ScheduledExecutorService 的任务抛出异常时不打印堆栈跟踪

Question

我正在通过 Dropwizard 的 LifecycleEnvironment.scheduledExecutorService() 创建一个 ScheduledExecutorService。我在上面安排了四个任务，它们在 3 秒后抛出异常。问题是没有为异常打印堆栈跟踪，因此我无法追踪它发生的原因。抛出异常一的任务永远不会重新启动。

我尝试设置一个默认的未捕获异常处理程序，但它也没有帮助：

Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
            @Override
            public void uncaughtException(Thread thread, Throwable throwable) {
                System.err.println("An exception occurred as below:");
                throwable.printStackTrace(System.err);
            }
        });

完整代码如下：

这是扩展应用程序的主要驱动 class：

App.java

import io.dropwizard.Application;
import io.dropwizard.setup.Environment;

import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class App extends Application<AppConfiguration> {

    public void run(AppConfiguration appConfiguration, Environment environment) throws Exception {
        final ScheduledExecutorService scheduledExecutorService = environment.lifecycle()
                .scheduledExecutorService("throwing-exception-threads").threads(4)
                .build();

        scheduledExecutorService.scheduleAtFixedRate(new ThreadToDie(), 0,5, TimeUnit.SECONDS);
        scheduledExecutorService.scheduleAtFixedRate(new ThreadToDie(), 0,5, TimeUnit.SECONDS);
        scheduledExecutorService.scheduleAtFixedRate(new ThreadToDie(), 0,5, TimeUnit.SECONDS);
        scheduledExecutorService.scheduleAtFixedRate(new ThreadToDie(), 0,5, TimeUnit.SECONDS);

        final HelloWorldResource resource = new HelloWorldResource();
        environment.jersey().register(resource);
    }

    public static void main(String[] args) throws Exception {
        new App().run(args);
    }
}

按固定时间间隔安排任务的代码如下。它打印每秒递增的计数器值。当计数器为 3 时，它抛出 NullPointerException。

ThreadToDie.java

public class ThreadToDie implements Runnable {

    int i = 0;

    @Override
    public void run() {
        i++;
        System.out.printf("Value of i: %d\n", i);
        if (i % 3 == 0) {
            System.out.printf("Throwing NullPointerException\n");
            throw new NullPointerException("This should be printed.");
        }
    }
}

为了完整起见，以下是配置 class 和 HelloWorld API class。尽管在问题中询问它们包含的内容无关紧要。

AppConfiguration.java

import io.dropwizard.Configuration;

public class AppConfiguration extends Configuration {
}

HelloWorldResource.java

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.MediaType;
import java.util.Optional;

@Path("/hello")
@Produces(MediaType.APPLICATION_JSON)
public class HelloWorldResource {

    @GET
    public String hello(@QueryParam("name") Optional<String> name) {
        final String retVal = String.format("Hello %s!", name.orElse("World"));
        return retVal;
    }
}

Answer 1

请参阅 Why is UncaughtExceptionHandler not called by ExecutorService? 了解为什么从未触发 UncaughtExceptionHandler - 您提供的每个任务都由捕获所有异常的工作人员处理。

当您将任务提交给执行者时，您会收到一个 Future 并且可以通过这种方式访问异常：

ScheduledFuture<?> future = scheduledExecutorService.scheduleAtFixedRate(new ThreadToDie(), 0,5, TimeUnit.SECONDS);
try {
   future.get();
} catch (ExecutionException ex) {
   ex.getCause().printStackTrace();
}

Future.get 将等待任务完成或出错。

ScheduledExecutorService 的任务抛出异常时不打印堆栈跟踪

No stack trace is printed when ScheduledExecutorService's task throws an exception

java

dropwizard