springCloud 后端使用webSocket向前端推送消息

1、webSocket
webSocket长连接是一种在单个tcp连接上进行全双工通信的协议，允许双向数据推送。一般微服务提供的restful API只是对前端请求做出相应。使用webSocket可以实现后端主动向前端推送消息。

2、springboot使用webSocket
1、pom文件添加依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-websocket</artifactId>
</dependency>
2、添加webSocket配置

@Configuration
@EnableWebSocket
public class WebSocketAutoConfig implements WebSocketConfigurer {

    @Override
    public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
        // webSocket通道
        // 指定处理器和路径
        registry.addHandler(new WebSocketHandler(), "/websocket")
                 // 指定自定义拦截器
                .addInterceptors(new WebSocketInterceptor())
                // 允许跨域
                .setAllowedOrigins("*");
        // sockJs通道
        registry.addHandler(new WebSocketHandler(), "/sock-js")
                .addInterceptors(new WebSocketInterceptor())
                .setAllowedOrigins("*")
                // 开启sockJs支持
                .withSockJS();
    }
}
处理器代码：

import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.commons.lang3.reflect.FieldUtils;
import org.springframework.stereotype.Component;
import org.springframework.web.socket.*;
import org.springframework.web.socket.handler.AbstractWebSocketHandler;
import org.springframework.web.socket.sockjs.transport.session.WebSocketServerSockJsSession;

@Component
public class WebSocketHandler extends AbstractWebSocketHandler {

    /**
     * 存储sessionId和webSocketSession
     * 需要注意的是，webSocketSession没有提供无参构造，不能进行序列化，也就不能通过redis存储
     * 在分布式系统中，要想别的办法实现webSocketSession共享
     */
    private static Map<String, WebSocketSession> sessionMap = new ConcurrentHashMap<>();
    private static Map<String, String> userMap = new ConcurrentHashMap<>();

    /**
     * 获取sessionId
     */
    private String getSessionId(WebSocketSession session) {
        if (session instanceof WebSocketServerSockJsSession) {
            // sock js 连接
            try {
                return  ((WebSocketSession) FieldUtils.readField(session, "webSocketSession", true)).getId();
            } catch (IllegalAccessException e) {
                throw new RuntimeException("get sessionId error");
            }
        }
        return session.getId();
    }

    /**
     * webSocket连接创建后调用
     */
    @Override
    public void afterConnectionEstablished(WebSocketSession session) {
        // 获取参数
        String user = String.valueOf(session.getAttributes().get("user"));
        String sessionId = getSessionId(session);
        userMap.put(user, getSessionId(session));
        sessionMap.put(sessionId, session);
    }

    /**
     * 接收到消息会调用
     */
    @Override
    public void handleMessage(WebSocketSession session, WebSocketMessage<?> message) throws Exception {
        if (message instanceof TextMessage) {

        } else if (message instanceof BinaryMessage) {

        } else if (message instanceof PongMessage) {

        } else {
            System.out.println("Unexpected WebSocket message type: " + message);
        }
    }

    /**
     * 连接出错会调用
     */
    @Override
    public void handleTransportError(WebSocketSession session, Throwable exception) {
        sessionMap.remove(getSessionId(session));
    }

    /**
     * 连接关闭会调用
     */
    @Override
    public void afterConnectionClosed(WebSocketSession session, CloseStatus status) {
        sessionMap.remove(getSessionId(session));
    }

    @Override
    public boolean supportsPartialMessages() {
        return false;
    }

    /**
     * 后端发送消息
     */
    public void sendMessage(String user, String message) {
        String sessionId = userMap.get(user);
        WebSocketSession session = sessionMap.get(sessionId);
        try {
            session.sendMessage(new TextMessage(message));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
自定义拦截器：

public class WebSocketInterceptor implements HandshakeInterceptor {

    /**
     * handler处理前调用,attributes属性最终在WebSocketSession里,可能通过webSocketSession.getAttributes().get(key值)获得
     */
    @Override
    public boolean beforeHandshake(ServerHttpRequest request, ServerHttpResponse response, WebSocketHandler wsHandler, Map<String, Object> attributes) {
        if (request instanceof ServletServerHttpRequest) {
            ServletServerHttpRequest serverHttpRequest = (ServletServerHttpRequest) request;
            // 获取请求路径携带的参数
            String user = serverHttpRequest.getServletRequest().getParameter("user");
            attributes.put("user", user);
            return true;
        } else {
            return false;
        }
    }

    @Override
    public void afterHandshake(ServerHttpRequest request, ServerHttpResponse response, WebSocketHandler wsHandler, Exception exception) {

    }
}
2、前端连接webSocket
WebSocket对象是H5新增的对象，低版本浏览器可能不支持，可以使用sockJs的方式连接

webSocket连接
// 打开一个 web socket
var ws = new WebSocket("ws://localhost:8080/websocket?user=Tony");
ws.onopen = function() {
    // Web Socket 已连接上，使用 send() 方法发送数据
    ws.send("测试发送");
    console.log('open');
};
ws.onmessage = function (e) { 
    console.log('message', e.data);
};
ws.onclose = function() { 
    console.log('close');
};
sockJs连接
<script src="//cdn.jsdelivr.net/sockjs/1.0.0/sockjs.min.js"></script>

var sock = new SockJS('http://localhost:8080/sock-js?user=Tony');  
sock.onopen = function() {
    sock.send("测试发送");
    console.log('open');
};
sock.onmessage = function(e) {
    console.log('message', e.data);
};
sock.onclose = function() {
    console.log('close');
};
3、springCloud使用zuul转发webSocket连接
zuul网关还需要做额外的配置，添加自定义过滤器：

@Component
public class WebSocketFilter extends ZuulFilter {
    @Override
    public String filterType() {
        return "pre";
    }
    @Override
    public int filterOrder() {
        return 0;
    }
    @Override
    public boolean shouldFilter() {
        return true;
    }
    @Override
    public Object run() {
        RequestContext context = RequestContext.getCurrentContext();
        HttpServletRequest request = context.getRequest();
        String upgradeHeader = request.getHeader("Upgrade");
        if (null == upgradeHeader) {
            upgradeHeader = request.getHeader("upgrade");
        }
        if (null != upgradeHeader && "websocket".equalsIgnoreCase(upgradeHeader)) {
            context.addZuulRequestHeader("connection", "Upgrade");
        }
        return null;
    }
}
配置文件添加配置：

hystrix:
  command:
    default:
      execution:
        isolation:
          thread:
            timeoutInMilliseconds: 60000  #设置API网关中路由转发请求的HystrixCommand执行超时时间
ribbon:
  ConnectTimeout: 3000 #设置路由转发请求的时候，创建请求连接的超时时间
  ReadTimeout: 60000  #用来设置路由转发请求的超时时间
4、网关使用springCloud Gateway无需做任何处理
5、若使用了Nginx，需要添加配置
配置示例：

    map $http_upgrade $connection_upgrade {
        default upgrade;
        '' close;
    }

    # 网关只有一个，写一个网关地址就行了
    upstream [服务器组名] {
        server [IP地址]:[端口号];
        server [IP地址]:[端口号];
        ...
    }

    server {
        listen 80;
        location / {
            proxy_pass http://[服务器组名];
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection $connection_upgrade;
        }
    }
前端连接示例：

sockJs连接
<script src="//cdn.jsdelivr.net/sockjs/1.0.0/sockjs.min.js"></script>

var sock = new SockJS('http://(网关路径)/(服务名称)/sock-js?user=Tony');  
sock.onopen = function() {
    sock.send("测试发送");
    console.log('open');
};
sock.onmessage = function(e) {
    console.log('message', e.data);
};
sock.onclose = function() {
    console.log('close');
};
webSocket连接

// 打开一个 web socket
var ws = new WebSocket("ws://(网关路径)/(服务名称)/websocket?user=Tony");
ws.onopen = function() {
    // Web Socket 已连接上，使用 send() 方法发送数据
    ws.send("测试发送");
    console.log('open');
};
ws.onmessage = function (e) { 
    console.log('message', e.data);
};
ws.onclose = function() { 
    console.log('close');
};