JDK7新特性 监听文件系统的更改

我们用IDE（例如Eclipse）编程，外部更改了代码文件，IDE马上提升“文件有更改”。Jdk7的NIO2.0也提供了这个功能，用于监听文件系统的更改。它采用类似观察者的模式，注册相关的文件更改事件（新建，删除……），当事件发生的，通知相关的监听者。

 

java.nio.file.*包提供了一个文件更改通知API,叫做Watch Service API.

 

实现流程如下

 

1.为文件系统创建一个WatchService 实例 watcher

2.为你想监听的目录注册 watcher。注册时，要注明监听那些事件。

3.在无限循环里面等待事件的触发。当一个事件发生时，key发出信号，并且加入到watcher的queue

4.从watcher的queue查找到key，你可以从中获取到文件名等相关信息

5.遍历key的各种事件

6.重置 key，重新等待事件

7.关闭服务

import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import static java.nio.file.StandardWatchEventKind.*;

/**
 * @author [e-mail]
 */
public class TestWatcherService {

    private WatchService watcher;

    public TestWatcherService(Path path)throws IOException{
        watcher = FileSystems.getDefault().newWatchService();
        path.register(watcher, ENTRY_CREATE,ENTRY_DELETE,ENTRY_MODIFY);
    }

    public void handleEvents() throws InterruptedException{
        while(true){
            WatchKey key = watcher.take();
            for(WatchEvent<?> event : key.pollEvents()){
                WatchEvent.Kind kind = event.kind();

                if(kind == OVERFLOW){//事件可能lost or discarded
                    continue;
                }

                WatchEvent<Path> e = (WatchEvent<Path>)event;
                Path fileName = e.context();

                System.out.printf("Event %s has happened,which fileName is %s%n"
                        ,kind.name(),fileName);
            }
            if(!key.reset()){
                break;
            }
        }
    }

    public static void main(String args[]) throws IOException, InterruptedException{
        if(args.length!=1){
            System.out.println("请设置要监听的文件目录作为参数");
            System.exit(-1);
        }
        new TestWatcherService(Paths.get(args[0])).handleEvents();
    }
}

import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import static java.nio.file.StandardWatchEventKind.*;

/**
 * @author [e-mail]
 */
public class TestWatcherService {
    
    private WatchService watcher;
    
    public TestWatcherService(Path path)throws IOException{
        watcher = FileSystems.getDefault().newWatchService();
        path.register(watcher, ENTRY_CREATE,ENTRY_DELETE,ENTRY_MODIFY);
    }
    
    public void handleEvents() throws InterruptedException{
        while(true){
            WatchKey key = watcher.take();
            for(WatchEvent<?> event : key.pollEvents()){
                WatchEvent.Kind kind = event.kind();
                
                if(kind == OVERFLOW){//事件可能lost or discarded
                    continue;
                }
                
                WatchEvent<Path> e = (WatchEvent<Path>)event;
                Path fileName = e.context();
                
                System.out.printf("Event %s has happened,which fileName is %s%n"
                        ,kind.name(),fileName);
            }
            if(!key.reset()){
                break;
            }
        }
    }
    
    public static void main(String args[]) throws IOException, InterruptedException{
        if(args.length!=1){
            System.out.println("请设置要监听的文件目录作为参数");
            System.exit(-1);
        }
        new TestWatcherService(Paths.get(args[0])).handleEvents();
    }
}

 

 

接下来，见证奇迹的时刻

1.随便新建一个文件夹例如 c:\\test

2.运行程序 java TestWatcherService c:\\test

3.在该文件夹下新建一个文件本件“新建文本文档.txt”

4.将上述文件改名为“abc.txt”

5.打开文件，输入点什么吧，再保存。

6.Over！看看命令行输出的信息吧

 

Event ENTRY_CREATE has happened,which fileName is 新建文本文档.txt
Event ENTRY_DELETE has happened,which fileName is 新建文本文档.txt
Event ENTRY_CREATE has happened,which fileName is abc.txt
Event ENTRY_MODIFY has happened,which fileName is abc.txt
Event ENTRY_MODIFY has happened,which fileName is abc.txt

Event ENTRY_CREATE has happened,which fileName is 新建文本文档.txt
Event ENTRY_DELETE has happened,which fileName is 新建文本文档.txt
Event ENTRY_CREATE has happened,which fileName is abc.txt
Event ENTRY_MODIFY has happened,which fileName is abc.txt
Event ENTRY_MODIFY has happened,which fileName is abc.txt