Java中基于DeferredResult的异步服务详解

DeferredResult<String> deferredResult = new DeferredResult<String>(5 * 1000L);
// 设置超时事件
deferredResult.onTimeout(() -> {
    System.out.println("异步线程执行超时, 异步线程的名称: " + Thread.currentThread().getName());
    deferredResult.setResult("异步线程执行超时");
});

DeferredResult<String> deferredResult = new DeferredResult<String>(5 * 1000L);
// 设置异常事件
deferredResult.onError((throwable) -> {
    System.out.println("异步请求出现错误，异步线程的名称: " + Thread.currentThread().getName() + "异常: " + throwable);
    deferredResult.setErrorResult("异步线程执行出错");
});

DeferredResult<String> deferredResult = new DeferredResult<String>(5 * 1000L);
// 设置完成事件
deferredResult.onCompletion(() -> {
    System.out.println("异步线程执行完毕，异步线程的名称: " + Thread.currentThread().getName());
});

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.context.request.async.DeferredResult;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
@RestController
public class DemoController {
    // 自定义线程池
    public static ExecutorService exec = Executors.newCachedThreadPool();
    @GetMapping("/demo")
    public DeferredResult<String> demoResult() {
        System.out.println("容器线程: " + Thread.currentThread().getName());
        // 创建DeferredResult对象，设置超时时长 20秒
        DeferredResult<String> deferredResult = new DeferredResult<String>(5 * 1000L);
        // 设置超时事件
        deferredResult.onTimeout(() -> {
            System.out.println("异步线程执行超时, 异步线程的名称: " + Thread.currentThread().getName());
            // throw new RuntimeException("超时事件报错了！");
            deferredResult.setResult("异步线程执行超时");
        });
        // 设置异常事件
        deferredResult.onError((throwable) -> {
            System.out.println("异步请求出现错误，异步线程的名称: " + Thread.currentThread().getName() + "异常: " + throwable);
            deferredResult.setErrorResult("异步线程执行出错");
        });
        // 设置完成事件
        deferredResult.onCompletion(() -> {
            System.out.println("异步线程执行完毕，异步线程的名称: " + Thread.currentThread().getName());
        });
        exec.execute(() -> {
            System.out.println("[线程池] 异步线程的名称: " + Thread.currentThread().getName());
            deferredResult.setResult("异步线程执行完毕");
        });
        System.out.println("Servlet thread release");
        return deferredResult;
    }
}

@SpringBootApplication
public class DemoApplication implements WebMvcConfigurer {
 
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

 
import com.google.common.collect.HashMultimap;
import com.google.common.collect.Multimap;
import com.google.common.collect.Multimaps;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.context.request.async.DeferredResult;
import java.util.Collection;
@RestController
public class ApolloController {
    private final Logger logger = LoggerFactory.getLogger(this.getClass());
    //guava中的Multimap，多值map,对map的增强，一个key可以保持多个value
    private Multimap<String, DeferredResult<String>> watchRequests = Multimaps.synchronizedSetMultimap(HashMultimap.create());
    //模拟长轮询
    @RequestMapping(value = "/watch/{namespace}", method = RequestMethod.GET, produces = "text/html")
    public DeferredResult<String> watch(@PathVariable("namespace") String namespace) {
        logger.info("Request received");
        DeferredResult<String> deferredResult = new DeferredResult<>();
        //当deferredResult完成时（不论是超时还是异常还是正常完成），移除watchRequests中相应的watch key
        deferredResult.onCompletion(new Runnable() {
            @Override
            public void run() {
                System.out.println("remove key:" + namespace);
                watchRequests.remove(namespace, deferredResult);
            }
        });
        watchRequests.put(namespace, deferredResult);
        logger.info("Servlet thread released");
        return deferredResult;
    }
    //模拟发布namespace配置
    @RequestMapping(value = "/publish/{namespace}", method = RequestMethod.GET, produces = "text/html")
    public Object publishConfig(@PathVariable("namespace") String namespace) {
        if (watchRequests.containsKey(namespace)) {
            Collection<DeferredResult<String>> deferredResults = watchRequests.get(namespace);
            Long time = System.currentTimeMillis();
            //通知所有watch这个namespace变更的长轮训配置变更结果
            for (DeferredResult<String> deferredResult : deferredResults) {
                deferredResult.setResult(namespace + " changed:" + time);
            }
        }
        return "success";
    }
}

 
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.context.request.async.AsyncRequestTimeoutException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@ControllerAdvice
class GlobalControllerExceptionHandler {
    protected static final Logger logger = LoggerFactory.getLogger(GlobalControllerExceptionHandler.class);
    @ResponseStatus(HttpStatus.NOT_MODIFIED)//返回304状态码
    @ResponseBody
    @ExceptionHandler(AsyncRequestTimeoutException.class) //捕获特定异常
    public void handleAsyncRequestTimeoutException(AsyncRequestTimeoutException e, HttpServletRequest request) {
        System.out.println("handleAsyncRequestTimeoutException");
    }
}