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Java应用层协议WebSocket实现消息推送

发布:2023-03-28 08:05:02 59


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Java WebSocket

前言

  大部分的web开发者,开发的业务都是基于Http协议的:前端请求后端接口,携带参数,后端执行业务代码,再返回结果给前端。作者参与开发的项目,有一个报警推送的功能,服务端实时推送报警信息给浏览器端;还有像抖音里面,如果有人关注、回复你的评论时,抖音就会推送相关消息给你了,你就会收到一条消息。

  有些同学会说了,基于Http协议也能实现啊:前端定时访问后端(每隔3s或者几秒),后端返回消息数据,前端拿到后弹出消息。这种方式太low了,而且每个浏览器都这样,使用系统的人一多,服务器的压力就太大了些。那到底用什么技术手段实现呢?我们的主角就登场了。

  WebSocket是在单个TCP连接上进行全双工通信的应用层协议(Http协议也是应用层),浏览器端和服务端都可主动发送数据给另一端。这样是不是比Http协议更适合消息推送这种场景。

浏览器端

  作者建了一个SpringBoot项目,Html放在src\main\resources\static下:

<!DOCTYPE html>
<html lang="zh" xmlns:th="http://www.thymeleaf.org">
<head>
<!--    解决中文乱码-->
    <meta charset="UTF-8"/>
    <title></title>
    <script type="text/javascript" src="./js/jquery.min.js"></script>
</head>
<body>
    <input id="input1" type="text" /><br/>
    <input type="button" value="浏览器发送服务端" onclick="btnClick()" />
    <input type="button" value="服务端发送浏览器" onclick="btnClick1()" />
    <input type="button" value="重新打开连接" onclick="btnClick2()" />
    <br/>
    <textarea id="textArea" style="height: 50px"></textarea>
<script>
    var ws;
    webSocketInit();
    function webSocketInit() {
        ws =new WebSocket('ws://localhost:8080/bootdemo/webSocket/10086');
        // 获取连接状态
        console.log('ws连接状态[初始]:' + ws.readyState);
        //监听是否连接成功
        ws.onopen = function () {
            console.log('ws连接状态[成功]:' + ws.readyState);
        };
        // 接听服务器发回的信息并处理展示
        ws.onmessage = function (obj) {
            console.log('接收到来自服务器的消息:');
            var txt = $("#textArea").val();
            $("#textArea").val(txt + "\n" + obj.data);
            $("#textArea").scrollTop($("#textArea")[0].scrollHeight);
            //完成通信后关闭WebSocket连接
            // ws.close();
        };
        // 监听连接关闭事件
        ws.onclose = function () {
            // 监听整个过程中websocket的状态
            console.log('ws连接状态[关闭]:' + ws.readyState);
        };
        // 监听并处理error事件
        ws.onerror = function (error) {
            console.log(error);
        };
    }
    function btnClick() {
        console.log("浏览器端发送消息:");
        //连接成功则发送一个数据
        ws.send($("#input1").val());
    }
    function btnClick1() {
        $.ajax({
            url: 'http://localhost:8080/bootdemo/pushWebSocket/publish?' +
            'userId=10086&message=' + $("#input1").val(),
            type: 'GET',
            success: function (data) {
                // console.log(data);
            }
        });
    }
    function btnClick2() {
        webSocketInit();
    }
</script>
</body>
</html>

服务器端

  先引入依赖:

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-thymeleaf</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-websocket</artifactId>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <scope>provided</scope>
    </dependency>

  bean上添加@ServerEndpoint,作为WebSocket的服务端。

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.CopyOnWriteArraySet;
@Component
@Slf4j
@ServerEndpoint("/webSocket/{userId}")
public class WebSocketServer {
    //与某个客户端的连接会话,需要通过它来给客户端发送数据
    private Session session;
    private static final CopyOnWriteArraySet<WebSocketServer> webSockets =
    new CopyOnWriteArraySet<>();
    // 用来存在线连接数
    private static final Map<String, Session> sessionPool = 
    new HashMap<String, Session>();
    /**
     * 连接成功调用的方法
     */
    @OnOpen
    public void onOpen(Session session, @PathParam(value = "userId") 
    String userId) {
        try {
            this.session = session;
            webSockets.add(this);
            sessionPool.put(userId, session);
        }
        catch (Exception e) {
        }
    }
    /**
     * 收到客户端消息后调用的方法
     */
    @OnMessage
    public void onMessage(String message) {
        log.info("websocket消息: 收到客户端消息:" + message);
    }
    public void sendOneMessage(String userId, String message) {
        Session session = sessionPool.get(userId);
        if (session != null && session.isOpen()) {
            try {
                log.info("服务端推送消息:" + message);
                session.getAsyncRemote().sendText(message);
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

  进行注册:

@Configuration
public class WebSocketConfigOne {
    /**
     * 这个bean会自动注册使用了@ServerEndpoint注解声明的对象
     * 没有的话会报404
     *
     * @return
     */
    @Bean
    public ServerEndpointExporter serverEndpointExporter() {
        return new ServerEndpointExporter();
    }
}

  推送消息的控制器:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import java.util.HashMap;
import java.util.Map;
@Controller
@RequestMapping("/pushWebSocket")
public class WebSocketController {
    @Autowired
    private WebSocketServer webSocketServer;
    @GetMapping("/publish")
    @ResponseBody
    public Map publish(String userId, String message) {
        webSocketServer.sendOneMessage(userId, message);
        HashMap<String, Object> map = new HashMap<>();
        map.put("code", 200);
        return map;
    }
}

  还有我的配置文件application.properties:

  # web port

  server.port=8080

  server.servlet.context-path=/bootdemo

  运行启动类后,访问html(localhost:8080/bootdemo/index.html)如下:

  有的同学一思索,点击图中的第2个按钮"服务端发送浏览器",你这好像也是前端先请求,再推送的消息;我们的WebSocketController#publish方法,在真实的场景下,可以在后端的定时任务中、消息中间件的消费者端调用,不用前端先发送请求。

  当然SpringBoot有专门构建WebSocket服务端的方式。

  核心配置类:

import lombok.extern.slf4j.Slf4j;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.web.servlet.HandlerMapping;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.config.annotation.EnableWebSocket;
import org.springframework.web.socket.config.annotation.WebSocketConfigurer;
import org.springframework.web.socket.config.annotation.WebSocketHandlerRegistry;
import org.springframework.web.socket.server.HandshakeInterceptor;
import javax.servlet.http.HttpServletRequest;
import java.util.Map;
@Configuration
@EnableWebSocket
@Slf4j
public class WebSocketConfig1 implements WebSocketConfigurer {
    @Override
    public void registerWebSocketHandlers(WebSocketHandlerRegistry 
    registry) {
        registry.addHandler(new MyWebSocketHandler(), "/webSocket/{userId}")//设置连接路径和处理
                .setAllowedOrigins("*")
                .addInterceptors(new MyWebSocketInterceptor());//设置拦截器
    }
    class MyWebSocketInterceptor implements HandshakeInterceptor {
        //前置拦截一般用来注册用户信息,绑定 WebSocketSession
        @Override
        public boolean beforeHandshake(ServerHttpRequest request, 
        ServerHttpResponse response, WebSocketHandler wsHandler, 
        Map<String, Object> attributes) throws Exception {
            log.info("前置拦截~~");
            if (!(request instanceof ServletServerHttpRequest)) {
                return true;
            }
            HttpServletRequest servletRequest = 
            ((ServletServerHttpRequest)request).getServletRequest();
            Map map = (Map)servletRequest.getAttribute(HandlerMapping.
            URI_TEMPLATE_VARIABLES_ATTRIBUTE);
            String userId = (String)map.get("userId");
            attributes.put("userId", userId);
            return true;
        }
        @Override
        public void afterHandshake(ServerHttpRequest request, 
        ServerHttpResponse response, WebSocketHandler wsHandler, 
        Exception exception) {
            log.info("后置拦截~~");
        }
    }
}

  核心处理器:

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import org.springframework.web.socket.*;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
@Slf4j
@Component
public class MyWebSocketHandler implements WebSocketHandler {
    private static final Map<String, WebSocketSession> SESSIONS = 
    new ConcurrentHashMap<>();
	/**
	 * 建立新的socket连接后回调的方法
	 */
    @Override
    public void afterConnectionEstablished(WebSocketSession session) 
    throws Exception {
        String userId = (String) session.getAttributes().get("userId");
        SESSIONS.put(userId, session);
    }
	/**
	 * 接收到浏览器端的消息后回调的方法
	 */
    @Override
    public void handleMessage(WebSocketSession session, 
    WebSocketMessage<?> message) throws Exception {
        String msg = message.getPayload().toString();
        log.info("收到客户端消息:" + msg);
    }
	/**
	 * 连接出错时回调的方法
	 */
    @Override
    public void handleTransportError(WebSocketSession session, 
    Throwable exception) throws Exception {
        log.info("连接出错");
        if (session.isOpen()) {
            session.close();
        }
    }
	/**
	 * 连接关闭时回调的方法
	 */
    @Override
    public void afterConnectionClosed(WebSocketSession session, 
    CloseStatus closeStatus) throws Exception {
        log.info("连接关闭:status:" + closeStatus);
    }
	/**
	 * 是否处理部分消息,返回false就行
	 */
    @Override
    public boolean supportsPartialMessages() {
        return false;
    }
	/**
	 * 推送消息给浏览器端
	 */
    public void sendMessage(String userId, String message) {
        WebSocketSession webSocketSession = SESSIONS.get(userId);
        if (webSocketSession == null || !webSocketSession.isOpen()) {
            return;
        }
        try {
            webSocketSession.sendMessage(new TextMessage(message));
        }
        catch (Exception ex) {
            log.error("推送消息异常:" + ex);
        }
    }
}

  控制器也改造下:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import java.util.HashMap;
import java.util.Map;
@Controller
@RequestMapping("/pushWebSocket")
public class WebSocketController {
    @Autowired
    private MyWebSocketHandler handler;
    @GetMapping("/publish")
    @ResponseBody
    public Map publish(String userId, String message) {
        handler.sendMessage(userId, message);
        HashMap<String, Object> map = new HashMap<>();
        map.put("code", 200);
        return map;
    }
}

  前端部分不用做修改,和之前一样的代码。

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