Spring HTTP Streaming

參考: https://www.jianshu.com/p/ecc6f5168aef

參考: https://www.logicbig.com/tutorials/spring-framework/spring-web-mvc/http_streaming.html

簡介:

控制器可以使用DeferredResult或Callable對象來異步地計算其返回值，這可以用於實現一些有用的技術，比如 long polling技術，讓服務器可以儘可能快地向客戶端推送事件。

如果你想在一個HTTP響應中同時推送多個事件，怎麼辦？這樣的技術已經存在，與"Long Polling"相關，叫"HTTP Streaming"。

Spring MVC支持這項技術，你可以通過讓方法返回一個ResponseBodyEmitter類型對象來實現，該對象可被用於發送多個對象。通常我們所使用的@ResponseBody只能返回一個對象，它是通過HttpMessageConverter寫到響應體中的。

實體:

1. ResponseBodyEmitter

2. SseEmitter

例子:

@RequestMapping("/test")
    public ResponseBodyEmitter test() {
        ResponseBodyEmitter emitter = new ResponseBodyEmitter();
        ExecutorService service = Executors.newSingleThreadExecutor();
//        ExecutorService service = Executors.newFixedThreadPool(10);
        service.execute(()-> {
            for (int i = 0; i < 100 ; i++) {
                try {
                    emitter.send(i+"-", MediaType.ALL);
                    Thread.sleep(100L);
                } catch (IOException | InterruptedException e) {
                    e.printStackTrace();
                    emitter.completeWithError(e);
                    return;
                }
            }
            emitter.complete();
        });

        return emitter;
    }

2. SseEmitter 和對應的HTML5 中的Server-Sent Events 特性,互相對應,sse 通道才能實現 服務器端主動向客戶端推送數據

參考: https://www.cnblogs.com/elonlee/p/3914704.html

例子:

package com.kzcm.controller;

import com.kzcm.entity.User;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
@RequestMapping("index")
public class IndexController {


    @RequestMapping("testSse")
    public String testSse(ModelMap model) {
        String path = "index/ssedemo";
//        model.addAttribute("name", name);
        return path;
    }
}

跳轉到 index/ssedemo 目錄下

如圖示,EventSource 訪問路徑爲 /async/testSse

package com.kzcm.controller;

import org.springframework.http.MediaType;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.context.request.async.DeferredResult;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyEmitter;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

import java.io.IOException;
import java.time.LocalTime;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

@Controller
@RequestMapping("/async")
public class AsyncController {


    

    @RequestMapping("/testSse")
    public SseEmitter testSse() {
        SseEmitter emitter = new SseEmitter();
        ExecutorService service = Executors.newSingleThreadExecutor();
//        ExecutorService service = Executors.newFixedThreadPool(10);
        service.execute(()-> {
            for (int i = 0; i < 5 ; i++) {
                try {
                    emitter.send(LocalTime.now().toString(), MediaType.ALL);
                    Thread.sleep(10);
                } catch (IOException | InterruptedException e) {
                    e.printStackTrace();
                    emitter.completeWithError(e);
                    return;
                }
            }
            emitter.complete();
        });

        return emitter;
    }
}

最後結果就像輪詢一樣,隔一段時間訪問一下 event 接口,