blocks|key|1638321|text|我使用的是Apache+Commons的VFS+API，下面是一个如何在不影响性能的情况下监控文件的示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1638322|DefaultFileMonitor|offset|length|1638323|entityMap|0|LINK|mutability|MUTABLE|url|http://commons.apache.org/proper/commons-vfs/commons-vfs2/apidocs/org/apache/commons/vfs2/impl/DefaultFileMonitor.html^0|0|0|I|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

I use the VFS API from Apache Commons, here is an example of how to monitor a file without much impact in performance:

<a href="http://commons.apache.org/proper/commons-vfs/commons-vfs2/apidocs/org/apache/commons/vfs2/impl/DefaultFileMonitor.html" rel="nofollow noreferrer">DefaultFileMonitor</a>

blocks|key|1423307|text|有一个名为jnotify的库，它包装了linux上的inotify，也支持windows。我从来没有用过它，我不知道它有多好，但我想说的是，它值得一试。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1423308|entityMap|0|LINK|mutability|MUTABLE|url|http://jnotify.sourceforge.net/|1|http://en.wikipedia.org/wiki/Inotify^0|5|7|0|Q|7|1|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]|$A|R|B|S|1|T]]|C|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]]]

There is a lib called <a href="http://jnotify.sourceforge.net/" rel="noreferrer">jnotify</a> that wraps <a href="http://en.wikipedia.org/wiki/Inotify" rel="noreferrer">inotify</a> on linux and has also support for windows. Never used it and I don't know how good it is, but it's worth a try I'd say.

blocks|key|1638535|text|Java+commons-io有一个FileAlterationObserver。它结合FileAlterationMonitor进行轮询。类似于commons+VFS。优点是它的依赖性要小得多。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1638536|编辑:更少的依赖项不是真的，它们对于VFS是可选的。但它使用的是java+File而不是VFS抽象层。|1638537|entityMap|0|LINK|mutability|MUTABLE|url|http://commons.apache.org/proper/commons-io//javadocs/api-release/org/apache/commons/io/monitor/FileAlterationObserver.html^0|I|M|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

Java commons-io has a <a href="http://commons.apache.org/proper/commons-io//javadocs/api-release/org/apache/commons/io/monitor/FileAlterationObserver.html">FileAlterationObserver</a>. it does polling in combination with a FileAlterationMonitor. Similar to commons VFS. The advantag is that it has much less dependencies.

edit: Less dependencies is not true, they are optional for VFS. But it uses java File instead of the VFS abstraction layer.

blocks|key|1638268|text|“更多NIO功能”具有文件监视功能，具体实现取决于底层操作系统。应该在JDK7中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1638269|更新:添加到JavaSE7中。Chris+Janicki提供了一个link+to+the+relevant+Java+tutorial。|offset|length|1638270|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/tutorial/essential/io/notification.html^0|0|X|Y|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

&quot;More NIO features&quot; has file watch functionality, with implementation dependent upon the underlying OS. Should be in JDK7.
Update: Was added to Java SE 7. Chris Janicki offers a <a href="https://docs.oracle.com/javase/tutorial/essential/io/notification.html" rel="nofollow noreferrer">link to the relevant Java tutorial</a>.

blocks|key|1638479|text|每次读取属性文件时，我都会运行这段代码，只有在自上次读取后修改过的情况下才实际读取该文件。希望这对某些人有帮助。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1638480|private+long+timeStamp;
private+File+file;

private+boolean+isFileUpdated(+File+file+)+{
++this.file+=+file;
++this.timeStamp+=+file.lastModified();

++if(+this.timeStamp+!=+timeStamp+)+{
++++this.timeStamp+=+timeStamp;
++++//Yes,+file+is+updated
++++return+true;
++}
++//No,+file+is+not+updated
++return+false;
}|code-block|syntax|javascript|1638481|在Log4J+FileWatchdog中也使用了类似的方法。|offset|length|style|CODE|1638482|entityMap|0|LINK|mutability|MUTABLE|url|http://grepcode.com/file/repo1.maven.org/maven2/log4j/log4j/1.2.17/org/apache/log4j/helpers/FileWatchdog.java#74^0|0|0|7|C|7|C|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@$I|X|J|Y|K|L]]|9|@$I|Z|J|10|1|11]]|A|$]]|$1|M|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

I run this snippet of code every time I go to read the properties file, only actually reading the file if it has been modified since the last time I read it. Hope this helps someone.

<pre><code>private long timeStamp;
private File file;

private boolean isFileUpdated( File file ) {
 this.file = file;
 this.timeStamp = file.lastModified();

 if( this.timeStamp != timeStamp ) {
 this.timeStamp = timeStamp;
 //Yes, file is updated
 return true;
 }
 //No, file is not updated
 return false;
}
</code></pre>

Similar approach is used in Log4J <a href="http://grepcode.com/file/repo1.maven.org/maven2/log4j/log4j/1.2.17/org/apache/log4j/helpers/FileWatchdog.java#74" rel="nofollow"><code>FileWatchdog</code></a>.

blocks|key|1423222|text|如果你愿意花点钱，JNIWrapper是一个很有用的带有Winpack的库，你将能够在某些文件上获得文件系统事件。不幸的是，只能在windows上运行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1423223|参见https://www.teamdev.com/jniwrapper。|offset|length|1423224|否则，求助于本机代码并不总是一件坏事，特别是当提供的最好的是轮询机制而不是本机事件时。|1423225|我注意到，在某些计算机上，Java文件系统操作可能很慢，如果处理不当，很容易影响应用程序的性能。|1423226|entityMap|0|LINK|mutability|MUTABLE|url|https://www.teamdev.com/jniwrapper^0|0|2|Y|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@$D|T|E|U|1|V]]|A|$]]|$1|F|3|G|5|6|7|W|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|X|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]]]

If you are willing to part with some money, JNIWrapper is a useful library with a Winpack, you will be able to get file system events on certain files. Unfortunately windows only.

See <a href="https://www.teamdev.com/jniwrapper" rel="nofollow noreferrer">https://www.teamdev.com/jniwrapper</a>.

Otherwise, resorting to native code is not always a bad thing especially when the best on offer is a polling mechanism as against a native event.

I've noticed that Java file system operations can be slow on some computers and can easily affect the application's performance if not handled well.

blocks|key|1638574|text|您可以使用FileReader监听文件更改。请看下面的例子|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1638575|//+File+content+change+listener+
private+String+fname;
private+Object+lck+=+new+Object();
...+
public+void+run()
{
++++try
++++{
++++++++BufferedReader+br+=+new+BufferedReader(+new+FileReader(+fname+)+);
++++++++String+s;
++++++++StringBuilder+buf+=+new+StringBuilder();
++++++++while(+true+)
++++++++{
++++++++++++s+=+br.readLine();
++++++++++++if(+s+==+null+)
++++++++++++{
++++++++++++++++synchronized(+lck+)
++++++++++++++++{
++++++++++++++++++++lck.wait(+500+);
++++++++++++++++}
++++++++++++}
++++++++++++else
++++++++++++{
+++++++++++++++System.out.println(+"s+=+"+%2B+s+);
++++++++++++}

++++++++}
++++}
++++catch(+Exception+e+)
++++{
++++++++e.printStackTrace();
++++}
}|code-block|syntax|javascript|1638576|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can listen file changes using a FileReader. Plz see the example below

<pre><code>// File content change listener 
private String fname;
private Object lck = new Object();
... 
public void run()
{
 try
 {
 BufferedReader br = new BufferedReader( new FileReader( fname ) );
 String s;
 StringBuilder buf = new StringBuilder();
 while( true )
 {
 s = br.readLine();
 if( s == null )
 {
 synchronized( lck )
 {
 lck.wait( 500 );
 }
 }
 else
 {
 System.out.println( "s = " + s );
 }

 }
 }
 catch( Exception e )
 {
 e.printStackTrace();
 }
}
</code></pre>

blocks|key|1638356|text|有一个用于文件和文件夹监视的商业跨桌面库，名为JxFileWatcher。可从此处下载：http://www.teamdev.com/jxfilewatcher/|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1638357|你也可以在网上看到它的实际效果：http://www.teamdev.com/jxfilewatcher/onlinedemo/|1638358|entityMap|0|LINK|mutability|MUTABLE|url|http://www.teamdev.com/jxfilewatcher/|1|http://www.teamdev.com/jxfilewatcher/onlinedemo/^0|18|11|0|0|G|1C|1|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]]|C|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]]|C|$]]|$1|F|3|-4|5|6|7|X|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]|N|$5|I|J|K|C|$L|O]]]]

There is a commercial cross-desktop library for files and folders watching called JxFileWatcher.
It can be downloaded from here:
<a href="http://www.teamdev.com/jxfilewatcher/" rel="nofollow noreferrer">http://www.teamdev.com/jxfilewatcher/</a>

Also you can see it in action online:
 <a href="http://www.teamdev.com/jxfilewatcher/onlinedemo/" rel="nofollow noreferrer">http://www.teamdev.com/jxfilewatcher/onlinedemo/</a>

blocks|key|1638404|text|您还可以考虑Apache+Commons+JCI+(Java编译器接口)。尽管此API似乎侧重于类的动态编译，但它在监视文件更改的API中也包含了类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1638405|示例：http://commons.apache.org/jci/usage.html|offset|length|1638406|entityMap|0|LINK|mutability|MUTABLE|url|http://commons.apache.org/jci/usage.html^0|0|3|14|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

You may also consider the Apache Commons JCI (Java Compiler Interface). Although this API seems to be focused on dynamic compilation of classes, it also includes classes in its API that monitors file changes.

Example:
<a href="http://commons.apache.org/jci/usage.html" rel="nofollow noreferrer">http://commons.apache.org/jci/usage.html</a>

blocks|key|1638432|text|Spring+Integration提供了一种很好的监视目录和文件的机制：http://static.springsource.org/spring-integration/reference/htmlsingle/#files。我非常确定它是跨平台的(我在mac、linux和windows上都用过它)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1638433|entityMap|0|LINK|mutability|MUTABLE|url|http://static.springsource.org/spring-integration/reference/htmlsingle/#files^0|11|25|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Spring Integration provides a nice mechanism for watching Directories and files: <a href="http://static.springsource.org/spring-integration/reference/htmlsingle/#files" rel="nofollow">http://static.springsource.org/spring-integration/reference/htmlsingle/#files</a>. Pretty sure it's cross platform (I've used it on mac, linux, and windows).

blocks|key|1638611|text|不过，轮询最后修改的文件属性是一个简单而有效的解决方案。只需定义一个类来扩展我的FileChangedWatcher并实现onModified()方法：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1638612|import+java.io.File;

public+abstract+class+FileChangedWatcher
{
++++private+File+file;

++++public+FileChangedWatcher(String+filePath)
++++{
++++++++file+=+new+File(filePath);
++++}

++++public+void+watch()+throws+InterruptedException
++++{
++++++++long+currentModifiedDate+=+file.lastModified();

++++++++while+(true)
++++++++{
++++++++++++long+newModifiedDate+=+file.lastModified();

++++++++++++if+(newModifiedDate+!=+currentModifiedDate)
++++++++++++{
++++++++++++++++currentModifiedDate+=+newModifiedDate;
++++++++++++++++onModified();
++++++++++++}

++++++++++++Thread.sleep(100);
++++++++}
++++}

++++public+String+getFilePath()
++++{
++++++++return+file.getAbsolutePath();
++++}

++++protected+abstract+void+onModified();
}|code-block|syntax|javascript|1638613|entityMap^0|14|I|1P|C|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

Polling the last modified file property is a simple yet effective solution though. Just define a class extending my <code>FileChangedWatcher</code> and implement the <code>onModified()</code> method:

<pre><code>import java.io.File;

public abstract class FileChangedWatcher
{
 private File file;

 public FileChangedWatcher(String filePath)
 {
 file = new File(filePath);
 }

 public void watch() throws InterruptedException
 {
 long currentModifiedDate = file.lastModified();

 while (true)
 {
 long newModifiedDate = file.lastModified();

 if (newModifiedDate != currentModifiedDate)
 {
 currentModifiedDate = newModifiedDate;
 onModified();
 }

 Thread.sleep(100);
 }
 }

 public String getFilePath()
 {
 return file.getAbsolutePath();
 }

 protected abstract void onModified();
}
</code></pre>

blocks|key|1423709|text|与其他答案类似，下面是我如何使用文件、计时器和TimerTask将其作为后台线程以设定的时间间隔轮询来运行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1423710|import+java.io.File;
import+java.util.Timer;
import+java.util.TimerTask;

public+class+FileModifiedWatcher
{
++private+static+File+file;
++private+static+int+pollingInterval;
++private+static+Timer+fileWatcher;
++private+static+long+lastReadTimeStamp+=+0L;

++public+static+boolean+init(String+_file,+int+_pollingInterval)
++{
++++file+=++new+File(_file);
++++pollingInterval+=+_pollingInterval;+//+In+seconds

++++watchFile();

++++return+true;
++}

++private+static+void+watchFile()
++{
++++if+(+null+==+fileWatcher+)
++++{
++++++System.out.println("START");

++++++fileWatcher+=+new+Timer();

++++++fileWatcher.scheduleAtFixedRate(new+TimerTask()
++++++{
++++++++@Override
++++++++public+void+run()
++++++++{

++++++++++if+(+file.lastModified()+>+lastReadTimeStamp+)
++++++++++{
++++++++++++System.out.println("File+Modified");
++++++++++}

++++++++++lastReadTimeStamp+=+System.currentTimeMillis();
++++++++}
++++++},+0,+1000+*+pollingInterval);
++++}

++}
}|code-block|syntax|javascript|1423711|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Similar to the other answers, here's how I did it using File, Timer, and TimerTask to let this run as a background thread polling at set intervals.

<pre><code>import java.io.File;
import java.util.Timer;
import java.util.TimerTask;

public class FileModifiedWatcher
{
 private static File file;
 private static int pollingInterval;
 private static Timer fileWatcher;
 private static long lastReadTimeStamp = 0L;

 public static boolean init(String _file, int _pollingInterval)
 {
 file = new File(_file);
 pollingInterval = _pollingInterval; // In seconds

 watchFile();

 return true;
 }

 private static void watchFile()
 {
 if ( null == fileWatcher )
 {
 System.out.println("START");

 fileWatcher = new Timer();

 fileWatcher.scheduleAtFixedRate(new TimerTask()
 {
 @Override
 public void run()
 {

 if ( file.lastModified() &gt; lastReadTimeStamp )
 {
 System.out.println("File Modified");
 }

 lastReadTimeStamp = System.currentTimeMillis();
 }
 }, 0, 1000 * pollingInterval);
 }

 }
}
</code></pre>

I'd like to be notified when a file has been changed in the file system. I have found nothing but a thread that polls the lastModified File property and clearly this solution is not optimal.

File changed listener in Java

文件系统

编译器

Java

当文件系统中的文件发生更改时，我希望收到通知。我只发现了一个轮询lastModified文件属性的线程，显然这个解决方案并不是最优的。

问Java中的文件更改监听器
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