SpringBoot集成WebSocket让后台主动给前端发送消息

     导包

<!--websocket-->
<dependency>
   <groupId>javax.websocket</groupId>
   <artifactId>javax.websocket-api</artifactId>
   <version>1.1</version>
   <scope>provided</scope>
</dependency>
<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-websocket</artifactId>
</dependency>

其实只要下面那个就可以了，没用springBoot的话就用上面那个

创建类WebSocket 

import com.alibaba.fastjson.JSONObject;
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.Map;
import java.util.concurrent.ConcurrentHashMap;

@ServerEndpoint("/webSocket/{username}")
@Component
public class WebSocket {
    private static int onlineCount = 0;
    private static Map<String, WebSocket> clients = new ConcurrentHashMap<String, WebSocket>();
    private Session session;
    private String username;

    //连接打开时执行
    @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");
    }

    //连接关闭时执行
    @OnClose
    public void onClose() throws IOException {
        clients.remove(username);
        subOnlineCount();
    }

    //收到消息时执行
    @OnMessage
    public void onMessage(String message) throws IOException {

        JSONObject jsonTo = JSONObject.parseObject(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");
        }
    }

    //连接错误时执行
    @OnError
    public void onError(Session session, Throwable error) {
        error.printStackTrace();
    }

    public void sendMessageTo(String message, String To) throws IOException {
        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 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;
    }
}

进行配置

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.server.standard.ServerEndpointExporter;

@Configuration
public class WebSocketConfig {

    /**
     * 注入一个ServerEndpointExporter,该Bean会自动注册使用@ServerEndpoint注解申明的websocket endpoint
     */
    @Bean
    public ServerEndpointExporter serverEndpointExporter() {
        return new ServerEndpointExporter();
    }

}

后端方法发送消息时的代码

        WebSocket ws = new WebSocket();
        JSONObject jo = new JSONObject();
        jo.put("message", "我是后端，收到这个就说明成功了。");
        jo.put("To", "admin");
        try {
            ws.onMessage(jo.toString());
        } catch (IOException e) {
            e.printStackTrace();
        } 

顺便附一个前端工程方便后端写的时候调试
https://files-cdn.cnblogs.com/files/best/WebSocketClient.rar