WatchService抛出ClosedWatchServiceException

Question

我正在使用java.nio.file.WatchService监视我的Spring boot应用程序中的一个目录。我一直收到以下异常，它似乎没有检测到监视文件夹中的任何文件更改：

java.nio.file.ClosedWatchServiceException: null
at sun.nio.fs.AbstractWatchService.checkOpen(AbstractWatchService.java:80)
at sun.nio.fs.AbstractWatchService.take(AbstractWatchService.java:117)
at com.company.MyFilesMonitor.monitorMappingFiles(MyMappingFilesMonitor.java:27)
at com.company.MyFilesMonitor$$FastClassBySpringCGLIB$$3d959079.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:752)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
at org.springframework.aop.interceptor.AsyncExecutionInterceptor.lambda$invoke$0(AsyncExecutionInterceptor.java:115)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)

下面是创建bean的代码：

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.util.ClassUtils;

import java.io.IOException;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.file.*;
import java.util.Objects;

@Configuration
public class MyFilesMonitorConfiguration {
    @Value("${company.integration.converter.mapper-files:mappers}")
    private String mapperFilesLocation;

    @Bean
    public WatchService mappingFilesWatch() throws IOException, URISyntaxException {
        URL url = Objects.requireNonNull(ClassUtils.getDefaultClassLoader()).getResource(mapperFilesLocation);
        try(WatchService watchService = FileSystems.getDefault().newWatchService()) {
            Path path = Paths.get(url.toURI());
            if (!Files.isDirectory(path)) {
                // ToDo: i18n
                throw new RuntimeException("Invalid mapping files path" + path);
            }
                path.register(
                        watchService,
                        StandardWatchEventKinds.ENTRY_DELETE,
                        StandardWatchEventKinds.ENTRY_MODIFY,
                        StandardWatchEventKinds.ENTRY_CREATE
                );
            return watchService;
        }
    }
}

下面是使用watchService bean的类：

import org.slf4j.Logger;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.scheduling.annotation.Async;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Service;

import java.nio.file.*;

@Service
public class MyMappingFilesMonitor {
    private final WatchService watchService;
    private static final Logger LOGGER = LoggerFactory.getLogger(MyMappingFilesMonitor.class);

    @Autowired
    public MyMappingFilesMonitor(WatchService watchService) {
        this.watchService = watchService;
    }

    @Async
    @Scheduled(fixedDelay = 1000)
    public void monitorMappingFiles() {
        final WatchKey key;
        try {
            key = watchService.take();
            for (WatchEvent<?> event : key.pollEvents()) {
                final WatchEvent.Kind<?> kind = event.kind();
                if (kind == StandardWatchEventKinds.OVERFLOW) {
                    continue;
                }
                @SuppressWarnings("unchecked")
                final WatchEvent<Path> watchEventPath = (WatchEvent<Path>) event;
                final Path filename = watchEventPath.context();
                System.out.println("******** kind: " + kind + " -> " + filename);
                key.reset();
            }
        } catch (InterruptedException e) {
            return;
        }
    }
}

我不知道我在这里错过了什么。我在这里和那里看了不同的示例代码，我没有做任何不同的事情，但我仍然总是得到这个异常。任何帮助或指点都是非常感谢的。

Answer 1

您将try与资源一起使用来创建新的监视服务，因此它总是在方法mappingFilesWatch()返回它时关闭：

try(WatchService watchService = FileSystems.getDefault().newWatchService()) {
    ...
    return watchService;  // THIS IS AUTO-CLOSED
}

您只需要删除try块。