1 /*
2 * Copyright (c) 1994, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.io;
27
28 import java.nio.channels.FileChannel;
29 import jdk.internal.access.SharedSecrets;
30 import jdk.internal.access.JavaIOFileDescriptorAccess;
31 import sun.nio.ch.FileChannelImpl;
32
33
34 /**
35 * A file output stream is an output stream for writing data to a
36 * <code>File</code> or to a <code>FileDescriptor</code>. Whether or not
37 * a file is available or may be created depends upon the underlying
38 * platform. Some platforms, in particular, allow a file to be opened
39 * for writing by only one {@code FileOutputStream} (or other
40 * file-writing object) at a time. In such situations the constructors in
41 * this class will fail if the file involved is already open.
42 *
43 * <p><code>FileOutputStream</code> is meant for writing streams of raw bytes
44 * such as image data. For writing streams of characters, consider using
45 * <code>FileWriter</code>.
46 *
47 * @apiNote
48 * To release resources used by this stream {@link #close} should be called
49 * directly or by try-with-resources. Subclasses are responsible for the cleanup
50 * of resources acquired by the subclass.
51 * Subclasses that override {@link #finalize} in order to perform cleanup
52 * should be modified to use alternative cleanup mechanisms such as
53 * {@link java.lang.ref.Cleaner} and remove the overriding {@code finalize} method.
54 *
55 * @implSpec
56 * If this FileOutputStream has been subclassed and the {@link #close}
57 * method has been overridden, the {@link #close} method will be
58 * called when the FileInputStream is unreachable.
59 * Otherwise, it is implementation specific how the resource cleanup described in
60 * {@link #close} is performed.
61 *
62 * @author Arthur van Hoff
63 * @see java.io.File
64 * @see java.io.FileDescriptor
65 * @see java.io.FileInputStream
66 * @see java.nio.file.Files#newOutputStream
67 * @since 1.0
68 */
69 public
70 class FileOutputStream extends OutputStream
71 {
72 /**
73 * Access to FileDescriptor internals.
74 */
75 private static final JavaIOFileDescriptorAccess fdAccess =
76 SharedSecrets.getJavaIOFileDescriptorAccess();
77
78 /**
79 * The system dependent file descriptor.
80 */
81 private final FileDescriptor fd;
82
83 /**
84 * The associated channel, initialized lazily.
85 */
86 private volatile FileChannel channel;
87
88 /**
89 * The path of the referenced file
90 * (null if the stream is created with a file descriptor)
91 */
92 private final String path;
93
94 private final Object closeLock = new Object();
95
96 private volatile boolean closed;
97
98 /**
99 * Creates a file output stream to write to the file with the
100 * specified name. A new <code>FileDescriptor</code> object is
101 * created to represent this file connection.
102 * <p>
103 * First, if there is a security manager, its <code>checkWrite</code>
104 * method is called with <code>name</code> as its argument.
105 * <p>
106 * If the file exists but is a directory rather than a regular file, does
107 * not exist but cannot be created, or cannot be opened for any other
108 * reason then a <code>FileNotFoundException</code> is thrown.
109 *
110 * @implSpec Invoking this constructor with the parameter {@code name} is
111 * equivalent to invoking {@link #FileOutputStream(String,boolean)
112 * new FileOutputStream(name, false)}.
113 *
114 * @param name the system-dependent filename
115 * @throws FileNotFoundException if the file exists but is a directory
116 * rather than a regular file, does not exist but cannot
117 * be created, or cannot be opened for any other reason
118 * @throws SecurityException if a security manager exists and its
119 * <code>checkWrite</code> method denies write access
120 * to the file.
121 * @see java.lang.SecurityManager#checkWrite(java.lang.String)
122 */
123 public FileOutputStream(String name) throws FileNotFoundException {
124 this(name != null ? new File(name) : null, false);
125 }
126
127 /**
128 * Creates a file output stream to write to the file with the specified
129 * name. If the second argument is <code>true</code>, then
130 * bytes will be written to the end of the file rather than the beginning.
131 * A new <code>FileDescriptor</code> object is created to represent this
132 * file connection.
133 * <p>
134 * First, if there is a security manager, its <code>checkWrite</code>
135 * method is called with <code>name</code> as its argument.
136 * <p>
137 * If the file exists but is a directory rather than a regular file, does
138 * not exist but cannot be created, or cannot be opened for any other
139 * reason then a <code>FileNotFoundException</code> is thrown.
140 *
141 * @param name the system-dependent file name
142 * @param append if <code>true</code>, then bytes will be written
143 * to the end of the file rather than the beginning
144 * @throws FileNotFoundException if the file exists but is a directory
145 * rather than a regular file, does not exist but cannot
146 * be created, or cannot be opened for any other reason.
147 * @throws SecurityException if a security manager exists and its
148 * <code>checkWrite</code> method denies write access
149 * to the file.
150 * @see java.lang.SecurityManager#checkWrite(java.lang.String)
151 * @since 1.1
152 */
153 public FileOutputStream(String name, boolean append)
154 throws FileNotFoundException
155 {
156 this(name != null ? new File(name) : null, append);
157 }
158
159 /**
160 * Creates a file output stream to write to the file represented by
161 * the specified <code>File</code> object. A new
162 * <code>FileDescriptor</code> object is created to represent this
163 * file connection.
164 * <p>
165 * First, if there is a security manager, its <code>checkWrite</code>
166 * method is called with the path represented by the <code>file</code>
167 * argument as its argument.
168 * <p>
169 * If the file exists but is a directory rather than a regular file, does
170 * not exist but cannot be created, or cannot be opened for any other
171 * reason then a <code>FileNotFoundException</code> is thrown.
172 *
173 * @param file the file to be opened for writing.
174 * @throws FileNotFoundException if the file exists but is a directory
175 * rather than a regular file, does not exist but cannot
176 * be created, or cannot be opened for any other reason
177 * @throws SecurityException if a security manager exists and its
178 * <code>checkWrite</code> method denies write access
179 * to the file.
180 * @see java.io.File#getPath()
181 * @see java.lang.SecurityException
182 * @see java.lang.SecurityManager#checkWrite(java.lang.String)
183 */
184 public FileOutputStream(File file) throws FileNotFoundException {
185 this(file, false);
186 }
187
188 /**
189 * Creates a file output stream to write to the file represented by
190 * the specified <code>File</code> object. If the second argument is
191 * <code>true</code>, then bytes will be written to the end of the file
192 * rather than the beginning. A new <code>FileDescriptor</code> object is
193 * created to represent this file connection.
194 * <p>
195 * First, if there is a security manager, its <code>checkWrite</code>
196 * method is called with the path represented by the <code>file</code>
197 * argument as its argument.
198 * <p>
199 * If the file exists but is a directory rather than a regular file, does
200 * not exist but cannot be created, or cannot be opened for any other
201 * reason then a <code>FileNotFoundException</code> is thrown.
202 *
203 * @param file the file to be opened for writing.
204 * @param append if <code>true</code>, then bytes will be written
205 * to the end of the file rather than the beginning
206 * @throws FileNotFoundException if the file exists but is a directory
207 * rather than a regular file, does not exist but cannot
208 * be created, or cannot be opened for any other reason
209 * @throws SecurityException if a security manager exists and its
210 * <code>checkWrite</code> method denies write access
211 * to the file.
212 * @see java.io.File#getPath()
213 * @see java.lang.SecurityException
214 * @see java.lang.SecurityManager#checkWrite(java.lang.String)
215 * @since 1.4
216 */
217 public FileOutputStream(File file, boolean append)
218 throws FileNotFoundException
219 {
220 String name = (file != null ? file.getPath() : null);
221 SecurityManager security = System.getSecurityManager();
222 if (security != null) {
223 security.checkWrite(name);
224 }
225 if (name == null) {
226 throw new NullPointerException();
227 }
228 if (file.isInvalid()) {
229 throw new FileNotFoundException("Invalid file path");
230 }
231 this.fd = new FileDescriptor();
232 fd.attach(this);
233 this.path = name;
234
235 open(name, append);
236 FileCleanable.register(fd); // open sets the fd, register the cleanup
237 }
238
239 /**
240 * Creates a file output stream to write to the specified file
241 * descriptor, which represents an existing connection to an actual
242 * file in the file system.
243 * <p>
244 * First, if there is a security manager, its <code>checkWrite</code>
245 * method is called with the file descriptor <code>fdObj</code>
246 * argument as its argument.
247 * <p>
248 * If <code>fdObj</code> is null then a <code>NullPointerException</code>
249 * is thrown.
250 * <p>
251 * This constructor does not throw an exception if <code>fdObj</code>
252 * is {@link java.io.FileDescriptor#valid() invalid}.
253 * However, if the methods are invoked on the resulting stream to attempt
254 * I/O on the stream, an <code>IOException</code> is thrown.
255 *
256 * @param fdObj the file descriptor to be opened for writing
257 * @throws SecurityException if a security manager exists and its
258 * <code>checkWrite</code> method denies
259 * write access to the file descriptor
260 * @see java.lang.SecurityManager#checkWrite(java.io.FileDescriptor)
261 */
262 public FileOutputStream(FileDescriptor fdObj) {
263 SecurityManager security = System.getSecurityManager();
264 if (fdObj == null) {
265 throw new NullPointerException();
266 }
267 if (security != null) {
268 security.checkWrite(fdObj);
269 }
270 this.fd = fdObj;
271 this.path = null;
272
273 fd.attach(this);
274 }
275
276 /**
277 * Opens a file, with the specified name, for overwriting or appending.
278 * @param name name of file to be opened
279 * @param append whether the file is to be opened in append mode
280 */
281 private native void open0(String name, boolean append)
282 throws FileNotFoundException;
283
284 // wrap native call to allow instrumentation
285 /**
286 * Opens a file, with the specified name, for overwriting or appending.
287 * @param name name of file to be opened
288 * @param append whether the file is to be opened in append mode
289 */
290 private void open(String name, boolean append)
291 throws FileNotFoundException {
292 open0(name, append);
293 }
294
295 /**
296 * Writes the specified byte to this file output stream.
297 *
298 * @param b the byte to be written.
299 * @param append {@code true} if the write operation first
300 * advances the position to the end of file
301 */
302 private native void write(int b, boolean append) throws IOException;
303
304 /**
305 * Writes the specified byte to this file output stream. Implements
306 * the <code>write</code> method of <code>OutputStream</code>.
307 *
308 * @param b the byte to be written.
309 * @throws IOException if an I/O error occurs.
310 */
311 public void write(int b) throws IOException {
312 write(b, fdAccess.getAppend(fd));
313 }
314
315 /**
316 * Writes a sub array as a sequence of bytes.
317 * @param b the data to be written
318 * @param off the start offset in the data
319 * @param len the number of bytes that are written
320 * @param append {@code true} to first advance the position to the
321 * end of file
322 * @throws IOException If an I/O error has occurred.
323 */
324 private native void writeBytes(byte b[], int off, int len, boolean append)
325 throws IOException;
326
327 /**
328 * Writes <code>b.length</code> bytes from the specified byte array
329 * to this file output stream.
330 *
331 * @param b the data.
332 * @throws IOException if an I/O error occurs.
333 */
334 public void write(byte b[]) throws IOException {
335 writeBytes(b, 0, b.length, fdAccess.getAppend(fd));
336 }
337
338 /**
339 * Writes <code>len</code> bytes from the specified byte array
340 * starting at offset <code>off</code> to this file output stream.
341 *
342 * @param b the data.
343 * @param off the start offset in the data.
344 * @param len the number of bytes to write.
345 * @throws IOException if an I/O error occurs.
346 */
347 public void write(byte b[], int off, int len) throws IOException {
348 writeBytes(b, off, len, fdAccess.getAppend(fd));
349 }
350
351 /**
352 * Closes this file output stream and releases any system resources
353 * associated with this stream. This file output stream may no longer
354 * be used for writing bytes.
355 *
356 * <p> If this stream has an associated channel then the channel is closed
357 * as well.
358 *
359 * @apiNote
360 * Overriding {@link #close} to perform cleanup actions is reliable
361 * only when called directly or when called by try-with-resources.
362 * Do not depend on finalization to invoke {@code close};
363 * finalization is not reliable and is deprecated.
364 * If cleanup of native resources is needed, other mechanisms such as
365 * {@linkplain java.lang.ref.Cleaner} should be used.
366 *
367 * @throws IOException if an I/O error occurs.
368 *
369 * @revised 1.4
370 * @spec JSR-51
371 */
372 public void close() throws IOException {
373 if (closed) {
374 return;
375 }
376 synchronized (closeLock) {
377 if (closed) {
378 return;
379 }
380 closed = true;
381 }
382
383 FileChannel fc = channel;
384 if (fc != null) {
385 // possible race with getChannel(), benign since
386 // FileChannel.close is final and idempotent
387 fc.close();
388 }
389
390 fd.closeAll(new Closeable() {
391 public void close() throws IOException {
392 fd.close();
393 }
394 });
395 }
396
397 /**
398 * Returns the file descriptor associated with this stream.
399 *
400 * @return the <code>FileDescriptor</code> object that represents
401 * the connection to the file in the file system being used
402 * by this <code>FileOutputStream</code> object.
403 *
404 * @throws IOException if an I/O error occurs.
405 * @see java.io.FileDescriptor
406 */
407 public final FileDescriptor getFD() throws IOException {
408 if (fd != null) {
409 return fd;
410 }
411 throw new IOException();
412 }
413
414 /**
415 * Returns the unique {@link java.nio.channels.FileChannel FileChannel}
416 * object associated with this file output stream.
417 *
418 * <p> The initial {@link java.nio.channels.FileChannel#position()
419 * position} of the returned channel will be equal to the
420 * number of bytes written to the file so far unless this stream is in
421 * append mode, in which case it will be equal to the size of the file.
422 * Writing bytes to this stream will increment the channel's position
423 * accordingly. Changing the channel's position, either explicitly or by
424 * writing, will change this stream's file position.
425 *
426 * @return the file channel associated with this file output stream
427 *
428 * @since 1.4
429 * @spec JSR-51
430 */
431 public FileChannel getChannel() {
432 FileChannel fc = this.channel;
433 if (fc == null) {
434 synchronized (this) {
435 fc = this.channel;
436 if (fc == null) {
437 this.channel = fc = FileChannelImpl.open(fd, path, false,
438 true, false, this);
439 if (closed) {
440 try {
441 // possible race with close(), benign since
442 // FileChannel.close is final and idempotent
443 fc.close();
444 } catch (IOException ioe) {
445 throw new InternalError(ioe); // should not happen
446 }
447 }
448 }
449 }
450 }
451 return fc;
452 }
453
454 private static native void initIDs();
455
456 static {
457 initIDs();
458 }
459 }