The file name is retrieved from the event context. The Email example retrieves the file name with this code:. The WatchDir example avoids this error by creating a utility cast method that suppresses the unchecked warning, as follows:. If you are unfamiliar with the SuppressWarnings syntax, see Annotations. The Watch Service API is designed for applications that need to be notified about file change events.
It is well suited for any application, like an editor or IDE, that potentially has many open files and needs to ensure that the files are synchronized with the file system. It is also well suited for an application server that watches a directory, perhaps waiting for.
This API is not designed for indexing a hard drive. Most file system implementations have native support for file change notification. However, when a file system does not support this mechanism, the Watch Service will poll the file system, waiting for events. All rights reserved. Hide TOC. The following sample dialog box shows how this notification looks with the free editor, jEdit : jEdit Dialog Box Showing That a Modified File Is Detected To implement this functionality, called file change notification , a program must be able to detect what is happening to the relevant directory on the file system.
Here are the basic steps required to implement a watch service: Create a WatchService "watcher" for the file system. For each directory that you want monitored, register it with the watcher. When registering a directory, you specify the type of events for which you want notification. This typically involves removing redundant names such as ".
Every pathname that denotes an existing file or directory has a unique canonical form. Every pathname that denotes a nonexistent file or directory also has a unique canonical form. The canonical form of the pathname of a nonexistent file or directory may be different from the canonical form of the same pathname after the file or directory is created. Similarly, the canonical form of the pathname of an existing file or directory may be different from the canonical form of the same pathname after the file or directory is deleted.
FileDescriptor method denies read access to the file Since: 1. Converts this abstract pathname into a file: URL. The exact form of the URL is system-dependent. If it can be determined that the file denoted by this abstract pathname is a directory, then the resulting URL will end with a slash.
The exact form of the URI is system-dependent. If it can be determined that the file denoted by this abstract pathname is a directory, then the resulting URI will end with a slash. For a given abstract pathname f , it is guaranteed that new File f.
Due to the system-dependent nature of abstract pathnames, however, this relationship typically does not hold when a file: URI that is created in a virtual machine on one operating system is converted into an abstract pathname in a virtual machine on a different operating system. The authority component is undefined, meaning that it is represented as null. The Path class defines the toUri method to encode the server name in the authority component of the resulting URI.
The toPath method may be used to obtain a Path representing this abstract pathname. Returns: An absolute, hierarchical URI with a scheme equal to "file" , a path representing this abstract pathname, and undefined authority, query, and fragment components Throws: SecurityException - If a required system property value cannot be accessed.
Returns: true if and only if the file specified by this abstract pathname exists and can be read by the application; false otherwise Throws: SecurityException - If a security manager exists and its SecurityManager.
String method denies read access to the file canWrite public boolean canWrite Tests whether the application can modify the file denoted by this abstract pathname. Returns: true if and only if the file system actually contains a file denoted by this abstract pathname and the application is allowed to write to the file; false otherwise.
String method denies write access to the file exists public boolean exists Tests whether the file or directory denoted by this abstract pathname exists. Returns: true if and only if the file or directory denoted by this abstract pathname exists; false otherwise Throws: SecurityException - If a security manager exists and its SecurityManager. String method denies read access to the file or directory isDirectory public boolean isDirectory Tests whether the file denoted by this abstract pathname is a directory.
Returns: true if and only if the file denoted by this abstract pathname exists and is a directory; false otherwise Throws: SecurityException - If a security manager exists and its SecurityManager. String method denies read access to the file isFile public boolean isFile Tests whether the file denoted by this abstract pathname is a normal file. A file is normal if it is not a directory and, in addition, satisfies other system-dependent criteria. Any non-directory file created by a Java application is guaranteed to be a normal file.
Returns: true if and only if the file denoted by this abstract pathname exists and is a normal file; false otherwise Throws: SecurityException - If a security manager exists and its SecurityManager.
String method denies read access to the file isHidden public boolean isHidden Tests whether the file named by this abstract pathname is a hidden file.
The exact definition of hidden is system-dependent. On UNIX systems, a file is considered to be hidden if its name begins with a period character '. On Microsoft Windows systems, a file is considered to be hidden if it has been marked as such in the filesystem. Returns: true if and only if the file denoted by this abstract pathname is hidden according to the conventions of the underlying platform Throws: SecurityException - If a security manager exists and its SecurityManager.
String method denies read access to the file Since: 1. String method denies read access to the file length public long length Returns the length of the file denoted by this abstract pathname. The return value is unspecified if this pathname denotes a directory. Returns: The length, in bytes, of the file denoted by this abstract pathname, or 0L if the file does not exist. Some operating systems may return 0L for pathnames denoting system-dependent entities such as devices or pipes. String method denies read access to the file createNewFile public boolean createNewFile throws IOException Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist.
The check for the existence of the file and the creation of the file if it does not exist are a single operation that is atomic with respect to all other filesystem activities that might affect the file.
Note: this method should not be used for file-locking, as the resulting protocol cannot be made to work reliably. The FileLock facility should be used instead. String method denies write access to the file Since: 1.
If this pathname denotes a directory, then the directory must be empty in order to be deleted. Note that the Files class defines the delete method to throw an IOException when a file cannot be deleted. This is useful for error reporting and to diagnose why a file cannot be deleted. Returns: true if and only if the file or directory is successfully deleted; false otherwise Throws: SecurityException - If a security manager exists and its SecurityManager.
String method denies delete access to the file deleteOnExit public void deleteOnExit Requests that the file or directory denoted by this abstract pathname be deleted when the virtual machine terminates. Files or directories are deleted in the reverse order that they are registered. Invoking this method to delete a file or directory that is already registered for deletion has no effect.
Deletion will be attempted only for normal termination of the virtual machine, as defined by the Java Language Specification. Once deletion has been requested, it is not possible to cancel the request.
This method should therefore be used with care. String method denies delete access to the file Since: 1. If this abstract pathname does not denote a directory, then this method returns null.
Otherwise an array of strings is returned, one for each file or directory in the directory. Names denoting the directory itself and the directory's parent directory are not included in the result. Each string is a file name rather than a complete path.
There is no guarantee that the name strings in the resulting array will appear in any specific order; they are not, in particular, guaranteed to appear in alphabetical order.
Note that the Files class defines the newDirectoryStream method to open a directory and iterate over the names of the files in the directory. This may use less resources when working with very large directories, and may be more responsive when working with remote directories.
Returns: An array of strings naming the files and directories in the directory denoted by this abstract pathname. The array will be empty if the directory is empty. The behavior of this method is the same as that of the list method, except that the strings in the returned array must satisfy the filter. If the given filter is null then all names are accepted. Otherwise, a name satisfies the filter if and only if the value true results when the FilenameFilter.
Parameters: filter - A filename filter Returns: An array of strings naming the files and directories in the directory denoted by this abstract pathname that were accepted by the given filter.
The array will be empty if the directory is empty or if no names were accepted by the filter. Otherwise an array of File objects is returned, one for each file or directory in the directory.
Pathnames denoting the directory itself and the directory's parent directory are not included in the result. Each resulting abstract pathname is constructed from this abstract pathname using the File File, String constructor. Therefore if this pathname is absolute then each resulting pathname is absolute; if this pathname is relative then each resulting pathname will be relative to the same directory. This may use less resources when working with very large directories.
Returns: An array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname. The behavior of this method is the same as that of the listFiles method, except that the pathnames in the returned array must satisfy the filter. If the given filter is null then all pathnames are accepted. Otherwise, a pathname satisfies the filter if and only if the value true results when the FilenameFilter.
Parameters: filter - A filename filter Returns: An array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname.
Otherwise, a pathname satisfies the filter if and only if the value true results when the FileFilter. Parameters: filter - A file filter Returns: An array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname.
Filter mkdir public boolean mkdir Creates the directory named by this abstract pathname. Returns: true if and only if the directory was created; false otherwise Throws: SecurityException - If a security manager exists and its SecurityManager. String method does not permit the named directory to be created mkdirs public boolean mkdirs Creates the directory named by this abstract pathname, including any necessary but nonexistent parent directories.
Note that if this operation fails it may have succeeded in creating some of the necessary parent directories. If the user enters an unavailable location, the mkdirs make it available by creating all the parent folders that do not exist in the system. JavaTpoint offers too many high quality services. Mail us on [email protected] , to get more information about given services. Please mail your requirement at [email protected] Duration: 1 week to 2 week. Java Training Java Tutorial. Abstract class Interface Abstract vs Interface.
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