Module java.base
Package java.io

Class FilePermission

  • All Implemented Interfaces:
    Serializable, Guard
    public final class FilePermission
extends Permission
implements Serializable
    This class represents access to a file or directory. A FilePermission consists of a pathname and a set of actions valid for that pathname.

    Pathname is the pathname of the file or directory granted the specified actions. A pathname that ends in "/*" (where "/" is the file separator character, File.separatorChar) indicates all the files and directories contained in that directory. A pathname that ends with "/-" indicates (recursively) all files and subdirectories contained in that directory. Such a pathname is called a wildcard pathname. Otherwise, it's a simple pathname.

    A pathname consisting of the special token "<<ALL FILES>>" matches any file.

    Note: A pathname consisting of a single "*" indicates all the files in the current directory, while a pathname consisting of a single "-" indicates all the files in the current directory and (recursively) all files and subdirectories contained in the current directory.

    The actions to be granted are passed to the constructor in a string containing a list of one or more comma-separated keywords. The possible keywords are "read", "write", "execute", "delete", and "readlink". Their meaning is defined as follows:

    read
    read permission
    write
    write permission
    execute
    execute permission. Allows Runtime.exec to be called. Corresponds to SecurityManager.checkExec.
    delete
    delete permission. Allows File.delete to be called. Corresponds to SecurityManager.checkDelete.
    readlink
    read link permission. Allows the target of a symbolic link to be read by invoking the readSymbolicLink method.

    The actions string is converted to lowercase before processing.

    Be careful when granting FilePermissions. Think about the implications of granting read and especially write access to various files and directories. The "<<ALL FILES>>" permission with write action is especially dangerous. This grants permission to write to the entire file system. One thing this effectively allows is replacement of the system binary, including the JVM runtime environment.

    Please note: Code can always read a file from the same directory it's in (or a subdirectory of that directory); it does not need explicit permission to do so.

    Since:
    1.2
    See Also:
    Permission, Permissions, PermissionCollection

    • Constructor Detail

      • FilePermission

        public FilePermission​(String path,
                      String actions)
        Creates a new FilePermission object with the specified actions. path is the pathname of a file or directory, and actions contains a comma-separated list of the desired actions granted on the file or directory. Possible actions are "read", "write", "execute", "delete", and "readlink".

        A pathname that ends in "/*" (where "/" is the file separator character, File.separatorChar) indicates all the files and directories contained in that directory. A pathname that ends with "/-" indicates (recursively) all files and subdirectories contained in that directory. The special pathname "<<ALL FILES>>" matches any file.

        A pathname consisting of a single "*" indicates all the files in the current directory, while a pathname consisting of a single "-" indicates all the files in the current directory and (recursively) all files and subdirectories contained in the current directory.

        A pathname containing an empty string represents an empty path.

        Implementation Note:
        In this implementation, the jdk.io.permissionsUseCanonicalPath system property dictates how the path argument is processed and stored.

        If the value of the system property is set to true, path is canonicalized and stored as a String object named cpath. This means a relative path is converted to an absolute path, a Windows DOS-style 8.3 path is expanded to a long path, and a symbolic link is resolved to its target, etc.

        If the value of the system property is set to false, path is converted to a Path object named npath after normalization. No canonicalization is performed which means the underlying file system is not accessed. If an InvalidPathException is thrown during the conversion, this FilePermission will be labeled as invalid.

        In either case, the "*" or "-" character at the end of a wildcard path is removed before canonicalization or normalization. It is stored in a separate wildcard flag field.

        The default value of the jdk.io.permissionsUseCanonicalPath system property is false in this implementation.

        Parameters:
        path - the pathname of the file/directory.
        actions - the action string.
        Throws:
        IllegalArgumentException - If actions is null, empty or contains an action other than the specified possible actions.

    • Method Detail

      • implies

        public boolean implies​(Permission p)
        Checks if this FilePermission object "implies" the specified permission.

        More specifically, this method returns true if:

        • p is an instanceof FilePermission,
        • p's actions are a proper subset of this object's actions, and
        • p's pathname is implied by this object's pathname. For example, "/tmp/*" implies "/tmp/foo", since "/tmp/*" encompasses all files in the "/tmp" directory, including the one named "foo".

        Precisely, a simple pathname implies another simple pathname if and only if they are equal. A simple pathname never implies a wildcard pathname. A wildcard pathname implies another wildcard pathname if and only if all simple pathnames implied by the latter are implied by the former. A wildcard pathname implies a simple pathname if and only if

        • if the wildcard flag is "*", the simple pathname's path must be right inside the wildcard pathname's path.
        • if the wildcard flag is "-", the simple pathname's path must be recursively inside the wildcard pathname's path.

        "<<ALL FILES>>" implies every other pathname. No pathname, except for "<<ALL FILES>>" itself, implies "<<ALL FILES>>".

        Specified by:
        implies in class Permission
        Implementation Note:
        If jdk.io.permissionsUseCanonicalPath is true, a simple cpath is inside a wildcard cpath if and only if after removing the base name (the last name in the pathname's name sequence) from the former the remaining part equals to the latter, a simple cpath is recursively inside a wildcard cpath if and only if the former starts with the latter.

        If jdk.io.permissionsUseCanonicalPath is false, a simple npath is inside a wildcard npath if and only if simple_npath.relativize(wildcard_npath) is exactly "..", a simple npath is recursively inside a wildcard npath if and only if simple_npath.relativize(wildcard_npath) is a series of one or more "..". This means "/-" implies "/foo" but not "foo".

        An invalid FilePermission does not imply any object except for itself. An invalid FilePermission is not implied by any object except for itself or a FilePermission on "<<ALL FILES>>" whose actions is a superset of this invalid FilePermission. Even if two FilePermission are created with the same invalid path, one does not imply the other.

        Parameters:
        p - the permission to check against.
        Returns:
        true if the specified permission is not null and is implied by this object, false otherwise.

      • equals

        public boolean equals​(Object obj)
        Checks two FilePermission objects for equality. Checks that obj is a FilePermission, and has the same pathname and actions as this object.
        Specified by:
        equals in class Permission
        Implementation Note:
        More specifically, two pathnames are the same if and only if they have the same wildcard flag and their cpath (if jdk.io.permissionsUseCanonicalPath is true) or npath (if jdk.io.permissionsUseCanonicalPath is false) are equal. Or they are both "<<ALL FILES>>".

        When jdk.io.permissionsUseCanonicalPath is false, an invalid FilePermission does not equal to any object except for itself, even if they are created using the same invalid path.

        Parameters:
        obj - the object we are testing for equality with this object.
        Returns:
        true if obj is a FilePermission, and has the same pathname and actions as this FilePermission object, false otherwise.
        See Also:
        Object.hashCode(), HashMap

      • getActions

        public String getActions()
        Returns the "canonical string representation" of the actions. That is, this method always returns present actions in the following order: read, write, execute, delete, readlink. For example, if this FilePermission object allows both write and read actions, a call to getActions will return the string "read,write".
        Specified by:
        getActions in class Permission
        Returns:
        the canonical string representation of the actions.

      • newPermissionCollection

        public PermissionCollection newPermissionCollection()
        Returns a new PermissionCollection object for storing FilePermission objects.

        FilePermission objects must be stored in a manner that allows them to be inserted into the collection in any order, but that also enables the PermissionCollection implies method to be implemented in an efficient (and consistent) manner.

        For example, if you have two FilePermissions:

        1. "/tmp/-", "read"
        2. "/tmp/scratch/foo", "write"

        and you are calling the implies method with the FilePermission: 

           "/tmp/scratch/foo", "read,write",
        then the implies function must take into account both the "/tmp/-" and "/tmp/scratch/foo" permissions, so the effective permission is "read,write", and implies returns true. The "implies" semantics for FilePermissions are handled properly by the PermissionCollection object returned by this newPermissionCollection method.
        Overrides:
        newPermissionCollection in class Permission
        Returns:
        a new PermissionCollection object suitable for storing FilePermissions.