使用FileSystems API。以下是一个示例代码：

import java.nio.file.*;
import java.util.*;

public class FolderWatcher {
    private final WatchService watchService;
    private final Map watchKeyPathMap;

    public FolderWatcher(Path folderPath) throws Exception {
        this.watchService = FileSystems.getDefault().newWatchService();
        this.watchKeyPathMap = new HashMap<>();

        registerFolder(folderPath);
    }

    private void registerFolder(Path folderPath) throws Exception {
        WatchKey watchKey = folderPath.register(
                watchService, 
                StandardWatchEventKinds.ENTRY_CREATE, 
                StandardWatchEventKinds.ENTRY_MODIFY, 
                StandardWatchEventKinds.ENTRY_DELETE);

        watchKeyPathMap.put(watchKey, folderPath);
    }

    public void startWatching() throws Exception {
        WatchKey watchKey;
        while ((watchKey = watchService.take()) != null) {
            for (WatchEvent watchEvent : watchKey.pollEvents()) {
                WatchEvent.Kind watchEventKind = watchEvent.kind();

                if (watchEventKind == StandardWatchEventKinds.OVERFLOW) {
                    continue;
                }

                WatchEvent pathWatchEvent = (WatchEvent) watchEvent;

                Path fileName = pathWatchEvent.context();
                Path folderPath = watchKeyPathMap.get(watchKey);

                Path absolutePath = folderPath.resolve(fileName);

                // Do something with the file
            }

            if (!watchKey.reset()) {
                watchKeyPathMap.remove(watchKey);

                if (watchKeyPathMap.isEmpty()) {
                    break;
                }
            }
        }
    }
}

在您的代码中，您可以使用以上示例代码来监听文件夹以进行文件更改，并根据需要进行修改。