DeferredResult使用方式和场景

时间：2019-05-17 19:31:38 阅读：811 评论：0 收藏：0 [点我收藏+]

标签：deferred ash col 处理 fail equals 推送 Servle autowired

为什么使用DeferredResult？

当一个请求到达API接口，如果该API接口的return返回值是DeferredResult，在没有超时或者DeferredResult对象设置setResult时，接口不会返回，但是Servlet容器线程会结束，DeferredResult另外会有线程来进行结果处理，并setResult，如此以来这个请求不会占用服务连接池太久，如果超时或设置setResult，接口会立即返回。

使用DeferredResult的流程：

浏览器发起异步请求
请求到达服务端被挂起
向浏览器进行响应，分为两种情况：
3.1 调用DeferredResult.setResult()，请求被唤醒，返回结果
3.2 超时，返回一个你设定的结果
浏览得到响应，再次重复1，处理此次响应结果

给人一种异步处理业务，但是却同步返回的感觉。

场景

浏览器向A系统发起请求，A系统需要等到B系统给A推送数据时，A才会立刻向浏览器返回数据。

Demo代码

接口代码：

/get是调用A系统的接口返回数据；

/result模拟B系统向A推送数据进行setResult。

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.context.request.async.DeferredResult;


@RestController
@RequestMapping(value = "/deferred-result")
public class DeferredResultController {

    @Autowired
    private DeferredResultService deferredResultService;

    /**
     * 为了方便测试，简单模拟一个
     * 多个请求用同一个requestId会出问题
     */
    private final String requestId = "haha";


    @GetMapping(value = "/get")
    public DeferredResult<DeferredResultResponse> get(@RequestParam(value = "timeout", required = false, defaultValue = "10000") Long timeout) {
        DeferredResult<DeferredResultResponse> deferredResult = new DeferredResult<>(timeout);

        deferredResultService.process(requestId, deferredResult);

        return deferredResult;
    }

    /**
     * 设置DeferredResult对象的result属性，模拟异步操作
     * @param desired
     * @return
     */
    @GetMapping(value = "/result")
    public String settingResult(@RequestParam(value = "desired", required = false, defaultValue = "成功") String desired) {
        DeferredResultResponse deferredResultResponse = new DeferredResultResponse();
        if (DeferredResultResponse.Msg.SUCCESS.getDesc().equals(desired)){
            deferredResultResponse.setCode(HttpStatus.OK.value());
            deferredResultResponse.setMsg(desired);
        }else{
            deferredResultResponse.setCode(HttpStatus.INTERNAL_SERVER_ERROR.value());
            deferredResultResponse.setMsg(DeferredResultResponse.Msg.FAILED.getDesc());
        }
        deferredResultService.settingResult(requestId, deferredResultResponse);

        return "Done";
    }
}

import org.springframework.http.HttpStatus;
import org.springframework.stereotype.Service;
import org.springframework.web.context.request.async.DeferredResult;

import java.util.Map;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Consumer;

@Service
public class DeferredResultService {

    private Map<String, Consumer<DeferredResultResponse>> taskMap;

    public DeferredResultService() {
        taskMap = new ConcurrentHashMap<>();
    }

    /**
     * 将请求id与setResult映射
     *
     * @param requestId
     * @param deferredResult
     */
    public void process(String requestId, DeferredResult<DeferredResultResponse> deferredResult) {
        // 请求超时的回调函数
        deferredResult.onTimeout(() -> {
            taskMap.remove(requestId);
            DeferredResultResponse deferredResultResponse = new DeferredResultResponse();
            deferredResultResponse.setCode(HttpStatus.REQUEST_TIMEOUT.value());
            deferredResultResponse.setMsg(DeferredResultResponse.Msg.TIMEOUT.getDesc());
            deferredResult.setResult(deferredResultResponse);
        });

        Optional.ofNullable(taskMap)
                .filter(t -> !t.containsKey(requestId))
                .orElseThrow(() -> new IllegalArgumentException(String.format("requestId=%s is existing", requestId)));

        // 这里的Consumer，就相当于是传入的DeferredResult对象的地址
        // 所以下面settingResult方法中"taskMap.get(requestId)"就是Controller层创建的对象
        taskMap.putIfAbsent(requestId, deferredResult::setResult);
    }

    /**
     * 这里相当于异步的操作方法
     * 设置DeferredResult对象的setResult方法
     *
     * @param requestId
     * @param deferredResultResponse
     */
    public void settingResult(String requestId, DeferredResultResponse deferredResultResponse) {
        if (taskMap.containsKey(requestId)) {
            Consumer<DeferredResultResponse> deferredResultResponseConsumer = taskMap.get(requestId);
            // 这里相当于DeferredResult对象的setResult方法
            deferredResultResponseConsumer.accept(deferredResultResponse);
            taskMap.remove(requestId);
        }
    }

}

import lombok.Data;
import lombok.Getter;

@Data
public class DeferredResultResponse {
    private Integer code;
    private String msg;

    public enum Msg {
        TIMEOUT("超时"),
        FAILED("失败"),
        SUCCESS("成功");

        @Getter
        private String desc;

        Msg(String desc) {
            this.desc = desc;
        }
    }
}