JavaSE: How to SET/GET your own Files and Directory Attributes

In the previous article “Determining Views Supported by a Particular File System” and see how to ask the file system store, and see supportability of a particular file attribute view.

We are going to explore in a nutshell, one of the most advanced and important files attribute views which is User-Defined File Attributes View.

Particularly, I am using this feature a lot in my exchanged files during integration between my systems, to hide my files meta-data and security related information from users and contents of the file. So the file content will be only regarding the content of the file only, no more irrelevant meta-data.

Therefore If you find that there are not enough built-in attributes for your needs or if you have some unique meta-data (meaningful to the file system) that you want to associate with a file, you can define your own attributes.

NIO.2 offers the user-defined file attributes view, extended attributes through the UserDefinedFileAttributeView interface. This facility allows you to associate to a file any attribute that you consider to be useful for your use cases.

Here you should know how to:

  1. Check User-Defined Attributes Supportability
  2. Operations on User-Defined Attributes as the following:
    1. Define a User Attribute.
    2. List User-Defined Attribute Names and Value Sizes.
    3. Get the Value of a User-Defined Attribute.
    4. Delete a File’s User-Defined Attribute.

Here is the class that has operations defined previously, also you need to use JDK 7+:

import static java.lang.System.err;
import static java.lang.System.out;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import static java.nio.file.Files.getFileStore;
import java.nio.file.Path;
import static java.nio.file.Paths.get;
import java.nio.file.attribute.UserDefinedFileAttributeView;
 
/**
 * GET/SET FILES METADATA THROUGH THE NEW JAVA.NIO.FILE.ATTRIBUTE API.
 *
 * @author mohamed_taman
 *
 * @see java.nio.file.attribute
 * @see java.nio.file.Files
 */
public class MetadataOperations {
 
    private static FileSystem fs = FileSystems.getDefault();
    private static Path path = get("C:", "workspace/NIO2", "resources", "TOC.txt");
 
    public static void main(String... args) {
 
       //User-Defined File Attributes View |
        userDefinedViewsOperations();
 
    }
 
    private static void userDefinedViewsOperations() {
 
        try {
             
            // Check User-Defined Attributes Supportability
 
            if (getFileStore(path)
                .supportsFileAttributeView(UserDefinedFileAttributeView.class)) {
                
                // 1- Define a User Attribute.
                 
                UserDefinedFileAttributeView udfav = Files.getFileAttributeView(path, 
                          UserDefinedFileAttributeView.class);
                 
                out.println("Attrs. before deletion. its size: " + udfav.list().size());
                 
                for (String name : udfav.list()) {
                    out.println(udfav.size(name) + " " + name);
                }
 
                int written = udfav.write("file.description", Charset.defaultCharset().
                        encode("This file contains private information about HOL2846!"));
 
                // 2- List User-Defined Attribute Names and Value Sizes.
                 
                for (String name : udfav.list()) {
                    out.println(udfav.size(name) + " " + name);
                }
 
                // 3- Get the Value of a User-Defined Attribute.
                  
                int size = udfav.size("file.description");
                ByteBuffer bb = ByteBuffer.allocateDirect(size);
                udfav.read("file.description", bb);
                bb.flip();
 
                out.println(Charset.defaultCharset().decode(bb).toString());
 
                /**
                 * Note: Using the UserDefinedFileAttributeView.size() method, 
                 * you can easily set the correct size of the buffer that represents 
                 * the value of the user-defined attribute.
                 * 
                 * Note: You can also read an attribute by using the getAttribute() method. 
                 * The value is returned as byte array (byte[]).
                 * 
                 */
                 
                 // 4- Delete a File’s User-Defined Attribute.
              
                out.println("Attrs. before deletion.");
                 
                for (String name : udfav.list()) {
                    out.println(udfav.size(name) + " " + name);
                }
 
                udfav.delete("file.description");
 
                out.println("Attrs. after deletion.");
                 
                for (String name : udfav.list()) {
                    out.println(udfav.size(name) + " " + name);
                }
 
            } else {
 
                out.println(path.toAbsolutePath().toString() + 
                         ", Doesn't support user defined attributes.");
            }
        } catch (Exception e) {
            err.println(e);
        }
    }
}

Resources

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