Java tutorial
/* * Copyright (c) 2007, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ 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 <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 {@code "user"}. */ @Override String name(); /** * 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. * * @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. * * <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. * * <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. * * @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; }