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25 
26 package java.nio.file.attribute;
27 
28 import static java.nio.file.attribute.PosixFilePermission.*;
29 import java.util.*;
30 
31 /**
32  * This class consists exclusively of static methods that operate on sets of
33  * {@link PosixFilePermission} objects.
34  *
35  * @since 1.7
36  */
37 
38 public final class PosixFilePermissions {
PosixFilePermissions()39     private PosixFilePermissions() { }
40 
41     // Write string representation of permission bits to {@code sb}.
writeBits(StringBuilder sb, boolean r, boolean w, boolean x)42     private static void writeBits(StringBuilder sb, boolean r, boolean w, boolean x) {
43         if (r) {
44             sb.append('r');
45         } else {
46             sb.append('-');
47         }
48         if (w) {
49             sb.append('w');
50         } else {
51             sb.append('-');
52         }
53         if (x) {
54             sb.append('x');
55         } else {
56             sb.append('-');
57         }
58     }
59 
60     /**
61      * Returns the {@code String} representation of a set of permissions. It
62      * is guaranteed that the returned {@code String} can be parsed by the
63      * {@link #fromString} method.
64      *
65      * <p> If the set contains {@code null} or elements that are not of type
66      * {@code PosixFilePermission} then these elements are ignored.
67      *
68      * @param   perms
69      *          the set of permissions
70      *
71      * @return  the string representation of the permission set
72      */
toString(Set<PosixFilePermission> perms)73     public static String toString(Set<PosixFilePermission> perms) {
74         StringBuilder sb = new StringBuilder(9);
75         writeBits(sb, perms.contains(OWNER_READ), perms.contains(OWNER_WRITE),
76           perms.contains(OWNER_EXECUTE));
77         writeBits(sb, perms.contains(GROUP_READ), perms.contains(GROUP_WRITE),
78           perms.contains(GROUP_EXECUTE));
79         writeBits(sb, perms.contains(OTHERS_READ), perms.contains(OTHERS_WRITE),
80           perms.contains(OTHERS_EXECUTE));
81         return sb.toString();
82     }
83 
isSet(char c, char setValue)84     private static boolean isSet(char c, char setValue) {
85         if (c == setValue)
86             return true;
87         if (c == '-')
88             return false;
89         throw new IllegalArgumentException("Invalid mode");
90     }
isR(char c)91     private static boolean isR(char c) { return isSet(c, 'r'); }
isW(char c)92     private static boolean isW(char c) { return isSet(c, 'w'); }
isX(char c)93     private static boolean isX(char c) { return isSet(c, 'x'); }
94 
95     /**
96      * Returns the set of permissions corresponding to a given {@code String}
97      * representation.
98      *
99      * <p> The {@code perms} parameter is a {@code String} representing the
100      * permissions. It has 9 characters that are interpreted as three sets of
101      * three. The first set refers to the owner's permissions; the next to the
102      * group permissions and the last to others. Within each set, the first
103      * character is {@code 'r'} to indicate permission to read, the second
104      * character is {@code 'w'} to indicate permission to write, and the third
105      * character is {@code 'x'} for execute permission. Where a permission is
106      * not set then the corresponding character is set to {@code '-'}.
107      *
108      * <p> <b>Usage Example:</b>
109      * Suppose we require the set of permissions that indicate the owner has read,
110      * write, and execute permissions, the group has read and execute permissions
111      * and others have none.
112      * <pre>
113      *   Set&lt;PosixFilePermission&gt; perms = PosixFilePermissions.fromString("rwxr-x---");
114      * </pre>
115      *
116      * @param   perms
117      *          string representing a set of permissions
118      *
119      * @return  the resulting set of permissions
120      *
121      * @throws  IllegalArgumentException
122      *          if the string cannot be converted to a set of permissions
123      *
124      * @see #toString(Set)
125      */
fromString(String perms)126     public static Set<PosixFilePermission> fromString(String perms) {
127         if (perms.length() != 9)
128             throw new IllegalArgumentException("Invalid mode");
129         Set<PosixFilePermission> result = EnumSet.noneOf(PosixFilePermission.class);
130         if (isR(perms.charAt(0))) result.add(OWNER_READ);
131         if (isW(perms.charAt(1))) result.add(OWNER_WRITE);
132         if (isX(perms.charAt(2))) result.add(OWNER_EXECUTE);
133         if (isR(perms.charAt(3))) result.add(GROUP_READ);
134         if (isW(perms.charAt(4))) result.add(GROUP_WRITE);
135         if (isX(perms.charAt(5))) result.add(GROUP_EXECUTE);
136         if (isR(perms.charAt(6))) result.add(OTHERS_READ);
137         if (isW(perms.charAt(7))) result.add(OTHERS_WRITE);
138         if (isX(perms.charAt(8))) result.add(OTHERS_EXECUTE);
139         return result;
140     }
141 
142     /**
143      * Creates a {@link FileAttribute}, encapsulating a copy of the given file
144      * permissions, suitable for passing to the {@link java.nio.file.Files#createFile
145      * createFile} or {@link java.nio.file.Files#createDirectory createDirectory}
146      * methods.
147      *
148      * @param   perms
149      *          the set of permissions
150      *
151      * @return  an attribute encapsulating the given file permissions with
152      *          {@link FileAttribute#name name} {@code "posix:permissions"}
153      *
154      * @throws  ClassCastException
155      *          if the set contains elements that are not of type {@code
156      *          PosixFilePermission}
157      */
158     public static FileAttribute<Set<PosixFilePermission>>
asFileAttribute(Set<PosixFilePermission> perms)159         asFileAttribute(Set<PosixFilePermission> perms)
160     {
161         // copy set and check for nulls (CCE will be thrown if an element is not
162         // a PosixFilePermission)
163         perms = new HashSet<PosixFilePermission>(perms);
164         for (PosixFilePermission p: perms) {
165             if (p == null)
166                 throw new NullPointerException();
167         }
168         final Set<PosixFilePermission> value = perms;
169         return new FileAttribute<Set<PosixFilePermission>>() {
170             @Override
171             public String name() {
172                 return "posix:permissions";
173             }
174             @Override
175             public Set<PosixFilePermission> value() {
176                 return Collections.unmodifiableSet(value);
177             }
178         };
179     }
180 }
181