How to Create a File with a Specific Owner and Group in Java ?

Java is a straightforward application that does not allow you to select the group or owner of a file at the time of creation. If we need to regulate certain characteristics, we have to rely on different approaches or third-party libraries. This article will demonstrate to us about how to use Java to create a file with a specified owner and group.

Methods for Generating a File with a Designated Owner and Group

Make sure the file has restricted access: When using Java's standard libraries to create a file, you are not able to designate the owner or group of the file explicitly. This indicates that the file originally has the ownership and group of the process (usually the application) that produced it.
Modify ownership: To change the owner and group settings of a file, you need to have elevated access or specific permissions once it has been created. These modifications usually need the granting of special operating system commands or administrative rights.

Note: The Java process needs to be running under a user who has the ability to alter file ownership, or it needs to have elevated privileges (root on Linux/macOS).

Java Program to Create a File with a Specific Owner and Group

The following are the steps required for completing the above task:

Step 1: To perform file operations and find user principals, we must import the required Java libraries.

Step 2: Set the preferred filename, group name (if applicable), and owner username.

Step 3: With Files, create the file.createFile with incredibly limited permissions (like 000).

Step 4: Make use of the UserPrincipalLookupService to obtain a UserPrincipal object that represents the intended owner.

Step 5: Files can be used to set the file's owner (and optional group). Higher privileges are necessary to setOwner.

Implementation:

FileName: FileCreationSpecificUserGroup.java

 
 import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.attribute.UserPrincipal;
import java.nio.file.attribute.UserPrincipalLookupService;
import java.nio.file.attribute.PosixFilePermission;
import java.util.Set;
import java.util.EnumSet;
import java.io.IOException;
public class FileCreationSpecificUserGroup 
{
    public static void main(String[] args) 
    {
        String filename = "HelloWorld.txt";
        String owner = "user_name"; // Replace with the preferred username.
        String group = "group_name"; // Replace with the preferred groupname.

        try 
        {
            // Check whether the file already exists or not
            Path path_file = Paths.get(filename);
            if (Files.exists(path_file)) 
            {
                System.out.println("The file already exists!");
                return;
            }
            // Create the file
            Files.createFile(path_file);
            // Retrieve the owner's UserPrincipal
            UserPrincipalLookupService lookup = path_file.getFileSystem().getUserPrincipalLookupService();
            UserPrincipal user = lookup.lookupPrincipalByName(owner);
            // Set the owner
            Files.setOwner(path_file, user);
            // If one is available, set up a group
            if (group != null) 
            {
                // Setting groups is not directly supported on Windows
                // You may need to use platform-specific commands or APIs
                System.out.println("On Windows, setting groups is not directly supported.");
            }
            // Set the permissions
            Set<PosixFilePermission> permissions = EnumSet.of(
                PosixFilePermission.OWNER_READ,
                PosixFilePermission.OWNER_WRITE,
                PosixFilePermission.GROUP_READ,
                PosixFilePermission.GROUP_WRITE,
                PosixFilePermission.OTHERS_READ
            );
            Files.setPosixFilePermissions(path_file, permissions);

            System.out.println("Ownership successfully changed and file created!");
        } 
        catch (IOException ex) 
        {
            System.err.println("An I/O error occurred: " + ex.getMessage());
        } 
        catch (UnsupportedOperationException ex) 
        {
            System.err.println("Operation not supported: " + ex.getMessage());
        }
    }
}  

Output: