java - 不断阅读java WatchEvents

Question

我正在尝试在客户端和服务器之间同步两个文件夹及其子目录。我有this class的修改版本我在下面发布了。在我的 Client 类中，我创建一个 WatchDir 对象并在无限循环中调用其 processEvents() 方法。

如果事件已注册，则该方法返回一个 myTuple 对象(一个包含事件类型和路径对象的结构)，否则返回 null。问题是，这似乎只适用于目录中发生的第一个事件(即，如果我将文件添加到监视文件夹中，我的 WatchDir object.processEvents() 返回一个带有 ENTRY_CREATE 事件，并且永远不会为之后发生的其他文件添加/删除/修改返回另一个元组)。我希望每次发生某个事件时都会连续调用 processEvents (因此是无限的 while)，返回一个元组。

我修改后的WatchDir:

import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.LinkOption.*;
import java.nio.file.attribute.*;
import java.io.*;
import java.util.*;
import java.util.concurrent.TimeUnit;

public class WatchDir {
    private final WatchService watcher;
    private final Map<WatchKey,Path> keys;
    private final boolean recursive;
    private boolean trace = false;

    public WatchDir(Path dir, boolean recursive) throws IOException {
        this.watcher = FileSystems.getDefault().newWatchService();
        this.keys = new HashMap<WatchKey,Path>(); //holds the key for each subdirectory
        this.recursive = true;

        registerAll(dir);
    }

    public void registerAll(Path start) throws IOException {
        Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
            @Override
            public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
                register(dir);
                return FileVisitResult.CONTINUE;
            }
        });
    }

    public void register(Path dir) throws IOException {
        WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
        keys.put(key, dir);
    }

    public myTuple processEvents() {
        WatchKey key;
        //while (true) {

            try {
                key = watcher.take();
            } catch (InterruptedException e) {
                return new myTuple("INTERRUPTED", null);
            }

            Path dir = keys.get(key); //get next subdirectory path
            if (dir == null)
                return new myTuple("NULL DIRECTORY", null);

            for (WatchEvent<?> event : key.pollEvents()) {
                WatchEvent.Kind kind = event.kind();
                WatchEvent<Path> ev = cast(event);
                Path name = ev.context();
                Path child = dir.resolve(name);

                return new myTuple(event.kind().name(), child);
            }
            return null;
        //}
    }

    @SuppressWarnings("unchecked")
    static <T> WatchEvent<T> cast(WatchEvent<?> event) {
        return (WatchEvent<T>)event;
    }
}

我的客户:

import java.nio.file.attribute.*;
import java.nio.file.*;
import java.util.concurrent.TimeUnit;

public class newClient {
    public static void main(String[] args) throws IOException {

        Path folder = Paths.get(System.getProperty("user.dir"));
        WatchDir watcher = new WatchDir(folder, true);
        myTuple thisTuple;

    while (true) {
        thisTuple = watcher.processEvents();
        String event = thisTuple.getEvent();
        Path path = thisTuple.getPath();

        System.out.println(event+": "+path.toString());
    }
}
}

Answer 1

您没有重置 key 。阅读docs再次:

Once the events have been processed the consumer invokes the key's reset method to reset the key which allows the key to be signalled and re-queued with further events.

大概在这里

       for (WatchEvent<?> event : key.pollEvents()) {
            WatchEvent.Kind kind = event.kind();
            WatchEvent<Path> ev = cast(event);
            Path name = ev.context();
            Path child = dir.resolve(name);

            return new myTuple(event.kind().name(), child);
        }
        key.reset();
        return null;