public void addObserver(FileChangeObserver observer, String filename, long delay) throws FileNotFoundException {
TimerTask task = new FileChangeTask(observer , filename );
List<TimerTask> tasks = fileObservers.get(filename );
if(tasks ==null){
tasks = new ArrayList<TimerTask>();
}
tasks.add( task);
fileObservers.put(filename , tasks );
timer.schedule( task, delay, delay);
}
在FileChangeTask的run()函数中，通过比对时间戳来判断文件是否修改，若发生改动，则通知其Observer进行相应处理。
public void run() {
try {
long newLastModified = file.lastModified();
if (newLastModified > lastModified )[ ] {
lastModified = newLastModified ;[ ]
observer.fileChanged( file.getPath());
}
} catch (Exception e ) {
System. err.println(e .getMessage());
}
}
测试用例FileMonitorTest中为sample1.txt添加了consoleObserver和emailObserver，为sample2.txt添加了consoleObserver。然后对这两个文件分别进行修改。
package com.cwind.file;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
public class FileMonitorTest {
File sampleFile1, sampleFile2 ;
FileChangeMonitor monitor;
ConsoleFileChangeObserver consoleObserver;
EmailFileChangeObserver emailObserver;
@Before
public void setUp() throws Exception {
sampleFile1 = new File("sample1.txt" );
sampleFile2 = new File("sample2.txt" );
monitor = FileChangeMonitor. getInstance();
consoleObserver = new ConsoleFileChangeObserver();
emailObserver = new EmailFileChangeObserver("billchen01@163.com");
}
@After
public void tearDown() throws Exception {
}
@Test
public void testMonitorSampleFile() throws InterruptedException, IOException{
monitor.addObserver( consoleObserver, sampleFile1 .getPath(), FileChangeMonitor.DELAY_TIME );
monitor.addObserver( emailObserver, sampleFile1 .getPath(), FileChangeMonitor.DELAY_TIME );
monitor.addObserver( consoleObserver, sampleFile2 .getPath(), FileChangeMonitor.DELAY_TIME );
FileOutputStream fos1 = new FileOutputStream(sampleFile1 );
FileOutputStream fos2 = new FileOutputStream(sampleFile2 );
fos1.write(0);
fos2.write(0);
fos1.flush();
fos2.flush();
fos1.close();
fos2.close();
Thread. sleep(3000);
}
}
输出结果如下：Console: File sample1.txt is changed, will print warning message to console. File sample1.txt is changed, will send email to billchen01@163.com. Console: File sample2.txt is changed, will print warning message to console.JDK 1.7 及之后版本：基于WatchService实现
package com.cwind.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;
public class WatchServerTest {
public static void main(String[] args) throws InterruptedException, IOException {
WatchService watchService = FileSystems.getDefault().newWatchService();
final Path path = Paths.get( ".");
final WatchKey watchKey = path.register( watchService, StandardWatchEventKinds.ENTRY_MODIFY ,
StandardWatchEventKinds. ENTRY_CREATE, StandardWatchEventKinds.ENTRY_DELETE );
boolean fileNotChanged = true;
int count = 0;
while (fileNotChanged ) {
final WatchKey wk = watchService .take();
System. out.println("Loop count: " + count );
for (WatchEvent<?> event : wk .pollEvents()) {
final Path changed = (Path) event.context();
System. out.println(changed + ", " + event .kind());
if (changed .endsWith("sample1.txt")) {
System. out.println("Sample file has changed" );
}
}
// reset the key
boolean valid = wk .reset();
if (!valid ) {
System. out.println("Key has been unregisterede" );
}
count++;
}
}
}
?总结，使用WatchService步骤如下：
原文：http://cwind.iteye.com/blog/2179068