Spring sseEmitter,在调用方法发送后不会立即发送事件

Question

我试图用Spring 4(tomcat 7,servlet-api 3.0.1)发送服务器发送的事件.

问题是Events在调用方法发送后我没有发送.它们都是在超时之后同时(具有相同的时间戳)到达客户端SseEmitter,带有EventSource错误事件.然后客户端正在尝试重新连接.知道发生了什么事吗？

我创建了一个简单的服务:

@RequestMapping(value = "subscribe", method = RequestMethod.GET)
public SseEmitter subscribe () throws IOException {
    final SseEmitter emitter = new SseEmitter();
    Executors.newScheduledThreadPool(1).scheduleAtFixedRate(new Runnable() {
        @Override
        public void run() {
            try {
                emitter.send(SseEmitter.event().data("Thread writing: " + Thread.currentThread()).name("ping"));
            } catch (Exception e) {
            }
        }
    } , 1000, 1000, TimeUnit.MILLISECONDS);
    return emitter;
}

使用客户代码:

sse = new EventSource(urlBuilder(base, url));
sse.addEventListener('ping', function (event) {
    dfd.notify(event);
});

sse.addEventListener('message', function(event){
    dfd.notify(event);
});

sse.addEventListener('close', function(event){
    dfd.notify(event);
});

sse.onerror = function (error) {
    console.log(error);
};

sse.onmessage = function (event){
    dfd.notify(event);
};

App initalizer代码

public class WebAppInitializer implements WebApplicationInitializer {
    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        AnnotationConfigWebApplicationContext ctx = new AnnotationConfigWebApplicationContext();
        ctx.register(AppConfig.class);
        ctx.setServletContext(servletContext);
        ctx.refresh();

        ServletRegistration.Dynamic dynamic = servletContext.addServlet("dispatcher", new DispatcherServlet(ctx));
        dynamic.setAsyncSupported(true);
        dynamic.addMapping("/api/*");
        dynamic.setLoadOnStartup(1);
        dynamic.setMultipartConfig(ctx.getBean(MultipartConfigElement.class));

        javax.servlet.FilterRegistration.Dynamic filter = servletContext
                .addFilter("StatelessAuthenticationFilter",
                        ctx.getBean("statelessAuthenticationFilter", StatelessAuthenticationFilter.class));
        filter.setAsyncSupported(true);
        filter.addMappingForUrlPatterns(null, false, "/api/*");

        filter = servletContext.addFilter("HibernateSessionRequestFilter",
                ctx.getBean("hibernateSessionRequestFilter", HibernateSessionRequestFilter.class));
        filter.setAsyncSupported(true);
        filter.addMappingForUrlPatterns(null, false, "/api/user/*");
    }
}

AppConfig.java

@Configuration
@ComponentScan("ru.esoft.workflow")
@EnableWebMvc
@PropertySource({"classpath:mail.properties", "classpath:fatclient.properties"})
@EnableAsync
@EnableScheduling
public class AppConfig extends WebMvcConfigurerAdapter {
...
}

我的客户日志的图片:

Answer 1

我自己在测试 SSEEmitter 时遇到了这个问题。从我在线阅读的所有内容来看，SSEEmitters 旨在与Reactive Streams的某些实现结合使用，例如RxJava。这有点复杂，但它绝对有效。这个想法是，您创建发射器和一个 Observable，并将后者订阅到 Publisher。Publisher 在单独的线程中执行其行为，当输出准备好时通知 Observable，并且 observable 会触发 emitter.send。这是一个示例片段，应该可以完成您想要的操作：

@RequestMapping("/whatever")
public SseEmitter index(    
    SseEmitter emitter = new SseEmitter();
    Publisher<String> responsePublisher = someResponseGenerator.getPublisher();
    Observable<String> responseObservable = RxReactiveStreams.toObservable(responsePublisher);

    responseObservable.subscribe(
        str -> {
            try {
                emitter.send(str);
            } catch (IOException ex) {
                emitter.completeWithError(ex);
            }
        },
        error -> {
            emitter.completeWithError(error);
        },
        emitter::complete
        );

        return emitter;
};

这是相应的发布者：

public class SomeResponseGenerator {    
    public Publisher<String> getPublisher() {
        Publisher<String> pub = new Publisher<String>() {
            @Override
            public void subscribe(Subscriber subscriber) {
                Executors.newScheduledThreadPool(1).scheduleAtFixedRate(new Runnable() {
                    @Override
                    public void run() {
                        subscriber.onNext("Thread writing: " + Thread.currentThread().getName());
                    }
                }, 1000, 1000, TimeUnit.MILLISECONDS);
            }
        };

        return pub;
    }
}

这里和这里在线有一些此模型的示例，您可以通过谷歌搜索“RxJava SseEmitter”找到更多信息。理解 Reactive Streams/RxJava/SseEmitter 交互需要一些时间，但一旦你做到了，它就非常优雅了。希望这能让您走上正确的道路！