018/10/11
 * @since 1.0.0
 */
@Component
public class AuthHandshakeInterceptor implements HandshakeInterceptor {
    private final Logger logger = LoggerFactory.getLogger(getClass());

    @Override
    public boolean beforeHandshake(ServerHttpRequest serverHttpRequest, ServerHttpResponse serverHttpResponse, WebSocketHandler webSocketHandler, Map<String, Object> map) throws Exception {
        HttpSession session = SpringContextUtils.getSession();
        User loginUser = (User) session.getAttribute(Constants.SESSION_USER);

        if(loginUser != null){
            logger.debug(MessageFormat.format("用户{0}请求建立WebSocket连接", loginUser.getUsername()));
            return true;
        }else{
            logger.error("未登录系统，禁止连接WebSocket");
            return false;
        }

    }

    @Override
    public void afterHandshake(ServerHttpRequest serverHttpRequest, ServerHttpResponse serverHttpResponse, WebSocketHandler webSocketHandler, Exception e) {

    }

}
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（2）自定义HandshakeHandler，用于在建立WebSocket的时候使用自定义的Principal：

package cn.zifangsky.stompwebsocket.interceptor.websocket;

import cn.zifangsky.stompwebsocket.common.Constants;
import cn.zifangsky.stompwebsocket.common.SpringContextUtils;
import cn.zifangsky.stompwebsocket.model.User;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.stereotype.Component;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.server.support.DefaultHandshakeHandler;

import javax.servlet.http.HttpSession;
import java.security.Principal;
import java.text.MessageFormat;
import java.util.Map;

/**
 * 自定义{@link org.springframework.web.socket.server.support.DefaultHandshakeHandler}，实现“生成自定义的{@link java.security.Principal}”
 *
 * @author zifangsky
 * @date 2018/10/11
 * @since 1.0.0
 */
@Component
public class MyHandshakeHandler extends DefaultHandshakeHandler{
    private final Logger logger = LoggerFactory.getLogger(getClass());

    @Override
    protected Principal determineUser(ServerHttpRequest request, WebSocketHandler wsHandler, Map<String, Object> attributes) {
        HttpSession session = SpringContextUtils.getSession();
        User loginUser = (User) session.getAttribute(Constants.SESSION_USER);

        if(loginUser != null){
            logger.debug(MessageFormat.format("WebSocket连接开始创建Principal，用户：{0}", loginUser.getUsername()));
            return new MyPrincipal(loginUser.getUsername());
        }else{
            logger.error("未登录系统，禁止连接WebSocket");
            return null;
        }
    }

}
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相应地，这里的 MyPrincipal 继承了 java.security.Principal 类：

package cn.zifangsky.stompwebsocket.interceptor.websocket;

import java.security.Principal;

/**
 * 自定义{@link java.security.Principal}
 *
 * @author zifangsky
 * @date 2018/10/11
 * @since 1.0.0
 */
public class MyPrincipal implements Principal {
    private String loginName;

    public MyPrincipal(String loginName) {
        this.loginName = loginName;
    }

    @Override
    public String getName() {
        return loginName;
    }
}
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（3）自定义ChannelInterceptor，用于在用户断开连接的时候记录日志：

package cn.zifangsky.stompwebsocket.interceptor.websocket;

import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.simp.stomp.StompCommand;
import org.springframework.messaging.simp.stomp.StompHeaderAccessor;
import org.springframework.messaging.support.ChannelInterceptor;
import org.springframework.stereotype.Component;

import java.security.Principal;
import java.text.MessageFormat;

/**
 * 自定义{@link org.springframework.messaging.support.ChannelInterceptor}，实现断开连接的处理
 *
 * @author zifangsky
 * @date 2018/10/10
 * @since 1.0.0
 */
@Component
public class MyChannelInterceptor implements ChannelInterceptor{
    private final Logger logger = LoggerFactory.getLogger(getClass());

    @Override
    public void afterSendCompletion(Message<?> message, MessageChannel channel, boolean sent, Exception ex) {
        StompHeaderAccessor accessor = StompHeaderAccessor.wrap(message);
        StompCommand command = accessor.getCommand();

        //用户已经断开连接
        if(StompCommand.DISCONNECT.equals(command)){
            String user = "";
            Principal principal = accessor.getUser();
            if(principal != null && StringUtils.isNoneBlank(principal.getName())){
                user = principal.getName();
            }else{
                user = accessor.getSessionId();
            }

            logger.debug(MessageFormat.format("用户{0}的WebSocket连接已经断开", user));
        }
    }

}
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（4）WebSocket相关的完整配置：

package cn.zifangsky.stompwebsocket.config;

import cn.zifangsky.stompwebsocket.interceptor.websocket.AuthHandshakeInterceptor;
import cn.zifangsky.stompwebsocket.interceptor.websocket.MyChannelInterceptor;
import cn.zifangsky.stompwebsocket.interceptor.websocket.MyHandshakeHandler;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.messaging.simp.config.ChannelRegistration;
import org.springframework.messaging.simp.config.MessageBrokerRegistry;
import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker;
import org.springframework.web.socket.config.annotation.StompEndpointRegistry;
import org.springframework.web.socket.config.annotation.WebSocketMessageBrokerConfigurer;

/**
 * WebSocket相关配置
 *
 * @author zifangsky
 * @date 2018/9/30
 * @since 1.0.0
 */
@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer{
    @Autowired
    private AuthHandshakeInterceptor authHandshakeInterceptor;

    @Autowired
    private MyHandshakeHandler myHandshakeHandler;

    @Autowired
    private MyChannelInterceptor myChannelInterceptor;

    @Override
    public void registerStompEndpoints(StompEndpointRegistry registry) {
        registry.addEndpoint("/stomp-websocket").withSockJS();

        registry.addEndpoint("/chat-websocket")
                .addInterceptors(authHandshakeInterceptor)
                .setHandshakeHandler(myHandshakeHandler)
                .withSockJS();
    }

    @Override
    public void configureMessageBroker(MessageBrokerRegistry registry) {
        //客户端需要把消息发送到/message/xxx地址
        registry.setApplicationDestinationPrefixes("/message");
        //服务端广播消息的路径前缀，客户端需要相应订阅/topic/yyy这个地址的消息
        registry.enableSimpleBroker("/topic");
    }

    @Override
    public void configureClientInboundChannel(ChannelRegistration registration) {
        registration.interceptors(myChannelInterceptor);
    }

}
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（5）Controller中的消息处理如下：

package cn.zifangsky.stompwebsocket.controller;

import cn.zifangsky.stompwebsocket.common.Constants;
import cn.zifangsky.stompwebsocket.common.SpringContextUtils;
import cn.zifangsky.stompwebsocket.enums.ExpireEnum;
import cn.zifangsky.stompwebsocket.model.User;
import cn.zifangsky.stompwebsocket.model.websocket.Greeting;
import cn.zifangsky.stompwebsocket.model.websocket.HelloMessage;
import cn.zifangsky.stompwebsocket.service.RedisService;
import cn.zifangsky.stompwebsocket.utils.JsonUtils;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.messaging.simp.SimpMessagingTemplate;
import org.springframework.messaging.simp.user.SimpUser;
import org.springframework.messaging.simp.user.SimpUserRegistry;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.annotation.Resource;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import java.text.MessageFormat;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * 测试{@link org.springframework.messaging.simp.SimpMessagingTemplate}类的基本用法
 * @author zifangsky
 * @date 2018/10/10
 * @since 1.0.0
 */
@Controller
@RequestMapping(("/wsTemplate"))
public class MessageTemplateController {
    private final Logger logger = LoggerFactory.getLogger(getClass());

    @Autowired
    private SimpMessagingTemplate messagingTemplate;

    @Autowired
    private SimpUserRegistry userRegistry;

    @Resource(name = "redisServiceImpl")
    private RedisService redisService;

    /**
     * 简单测试SimpMessagingTemplate的用法
     */
    @PostMapping("/greeting")
    @ResponseBody
    public String greeting(@RequestBody Greeting greeting) {
        this.messagingTemplate.convertAndSend("/topic/greeting", new HelloMessage("Hello," + greeting.getName() + "!"));

        return "ok";
    }

    /**
     * 给指定用户发送WebSocket消息
     */
    @PostMapping("/sendToUser")
    @ResponseBody
    public String chat(HttpServletRequest request) {
        //消息接收者
        String receiver = request.getParameter("receiver");
        //消息内容
        String msg = request.getParameter("msg");
        HttpSession session = SpringContextUtils.getSession();
        User loginUser = (User) session.getAttribute(Constants.SESSION_USER);

        HelloMessage resultData = new HelloMessage(MessageFormat.format("{0} say: {1}", loginUser.getUsername(), msg));
        this.sendToUser(loginUser.getUsername(), receiver, "/topic/reply", JsonUtils.toJson(resultData));

        return "ok";
    }

    /**
     * 给指定用户发送消息，并处理接收者不在线的情况
     * @param sender 消息发送者
     * @param receiver 消息接收者
     * @param destination 目的地
     * @param payload 消息正文
     */
    private void sendToUser(String sender, String receiver, String destination, String payload){
        SimpUser simpUser = userRegistry.getUser(receiver);

        //如果接收者存在，则发送消息
        if(simpUser != null && StringUtils.isNoneBlank(simpUser.getName())){
            this.messagingTemplate.convertAndSendToUser(receiver, destination, payload);
        }
        //否则将消息存储到redis，等用户上线后主动拉取未读消息
        else{
            //存储消息的Redis列表名
            String listKey = Constants.REDIS_UNREAD_MSG_PREFIX + receiver + ":" + destination;
            logger.info(MessageFormat.format("消息接收者{0}还未建立WebSocket连接，{1}发送的消息【{2}】将被存储到Redis的【{3}】列表中", receiver, sender, payload, listKey));

            //存储消息到Redis中
            redisService.addToListRight(listKey, ExpireEnum.UNREAD_MSG, payload);
        }

    }


    /**
     * 拉取指定监听路径的未读的WebSocket消息
     * @param destination 指定监听路径
     * @return java.util.Map<java.lang.String,java.lang.Object>
     */
    @PostMapping("/pullUnreadMessage")
    @ResponseBody
    public Map<String, Object> pullUnreadMessage(String destination){
        Map<String, Object> result = new HashMap<>();
        try {
            HttpSession session = SpringContextUtils.getSession();
            //当前登录用户
            User loginUser = (User) session.getAttribute(Constants.SESSION_USER);

            //存储消息的Redis列表名
            String listKey = Constants.REDIS_UNREAD_MSG_PREFIX + loginUser.getUsername() + ":" + destination;
            //从Redis中拉取所有未读消息
            List<Object> messageList = redisService.rangeList(listKey, 0, -1);

            result.put("code", "200");
            if(messageList !=null && messageList.size() > 0){
                //删除Redis中的这个未读消息列表
                redisService.delete(listKey);
                //将数据添加到返回集，供前台页面展示
                result.put("result", messageList);
            }
        }catch (Exception e){
            result.put("code", "500");
            result.put("msg", e.getMessage());
        }

        return result;
    }

}
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注：这里对应的几个Redis操作的方法如下：

@Override
public boolean delete(String key) {
	return redisTemplate.delete(key);
}

@Override
public void addToListLeft(String listKey, ExpireEnum expireEnum, Object... values) {
	//绑定操作
	BoundListOperations<String, Object> boundValueOperations = redisTemplate.boundListOps(listKey);
	//插入数据
	boundValueOperations.leftPushAll(values);
	//设置过期时间
	boundValueOperations.expire(expireEnum.getTime(),expireEnum.getTimeUnit());
}

@Override
public void addToListRight(String listKey, ExpireEnum expireEnum, Object... values) {
	//绑定操作
	BoundListOperations<String, Object> boundValueOperations = redisTemplate.boundListOps(listKey);
	//插入数据
	boundValueOperations.rightPushAll(values);
	//设置过期时间
	boundValueOperations.expire(expireEnum.getTime(),expireEnum.getTimeUnit());
}

@Override
public List<Object> rangeList(String listKey, long start, long end) {
	//绑定操作
	BoundListOperations<String, Object> boundValueOperations = redisTemplate.boundListOps(listKey);
	//查询数据
	return boundValueOperations.range(start, end);
}
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（6）示例页面：

<html xmlns:th="http://www.thymeleaf.org">
<head>
    <meta content="text/html;charset=UTF-8"/>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
    <meta http-equiv="X-UA-Compatible" content="IE=edge"/>
    <meta name="viewport" content="width=device-width, initial-scale=1"/>
    <title>Chat With STOMP Message</title>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/sockjs-client/1.1.4/sockjs.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/stomp.js/2.3.3/stomp.min.js"></script>
    <script th:src="@{/layui/layui.js}"></script>
    <script th:src="@{/layui/lay/modules/layer.js}"></script>
    <link th:href="@{/layui/css/layui.css}" rel="stylesheet">
    <link th:href="@{/layui/css/modules/layer/default/layer.css}" rel="stylesheet">
    <link th:href="@{/css/style.css}" rel="stylesheet">
    <style type="text/css">
        #connect-container {
            margin: 0 auto;
            width: 400px;
        }

        #connect-container div {
            padding: 5px;
            margin: 0 7px 10px 0;
        }

        .message input {
            padding: 5px;
            margin: 0 7px 10px 0;
        }

        .layui-btn {
            display: inline-block;
        }
    </style>
    <script type="text/javascript">
        var stompClient = null;

        $(function () {
            var target = $("#target");
            if (window.location.protocol === 'http:') {
                target.val('http://' + window.location.host + target.val());
            } else {
                target.val('https://' + window.location.host + target.val());
            }
        });

        function setConnected(connected) {
            var connect = $("#connect");
            var disconnect = $("#disconnect");
            var echo = $("#echo");

            if (connected) {
                connect.addClass("layui-btn-disabled");
                disconnect.removeClass("layui-btn-disabled");
                echo.removeClass("layui-btn-disabled");
            } else {
                connect.removeClass("layui-btn-disabled");
                disconnect.addClass("layui-btn-disabled");
                echo.addClass("layui-btn-disabled");
            }

            connect.attr("disabled", connected);
            disconnect.attr("disabled", !connected);
            echo.attr("disabled", !connected);
        }

        //连接
        function connect() {
            var target = $("#target").val();

            var ws = new SockJS(target);
            stompClient = Stomp.over(ws);

            stompClient.connect({}, function () {
                setConnected(true);
                log('Info: STOMP connection opened.');

                //连接成功后，主动拉取未读消息
                pullUnreadMessage("/topic/reply");

                //订阅服务端的/topic/reply地址
                stompClient.subscribe("/user/topic/reply", function (response) {
                    log(JSON.parse(response.body).content);
                })
            },function () {
                //断开处理
                setConnected(false);
                log('Info: STOMP connection closed.');
            });
        }

        //断开连接
        function disconnect() {
            if (stompClient != null) {
                stompClient.disconnect();
                stompClient = null;
            }
            setConnected(false);
            log('Info: STOMP connection closed.');
        }

        //向指定用户发送消息
        function sendMessage() {
            if (stompClient != null) {
                var receiver = $("#receiver").val();
                var msg = $("#message").val();
                log('Sent: ' + JSON.stringify({'receiver': receiver, 'msg':msg}));

                $.ajax({
                    url: "/wsTemplate/sendToUser",
                    type: "POST",
                    dataType: "json",
                    async: true,
                    data: {
                        "receiver": receiver,
                        "msg": msg
                    },
                    success: function (data) {

                    }
                });
            } else {
                layer.msg('STOMP connection not established, please connect.', {
                    offset: 'auto'
                    ,icon: 2
                });
            }
        }

        //从服务器拉取未读消息
        function pullUnreadMessage(destination) {
            $.ajax({
                url: "/wsTemplate/pullUnreadMessage",
                type: "POST",
                dataType: "json",
                async: true,
                data: {
                    "destination": destination
                },
                success: function (data) {
                    if (data.result != null) {
                        $.each(data.result, function (i, item) {
                            log(JSON.parse(item).content);
                        })
                    } else if (data.code !=null && data.code == "500") {
                        layer.msg(data.msg, {
                            offset: 'auto'
                            ,icon: 2
                        });
                    }
                }
            });
        }

        //日志输出
        function log(message) {
            console.debug(message);
        }
    </script>
</head>
<body>
    <noscript><h2 style="color: #ff0000">Seems your browser doesn't support Javascript! Websockets rely on Javascript being
        enabled. Please enable
        Javascript and reload this page!</h2></noscript>
    <div>
        <div id="connect-container" class="layui-elem-field">
            <legend>Chat With STOMP Message</legend>
            <div>
                <input id="target" type="text" class="layui-input" size="40" style="width: 350px" value="/chat-websocket"/>
            </div>
            <div>
                <button id="connect" class="layui-btn layui-btn-normal" onclick="connect();">Connect</button>
                <button id="disconnect" class="layui-btn layui-btn-normal layui-btn-disabled" disabled="disabled"
                        onclick="disconnect();">Disconnect
                </button>

            </div>
            <div class="message">
                <input id="receiver" type="text" class="layui-input" size="40" style="width: 350px" placeholder="接收者姓名" value=""/>
                <input id="message" type="text" class="layui-input" size="40" style="width: 350px" placeholder="消息内容" value=""/>
            </div>
            <div>
                <button id="echo" class="layui-btn layui-btn-normal layui-btn-disabled" disabled="disabled"
                        onclick="sendMessage();">Send Message
                </button>
            </div>
        </div>
    </div>
</body>
</html>
复制代码

启动项目后，分别在两个浏览器中使用不同的账号登录，接着互相给对方发送消息，效果如下：

界面一：