Java example source code file (PosixFilePermissions.java)

This example Java source code file (PosixFilePermissions.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

fileattribute, hashset, illegalargumentexception, invalid, nullpointerexception, override, posixfilepermissions, set, string, stringbuilder, util

The PosixFilePermissions.java Java example source code

/*
 * Copyright (c) 2007, 2011, 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 static java.nio.file.attribute.PosixFilePermission.*;
import java.util.*;

/**
 * This class consists exclusively of static methods that operate on sets of
 * {@link PosixFilePermission} objects.
 *
 * @since 1.7
 */

public final class PosixFilePermissions {
    private PosixFilePermissions() { }

    // Write string representation of permission bits to {@code sb}.
    private static void writeBits(StringBuilder sb, boolean r, boolean w, boolean x) {
        if (r) {
            sb.append('r');
        } else {
            sb.append('-');
        }
        if (w) {
            sb.append('w');
        } else {
            sb.append('-');
        }
        if (x) {
            sb.append('x');
        } else {
            sb.append('-');
        }
    }

    /**
     * Returns the {@code String} representation of a set of permissions. It
     * is guaranteed that the returned {@code String} can be parsed by the
     * {@link #fromString} method.
     *
     * <p> If the set contains {@code null} or elements that are not of type
     * {@code PosixFilePermission} then these elements are ignored.
     *
     * @param   perms
     *          the set of permissions
     *
     * @return  the string representation of the permission set
     */
    public static String toString(Set<PosixFilePermission> perms) {
        StringBuilder sb = new StringBuilder(9);
        writeBits(sb, perms.contains(OWNER_READ), perms.contains(OWNER_WRITE),
          perms.contains(OWNER_EXECUTE));
        writeBits(sb, perms.contains(GROUP_READ), perms.contains(GROUP_WRITE),
          perms.contains(GROUP_EXECUTE));
        writeBits(sb, perms.contains(OTHERS_READ), perms.contains(OTHERS_WRITE),
          perms.contains(OTHERS_EXECUTE));
        return sb.toString();
    }

    private static boolean isSet(char c, char setValue) {
        if (c == setValue)
            return true;
        if (c == '-')
            return false;
        throw new IllegalArgumentException("Invalid mode");
    }
    private static boolean isR(char c) { return isSet(c, 'r'); }
    private static boolean isW(char c) { return isSet(c, 'w'); }
    private static boolean isX(char c) { return isSet(c, 'x'); }

    /**
     * Returns the set of permissions corresponding to a given {@code String}
     * representation.
     *
     * <p> The {@code perms} parameter is a {@code String} representing the
     * permissions. It has 9 characters that are interpreted as three sets of
     * three. The first set refers to the owner's permissions; the next to the
     * group permissions and the last to others. Within each set, the first
     * character is {@code 'r'} to indicate permission to read, the second
     * character is {@code 'w'} to indicate permission to write, and the third
     * character is {@code 'x'} for execute permission. Where a permission is
     * not set then the corresponding character is set to {@code '-'}.
     *
     * <p> Usage Example:
     * Suppose we require the set of permissions that indicate the owner has read,
     * write, and execute permissions, the group has read and execute permissions
     * and others have none.
     * <pre>
     *   Set<PosixFilePermission> perms = PosixFilePermissions.fromString("rwxr-x---");
     * </pre>
     *
     * @param   perms
     *          string representing a set of permissions
     *
     * @return  the resulting set of permissions
     *
     * @throws  IllegalArgumentException
     *          if the string cannot be converted to a set of permissions
     *
     * @see #toString(Set)
     */
    public static Set<PosixFilePermission> fromString(String perms) {
        if (perms.length() != 9)
            throw new IllegalArgumentException("Invalid mode");
        Set<PosixFilePermission> result = EnumSet.noneOf(PosixFilePermission.class);
        if (isR(perms.charAt(0))) result.add(OWNER_READ);
        if (isW(perms.charAt(1))) result.add(OWNER_WRITE);
        if (isX(perms.charAt(2))) result.add(OWNER_EXECUTE);
        if (isR(perms.charAt(3))) result.add(GROUP_READ);
        if (isW(perms.charAt(4))) result.add(GROUP_WRITE);
        if (isX(perms.charAt(5))) result.add(GROUP_EXECUTE);
        if (isR(perms.charAt(6))) result.add(OTHERS_READ);
        if (isW(perms.charAt(7))) result.add(OTHERS_WRITE);
        if (isX(perms.charAt(8))) result.add(OTHERS_EXECUTE);
        return result;
    }

    /**
     * Creates a {@link FileAttribute}, encapsulating a copy of the given file
     * permissions, suitable for passing to the {@link java.nio.file.Files#createFile
     * createFile} or {@link java.nio.file.Files#createDirectory createDirectory}
     * methods.
     *
     * @param   perms
     *          the set of permissions
     *
     * @return  an attribute encapsulating the given file permissions with
     *          {@link FileAttribute#name name} {@code "posix:permissions"}
     *
     * @throws  ClassCastException
     *          if the set contains elements that are not of type {@code
     *          PosixFilePermission}
     */
    public static FileAttribute<Set
        asFileAttribute(Set<PosixFilePermission> perms)
    {
        // copy set and check for nulls (CCE will be thrown if an element is not
        // a PosixFilePermission)
        perms = new HashSet<PosixFilePermission>(perms);
        for (PosixFilePermission p: perms) {
            if (p == null)
                throw new NullPointerException();
        }
        final Set<PosixFilePermission> value = perms;
        return new FileAttribute<Set() {
            @Override
            public String name() {
                return "posix:permissions";
            }
            @Override
            public Set<PosixFilePermission> value() {
                return Collections.unmodifiableSet(value);
            }
        };
    }
}