如何在Java7中为特定用户设置文件访问属性

Question

i am using java7 File api. for setting owner of a file i searched and able to change owner attribute. my code is

public static void main(String[] args){

    Path zip=Paths.get("/home/ritesh/hello");
    try{ 
        FileOwnerAttributeView view 
             = Files.getFileAttributeView(zip,FileOwnerAttributeView.class);

        UserPrincipalLookupService lookupService
             =FileSystems.getDefaullt().getUserPrincipalLookupService();

        UserPrincipal owner=null;

        try{ owner =lookupService.lookupPrincipalByName("rashmi");}
        catch(UserPrincipalNotFoundException e){System.out.println("User not found");}

        view.setOwner(owner);

    } catch (IOException e){
        e.printStackTrace();}
    }

from this code i can set the owner of the file .but my task is to give a user(rashmi) Read access to a file and one more user to give Read/Write access.how to give particular access to a user please give some code or link so that i can accomplish my task.

Answer 1

This is taken from the Java 7 Javadoc for AclFileAttributeView (with a little reformatting):

 // lookup "joe"
 UserPrincipal joe = file.getFileSystem().getUserPrincipalLookupService()
     .lookupPrincipalByName("joe");

 // get view
 AclFileAttributeView view = Files.getFileAttributeView(file,
                                       AclFileAttributeView.class);

 // create ACE to give "joe" read access
 AclEntry entry = AclEntry.newBuilder()
     .setType(AclEntryType.ALLOW)
     .setPrincipal(joe)
     .setPermissions(AclEntryPermission.READ_DATA,
                     AclEntryPermission.READ_ATTRIBUTES)
     .build();

 // read ACL, insert ACE, re-write ACL
 List<AclEntry> acl = view.getAcl();
 acl.add(0, entry);   // insert before any DENY entries
 view.setAcl(acl);

You need to use the right AclEntry code. See the AclFileAttributeView Javadoc .

Answer 2

you have to understand permission policy of the OS, you cant specify different permissions for different users, you have to do it other way.

file permissions is defined with 3 Octal numbers (base 8), which is 3 groups of 3 binary numbers, each 3 bits stands for Read,Write,Execute the first group is the Owner , second is Group , third is Other

so, if you want to give different permissions you can set the Group attribute to have access for reading and writing, and the Other just to reading, afterwards, you have to add the user you want to be able to Read and Write to this group.