Java tutorial
/* * Copyright (c) 2007, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ 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 bits 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 class="striped"> * <caption style="display:none">Supported attributes</caption> * <thead> * <tr> * <th scope="col"> Name </th> * <th scope="col"> Type </th> * </tr> * </thead> * <tbody> * <tr> * <th scope="row"> "permissions" </th> * <td> {@link Set}<{@link PosixFilePermission}> </td> * </tr> * <tr> * <th scope="row"> "group" </th> * <td> {@link GroupPrincipal} </td> * </tr> * </tbody> * </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 from 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}{@code ("accessUserInformation")} * 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}{@code ("accessUserInformation")} * 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}{@code ("accessUserInformation")} * or its {@link SecurityManager#checkWrite(String) checkWrite} * method denies write access to the file. */ void setGroup(GroupPrincipal group) throws IOException; }