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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}&lt;{@link PosixFilePermission}&gt; </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&lt;PosixFilePermission&gt; 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;
  }
  