WebSocket和kafka实现数据实时推送到前端

一. 需求背景
最近新接触一个需求，需要将kafka中的数据实时推送到前端展示。最开始想到的是前端轮询接口数据，但是无法保证轮询的频率和消费的频率完全一致，或造成数据缺失等问题。最终确定用利用WebSocket实现数据的实时推送。

二. websocket简介
网上已经有好多介绍WebSocket的文章了，就不详细介绍了，这里只做简单介绍。 WebSocket协议是基于TCP的一种新的网络协议。它实现了浏览器与服务器全双工(full-duplex)通信——允许服务器主动发送信息给客户端。

三. 服务端实现
　　1. pom文件

　　这里需要引用三个依赖。第一个为WebSocket需要的依赖，另外两个为kafka的依赖

<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0"         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">    <modelVersion>4.0.0</modelVersion>    <groupId>person</groupId>    <artifactId>wbSocketkafka</artifactId>    <version>1.0-SNAPSHOT</version>    <dependencies>        <!-- webSocket所需依赖 -->        <dependency>            <groupId>javax</groupId>            <artifactId>javaee-api</artifactId>            <version>7.0</version>        </dependency>        <!-- kafka 所需依赖 -->        <dependency>            <groupId>org.apache.kafka</groupId>            <artifactId>kafka_2.9.2</artifactId>            <version>0.8.1.1</version>        </dependency>        <dependency>            <groupId>org.apache.kafka</groupId>            <artifactId>kafka-clients</artifactId>            <version>RELEASE</version>        </dependency>     </dependencies></project>

2. webSocket服务端实现

//此处定义接口的uri@ServerEndpoint("/wbSocket")public class WebSocket {    private Session session;    public static CopyOnWriteArraySet<WebSocket> wbSockets = new CopyOnWriteArraySet<WebSocket>(); //此处定义静态变量，以在其他方法中获取到所有连接        /**     * 建立连接。     * 建立连接时入参为session     */    @OnOpen    public void onOpen(Session session){        this.session = session;        wbSockets.add(this); //将此对象存入集合中以在之后广播用，如果要实现一对一订阅，则类型对应为Map。由于这里广播就可以了随意用Set        System.out.println("New session insert,sessionId is "+ session.getId());    }    /**     * 关闭连接     */    @OnClose    public void onClose(){        wbSockets.remove(this);//将socket对象从集合中移除，以便广播时不发送次连接。如果不移除会报错(需要测试)        System.out.println("A session insert,sessionId is "+ session.getId());    }    /**     * 接收前端传过来的数据。     * 虽然在实现推送逻辑中并不需要接收前端数据，但是作为一个webSocket的教程或叫备忘，还是将接收数据的逻辑加上了。     */    @OnMessage    public void onMessage(String message ,Session session){        System.out.println(message + "from " + session.getId());    }    public void sendMessage(String message) throws IOException {        this.session.getBasicRemote().sendText(message);    }}

3. kafka消费者实现

public class ConsumerKafka extends Thread {    private KafkaConsumer<String,String> consumer;    private String topic = "kafkaTopic";    public ConsumerKafka(){    }    @Override    public void run(){        //加载kafka消费者参数        Properties props = new Properties();        props.put("bootstrap.servers", "localhost:9092");        props.put("group.id", "ytna");        props.put("enable.auto.commit", "true");        props.put("auto.commit.interval.ms", "1000");        props.put("session.timeout.ms", "15000");        props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");        props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");        //创建消费者对象        consumer = new KafkaConsumer<String,String>(props);        consumer.subscribe(Arrays.asList(this.topic));        //死循环，持续消费kafka        while (true){            try {               //消费数据，并设置超时时间                ConsumerRecords<String, String> records = consumer.poll(100);                //Consumer message                for (ConsumerRecord<String, String> record : records) {                    //Send message to every client                    for (WebSocket webSocket :wbSockets){                        webSocket.sendMessage(record.value());                    }                }            }catch (IOException e){                System.out.println(e.getMessage());                continue;            }        }    }    public void close() {        try {            consumer.close();        } catch (Exception e) {            System.out.println(e.getMessage());        }    }    //供测试用，若通过tomcat启动需通过其他方法启动线程    public static void main(String[] args){        ConsumerKafka consumerKafka = new ConsumerKafka();        consumerKafka.start();    }}

P.S. 需要注意的是WebSocket对tomcat版本是有要求的

四. 前端简单实现

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <title>WebSocket client</title>    <script type="text/javascript">        var socket;        if (typeof (WebSocket) == "undefined"){            alert("This explorer don't support WebSocket")        }        function connect() {            //Connect WebSocket server            socket =new WebSocket("ws://127.0.0.1:8080/wbSocket");            //open            socket.onopen = function () {                alert("WebSocket is open");            }            //Get message            socket.onmessage = function (msg) {                alert("Message is " + msg);            }            //close            socket.onclose = function () {                alert("WebSocket is closed");            }            //error            socket.onerror = function (e) {                alert("Error is " + e);            }        }        function close() {            socket.close();        }        function sendMsg() {            socket.send("This is a client message ");        }    </script></head><body>    <button onclick="connect()">connect</button>    <button onclick="close()">close</button>    <button onclick="sendMsg()">sendMsg</button></body></html>