Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class FilePermission - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.io
Class FilePermission

java.lang.Object
  |
  +--java.security.Permission
        |
        +--java.io.FilePermission

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", and "delete". 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.

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.

See Also:: Permission, Permissions, PermissionCollection, Serialized Form

Constructor Summary

FilePermission(String path, String actions)
          Creates a new FilePermission object with the specified actions.

Method Summary

boolean equals(Object obj)
          Checks two FilePermission objects for equality.

String getActions()
          Returns the "canonical string representation" of the actions.

int hashCode()
          Returns the hash code value for this object.

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

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

Methods inherited from class java.security.Permission

checkGuard, getName, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

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", and "delete".

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

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.

Parameters:: path - the pathname of the file/directory.; actions - the action string.

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 the "/tmp" directory and all files in that directory, including the one named "foo".

Overrides:: implies in class Permission

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

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.

Overrides:: 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.

hashCode

public int hashCode()

Returns the hash code value for this object.

Overrides:: hashCode in class Permission

Returns:: a hash code value for this object.

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. For example, if this FilePermission object allows both write and read actions, a call to getActions will return the string "read,write".

Overrides:: 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:

"/tmp/-", "read"
"/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.