1 /* 2 * Copyright (c) 2007, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.nio.file.attribute; 27 28 import java.nio.file.*; 29 import java.util.Set; 30 import java.io.IOException; 31 32 /** 33 * A file attribute view that provides a view of the file attributes commonly 34 * associated with files on file systems used by operating systems that implement 35 * the Portable Operating System Interface (POSIX) family of standards. 36 * 37 * <p> Operating systems that implement the <a href="http://www.opengroup.org"> 38 * POSIX</a> family of standards commonly use file systems that have a 39 * file <em>owner</em>, <em>group-owner</em>, and related <em>access 40 * permissions</em>. This file attribute view provides read and write access 41 * to these attributes. 42 * 43 * <p> The {@link #readAttributes() readAttributes} method is used to read the 44 * file's attributes. The file {@link PosixFileAttributes#owner() owner} is 45 * represented by a {@link UserPrincipal} that is the identity of the file owner 46 * for the purposes of access control. The {@link PosixFileAttributes#group() 47 * group-owner}, represented by a {@link GroupPrincipal}, is the identity of the 48 * group owner, where a group is an identity created for administrative purposes 49 * so as to determine the access rights for the members of the group. 50 * 51 * <p> The {@link PosixFileAttributes#permissions() permissions} attribute is a 52 * set of access permissions. This file attribute view provides access to the nine 53 * permission defined by the {@link PosixFilePermission} class. 54 * These nine permission bits determine the <em>read</em>, <em>write</em>, and 55 * <em>execute</em> access for the file owner, group, and others (others 56 * meaning identities other than the owner and members of the group). Some 57 * operating systems and file systems may provide additional permission bits 58 * but access to these other bits is not defined by this class in this release. 59 * 60 * <p> <b>Usage Example:</b> 61 * Suppose we need to print out the owner and access permissions of a file: 62 * <pre> 63 * Path file = ... 64 * PosixFileAttributes attrs = Files.getFileAttributeView(file, PosixFileAttributeView.class) 65 * .readAttributes(); 66 * System.out.format("%s %s%n", 67 * attrs.owner().getName(), 68 * PosixFilePermissions.toString(attrs.permissions())); 69 * </pre> 70 * 71 * <h2> Dynamic Access </h2> 72 * <p> Where dynamic access to file attributes is required, the attributes 73 * supported by this attribute view are as defined by {@link 74 * BasicFileAttributeView} and {@link FileOwnerAttributeView}, and in addition, 75 * the following attributes are supported: 76 * <blockquote> 77 * <table border="1" cellpadding="8" summary="Supported attributes"> 78 * <tr> 79 * <th> Name </th> 80 * <th> Type </th> 81 * </tr> 82 * <tr> 83 * <td> "permissions" </td> 84 * <td> {@link Set}<{@link PosixFilePermission}> </td> 85 * </tr> 86 * <tr> 87 * <td> "group" </td> 88 * <td> {@link GroupPrincipal} </td> 89 * </tr> 90 * </table> 91 * </blockquote> 92 * 93 * <p> The {@link Files#getAttribute getAttribute} method may be used to read 94 * any of these attributes, or any of the attributes defined by {@link 95 * BasicFileAttributeView} as if by invoking the {@link #readAttributes 96 * readAttributes()} method. 97 * 98 * <p> The {@link Files#setAttribute setAttribute} method may be used to update 99 * the file's last modified time, last access time or create time attributes as 100 * defined by {@link BasicFileAttributeView}. It may also be used to update 101 * the permissions, owner, or group-owner as if by invoking the {@link 102 * #setPermissions setPermissions}, {@link #setOwner setOwner}, and {@link 103 * #setGroup setGroup} methods respectively. 104 * 105 * <h2> Setting Initial Permissions </h2> 106 * <p> Implementations supporting this attribute view may also support setting 107 * the initial permissions when creating a file or directory. The 108 * initial permissions are provided to the {@link Files#createFile createFile} 109 * or {@link Files#createDirectory createDirectory} methods as a {@link 110 * FileAttribute} with {@link FileAttribute#name name} {@code "posix:permissions"} 111 * and a {@link FileAttribute#value value} that is the set of permissions. The 112 * following example uses the {@link PosixFilePermissions#asFileAttribute 113 * asFileAttribute} method to construct a {@code FileAttribute} when creating a 114 * file: 115 * 116 * <pre> 117 * Path path = ... 118 * Set<PosixFilePermission> perms = 119 * EnumSet.of(OWNER_READ, OWNER_WRITE, OWNER_EXECUTE, GROUP_READ); 120 * Files.createFile(path, PosixFilePermissions.asFileAttribute(perms)); 121 * </pre> 122 * 123 * <p> When the access permissions are set at file creation time then the actual 124 * value of the permissions may differ that the value of the attribute object. 125 * The reasons for this are implementation specific. On UNIX systems, for 126 * example, a process has a <em>umask</em> that impacts the permission bits 127 * of newly created files. Where an implementation supports the setting of 128 * the access permissions, and the underlying file system supports access 129 * permissions, then it is required that the value of the actual access 130 * permissions will be equal or less than the value of the attribute 131 * provided to the {@link Files#createFile createFile} or {@link 132 * Files#createDirectory createDirectory} methods. In other words, the file may 133 * be more secure than requested. 134 * 135 * @since 1.7 136 */ 137 138 public interface PosixFileAttributeView 139 extends BasicFileAttributeView, FileOwnerAttributeView 140 { 141 /** 142 * Returns the name of the attribute view. Attribute views of this type 143 * have the name {@code "posix"}. 144 */ 145 @Override name()146 String name(); 147 148 /** 149 * @throws IOException {@inheritDoc} 150 * @throws SecurityException 151 * In the case of the default provider, a security manager is 152 * installed, and it denies {@link RuntimePermission}<tt>("accessUserInformation")</tt> 153 * or its {@link SecurityManager#checkRead(String) checkRead} method 154 * denies read access to the file. 155 */ 156 @Override readAttributes()157 PosixFileAttributes readAttributes() throws IOException; 158 159 /** 160 * Updates the file permissions. 161 * 162 * @param perms 163 * the new set of permissions 164 * 165 * @throws ClassCastException 166 * if the sets contains elements that are not of type {@code 167 * PosixFilePermission} 168 * @throws IOException 169 * if an I/O error occurs 170 * @throws SecurityException 171 * In the case of the default provider, a security manager is 172 * installed, and it denies {@link RuntimePermission}<tt>("accessUserInformation")</tt> 173 * or its {@link SecurityManager#checkWrite(String) checkWrite} 174 * method denies write access to the file. 175 */ setPermissions(Set<PosixFilePermission> perms)176 void setPermissions(Set<PosixFilePermission> perms) throws IOException; 177 178 /** 179 * Updates the file group-owner. 180 * 181 * @param group 182 * the new file group-owner 183 * 184 * @throws IOException 185 * if an I/O error occurs 186 * @throws SecurityException 187 * In the case of the default provider, and a security manager is 188 * installed, it denies {@link RuntimePermission}<tt>("accessUserInformation")</tt> 189 * or its {@link SecurityManager#checkWrite(String) checkWrite} 190 * method denies write access to the file. 191 */ setGroup(GroupPrincipal group)192 void setGroup(GroupPrincipal group) throws IOException; 193 } 194