Java tutorial
/* * Copyright (c) 1994, 2018, 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.io; import java.nio.channels.FileChannel; import jdk.internal.access.SharedSecrets; import jdk.internal.access.JavaIOFileDescriptorAccess; import sun.nio.ch.FileChannelImpl; /** * A file output stream is an output stream for writing data to a * <code>File</code> or to a <code>FileDescriptor</code>. Whether or not * a file is available or may be created depends upon the underlying * platform. Some platforms, in particular, allow a file to be opened * for writing by only one {@code FileOutputStream} (or other * file-writing object) at a time. In such situations the constructors in * this class will fail if the file involved is already open. * * <p><code>FileOutputStream</code> is meant for writing streams of raw bytes * such as image data. For writing streams of characters, consider using * <code>FileWriter</code>. * * @apiNote * To release resources used by this stream {@link #close} should be called * directly or by try-with-resources. Subclasses are responsible for the cleanup * of resources acquired by the subclass. * Subclasses that override {@link #finalize} in order to perform cleanup * should be modified to use alternative cleanup mechanisms such as * {@link java.lang.ref.Cleaner} and remove the overriding {@code finalize} method. * * @implSpec * If this FileOutputStream has been subclassed and the {@link #close} * method has been overridden, the {@link #close} method will be * called when the FileInputStream is unreachable. * Otherwise, it is implementation specific how the resource cleanup described in * {@link #close} is performed. * * @author Arthur van Hoff * @see java.io.File * @see java.io.FileDescriptor * @see java.io.FileInputStream * @see java.nio.file.Files#newOutputStream * @since 1.0 */ public class FileOutputStream extends OutputStream { /** * Access to FileDescriptor internals. */ private static final JavaIOFileDescriptorAccess fdAccess = SharedSecrets.getJavaIOFileDescriptorAccess(); /** * The system dependent file descriptor. */ private final FileDescriptor fd; /** * The associated channel, initialized lazily. */ private volatile FileChannel channel; /** * The path of the referenced file * (null if the stream is created with a file descriptor) */ private final String path; private final Object closeLock = new Object(); private volatile boolean closed; /** * Creates a file output stream to write to the file with the * specified name. A new <code>FileDescriptor</code> object is * created to represent this file connection. * <p> * First, if there is a security manager, its <code>checkWrite</code> * method is called with <code>name</code> as its argument. * <p> * If the file exists but is a directory rather than a regular file, does * not exist but cannot be created, or cannot be opened for any other * reason then a <code>FileNotFoundException</code> is thrown. * * @implSpec Invoking this constructor with the parameter {@code name} is * equivalent to invoking {@link #FileOutputStream(String,boolean) * new FileOutputStream(name, false)}. * * @param name the system-dependent filename * @exception FileNotFoundException if the file exists but is a directory * rather than a regular file, does not exist but cannot * be created, or cannot be opened for any other reason * @exception SecurityException if a security manager exists and its * <code>checkWrite</code> method denies write access * to the file. * @see java.lang.SecurityManager#checkWrite(java.lang.String) */ public FileOutputStream(String name) throws FileNotFoundException { this(name != null ? new File(name) : null, false); } /** * Creates a file output stream to write to the file with the specified * name. If the second argument is <code>true</code>, then * bytes will be written to the end of the file rather than the beginning. * A new <code>FileDescriptor</code> object is created to represent this * file connection. * <p> * First, if there is a security manager, its <code>checkWrite</code> * method is called with <code>name</code> as its argument. * <p> * If the file exists but is a directory rather than a regular file, does * not exist but cannot be created, or cannot be opened for any other * reason then a <code>FileNotFoundException</code> is thrown. * * @param name the system-dependent file name * @param append if <code>true</code>, then bytes will be written * to the end of the file rather than the beginning * @exception FileNotFoundException if the file exists but is a directory * rather than a regular file, does not exist but cannot * be created, or cannot be opened for any other reason. * @exception SecurityException if a security manager exists and its * <code>checkWrite</code> method denies write access * to the file. * @see java.lang.SecurityManager#checkWrite(java.lang.String) * @since 1.1 */ public FileOutputStream(String name, boolean append) throws FileNotFoundException { this(name != null ? new File(name) : null, append); } /** * Creates a file output stream to write to the file represented by * the specified <code>File</code> object. A new * <code>FileDescriptor</code> object is created to represent this * file connection. * <p> * First, if there is a security manager, its <code>checkWrite</code> * method is called with the path represented by the <code>file</code> * argument as its argument. * <p> * If the file exists but is a directory rather than a regular file, does * not exist but cannot be created, or cannot be opened for any other * reason then a <code>FileNotFoundException</code> is thrown. * * @param file the file to be opened for writing. * @exception FileNotFoundException if the file exists but is a directory * rather than a regular file, does not exist but cannot * be created, or cannot be opened for any other reason * @exception SecurityException if a security manager exists and its * <code>checkWrite</code> method denies write access * to the file. * @see java.io.File#getPath() * @see java.lang.SecurityException * @see java.lang.SecurityManager#checkWrite(java.lang.String) */ public FileOutputStream(File file) throws FileNotFoundException { this(file, false); } /** * Creates a file output stream to write to the file represented by * the specified <code>File</code> object. If the second argument is * <code>true</code>, then bytes will be written to the end of the file * rather than the beginning. A new <code>FileDescriptor</code> object is * created to represent this file connection. * <p> * First, if there is a security manager, its <code>checkWrite</code> * method is called with the path represented by the <code>file</code> * argument as its argument. * <p> * If the file exists but is a directory rather than a regular file, does * not exist but cannot be created, or cannot be opened for any other * reason then a <code>FileNotFoundException</code> is thrown. * * @param file the file to be opened for writing. * @param append if <code>true</code>, then bytes will be written * to the end of the file rather than the beginning * @exception FileNotFoundException if the file exists but is a directory * rather than a regular file, does not exist but cannot * be created, or cannot be opened for any other reason * @exception SecurityException if a security manager exists and its * <code>checkWrite</code> method denies write access * to the file. * @see java.io.File#getPath() * @see java.lang.SecurityException * @see java.lang.SecurityManager#checkWrite(java.lang.String) * @since 1.4 */ public FileOutputStream(File file, boolean append) throws FileNotFoundException { String name = (file != null ? file.getPath() : null); SecurityManager security = System.getSecurityManager(); if (security != null) { security.checkWrite(name); } if (name == null) { throw new NullPointerException(); } if (file.isInvalid()) { throw new FileNotFoundException("Invalid file path"); } this.fd = new FileDescriptor(); fd.attach(this); this.path = name; open(name, append); FileCleanable.register(fd); // open sets the fd, register the cleanup } /** * Creates a file output stream to write to the specified file * descriptor, which represents an existing connection to an actual * file in the file system. * <p> * First, if there is a security manager, its <code>checkWrite</code> * method is called with the file descriptor <code>fdObj</code> * argument as its argument. * <p> * If <code>fdObj</code> is null then a <code>NullPointerException</code> * is thrown. * <p> * This constructor does not throw an exception if <code>fdObj</code> * is {@link java.io.FileDescriptor#valid() invalid}. * However, if the methods are invoked on the resulting stream to attempt * I/O on the stream, an <code>IOException</code> is thrown. * * @param fdObj the file descriptor to be opened for writing * @exception SecurityException if a security manager exists and its * <code>checkWrite</code> method denies * write access to the file descriptor * @see java.lang.SecurityManager#checkWrite(java.io.FileDescriptor) */ public FileOutputStream(FileDescriptor fdObj) { SecurityManager security = System.getSecurityManager(); if (fdObj == null) { throw new NullPointerException(); } if (security != null) { security.checkWrite(fdObj); } this.fd = fdObj; this.path = null; fd.attach(this); } /** * Opens a file, with the specified name, for overwriting or appending. * @param name name of file to be opened * @param append whether the file is to be opened in append mode */ private native void open0(String name, boolean append) throws FileNotFoundException; // wrap native call to allow instrumentation /** * Opens a file, with the specified name, for overwriting or appending. * @param name name of file to be opened * @param append whether the file is to be opened in append mode */ private void open(String name, boolean append) throws FileNotFoundException { open0(name, append); } /** * Writes the specified byte to this file output stream. * * @param b the byte to be written. * @param append {@code true} if the write operation first * advances the position to the end of file */ private native void write(int b, boolean append) throws IOException; /** * Writes the specified byte to this file output stream. Implements * the <code>write</code> method of <code>OutputStream</code>. * * @param b the byte to be written. * @exception IOException if an I/O error occurs. */ public void write(int b) throws IOException { write(b, fdAccess.getAppend(fd)); } /** * Writes a sub array as a sequence of bytes. * @param b the data to be written * @param off the start offset in the data * @param len the number of bytes that are written * @param append {@code true} to first advance the position to the * end of file * @exception IOException If an I/O error has occurred. */ private native void writeBytes(byte b[], int off, int len, boolean append) throws IOException; /** * Writes <code>b.length</code> bytes from the specified byte array * to this file output stream. * * @param b the data. * @exception IOException if an I/O error occurs. */ public void write(byte b[]) throws IOException { writeBytes(b, 0, b.length, fdAccess.getAppend(fd)); } /** * Writes <code>len</code> bytes from the specified byte array * starting at offset <code>off</code> to this file output stream. * * @param b the data. * @param off the start offset in the data. * @param len the number of bytes to write. * @exception IOException if an I/O error occurs. */ public void write(byte b[], int off, int len) throws IOException { writeBytes(b, off, len, fdAccess.getAppend(fd)); } /** * Closes this file output stream and releases any system resources * associated with this stream. This file output stream may no longer * be used for writing bytes. * * <p> If this stream has an associated channel then the channel is closed * as well. * * @apiNote * Overriding {@link #close} to perform cleanup actions is reliable * only when called directly or when called by try-with-resources. * Do not depend on finalization to invoke {@code close}; * finalization is not reliable and is deprecated. * If cleanup of native resources is needed, other mechanisms such as * {@linkplain java.lang.ref.Cleaner} should be used. * * @exception IOException if an I/O error occurs. * * @revised 1.4 * @spec JSR-51 */ public void close() throws IOException { if (closed) { return; } synchronized (closeLock) { if (closed) { return; } closed = true; } FileChannel fc = channel; if (fc != null) { // possible race with getChannel(), benign since // FileChannel.close is final and idempotent fc.close(); } fd.closeAll(new Closeable() { public void close() throws IOException { fd.close(); } }); } /** * Returns the file descriptor associated with this stream. * * @return the <code>FileDescriptor</code> object that represents * the connection to the file in the file system being used * by this <code>FileOutputStream</code> object. * * @exception IOException if an I/O error occurs. * @see java.io.FileDescriptor */ public final FileDescriptor getFD() throws IOException { if (fd != null) { return fd; } throw new IOException(); } /** * Returns the unique {@link java.nio.channels.FileChannel FileChannel} * object associated with this file output stream. * * <p> The initial {@link java.nio.channels.FileChannel#position() * position} of the returned channel will be equal to the * number of bytes written to the file so far unless this stream is in * append mode, in which case it will be equal to the size of the file. * Writing bytes to this stream will increment the channel's position * accordingly. Changing the channel's position, either explicitly or by * writing, will change this stream's file position. * * @return the file channel associated with this file output stream * * @since 1.4 * @spec JSR-51 */ public FileChannel getChannel() { FileChannel fc = this.channel; if (fc == null) { synchronized (this) { fc = this.channel; if (fc == null) { this.channel = fc = FileChannelImpl.open(fd, path, false, true, false, this); if (closed) { try { // possible race with close(), benign since // FileChannel.close is final and idempotent fc.close(); } catch (IOException ioe) { throw new InternalError(ioe); // should not happen } } } } } return fc; } private static native void initIDs(); static { initIDs(); } }