webSocket 推送消息到 客户端

<!-- webSocket 开始-->
    <dependency>
        <groupId>javax.websocket</groupId>
        <artifactId>javax.websocket-api</artifactId>
        <version>1.1</version>
        <scope>provided</scope>
    </dependency>

    <dependency>
        <groupId>javax</groupId>
        <artifactId>javaee-api</artifactId>
        <version>7.0</version>
        <scope>provided</scope>
    </dependency>
    <!-- webSocket 结束-->

    <dependency>
        <groupId>com.google.code.gson</groupId>
        <artifactId>gson</artifactId>
        <version>2.8.5</version>
    </dependency>
    <dependency>
        <groupId>net.sf.json-lib</groupId>
        <artifactId>json-lib</artifactId>
        <version>2.4</version>
        <classifier>jdk15</classifier>
    </dependency>
</dependencies>

package com.example.demo.controller;

import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import net.sf.json.JSONObject;
import org.springframework.stereotype.Component;

@Component
@ServerEndpoint("/webSocket/{username}")
public class WebSocket {
    private static int onlineCount = 0;
    private static Map<String, WebSocket> clients = new ConcurrentHashMap<String, WebSocket>();
    private Session session;
    private String username;
    @OnOpen
    public void onOpen(@PathParam("username") String username, Session session) throws IOException {
        this.username = username;
        this.session = session;
        addOnlineCount();
        clients.put(username, this);
        System.out.println("已连接");

    }
    @OnClose
    public void onClose() throws IOException {
        clients.remove(username);
        subOnlineCount();
    }
    @OnMessage
    public void onMessage(String message) throws IOException {
        JSONObject jsonTo = JSONObject.fromObject(message);
        String mes = (String) jsonTo.get("message");
        if (!jsonTo.get("To").equals("All")){
            sendMessageTo(mes, jsonTo.get("To").toString());
        }else{
            sendMessageAll("给所有人");
        }

    }
    @OnError
    public void onError(Session session, Throwable error) {
        error.printStackTrace();
    }
    public void sendMessageTo(String message, String To) throws IOException {
        // session.getBasicRemote().sendText(message);
        //session.getAsyncRemote().sendText(message);
        for (WebSocket item : clients.values()) {
            if (item.username.equals(To) )
                item.session.getAsyncRemote().sendText(message);
        }
    }
    
    public void sendMessageAll(String message) throws IOException {
        for (WebSocket item : clients.values()) {
            item.session.getAsyncRemote().sendText(message);
        }

    }

    public void sendMessage(String message) {
        for (WebSocket webSocket: clients.values()) {
            try {
                webSocket.session.getBasicRemote().sendText(message);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    public static synchronized int getOnlineCount() {
        return onlineCount;
    }



    public static synchronized void addOnlineCount() {
        WebSocket.onlineCount++;
    }
    
    public static synchronized void subOnlineCount() {
        WebSocket.onlineCount--;
    }
    public static synchronized Map<String, WebSocket> getClients() {
        return clients;
    }

}

package com.example.demo.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

import java.io.IOException;

@Controller
public class TestController {

    @Autowired
    private WebSocket webSocket;
    
    @RequestMapping("/test")
    public String test(){
        return "test";
    }
    
    @RequestMapping("/sendMessage")
    @ResponseBody
    public String sendMessage() throws IOException {
        webSocket.sendMessage("发送的第一条消息");
        return "";
    }
}

<script>
    var websocket = null;
    var host = document.location.host;
    var username = "root"; // 获得当前登录人员的userName
    // alert(username)
    //判断当前浏览器是否支持WebSocket
    if ('WebSocket' in window) {
        alert("浏览器支持Websocket")
        websocket = new WebSocket('ws://'+host+'/webSocket/'+username);
    } else {
        alert('当前浏览器 Not support websocket')
    }
    
    //连接发生错误的回调方法
    websocket.onerror = function() {
        alert("WebSocket连接发生错误")
        setMessageInnerHTML("WebSocket连接发生错误");
    };
    //连接成功建立的回调方法
    websocket.onopen = function() {
        alert("WebSocket连接成功")
        setMessageInnerHTML("WebSocket连接成功");
    }
    //接收到消息的回调方法
    websocket.onmessage = function(event) {
        alert("这是后台推送的消息："+event.data);
        setMessageInnerHTML(event.data);
        alert("接收到消息的回调方法")
       

    }
    
    //连接关闭的回调方法
    websocket.onclose = function() {
        setMessageInnerHTML("WebSocket连接关闭");
    }
    //监听窗口关闭事件，当窗口关闭时，主动去关闭websocket连接，防止连接还没断开就关闭窗口，server端会抛异常。
    window.onbeforeunload = function() {
        closeWebSocket();
    }
    //关闭WebSocket连接
    function closeWebSocket() {
        websocket.close();

    }
    //将消息显示在网页上
    function setMessageInnerHTML(innerHTML) {
        document.getElementById('message').innerHTML += innerHTML + '<br/>';
    }
</script>