使用SseEmitter不断向网页输出结果

序

之前写过一篇文章：springmvc不断输出文本到网页，采用的是对response不断进行write和flush实现的。在spring 4.2版本的时候提供了一个SseEmitter可以直接用来实现这个功能。

实例

@Controller
@RequestMapping("/sse")
public class SseEmitterController {

    private static final Logger LOGGER = LoggerFactory.getLogger(SseEmitterController.class);

    @Autowired
    @Qualifier("mvcTaskExecutor")
    ThreadPoolTaskExecutor mvcTaskExecutor;

    @GetMapping("")
    public SseEmitter sseDemo() throws InterruptedException {
        final SseEmitter emitter = new SseEmitter(0L); //timeout设置为0表示不超时
        mvcTaskExecutor.execute(() -> {
            try {
                for(int i=0;i<100;i++){
                    emitter.send("hello"+i);
                    LOGGER.info("emit:{}","hello"+i);
                    Thread.sleep(1000*1);
                }
                emitter.complete();
            } catch (Exception e) {
                emitter.completeWithError(e);
            }
        });
        return emitter;
    }
}

输出实例

data:"hello0"

data:"hello1"

data:"hello2"

data:"hello3"

data:"hello4"

data:"hello5"

//......

注意事项

• 这里的SseEmitter的send不能阻塞mvc线程，必须提前返回，然后把send放到异步里头

除了使用上述的放入线程池的方式，也可以直接调用标记有async的方法

• 这里SseEmitter的timeout设置为0，表示不超时.
  如果不设置为0，那么如果SseEmitter在指定的时间（AsyncSupportConfigurer设置的timeout,默认为30秒)未完成会抛出异常

org.springframework.web.context.request.async.AsyncRequestTimeoutException: null
    at org.springframework.web.context.request.async.TimeoutDeferredResultProcessingInterceptor.handleTimeout(TimeoutDeferredResultProcessingInterceptor.java:42) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE]
    at org.springframework.web.context.request.async.DeferredResultInterceptorChain.triggerAfterTimeout(DeferredResultInterceptorChain.java:75) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE]
    at org.springframework.web.context.request.async.WebAsyncManager$5.run(WebAsyncManager.java:392) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE]
    at org.springframework.web.context.request.async.StandardServletAsyncWebRequest.onTimeout(StandardServletAsyncWebRequest.java:143) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE]
    at org.apache.catalina.core.AsyncListenerWrapper.fireOnTimeout(AsyncListenerWrapper.java:44) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.core.AsyncContextImpl.timeout(AsyncContextImpl.java:134) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.connector.CoyoteAdapter.asyncDispatch(CoyoteAdapter.java:153) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.coyote.AbstractProcessor.dispatch(AbstractProcessor.java:224) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:53) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1455) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_71]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_71]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at java.lang.Thread.run(Thread.java:745) [na:1.8.0_71]

小结

SseEmitter在运行比较耗时的任务时非常好用，比如实时查看部署进度，比如查看定时任务的实时输出等。

doc

• SseEmitter
• springmvc不断输出文本到网页
• 实现后台长时间任务的监控
• 理解Spring MVC中的异步处理请求（下）