- All Superinterfaces:
AttributeView
,FileAttributeView
public interface UserDefinedFileAttributeView extends FileAttributeView
This FileAttributeView
provides a view of a file's user-defined
attributes as a set of name/value pairs, where the attribute name is
represented by a String
. An implementation may require to encode and
decode from the platform or file system representation when accessing the
attribute. The value has opaque content. This attribute view defines the
read
and write
methods to read the value into
or write from a ByteBuffer
. This FileAttributeView
is not
intended for use where the size of an attribute value is larger than Integer.MAX_VALUE
.
User-defined attributes may be used in some implementations to store
security related attributes so consequently, in the case of the default
provider at least, all methods that access user-defined attributes require the
RuntimePermission("accessUserDefinedAttributes")
permission when a
security manager is installed.
The supportsFileAttributeView
method may be used to test if a specific FileStore
supports the storage of user-defined
attributes.
Where dynamic access to file attributes is required, the getAttribute
method may be used to read
the attribute value. The attribute value is returned as a byte array (byte[]).
The setAttribute
method may be used
to write the value of a user-defined attribute from a buffer (as if by
invoking the write
method), or byte array (byte[]).
- Since:
- 1.7
-
Method Summary
Modifier and TypeMethodDescriptionvoid
Deletes a user-defined attribute.list()
Returns a list containing the names of the user-defined attributes.name()
Returns the name of this attribute view.int
read(String name, ByteBuffer dst)
Read the value of a user-defined attribute into a buffer.int
Returns the size of the value of a user-defined attribute.int
write(String name, ByteBuffer src)
Writes the value of a user-defined attribute from a buffer.
-
Method Details
-
name
String name()Returns the name of this attribute view. Attribute views of this type have the name"user"
.- Specified by:
name
in interfaceAttributeView
- Returns:
- the name of the attribute view
-
list
Returns a list containing the names of the user-defined attributes.- Returns:
- An unmodifiable list containing the names of the file's user-defined
- Throws:
IOException
- If an I/O error occursSecurityException
- In the case of the default provider, a security manager is installed, and it deniesRuntimePermission
("accessUserDefinedAttributes")
or itscheckRead
method denies read access to the file.
-
size
Returns the size of the value of a user-defined attribute.- Parameters:
name
- The attribute name- Returns:
- The size of the attribute value, in bytes.
- Throws:
ArithmeticException
- If the size of the attribute is larger thanInteger.MAX_VALUE
IOException
- If an I/O error occursSecurityException
- In the case of the default provider, a security manager is installed, and it deniesRuntimePermission
("accessUserDefinedAttributes")
or itscheckRead
method denies read access to the file.
-
read
Read the value of a user-defined attribute into a buffer.This method reads the value of the attribute into the given buffer as a sequence of bytes, failing if the number of bytes remaining in the buffer is insufficient to read the complete attribute value. The number of bytes transferred into the buffer is
n
, wheren
is the size of the attribute value. The first byte in the sequence is at indexp
and the last byte is at indexp + n - 1
, wherep
is the buffer's position. Upon return the buffer's position will be equal top + n
; its limit will not have changed.Usage Example: Suppose we want to read a file's MIME type that is stored as a user-defined attribute with the name "
user.mimetype
".UserDefinedFileAttributeView view = Files.getFileAttributeView(path, UserDefinedFileAttributeView.class); String name = "user.mimetype"; ByteBuffer buf = ByteBuffer.allocate(view.size(name)); view.read(name, buf); buf.flip(); String value = Charset.defaultCharset().decode(buf).toString();
- Parameters:
name
- The attribute namedst
- The destination buffer- Returns:
- The number of bytes read, possibly zero
- Throws:
IllegalArgumentException
- If the destination buffer is read-onlyIOException
- If an I/O error occurs or there is insufficient space in the destination buffer for the attribute valueSecurityException
- In the case of the default provider, a security manager is installed, and it deniesRuntimePermission
("accessUserDefinedAttributes")
or itscheckRead
method denies read access to the file.- See Also:
size(java.lang.String)
-
write
Writes the value of a user-defined attribute from a buffer.This method writes the value of the attribute from a given buffer as a sequence of bytes. The size of the value to transfer is
r
, wherer
is the number of bytes remaining in the buffer, that issrc.remaining()
. The sequence of bytes is transferred from the buffer starting at indexp
, wherep
is the buffer's position. Upon return, the buffer's position will be equal top + n
, wheren
is the number of bytes transferred; its limit will not have changed.If an attribute of the given name already exists then its value is replaced. If the attribute does not exist then it is created. If it implementation specific if a test to check for the existence of the attribute and the creation of attribute are atomic with respect to other file system activities.
Where there is insufficient space to store the attribute, or the attribute name or value exceed an implementation specific maximum size then an
IOException
is thrown.Usage Example: Suppose we want to write a file's MIME type as a user-defined attribute:
UserDefinedFileAttributeView view = Files.getFileAttributeView(path, UserDefinedFileAttributeView.class); view.write("user.mimetype", Charset.defaultCharset().encode("text/html"));
- Parameters:
name
- The attribute namesrc
- The buffer containing the attribute value- Returns:
- The number of bytes written, possibly zero
- Throws:
IOException
- If an I/O error occursSecurityException
- In the case of the default provider, a security manager is installed, and it deniesRuntimePermission
("accessUserDefinedAttributes")
or itscheckWrite
method denies write access to the file.
-
delete
Deletes a user-defined attribute.- Parameters:
name
- The attribute name- Throws:
IOException
- If an I/O error occurs or the attribute does not existSecurityException
- In the case of the default provider, a security manager is installed, and it deniesRuntimePermission
("accessUserDefinedAttributes")
or itscheckWrite
method denies write access to the file.
-