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package java.nio.file.attribute;
import java.nio.file.*;
import java.util.Set;
import java.io.IOException;
/**
* A file attribute view that provides a view of the file attributes commonly
* associated with files on file systems used by operating systems that implement
* the Portable Operating System Interface (POSIX) family of standards.
*
* <p> Operating systems that implement the <a href="http://www.opengroup.org">
* POSIX</a> family of standards commonly use file systems that have a
* file <em>owner</em>, <em>group-owner</em>, and related <em>access
* permissions</em>. This file attribute view provides read and write access
* to these attributes.
*
* <p> The {@link #readAttributes() readAttributes} method is used to read the
* file's attributes. The file {@link PosixFileAttributes#owner() owner} is
* represented by a {@link UserPrincipal} that is the identity of the file owner
* for the purposes of access control. The {@link PosixFileAttributes#group()
* group-owner}, represented by a {@link GroupPrincipal}, is the identity of the
* group owner, where a group is an identity created for administrative purposes
* so as to determine the access rights for the members of the group.
*
* <p> The {@link PosixFileAttributes#permissions() permissions} attribute is a
* set of access permissions. This file attribute view provides access to the nine
* permission defined by the {@link PosixFilePermission} class.
* These nine permission bits determine the <em>read</em>, <em>write</em>, and
* <em>execute</em> access for the file owner, group, and others (others
* meaning identities other than the owner and members of the group). Some
* operating systems and file systems may provide additional permission bits
* but access to these other bits is not defined by this class in this release.
*
* <p> <b>Usage Example:</b>
* Suppose we need to print out the owner and access permissions of a file:
* <pre>
* Path file = ...
* PosixFileAttributes attrs = Files.getFileAttributeView(file, PosixFileAttributeView.class)
* .readAttributes();
* System.out.format("%s %s%n",
* attrs.owner().getName(),
* PosixFilePermissions.toString(attrs.permissions()));
* </pre>
*
* <h2> Dynamic Access </h2>
* <p> Where dynamic access to file attributes is required, the attributes
* supported by this attribute view are as defined by {@link
* BasicFileAttributeView} and {@link FileOwnerAttributeView}, and in addition,
* the following attributes are supported:
* <blockquote>
* <table border="1" cellpadding="8" summary="Supported attributes">
* <tr>
* <th> Name </th>
* <th> Type </th>
* </tr>
* <tr>
* <td> "permissions" </td>
* <td> {@link Set}<{@link PosixFilePermission}> </td>
* </tr>
* <tr>
* <td> "group" </td>
* <td> {@link GroupPrincipal} </td>
* </tr>
* </table>
* </blockquote>
*
* <p> The {@link Files#getAttribute getAttribute} method may be used to read
* any of these attributes, or any of the attributes defined by {@link
* BasicFileAttributeView} as if by invoking the {@link #readAttributes
* readAttributes()} method.
*
* <p> The {@link Files#setAttribute setAttribute} method may be used to update
* the file's last modified time, last access time or create time attributes as
* defined by {@link BasicFileAttributeView}. It may also be used to update
* the permissions, owner, or group-owner as if by invoking the {@link
* #setPermissions setPermissions}, {@link #setOwner setOwner}, and {@link
* #setGroup setGroup} methods respectively.
*
* <h2> Setting Initial Permissions </h2>
* <p> Implementations supporting this attribute view may also support setting
* the initial permissions when creating a file or directory. The
* initial permissions are provided to the {@link Files#createFile createFile}
* or {@link Files#createDirectory createDirectory} methods as a {@link
* FileAttribute} with {@link FileAttribute#name name} {@code "posix:permissions"}
* and a {@link FileAttribute#value value} that is the set of permissions. The
* following example uses the {@link PosixFilePermissions#asFileAttribute
* asFileAttribute} method to construct a {@code FileAttribute} when creating a
* file:
*
* <pre>
* Path path = ...
* Set<PosixFilePermission> perms =
* EnumSet.of(OWNER_READ, OWNER_WRITE, OWNER_EXECUTE, GROUP_READ);
* Files.createFile(path, PosixFilePermissions.asFileAttribute(perms));
* </pre>
*
* <p> When the access permissions are set at file creation time then the actual
* value of the permissions may differ that the value of the attribute object.
* The reasons for this are implementation specific. On UNIX systems, for
* example, a process has a <em>umask</em> that impacts the permission bits
* of newly created files. Where an implementation supports the setting of
* the access permissions, and the underlying file system supports access
* permissions, then it is required that the value of the actual access
* permissions will be equal or less than the value of the attribute
* provided to the {@link Files#createFile createFile} or {@link
* Files#createDirectory createDirectory} methods. In other words, the file may
* be more secure than requested.
*
* @since 1.7
*/
public interface PosixFileAttributeView
extends BasicFileAttributeView, FileOwnerAttributeView
{
/**
* Returns the name of the attribute view. Attribute views of this type
* have the name {@code "posix"}.
*/
@Override
String name();
/**
* @throws IOException {@inheritDoc}
* @throws SecurityException
* In the case of the default provider, a security manager is
* installed, and it denies {@link RuntimePermission}<tt>("accessUserInformation")</tt>
* or its {@link SecurityManager#checkRead(String) checkRead} method
* denies read access to the file.
*/
@Override
PosixFileAttributes readAttributes() throws IOException;
/**
* Updates the file permissions.
*
* @param perms
* the new set of permissions
*
* @throws ClassCastException
* if the sets contains elements that are not of type {@code
* PosixFilePermission}
* @throws IOException
* if an I/O error occurs
* @throws SecurityException
* In the case of the default provider, a security manager is
* installed, and it denies {@link RuntimePermission}<tt>("accessUserInformation")</tt>
* or its {@link SecurityManager#checkWrite(String) checkWrite}
* method denies write access to the file.
*/
void setPermissions(Set<PosixFilePermission> perms) throws IOException;
/**
* Updates the file group-owner.
*
* @param group
* the new file group-owner
*
* @throws IOException
* if an I/O error occurs
* @throws SecurityException
* In the case of the default provider, and a security manager is
* installed, it denies {@link RuntimePermission}<tt>("accessUserInformation")</tt>
* or its {@link SecurityManager#checkWrite(String) checkWrite}
* method denies write access to the file.
*/
void setGroup(GroupPrincipal group) throws IOException;
}