EJB 3.1和NIO2:监视文件系统 [英] EJB 3.1 and NIO2: Monitoring the file system

问题描述

我想我们大多数人都同意，使用NIO2是一件好事.假设您要监视文件系统的某些部分是否有传入的xml-文件，这是一件容易的事.但是，如果我想将这些东西集成到现有的Java EE应用程序中，而不必启动另一项服务(应用服务器 AND 监视文件系统的服务)怎么办? 因此，我拥有重量级的app-server，其中包含所有EJB 3.1内容以及某种监视文件系统的服务，并在文件显示后采取适当的措施.有趣的是，适当的操作是创建一条消息，然后通过JMS发送该消息，最好将两者都集成到应用服务器中.

I guess most of us agree, that NIO2 is a fine thing to make use of. Presumed you want to monitor some part of the file system for incoming xml - files it is an easy task now. But what if I want to integrate the things into an existing Java EE application so I don't have to start another service (app-server AND the one which monitors the file system)? So I have the heavy weight app-server with all the EJB 3.1 stuff and some kind of service monitoring the file system and take appropriate action once a file shows up. Interestingly the appropriate action is to create a Message and send it by JMS and it might be nice to integrate both into the app server.

我尝试了@Startup，但是部署冻结了(我知道我不应该在其中使用I/O，只是尝试一下).无论如何...有什么建议吗?

I tried @Startup but deployment freezes (and I know that I shouldn't make use of I/O in there, was just a try). Anyhow ... any suggestions?

推荐答案

您可以创建一个在启动时加载并将监视委托给异步bean的单例

You could create a singleton that loads at startup and delegates the monitoring to an Asynchronous bean

@Singleton
@Startup
public class Initialiser {

    @EJB
    private FileSystemMonitor fileSystemMonitor;

    @PostConstruct
    public void init() {
        String fileSystemPath = ....;
        fileSystemMonitor.poll(fileSystemPath);
    }

}

然后，异步bean看起来像这样

Then the Asynchronous bean looks something like this

@Stateless
public class FileSystemMonitor {

    @Asynchronous
    public void poll(String fileSystemPath) {
        WatchService watcher = ....;
        for (;;) {
            WatchKey key = null;
            try {
                key = watcher.take();
                for (WatchEvent<?> event: key.pollEvents()) {
                    WatchEvent.Kind<?> kind = event.kind();
                    if (kind == StandardWatchEventKinds.OVERFLOW) {
                        continue; // If events are lost or discarded
                    }
                    WatchEvent<Path> watchEvent = (WatchEvent<Path>)event;

                    //Process files....

                }
            } catch (InterruptedException e) {
                e.printStackTrace();
                return;
            } finally {
                if (key != null) {
                    boolean valid = key.reset();
                    if (!valid) break; // If the key is no longer valid, the directory is inaccessible so exit the loop.
                }
            }
        }
    }

}

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