Monitor directory changes

Quartz定时器 or Timer + Thread：开启线程定时去读取文件内容，查看文件内容是否发生变化，但对于文件内容过大或者过于复杂的(不推荐)，或者通过定时检查文件的修改时间lastModifyTime，但是可能出现问题(不推荐)，还有通过读取文件流生成MD5对应的MD5码，如果MD5不同则文件发生变化，对于大型文件也有问题，适合小文件。

JDK watch：使用JDK 7自带的 watch。

Commons-io.monitor：File Monitor - a component for monitoring file system events。

JDK watch

有三种监听事件类型，ENTRY_CREATE、ENTRY_DELETE、ENTRY_MODIFY。Watch只能监控目录，而不能监听某个具体的文件，需手动实现监听具体的文件。如果直接监听文件，则会报错 NotDirectoryException。

public static void jdkWatchDirectory() {// define a folder rootPath myDir = Paths.get("D:/deploy");try {WatchService watcher = myDir.getFileSystem().newWatchService();myDir.register(watcher, StandardWatchEventKinds.ENTRY_MODIFY);WatchKey watckKey = watcher.take();while (true) {List<WatchEvent<?>> events = watckKey.pollEvents();for (WatchEvent event : events)if (event.kind() == StandardWatchEventKinds.ENTRY_MODIFY)System.out.println("Modify: " + event.context().toString());}} catch (Exception e) {System.out.println("Error: " + e.toString());}}

使用JDK Watch方式监控Directory，当文件内容发生变更时，有可能会触发两次MODIFY。

Commons-io Monitor

Commons-io Monitor class as follows：

FileAlterationListener Interface： A listener that receives events of file system modifications.

public interface FileAlterationListener {/*** File system observer started checking event.** @param observer The file system observer*/void onStart(final FileAlterationObserver observer);/*** Directory created Event.* * @param directory The directory created*/void onDirectoryCreate(final File directory);/*** Directory changed Event.* * @param directory The directory changed*/void onDirectoryChange(final File directory);/*** Directory deleted Event.* * @param directory The directory deleted*/void onDirectoryDelete(final File directory);/*** File created Event.* * @param file The file created*/void onFileCreate(final File file);/*** File changed Event.* * @param file The file changed*/void onFileChange(final File file);/*** File deleted Event.* * @param file The file deleted*/void onFileDelete(final File file);/*** File system observer finished checking event.** @param observer The file system observer*/void onStop(final FileAlterationObserver observer);
}

FileAlterationListenerAdaptor：a dapter ，fileAlterationListener implementation that does nothing.rewrite required methods。

example

public class FileListener extends FileAlterationListenerAdaptor {@Override  public void onFileChange(File file) {if (file.getName().contains("mail_profile.xml")) {// TODO do something}System.out.println("Modify:" + file.getAbsolutePath());  }  @Override  public void onStart(FileAlterationObserver observer) {  super.onStart(observer);  }  @Override  public void onStop(FileAlterationObserver observer) {  super.onStop(observer);  }  public static void main(String[] args) throws Exception{    String targetDirectory = "D:\\deploy";    long listeningInterval = TimeUnit.SECONDS.toMillis(2);  FileAlterationObserver observer = new FileAlterationObserver(targetDirectory);observer.addListener(new FileListener());    FileAlterationMonitor monitor = new FileAlterationMonitor(listeningInterval, observer); monitor.start();    }
}

Monitor directory "d:\deploy" file changes. 如果想监听某类文件的变化，需要添加FileFilter。

/*** Construct an observer for the specified directory and file filter.** @param directoryName the name of the directory to observe* @param fileFilter The file filter or null if none*/public FileAlterationObserver(String directoryName, FileFilter fileFilter) {this(new File(directoryName), fileFilter);}

implementation

String targetDirectory = "D:\\deploy";
long listeningInterval = TimeUnit.SECONDS.toMillis(2);
IOFileFilter fileFilter = FileFilterUtils.and(FileFilterUtils.fileFileFilter(),FileFilterUtils.suffixFileFilter(".xml"),FileFilterUtils.nameFileFilter("mail_profile.xml"));
Collection<File> files = FileUtils.listFiles(new File(rootDir),fileFilter, TrueFileFilter.INSTANCE);
System.out.println(files);
FileAlterationObserver observerFilter = new FileAlterationObserver(targetDirectory, fileFilter);
observerFilter.addListener(new FileListener());
FileAlterationMonitor monitor = new FileAlterationMonitor(listeningInterval, observerFilter );
monitor.start();    

但是FileFilter没有生效，并且整个目录的文件变化都未触发事件。所以只能不加FileFilter，并且在onFileChange中判断需要监听的具体类型或具体某个文件。