java - 基于触发器java运行任务

Question

如果 Java 中存在触发器(即某些事件，例如新文件添加到目录)，我想运行一个任务。 Java 对此有内置支持吗？ 如果没有，我可以使用什么第三方库来实现这一点？

Answer 1

在 Java 7 中，有一个监视服务，允许在文件或目录上检测到更改或事件时执行任务。

教程:http://docs.oracle.com/javase/tutorial/essential/io/notification.html#overview

API文档:http://docs.oracle.com/javase/7/docs/api/java/nio/file/WatchService.html

这是我编写的一个简单示例:

package watcher;

import java.io.IOException;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.StandardWatchEventKinds;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;

public class Watcher {

    private final FileCreatedAction action;
    private final String pathToWatchString;

    public Watcher(FileCreatedAction action, String pathToWatchString) {
        this.action = action;
        this.pathToWatchString = pathToWatchString;
    }

    public void start() throws IOException {
        FileSystem defaultFileSystem = FileSystems.getDefault();
        WatchService watchService = defaultFileSystem.newWatchService();
        Path pathToWatch = defaultFileSystem.getPath(pathToWatchString);
        pathToWatch.register(watchService, StandardWatchEventKinds.ENTRY_CREATE);
        while(true) {
            try {
                WatchKey key = watchService.take();
                if (key != null) {
                    for (WatchEvent<?> event: key.pollEvents()) {
                        if (event.kind().equals(StandardWatchEventKinds.ENTRY_CREATE))
                        {
                            WatchEvent<Path> ev = (WatchEvent<Path>)event;
                            Path filename = ev.context();
                            Path fullFilename = pathToWatch.resolve(filename);
                            action.performAction(fullFilename);
                        }
                    }
                }
            } catch (InterruptedException error) {
                return;
            }
        }
    }

    public static void main(String[] args) throws IOException {
        FileCreatedAction action = new FileCreatedAction() {

            @Override
            public void performAction(Path fullPath) {
                System.out.printf("Found file %s", fullPath);
            }
        };

        Watcher watcher = new Watcher(action, "/foo");
        watcher.start();
    }

}

interface FileCreatedAction {
    void performAction(Path fullPath);
}