java.io

Class FilePermission

Inhaltsverzeichnis
  • 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. 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.

        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".
        Specified by:
        implies in class Permission
        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
        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.

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Dokument erstellt 11/06/2005, zuletzt geändert 04/03/2020
Quelle des gedruckten Dokuments:https://www.gaudry.be/de/java-api-rf-java/io/FilePermission.html

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