Directory and Filesystem Operations - Java - page 460

3. Create an array of Kind enumerations for the things you want to watch (in our ex-
ample we watch for files being created or modified).

4. Register the WatchService and the Kind array onto the Path object.

5. From then on, you wait for the watcher to notify you. A typical implementation is to
enter a while (true) loop calling the WatchService 's take() method to get an
“event,” and interpret these to figure out “what just happened.”

Example 11-1 is a program that does just that. In addition, it starts another thread to actually
do some filesystem operations, so that you can see the Watcher Service operating.

Example 11-1. src/main/java/nio/FileWatchServiceDemo.java
public public class class FileWatchServiceDemo FileWatchServiceDemo {

final final static static String tempDirPath = "/tmp" ;

static static Thread mainRunner ;

static static volatile volatile boolean boolean done = false false ;

public public static static void void main ( String [] args ) throws throws Throwable {

String tempDirPath = "/tmp" ;
System . out . println ( "Starting watcher for " + tempDirPath );
Path p = Paths . get ( tempDirPath );
WatchService watcher =
FileSystems . getDefault (). newWatchService ();
Kind <?>[] watchKinds = { ENTRY_CREATE , ENTRY_MODIFY };
p . register ( watcher , watchKinds );
mainRunner = Thread . currentThread ();
new new Thread ( new new DemoService ()). start ();

while while (! done ) {

WatchKey key = watcher . take ();
for for ( WatchEvent <?> e : key . pollEvents ()) {

System . out . println (
"Saw event " + e . kind () + " on " +
e . context ());
iif ( e . context (). toString (). equals ( "MyFileSema.for" )) {
System . out . println ( "Semaphore found, shutting down watcher" );
done = true true ;

}

}
iif (! key . reset ()) {
System . err . println ( "Key failed to reset!" );

}

}