File Attributes using Java NIO

This Java NIO tutorial is to learn about how to access file attributes and if possible modify it. java.nio.file.attribute package contains classes that helps to get and set file attributes. Before Java SE 7 we did not have direct support to access the large array file attributes. Now the NIO API is advanced, it has abstracted the underlying OS and its file system by providing seamless less access to the attributes and a way of manipulating them. This tutorial is part of the Java NIO tutorial series.

Basic File Attributes with NIO

Again the NIO Files util class comes into play. We can use it to get an instance of BasicFileAttributes by passing its class as argument using the method readAttributes. Once we get an instance of BasicFileAttributes then its just about accessing the attributes using its get accessor methods. We can modify some attributes like lastModifiedTime. The below example code demonstrates accessing the basic file attributes. It also showcases how we can modify the last modified time for a file.

	
		
//Path path = Paths.get("temp.txt");
//nioBasicFileAttributes(path);

public static void nioBasicFileAttributes(Path path) throws IOException {

	BasicFileAttributes basicFileAttributes = Files.readAttributes(path,
		BasicFileAttributes.class);

	// Print basic file attributes
	System.out.println("Creation Time: "
			+ basicFileAttributes.creationTime());
	System.out.println("Last Access Time: "
			+ basicFileAttributes.lastAccessTime());
	System.out.println("Last Modified Time: "
			+ basicFileAttributes.lastModifiedTime());
	System.out.println("Size: " + basicFileAttributes.size());
	System.out.println("Is Regular file: "
			+ basicFileAttributes.isRegularFile());
	System.out
			.println("Is Directory: " + basicFileAttributes.isDirectory());
	System.out.println("Is Symbolic Link: "
			+ basicFileAttributes.isSymbolicLink());
	System.out.println("Other: " + basicFileAttributes.isOther());

	// modify the lastmodifiedtime
	FileTime newModifiedTime = FileTime.fromMillis(basicFileAttributes
			.lastModifiedTime().toMillis() + 60000);
	Files.setLastModifiedTime(path, newModifiedTime);
	// check if the lastmodifiedtime is changed
	System.out.println("After Changing lastModifiedTime, ");
	System.out.println("Creation Time: "
			+ basicFileAttributes.creationTime());
	System.out.println("Last Access Time: "
			+ basicFileAttributes.lastAccessTime());
	System.out.println("Last Moodified Time: "
			+ basicFileAttributes.lastModifiedTime());
	}

NIO File Attributes Example Output:

Creation Time: 2015-07-21T05:02:46.120261Z
Last Access Time: 2015-07-21T05:02:46.120261Z
Last Modified Time: 2015-07-21T15:22:41.408Z
Size: 4
Is Regular file: true
Is Directory: false
Is Symbolic Link: false
Other: false
After Changing lastModifiedTime, 
Creation Time: 2015-07-21T05:02:46.120261Z
Last Access Time: 2015-07-21T05:02:46.120261Z
Last Moodified Time: 2015-07-21T15:22:41.408Z

File Owner via UserPrincipal with NIO

Let us see how we can get and set the owner of a file using Java NIO. We can use the same NIO Files util class and use method getFileAttributeView by passing argument FileOwnerAttributeView class. Then we get the UserPrincipal using which we can get and set the file owner name. Setting will throw exception if the passed name is not present in the user principle or if access is denied to set the owner name. Following is the example code demonstrating it.

//Path path = Paths.get("temp.txt");
//nioBasicFileAttributes(path);

public static void nioFileOwnerAttributeView(Path path) throws IOException {

	FileOwnerAttributeView fileOwnerAttributeView = Files
			.getFileAttributeView(path, FileOwnerAttributeView.class);
	UserPrincipal userPrincipal = fileOwnerAttributeView.getOwner();
	System.out.println("File Owner: " + userPrincipal.getName());

	FileSystem fileSystem = FileSystems.getDefault();
	UserPrincipalLookupService userPLS = fileSystem
			.getUserPrincipalLookupService();

	// java.nio.file.attribute.UserPrincipalNotFoundException possible here
	// if the user name passed is not present
	// java.nio.file.AccessDeniedException possible if not enough rights
	UserPrincipal newUserPrincipal = userPLS
			.lookupPrincipalByName("accountgroup\\username");
	fileOwnerAttributeView.setOwner(newUserPrincipal);

	UserPrincipal changedUserPrincipal = fileOwnerAttributeView.getOwner();
	System.out.println("Changed File Owner: " + changedUserPrincipal);

}

FileStore Space with NIO

Let us see how we can get space related information of the underlying disk. We can use NIO classes FileSystems and FileStore to get the space information.

public static void nioFileStoreSpace() throws IOException {

	// Loop through the set of FileStores for the default FileSystem
	for (FileStore fileStore : FileSystems.getDefault().getFileStores()) {
		System.out.println("Name: " + fileStore.name());
		System.out.println("Type: " + fileStore.type());
		System.out.println("Total Space (MB): " + fileStore.getTotalSpace()
				/ 1024 / 1024);
		System.out.println("Unallocated Space (MB): "
				+ fileStore.getUnallocatedSpace() / 1024 / 1024);
		System.out.println("Usable Space (MB): "
				+ fileStore.getUsableSpace() / 1024 / 1024);
	}
}

NIO FileStore Space Example Output:

Name: PROG
Type: NTFS
Total Space (MB): 93889
Unallocated Space (MB): 38873
Usable Space (MB): 38873
Name: INF
Type: NTFS
Total Space (MB): 20479
Unallocated Space (MB): 9280
Usable Space (MB): 9280
Name: System Reserved
Type: NTFS
Total Space (MB): 99
Unallocated Space (MB): 71
Usable Space (MB): 71

User Defined File Attribute with NIO

NIO provides API to get and set an user defined attribute to a file. This will be hand in many real time situations. We can use the NIO API UserDefinedFileAttributeView and Files class to write and read a custom attribute to a file.

// Path path = Paths.get("temp.txt");
// nioUserDefinedFileAttributeView(path);
public static void nioUserDefinedFileAttributeView(Path path)
		throws IOException {

	if (File.separatorChar != '\\') {
		System.out.println("This is Windows specific and so exit!");
		return;
	}
	UserDefinedFileAttributeView userDefinedFAView = Files
			.getFileAttributeView(path, UserDefinedFileAttributeView.class);
	List attributeList = userDefinedFAView.list();
	System.out.println("User Defined Attribute List Size Before Adding: "
			+ attributeList.size());

	// set user define attribute
	String attributeName = "foo";
	String attributeValue = "bar";
	userDefinedFAView.write(attributeName,
			Charset.defaultCharset().encode(attributeValue));

	attributeList = userDefinedFAView.list();
	if (attributeList.size() > 0) {
		for (String attName : attributeList) {
			ByteBuffer attValue = ByteBuffer.allocate(userDefinedFAView
					.size(attName));
			userDefinedFAView.read(attName, attValue);
			attValue.flip();
			System.out.println("User Defined Attribute Name: " + attName);
			System.out.println("User Defined Attribute Value: "
					+ Charset.defaultCharset().decode(attValue).toString());
		}
	} else {
		System.out
				.println("User define attribute count should be at least 1"
						+ " as we have set an attribute just now!");
	}

	userDefinedFAView.delete(attributeName);

	// And list the attributes again to check they're back to 0
	attributeList = userDefinedFAView.list();
	System.out.println("User Defined Attribute List Size After Deleting: "
			+ attributeList.size());
}

NIO User Defined Attribute Example Output:

User Defined Attribute List Size Before Adding: 0
User Defined Attribute Name: foo
User Defined Attribute Value: bar
User Defined Attribute List Size After Deleting: 0

This Java tutorial was added on 21/07/2015.

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