服务器端实时推送技术之SseEmitter的用法

这是SpringMVC提供的一种技术,可以实现服务端向客户端实时推送数据.用法非常简单,只需要在Controller提供一个接口,创建并返回SseEmitter对象,发送数据可以在另一个接口调用其send方法发送数据.这个SseEmitter对象和DeferredResult有异曲同工之妙,只是SseEmitter可以在一次请求中返回多条数据,而DeferredResult只能返回一条.关于DeferredResult的用法请求参考我的另一篇博客:https://www.cnblogs.com/jun1019/p/10807055.html

 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

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

 /**
  * 服务器端实时推送技术之 SseEmitter 的用法测试
  * <p>
  * 测试步骤:
  * 1.请求http://localhost:8888/sse/start?clientId=111接口,浏览器会阻塞,等待服务器返回结果;
  * 2.请求http://localhost:8888/sse/send?clientId=111接口,可以请求多次,并观察第1步的浏览器返回结果;
  * 3.请求http://localhost:8888/sse/end?clientId=111接口结束某个请求,第1步的浏览器将结束阻塞;
  * 其中clientId代表请求的唯一标志;
  *
  * @author syj
  */
 @RestController
 @RequestMapping("/sse")
 public class SseEmitterController {
     private static final Logger logger = LoggerFactory.getLogger(SseEmitterController.class);

     // 用于保存每个请求对应的 SseEmitter
     private Map<String, Result> sseEmitterMap = new ConcurrentHashMap<>();

     /**
      * 返回SseEmitter对象
      *
      * @param clientId
      * @return
      */
     @RequestMapping("/start")
     public SseEmitter testSseEmitter(String clientId) {
         // 默认30秒超时,设置为0L则永不超时
         SseEmitter sseEmitter = new SseEmitter(0L);
         sseEmitterMap.put(clientId, new Result(clientId, System.currentTimeMillis(), sseEmitter));
         return sseEmitter;
     }

     /**
      * 向SseEmitter对象发送数据
      *
      * @param clientId
      * @return
      */
     @RequestMapping("/send")
     public String setSseEmitter(String clientId) {
         try {
             Result result = sseEmitterMap.get(clientId);
             if (result != null && result.sseEmitter != null) {
                 long timestamp = System.currentTimeMillis();
                 result.sseEmitter.send(timestamp);
             }
         } catch (IOException e) {
             logger.error("IOException!", e);
             return "error";
         }

         return "Succeed!";
     }

     /**
      * 将SseEmitter对象设置成完成
      *
      * @param clientId
      * @return
      */
     @RequestMapping("/end")
     public String completeSseEmitter(String clientId) {
         Result result = sseEmitterMap.get(clientId);
         if (result != null) {
             sseEmitterMap.remove(clientId);
             result.sseEmitter.complete();
         }
         return "Succeed!";
     }

     private class Result {
         public String clientId;
         public long timestamp;
         public SseEmitter sseEmitter;

         public Result(String clientId, long timestamp, SseEmitter sseEmitter) {
             this.clientId = clientId;
             this.timestamp = timestamp;
             this.sseEmitter = sseEmitter;
         }
     }
 }

这个技术有什么用呢? 就看你的想象力了, 比如可以用于和进度有关的操作: 安装进度, 部署进度, 任务执行进度等等.