本篇文章给大家分享的是有关java中怎么实现异步处理,小编觉得挺实用的,因此分享给大家学习,希望大家阅读完这篇文章后可以有所收获,话不多说,跟着小编一起来看看吧。
1.DeferredResult 加线程池 (DeferredResult 提供了超时、错误处理,功能非常完善,再加上多线程处理请求效果很不错)
2.新开个定时任务线程池 定时轮询当前任务列表 超时就停止(需要自己维护任务列表)Hystrix就是这种方案
3.JDK9 可以采用CompletableFuture orTimeout、completeOnTimeout 方法处理 前者抛出异常后者返回默认值
总结,其实线程池统一设置超时这个需求本身就是伪需求,线程执行任务时间本身就是参差不齐的,而且这个控制权应该交给Runable或Callable内部业务处理,不同的业务处理超时、异常、报警等各不相同。CompletableFuture、ListenableFuture 、DeferredResult 的功能相当丰富,建议在多线程处理的场景多使用这些api。
具体实现:
DeferredResult 先建个工具类。调用方使用execute方法,传入new的DeferredResultDTO(DeferredResultDTO只有msgId,也可以自定义一些成员变量方便后期业务扩展使用)
然后在其他线程业务处理完设置结果,调用setResult方法,传入msgId相同的DeferredResultDTO和result对象
/**
* DeferredResult 工具类
*
* @author tiancong
* @date 2020/10/14 19:23
*/
@UtilityClass
@Slf4j
public class DeferredResultUtil {
private Map<DeferredResultDTO, DeferredResult<ResultVO<Object>>> taskMap = new ConcurrentHashMap<>(16);
public DeferredResult<ResultVO<Object>> execute(DeferredResultDTO dto) {
return execute(dto, 5000L);
}
public DeferredResult<ResultVO<Object>> execute(DeferredResultDTO dto, Long time) {
if (taskMap.containsKey(dto)) {
throw new BusinessException(String.format("msgId=%s 已经存在,请勿重发消息", dto.getMsgId()));
}
DeferredResult<ResultVO<Object>> deferredResult = new DeferredResult<>(time);
deferredResult.onError((e) -> {
taskMap.remove(dto);
log.info("处理失败 ", e);
deferredResult.setResult(ResultVoUtil.fail("处理失败"));
});
deferredResult.onTimeout(() -> {
taskMap.remove(dto);
if (dto.getType().equals(DeferredResultTypeEnum.CLOTHES_DETECTION)) {
ExamController.getCURRENT_STUDENT().remove(dto.getMsgId());
}
deferredResult.setResult(ResultVoUtil.fail("请求超时,请联系工作人员!"));
});
taskMap.putIfAbsent(dto, deferredResult);
return deferredResult;
}
public void setResult(DeferredResultDTO dto, ResultVO<Object> resultVO) {
if (taskMap.containsKey(dto)) {
DeferredResult<ResultVO<Object>> deferredResult = taskMap.get(dto);
deferredResult.setResult(resultVO);
taskMap.remove(dto);
} else {
log.error("ERROR 未找到该消息msgId:{}", dto.getMsgId());
}
}
}
2. 新开个定时任务线程池 定时轮询当前任务列表
/**
* @author tiancong
* @date 2021/4/10 11:06
*/
@Slf4j
public class T {
private static final ScheduledExecutorService scheduler =
Executors.newScheduledThreadPool(
2,
r -> {
Thread thread = new Thread(r);
thread.setName("failAfter-%d");
thread.setDaemon(true);
return thread;
});
private static int timeCount;
public static void main(String[] args) throws InterruptedException {
ThreadPoolTaskExecutor executorService = new ThreadPoolTaskExecutor();
executorService.setCorePoolSize(4);
executorService.setQueueCapacity(10);
executorService.setMaxPoolSize(100);
executorService.initialize();
// executorService.setAwaitTerminationSeconds(5);
// executorService.getThreadPoolExecutor().awaitTermination(3, TimeUnit.SECONDS);
executorService.setWaitForTasksToCompleteOnShutdown(true);
Random random = new Random();
long start = System.currentTimeMillis();
List<ListenableFuture<Boolean>> asyncResultList = new ArrayList<>();
for (int i = 0; i < 100; i++) {
ListenableFuture<Boolean> asyncResult = executorService.submitListenable(() -> {
int r = random.nextInt(10);
log.info("{} 开始睡{}s", Thread.currentThread().getName(), r);
TimeUnit.SECONDS.sleep(r);
log.info("{} 干完了 {}s", Thread.currentThread().getName(), r);
//throw new RuntimeException("出现异常");
return true;
});
asyncResult.addCallback(data -> {
try {
// 休息3毫秒模拟获取到执行结果后的操作
TimeUnit.MILLISECONDS.sleep(3);
log.info("{} 收到结果:{}", Thread.currentThread().getName(), data);
} catch (Exception e) {
e.printStackTrace();
}
}, ex -> log.info("**异常信息**", ex));
asyncResultList.add(asyncResult);
}
System.out.println(String.format("总结耗时:%s ms", System.currentTimeMillis() - start));
// 守护进程 定时轮询 终止超时的任务
scheduler.scheduleAtFixedRate(() -> {
// 模拟守护进程 终止超过6s的任务
timeCount++;
if (timeCount > 6) {
for (ListenableFuture<Boolean> future : asyncResultList) {
if (!future.isDone()) {
log.error("future 因超时终止任务,{}", future);
future.cancel(true);
}
}
}
}, 0, 1000, TimeUnit.MILLISECONDS);
}
}
额外补充:
CompletableFuture实现了CompletionStage接口,里面很多丰富的异步编程接口。
applyToEither方法是哪个先完成,就apply哪一个结果(但是两个任务都会最终走完)
/**
* @author tiancong
* @date 2021/4/10 11:06
*/
@Slf4j
public class T {
public static void main(String[] args) throws InterruptedException {
// CompletableFuture<String> responseFuture = within(
// createTaskSupplier("5"), 3000, TimeUnit.MILLISECONDS);
// responseFuture
// .thenAccept(T::send)
// .exceptionally(throwable -> {
// log.error("Unrecoverable error", throwable);
// return null;
// });
//
// 注意 exceptionally是new 的CompletableFuture
CompletableFuture<Object> timeoutCompletableFuture = timeoutAfter(1000, TimeUnit.MILLISECONDS).exceptionally(xxx -> "超时");
// 异步任务超时、异常处理
List<Object> collect = Stream.of("1", "2", "3", "4", "5", "6", "7")
// .map(x -> within(
// createTaskSupplier(x), 3000, TimeUnit.MILLISECONDS)
// .thenAccept(T::send)
// .exceptionally(throwable -> {
// log.error("Unrecoverable error", throwable);
// return null;
// }))
.map(x -> CompletableFuture.anyOf(createTaskSupplier(x)
, timeoutCompletableFuture))
.collect(Collectors.toList())
.stream()
.map(CompletableFuture::join)
.collect(Collectors.toList());
// .map(x -> CompletableFuture.anyOf(createTaskSupplier(x)
// , oneSecondTimeout).join())
// .collect(Collectors.toList());
System.out.println("-------结束------");
System.out.println(collect.toString());
}
private static final ScheduledExecutorService scheduler =
Executors.newScheduledThreadPool(
2,
r -> {
Thread thread = new Thread(r);
thread.setName("failAfter-%d");
thread.setDaemon(true);
return thread;
});
private static String send(String s) {
log.info("最终结果是{}", s);
return s;
}
private static CompletableFuture<String> createTaskSupplier(String x) {
return CompletableFuture.supplyAsync(getStringSupplier(x))
.exceptionally(Throwable::getMessage);
}
private static Supplier<String> getStringSupplier(String text) {
return () -> {
System.out.println("开始 " + text);
if ("1".equals(text)) {
throw new RuntimeException("运行时错误");
}
try {
if ("5".equals(text)) {
TimeUnit.SECONDS.sleep(5);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("结束 " + text);
return text + "号";
};
}
private static <T> CompletableFuture<T> within(CompletableFuture<T> future, long timeout, TimeUnit unit) {
final CompletableFuture<T> timeoutFuture = timeoutAfter(timeout, unit);
// 哪个先完成 就apply哪一个结果 这是一个关键的API
return future.applyToEither(timeoutFuture, Function.identity());
}
private static <T> CompletableFuture<T> timeoutAfter(long timeout, TimeUnit unit) {
CompletableFuture<T> result = new CompletableFuture<T>();
// timeout 时间后 抛出TimeoutException 类似于sentinel / watcher
scheduler.schedule(() -> result.completeExceptionally(new TimeoutException("超时:" + timeout)), timeout, unit);
// return CompletableFuture.supplyAsync(()-> (T)"另一个分支任务");
return result;
}
}
以上就是java中怎么实现异步处理,小编相信有部分知识点可能是我们日常工作会见到或用到的。希望你能通过这篇文章学到更多知识。更多详情敬请关注亿速云行业资讯频道。
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原文链接:https://my.oschina.net/pentakill/blog/5014869