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.