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长轮询，iframe和sse三种web消息实时推送demo实践

2022-07-28 18:10:00 【Fire king】

长轮询，iframe和sse三种web消息实时推送demo实践

长轮询

@Controller
@RequestMapping("/polling")
public class PollingController {
    

    private static final Long TIME_OUT = 10000l;
    // 存放监听某个Id的长轮询集合
    // 线程同步结构
    public static Multimap<String, DeferredResult<String>> watchRequests = Multimaps.synchronizedMultimap(HashMultimap.create());

    /** * * 设置监听 */
    @GetMapping(path = "watch/{id}")
    @ResponseBody
    public DeferredResult<String> watch(@PathVariable String id) {
    
        // 延迟对象设置超时时间
        DeferredResult<String> deferredResult = new DeferredResult<>(TIME_OUT);
        // 异步请求完成时移除 key，防止内存溢出
        deferredResult.onCompletion(() -> {
    
            watchRequests.remove(id, deferredResult);
        });
        // 注册长轮询请求
        watchRequests.put(id, deferredResult);
        return deferredResult;
    }

    /** * * 变更数据 */
    @GetMapping(path = "publish/{id}")
    @ResponseBody
    public String publish(@PathVariable String id) {
    
        // 数据变更 取出监听ID的所有长轮询请求(多个浏览器，单个浏览器不同窗口只认为一个，每次publish只响改变一个)，并一一响应处理
        if (watchRequests.containsKey(id)) {
    
            Collection<DeferredResult<String>> deferredResults = watchRequests.get(id);
            System.out.println(deferredResults.size());
            for (DeferredResult<String> deferredResult : deferredResults) {
    
                //只要set，就认为改变了
                deferredResult.setResult("我更新了" + new Date());
            }
        }
        return "success";
    }
    //当请求超过设置的超时时间，会抛出AsyncRequestTimeoutException异常，这里直接用@ControllerAdvice全局捕获统一返回即可，前端获取约定好的状态码后再次发起长轮询请求，如此往复调用。

    @ControllerAdvice
    public class AsyncRequestTimeoutHandler {
    

        @ResponseStatus(HttpStatus.NOT_MODIFIED)
        @ResponseBody
        @ExceptionHandler(AsyncRequestTimeoutException.class)
        public String asyncRequestTimeoutHandler(AsyncRequestTimeoutException e) {
    
            System.out.println("异步请求超时");
            return "304";
        }
    }
}

iframe

IframeController

@Controller
@RequestMapping("/iframe")
public class IframeController {
    
    @GetMapping(path = "message")
    public void message(HttpServletResponse response) throws IOException, InterruptedException {
    
       int count = 0;
        while (true) {
    
            count++;
            response.setHeader("Pragma", "no-cache");
            response.setDateHeader("Expires", 0);
            response.setHeader("Cache-Control", "no-cache,no-store");
            response.setStatus(HttpServletResponse.SC_OK);
            response.getWriter().print(" <script type=\"text/javascript\">\n" +
                    "parent.document.getElementById('clock').innerHTML = \"" + count + "\";" +
                    "parent.document.getElementById('count').innerHTML = \"" + count + "\";" +
                    "</script>");
        }
    }

    @GetMapping(path = "toIframePage")
    public String toIframePage() {
    
        return "/iframe";
    }
}

iframe.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>iframe长轮询</title>
</head>
<body>
<iframe src="/iframe/message" style="display:none"></iframe>
<h1 id="clock"></h1>
<h1 id="count"></h1>
</body>
</html>

sse

SseEmitterServer

@Slf4j
public class SseEmitterServer {
    
    private static Map<String, SseEmitter> sseEmitterMap = new ConcurrentHashMap<>();
    /** * 当前连接数 */
    private static AtomicInteger count = new AtomicInteger(0);
    /** * 创建连接 * * @date: 2022/7/12 14:51 * @auther: */
    public static SseEmitter connect(String userId) {
    
        try {
    
            // 设置超时时间，0表示不过期。默认30秒
            SseEmitter sseEmitter = new SseEmitter(0L);
            // 注册回调
            sseEmitter.onCompletion(completionCallBack(userId));
            sseEmitter.onError(errorCallBack(userId));
            sseEmitter.onTimeout(timeoutCallBack(userId));
            sseEmitterMap.put(userId, sseEmitter);
            count.getAndIncrement();
                return sseEmitter;
        } catch (Exception e) {
    
            log.info("创建新的sse连接异常，当前用户：{}", userId);
        }
        return null;
    }

    private static Consumer<Throwable> errorCallBack(String userId) {
    
        return throwable -> {
    
            log.info("连接异常：{}", userId);
            removeUser(userId);
        };
    }

    private static Runnable timeoutCallBack(String userId) {
    
        return () -> {
    
            log.info("连接超时：{}", userId);
            removeUser(userId);
        };
    }

    private static Runnable completionCallBack(String userId) {
    
        return () -> {
    
            log.info("结束连接：{}", userId);
            removeUser(userId);
        };
    }

    public static void removeUser(String userId) {
    
        sseEmitterMap.remove(userId);
        // 数量-1
        count.getAndDecrement();
        log.info("移除用户：{}", userId);
    }

    /** * 给指定用户发送消息 * * @date: 2022/7/12 14:51 * @auther: */
    public static void sendMessage(String userId, String message) {
    

        if (sseEmitterMap.containsKey(userId)) {
    
            try {
    
                sseEmitterMap.get(userId).send(message);
                //不同SpringBoot的版本可能要加
                // sseEmitterMap.get(userId).complete();
            } catch (IOException e) {
    
                log.error("用户[{}]推送异常:{}", userId, e.getMessage());
                removeUser(userId);
            }
        }
    }
}

SseEmitterController

@CrossOrigin
@RestController
@RequestMapping("/sse")
public class SseEmitterController {
    
    /** * 用于创建连接 */
    @GetMapping("/connect/{userId}")
    public SseEmitter connect(@PathVariable String userId) {
    
        return SseEmitterServer.connect(userId);
    }

    /** * 推送给所有人 * * @param message * @return */
   /* @GetMapping("/push/{message}") public ResponseEntity<String> push(@PathVariable(name = "message") String message) { SseEmitterServer.batchSendMessage(message); return ResponseEntity.ok("WebSocket 推送消息给所有人"); }*/

    /** * 发送给单个人 * * @param message * @param userid * @return */
    @RequestMapping("/push_one")
    public ResponseEntity<String> pushOne( String message,  String userid) {
    
        SseEmitterServer.sendMessage(userid, message);
        return ResponseEntity.ok("WebSocket 推送消息给" + userid);
    }

    /** * 关闭连接 */
    @GetMapping("/close/{userid}")
    public ResponseEntity<String> close(@PathVariable("userid") String userid) {
    
        SseEmitterServer.removeUser(userid);
        return ResponseEntity.ok("连接关闭");
    }

}

PageController

@Controller
public class PageController {
    

    @RequestMapping("/toSsePage")
    public String toSsePage() {
    
        return "/sse";
    }
}

sse.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>SseEmitter</title>
</head>

<body>
<button onclick="closeSse()">关闭连接</button>
<div id="message"></div>
</body>
<script> let source = null; // 用时间戳模拟登录用户 //const userId = new Date().getTime(); const userId = "1"; if (window.EventSource) {
       // 建立连接 source = new EventSource('http://localhost:8080/sse/connect/' + userId); /** * 连接一旦建立，就会触发open事件 * 另一种写法：source.onopen = function (event) {} */ source.addEventListener('open', function(e) {
       setMessageInnerHTML("建立连接。。。"); }, false); /** * 客户端收到服务器发来的数据 * 另一种写法：source.onmessage = function (event) {} */ source.addEventListener('message', function(e) {
       setMessageInnerHTML(e.data); }); /** * 如果发生通信错误（比如连接中断），就会触发error事件 * 或者： * 另一种写法：source.onerror = function (event) {} */ source.addEventListener('error', function(e) {
       if (e.readyState === EventSource.CLOSED) {
       setMessageInnerHTML("连接关闭"); } else {
       console.log(e); } }, false); } else {
       setMessageInnerHTML("你的浏览器不支持SSE"); } // 监听窗口关闭事件，主动去关闭sse连接，如果服务端设置永不过期，浏览器关闭后手动清理服务端数据 window.onbeforeunload = function() {
       closeSse(); }; // 关闭Sse连接 function closeSse() {
       source.close(); const httpRequest = new XMLHttpRequest(); httpRequest.open('GET', 'http://localhost:8080/sse/close/' + userId, true); httpRequest.send(); console.log("close"); } // 将消息显示在网页上 function setMessageInnerHTML(innerHTML) {
       document.getElementById('message').innerHTML += innerHTML + '<br/>'; } </script>

</html>