[网络协议]java使用websocket向前端推送消息

?websocket所需pom依赖：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-websocket</artifactId>
    <version>2.1.8.RELEASE</version>
</dependency>

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

<dependency>
    <groupId>org.java-websocket</groupId>
    <artifactId>Java-WebSocket</artifactId>
    <version>1.3.7</version>
</dependency>

?websocket接口实现类：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import javax.websocket.*;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;


/**
 * 前后端交互的类实现消息的接收推送(自己发送给另一个人)
 *
 * @ServerEndpoint(value = "/websocket") 前端通过此URI 和后端交互，建立连接
 */
@ServerEndpoint(value = "/websocket")
@Component
public class WebSocketServer  {
    private static final Logger logger = LoggerFactory.getLogger(WebSocketServer.class);

    /**
     * 存放所有在线的客户端
     */
    private static Map<String, Session> sessionMap = new ConcurrentHashMap<>();
    /**
     * 连接建立成功调用的方法
     */

    /**
     * websocket建立连接时调用
     *
     * @param session
     */
    @OnOpen
    public void onOpen(Session session) {
        if (session == null) {
            return;
        }
        logger.debug("创建websocket会话, 会话号: {}", session.getId());
        String sessionId = session.getId();
        sessionMap.put(sessionId, session);
    }

    private synchronized void removeOldSession(String sessionId) {
        try {
            Session oldSession = sessionMap.get(sessionId);
            if (oldSession != null && oldSession.isOpen()) {
                removeSession(sessionId);
                oldSession.getBasicRemote().sendText("{\"type\":\"LOGIN_CONFLICT\"}");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * websocket 断开连接时调用
     *
     * @param session
     */
    @OnClose
    public void onClose(Session session) {
        if (session == null) {
            return;
        }
        logger.debug("websocket会话断开, 会话号: {}", session.getId());
        closeSession(session);
    }

    /**
     * websocket客戶端消息
     *
     * @param message
     */
    @OnMessage
    public void onWsMessage(String message) {
        logger.info("收到websocket消息: {}", message);
    }

    @OnError
    public void onError(Session session, Throwable error) {
        logger.error("发生错误");
        error.printStackTrace();
    }

    /**
     * 服务端发送消息给客户端
     */
    public void sendMessage(String message) {
        Iterator<String> iterator = sessionMap.keySet().iterator();
        while (iterator.hasNext()) {
            String sessionId = iterator.next();
            Session session = sessionMap.get(sessionId);
            if (session != null && session.isOpen()) {
                try {
                    session.getBasicRemote().sendText(message);
                } catch (Exception e) {
                    logger.error("发送websocket消息失败, 消息: {},", message, e);
                    // 发送消息出现异常，终止循环
                    closeSession(session);
                    iterator.remove();
                }
            }
        }
    }

    private void closeSession(Session session) {
        if (session == null) {
            return;
        }
        try {
            String sessionId = session.getId();
            removeSession(sessionId);
            if (session.isOpen()) {
                session.close();
            }
        } catch (IOException e) {
            logger.error("关闭 websocket会话 失败, ", e);
        }
    }

    private synchronized void removeSession(String sessionId) {
        sessionMap.remove(sessionId);

    }

}

?websocket配置类：

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();
    }
}

业务类引用websocket服务：

@Autowired
WebSocketServer webSocketServer;

?postman测试：

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