1 /*
2 * Copyright (c) 2007, 2009, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
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7 * published by the Free Software Foundation. Oracle designates this
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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).
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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 * <h4> Dynamic Access </h4>
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">
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 * <h4> Setting Initial Permissions </h4>
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
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
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 */
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 */
192 void setGroup(GroupPrincipal group) throws IOException;
193 }