java.nio.file.WatchService 实时监控文件变化的示例代码

package org.learn.file;

import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardWatchEventKinds;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.List;

/**
 * 实时监控文件的变化
 *
 * @author zhibo
 * @date 2019-07-30 20:37
 */
public class FileWatchedService {
    private WatchService watchService;

    private FileWatchedListener listener;

    /**
     *
     * @param path 要监听的目录，注意该 Path 只能是目录，否则会报错 java.nio.file.NotDirectoryException: /Users/zhibo/logs/a.log
     * @param listener 自定义的 listener，用来处理监听到的创建、修改、删除事件
     * @throws IOException
     */
    public FileWatchedService(Path path, FileWatchedListener listener) throws IOException {
        watchService = FileSystems.getDefault().newWatchService();
        path.register(watchService,
                /// 监听文件创建事件
                StandardWatchEventKinds.ENTRY_CREATE,
                /// 监听文件删除事件
                StandardWatchEventKinds.ENTRY_DELETE,
                /// 监听文件修改事件
                StandardWatchEventKinds.ENTRY_MODIFY);
//
//            path.register(watchService,
//                    new WatchEvent.Kind[]{
//                            StandardWatchEventKinds.ENTRY_MODIFY,
//                            StandardWatchEventKinds.ENTRY_CREATE,
//                            StandardWatchEventKinds.ENTRY_DELETE
//                    },
//                    SensitivityWatchEventModifier.HIGH);

        this.listener = listener;
    }

    private void watch() throws InterruptedException {
        while (true) {
            WatchKey watchKey = watchService.take();
            List<WatchEvent<?>> watchEventList = watchKey.pollEvents();
            for (WatchEvent<?> watchEvent : watchEventList) {
                WatchEvent.Kind kind = watchEvent.kind();

                WatchEvent<Path> curEvent = (WatchEvent<Path>) watchEvent;
                if (kind == StandardWatchEventKinds.OVERFLOW) {
                    listener.onOverflowed(curEvent);
                    continue;
                } else if (kind == StandardWatchEventKinds.ENTRY_CREATE) {
                    listener.onCreated(curEvent);
                    continue;
                } else if (kind == StandardWatchEventKinds.ENTRY_MODIFY) {
                    listener.onModified(curEvent);
                    continue;
                } else if (kind == StandardWatchEventKinds.ENTRY_DELETE) {
                    listener.onDeleted(curEvent);
                    continue;
                }
            }

            /**
             * WatchKey 有两个状态：
             * {@link sun.nio.fs.AbstractWatchKey.State.READY ready} 就绪状态：表示可以监听事件
             * {@link sun.nio.fs.AbstractWatchKey.State.SIGNALLED signalled} 有信息状态：表示已经监听到事件，不可以接续监听事件
             * 每次处理完事件后，必须调用 reset 方法重置 watchKey 的状态为 ready，否则 watchKey 无法继续监听事件
             */
            if (!watchKey.reset()) {
                break;
            }

        }
    }

    public static void main(String[] args) {
        try {
            Path path = Paths.get("/Users/zhibo/logs/");
            FileWatchedService fileWatchedService = new FileWatchedService(path, new FileWatchedAdapter());
            fileWatchedService.watch();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

package org.learn.file;

import java.nio.file.Path;
import java.nio.file.WatchEvent;

public interface FileWatchedListener {
    void onCreated(WatchEvent<Path> watchEvent);

    void onDeleted(WatchEvent<Path> watchEvent);

    void onModified(WatchEvent<Path> watchEvent);

    void onOverflowed(WatchEvent<Path> watchEvent);
}

package org.learn.file;

import java.nio.file.Path;
import java.nio.file.WatchEvent;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;

/**
 * 文件监听适配器
 *
 * @author zhibo
 * @date 2019-07-31 11:07
 */
public class FileWatchedAdapter implements FileWatchedListener {

    @Override
    public void onCreated(WatchEvent<Path> watchEvent) {
        Path fileName = watchEvent.context();
        System.out.println(String.format("文件【%s】被创建，时间：%s", fileName, now()));
    }

    @Override
    public void onDeleted(WatchEvent<Path> watchEvent) {
        Path fileName = watchEvent.context();
        System.out.println(String.format("文件【%s】被删除，时间：%s", fileName, now()));
    }

    @Override
    public void onModified(WatchEvent<Path> watchEvent) {
        Path fileName = watchEvent.context();
        System.out.println(String.format("文件【%s】被修改，时间：%s", fileName, now()));
    }

    @Override
    public void onOverflowed(WatchEvent<Path> watchEvent) {
        Path fileName = watchEvent.context();
        System.out.println(String.format("文件【%s】被丢弃，时间：%s", fileName, now()));
    }

    private String now(){
        DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss SSS");
        return dateFormat.format(Calendar.getInstance().getTime());
    }
}

package com.sun.nio.file;

import java.nio.file.WatchEvent.Modifier;

public enum SensitivityWatchEventModifier implements Modifier {
    HIGH(2),
    MEDIUM(10),
    LOW(30);

    private final int sensitivity;

    public int sensitivityValueInSeconds() {
        return this.sensitivity;
    }

    private SensitivityWatchEventModifier(int var3) {
        this.sensitivity = var3;
    }
}

        path.register(watchService,
                /// 监听文件创建事件
                StandardWatchEventKinds.ENTRY_CREATE,
                /// 监听文件删除事件
                StandardWatchEventKinds.ENTRY_DELETE,
                /// 监听文件修改事件
                StandardWatchEventKinds.ENTRY_MODIFY);

    path.register(watchService,
                    new WatchEvent.Kind[]{
                            StandardWatchEventKinds.ENTRY_MODIFY,
                            StandardWatchEventKinds.ENTRY_CREATE,
                            StandardWatchEventKinds.ENTRY_DELETE
                    },
                    SensitivityWatchEventModifier.HIGH);