java/11 : java.base/java/nio/file/attribute/UserDefinedFileAttributeView.java

UserDefinedFileAttributeView

https://openjdk.java.net/

GPLv2 + Classpath Exception

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package java.nio.file.attribute;

import java.nio.ByteBuffer;
import java.util.List;
import java.io.IOException;

A file attribute view that provides a view of a file's user-defined
attributes, sometimes known as extended attributes. User-defined
file attributes are used to store metadata with a file that is not meaningful
to the file system. It is primarily intended for file system implementations
that support such a capability directly but may be emulated. The details of
such emulation are highly implementation specific and therefore not specified.
 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/**
 * A file attribute view that provides a view of a file's user-defined
 * attributes, sometimes known as <em>extended attributes</em>. User-defined
 * file attributes are used to store metadata with a file that is not meaningful
 * to the file system. It is primarily intended for file system implementations
 * that support such a capability directly but may be emulated. The details of
 * such emulation are highly implementation specific and therefore not specified.
 *
 * <p> This {@code 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 {@code 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
 * {@link #read read} and {@link #write write} methods to read the value into
 * or write from a {@link ByteBuffer}. This {@code FileAttributeView} is not
 * intended for use where the size of an attribute value is larger than {@link
 * Integer#MAX_VALUE}.
 *
 * <p> 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
 * {@code RuntimePermission("accessUserDefinedAttributes")} permission when a
 * security manager is installed.
 *
 * <p> The {@link java.nio.file.FileStore#supportsFileAttributeView
 * supportsFileAttributeView} method may be used to test if a specific {@link
 * java.nio.file.FileStore FileStore} supports the storage of user-defined
 * attributes.
 *
 * <p> Where dynamic access to file attributes is required, the {@link
 * java.nio.file.Files#getAttribute getAttribute} method may be used to read
 * the attribute value. The attribute value is returned as a byte array (byte[]).
 * The {@link java.nio.file.Files#setAttribute setAttribute} method may be used
 * to write the value of a user-defined attribute from a buffer (as if by
 * invoking the {@link #write write} method), or byte array (byte[]).
 *
 * @since 1.7
 */

public interface UserDefinedFileAttributeView
    extends FileAttributeView
{
    Returns the name of this attribute view. Attribute views of this type have the name "user". /**
     * Returns the name of this attribute view. Attribute views of this type
     * have the name {@code "user"}.
     */
    @Override
    String name();

    Returns a list containing the names of the user-defined attributes.
Throws: IOException – 
         If an I/O error occurs
SecurityException –  In the case of the default provider, a security manager is installed, and it denies RuntimePermission("accessUserDefinedAttributes") or its checkRead method denies read access to the file.
Returns:  An unmodifiable list containing the names of the file's
         user-defined/**
     * Returns a list containing the names of the user-defined attributes.
     *
     * @return  An unmodifiable list containing the names of the file's
     *          user-defined
     *
     * @throws  IOException
     *          If an I/O error occurs
     * @throws  SecurityException
     *          In the case of the default provider, a security manager is
     *          installed, and it denies {@link
     *          RuntimePermission}{@code ("accessUserDefinedAttributes")}
     *          or its {@link SecurityManager#checkRead(String) checkRead} method
     *          denies read access to the file.
     */
    List<String> list() throws IOException;

    Returns the size of the value of a user-defined attribute.
Params: name – 
         The attribute name
Throws: ArithmeticException –  If the size of the attribute is larger than Integer.MAX_VALUE
IOException – 
         If an I/O error occurs
SecurityException –  In the case of the default provider, a security manager is installed, and it denies RuntimePermission("accessUserDefinedAttributes") or its checkRead method denies read access to the file.
Returns:  The size of the attribute value, in bytes./**
     * Returns the size of the value of a user-defined attribute.
     *
     * @param   name
     *          The attribute name
     *
     * @return  The size of the attribute value, in bytes.
     *
     * @throws  ArithmeticException
     *          If the size of the attribute is larger than {@link Integer#MAX_VALUE}
     * @throws  IOException
     *          If an I/O error occurs
     * @throws  SecurityException
     *          In the case of the default provider, a security manager is
     *          installed, and it denies {@link
     *          RuntimePermission}{@code ("accessUserDefinedAttributes")}
     *          or its {@link SecurityManager#checkRead(String) checkRead} method
     *          denies read access to the file.
     */
    int size(String name) throws IOException;

    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, where n is the size of the attribute value. The first byte in the sequence is at index p and the last byte is at index p + n - 1, where p is the buffer's position. Upon return the buffer's position will be equal to p + 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();

Params: name – 
         The attribute name
dst – 
         The destination buffer
Throws: IllegalArgumentException – 
         If the destination buffer is read-only
IOException – 
         If an I/O error occurs or there is insufficient space in the
         destination buffer for the attribute value
SecurityException –  In the case of the default provider, a security manager is installed, and it denies RuntimePermission("accessUserDefinedAttributes") or its checkRead method denies read access to the file.
See Also: size
Returns:  The number of bytes read, possibly zero/**
     * Read the value of a user-defined attribute into a buffer.
     *
     * <p> 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 {@code n}, where {@code n}
     * is the size of the attribute value. The first byte in the sequence is at
     * index {@code p} and the last byte is at index {@code p + n - 1}, where
     * {@code p} is the buffer's position. Upon return the buffer's position
     * will be equal to {@code p + n}; its limit will not have changed.
     *
     * <p> <b>Usage Example:</b>
     * Suppose we want to read a file's MIME type that is stored as a user-defined
     * attribute with the name "{@code user.mimetype}".
     * <pre>
     *    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();
     * </pre>
     *
     * @param   name
     *          The attribute name
     * @param   dst
     *          The destination buffer
     *
     * @return  The number of bytes read, possibly zero
     *
     * @throws  IllegalArgumentException
     *          If the destination buffer is read-only
     * @throws  IOException
     *          If an I/O error occurs or there is insufficient space in the
     *          destination buffer for the attribute value
     * @throws  SecurityException
     *          In the case of the default provider, a security manager is
     *          installed, and it denies {@link
     *          RuntimePermission}{@code ("accessUserDefinedAttributes")}
     *          or its {@link SecurityManager#checkRead(String) checkRead} method
     *          denies read access to the file.
     *
     * @see #size
     */
    int read(String name, ByteBuffer dst) throws IOException;

    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, where r is the number of bytes remaining in the buffer, that is src.remaining(). The sequence of bytes is transferred from the buffer starting at index p, where p is the buffer's position. Upon return, the buffer's position will be equal to 
p + n, where n 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"));

Params: name – 
         The attribute name
src – 
         The buffer containing the attribute value
Throws: IOException – 
         If an I/O error occurs
SecurityException –  In the case of the default provider, a security manager is installed, and it denies RuntimePermission("accessUserDefinedAttributes") or its checkWrite method denies write access to the file.
Returns:  The number of bytes written, possibly zero/**
     * Writes the value of a user-defined attribute from a buffer.
     *
     * <p> 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 {@code r},
     * where {@code r} is the number of bytes remaining in the buffer, that is
     * {@code src.remaining()}. The sequence of bytes is transferred from the
     * buffer starting at index {@code p}, where {@code p} is the buffer's
     * position. Upon return, the buffer's position will be equal to {@code
     * p + n}, where {@code n} is the number of bytes transferred; its limit
     * will not have changed.
     *
     * <p> 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.
     *
     * <p> Where there is insufficient space to store the attribute, or the
     * attribute name or value exceed an implementation specific maximum size
     * then an {@code IOException} is thrown.
     *
     * <p> <b>Usage Example:</b>
     * Suppose we want to write a file's MIME type as a user-defined attribute:
     * <pre>
     *    UserDefinedFileAttributeView view =
     *        FIles.getFileAttributeView(path, UserDefinedFileAttributeView.class);
     *    view.write("user.mimetype", Charset.defaultCharset().encode("text/html"));
     * </pre>
     *
     * @param   name
     *          The attribute name
     * @param   src
     *          The buffer containing the attribute value
     *
     * @return  The number of bytes written, possibly zero
     *
     * @throws  IOException
     *          If an I/O error occurs
     * @throws  SecurityException
     *          In the case of the default provider, a security manager is
     *          installed, and it denies {@link
     *          RuntimePermission}{@code ("accessUserDefinedAttributes")}
     *          or its {@link SecurityManager#checkWrite(String) checkWrite}
     *          method denies write access to the file.
     */
    int write(String name, ByteBuffer src) throws IOException;

    Deletes a user-defined attribute.
Params: name – 
         The attribute name
Throws: IOException – 
         If an I/O error occurs or the attribute does not exist
SecurityException –  In the case of the default provider, a security manager is installed, and it denies RuntimePermission("accessUserDefinedAttributes") or its checkWrite method denies write access to the file./**
     * Deletes a user-defined attribute.
     *
     * @param   name
     *          The attribute name
     *
     * @throws  IOException
     *          If an I/O error occurs or the attribute does not exist
     * @throws  SecurityException
     *          In the case of the default provider, a security manager is
     *          installed, and it denies {@link
     *          RuntimePermission}{@code ("accessUserDefinedAttributes")}
     *          or its {@link SecurityManager#checkWrite(String) checkWrite}
     *          method denies write access to the file.
     */
    void delete(String name) throws IOException;
}

Throws:	IOException – If an I/O error occurs SecurityException – In the case of the default provider, a security manager is installed, and it denies `RuntimePermission("accessUserDefinedAttributes")` or its `checkRead` method denies read access to the file.
Returns:	An unmodifiable list containing the names of the file's user-defined

Params:	name – The attribute name
Throws:	ArithmeticException – If the size of the attribute is larger than `Integer.MAX_VALUE` IOException – If an I/O error occurs SecurityException – In the case of the default provider, a security manager is installed, and it denies `RuntimePermission("accessUserDefinedAttributes")` or its `checkRead` method denies read access to the file.
Returns:	The size of the attribute value, in bytes.

Params:	name – The attribute name dst – The destination buffer
Throws:	IllegalArgumentException – If the destination buffer is read-only IOException – If an I/O error occurs or there is insufficient space in the destination buffer for the attribute value SecurityException – In the case of the default provider, a security manager is installed, and it denies `RuntimePermission("accessUserDefinedAttributes")` or its `checkRead` method denies read access to the file.
See Also:	size
Returns:	The number of bytes read, possibly zero

Params:	name – The attribute name src – The buffer containing the attribute value
Throws:	IOException – If an I/O error occurs SecurityException – In the case of the default provider, a security manager is installed, and it denies `RuntimePermission("accessUserDefinedAttributes")` or its `checkWrite` method denies write access to the file.
Returns:	The number of bytes written, possibly zero

/

java/ 11/ java.base/java/nio/file/attribute/UserDefinedFileAttributeView.java