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 /**
29 * A <code>PushbackInputStream</code> adds
30 * functionality to another input stream, namely
31 * the ability to "push back" or "unread" bytes,
32 * by storing pushed-back bytes in an internal buffer.
33 * This is useful in situations where
34 * it is convenient for a fragment of code
35 * to read an indefinite number of data bytes
36 * that are delimited by a particular byte
37 * value; after reading the terminating byte,
38 * the code fragment can "unread" it, so that
39 * the next read operation on the input stream
40 * will reread the byte that was pushed back.
41 * For example, bytes representing the characters
42 * constituting an identifier might be terminated
43 * by a byte representing an operator character;
44 * a method whose job is to read just an identifier
45 * can read until it sees the operator and
46 * then push the operator back to be re-read.
47 *
48 * @author David Connelly
49 * @author Jonathan Payne
50 * @since 1.0
51 */
52 public
53 class PushbackInputStream extends FilterInputStream {
54 /**
55 * The pushback buffer.
56 * @since 1.1
57 */
58 protected byte[] buf;
59
60 /**
61 * The position within the pushback buffer from which the next byte will
62 * be read. When the buffer is empty, <code>pos</code> is equal to
63 * <code>buf.length</code>; when the buffer is full, <code>pos</code> is
64 * equal to zero.
65 *
66 * @since 1.1
67 */
68 protected int pos;
69
70 /**
71 * Check to make sure that this stream has not been closed
72 */
73 private void ensureOpen() throws IOException {
74 if (in == null)
75 throw new IOException("Stream closed");
76 }
77
78 /**
79 * Creates a <code>PushbackInputStream</code>
80 * with a pushback buffer of the specified <code>size</code>,
81 * and saves its argument, the input stream
82 * <code>in</code>, for later use. Initially,
83 * the pushback buffer is empty.
84 *
85 * @param in the input stream from which bytes will be read.
86 * @param size the size of the pushback buffer.
87 * @exception IllegalArgumentException if {@code size <= 0}
88 * @since 1.1
89 */
90 public PushbackInputStream(InputStream in, int size) {
91 super(in);
92 if (in == null) {
93 throw new NullPointerException();
94 }
95 if (size <= 0) {
96 throw new IllegalArgumentException("size <= 0");
97 }
98 this.buf = new byte[size];
99 this.pos = size;
100 }
101
102 /**
103 * Creates a <code>PushbackInputStream</code>
104 * with a 1-byte pushback buffer, and saves its argument, the input stream
105 * <code>in</code>, for later use. Initially,
106 * the pushback buffer is empty.
107 *
108 * @param in the input stream from which bytes will be read.
109 */
110 public PushbackInputStream(InputStream in) {
111 this(in, 1);
112 }
113
114 /**
115 * Reads the next byte of data from this input stream. The value
116 * byte is returned as an <code>int</code> in the range
117 * <code>0</code> to <code>255</code>. If no byte is available
118 * because the end of the stream has been reached, the value
119 * <code>-1</code> is returned. This method blocks until input data
120 * is available, the end of the stream is detected, or an exception
121 * is thrown.
122 *
123 * <p> This method returns the most recently pushed-back byte, if there is
124 * one, and otherwise calls the <code>read</code> method of its underlying
125 * input stream and returns whatever value that method returns.
126 *
127 * @return the next byte of data, or <code>-1</code> if the end of the
128 * stream has been reached.
129 * @exception IOException if this input stream has been closed by
130 * invoking its {@link #close()} method,
131 * or an I/O error occurs.
132 * @see java.io.InputStream#read()
133 */
134 public int read() throws IOException {
135 ensureOpen();
136 if (pos < buf.length) {
137 return buf[pos++] & 0xff;
138 }
139 return super.read();
140 }
141
142 /**
143 * Reads up to <code>len</code> bytes of data from this input stream into
144 * an array of bytes. This method first reads any pushed-back bytes; after
145 * that, if fewer than <code>len</code> bytes have been read then it
146 * reads from the underlying input stream. If <code>len</code> is not zero, the method
147 * blocks until at least 1 byte of input is available; otherwise, no
148 * bytes are read and <code>0</code> is returned.
149 *
150 * @param b the buffer into which the data is read.
151 * @param off the start offset in the destination array <code>b</code>
152 * @param len the maximum number of bytes read.
153 * @return the total number of bytes read into the buffer, or
154 * <code>-1</code> if there is no more data because the end of
155 * the stream has been reached.
156 * @exception NullPointerException If <code>b</code> is <code>null</code>.
157 * @exception IndexOutOfBoundsException If <code>off</code> is negative,
158 * <code>len</code> is negative, or <code>len</code> is greater than
159 * <code>b.length - off</code>
160 * @exception IOException if this input stream has been closed by
161 * invoking its {@link #close()} method,
162 * or an I/O error occurs.
163 * @see java.io.InputStream#read(byte[], int, int)
164 */
165 public int read(byte[] b, int off, int len) throws IOException {
166 ensureOpen();
167 if (b == null) {
168 throw new NullPointerException();
169 } else if (off < 0 || len < 0 || len > b.length - off) {
170 throw new IndexOutOfBoundsException();
171 } else if (len == 0) {
172 return 0;
173 }
174
175 int avail = buf.length - pos;
176 if (avail > 0) {
177 if (len < avail) {
178 avail = len;
179 }
180 System.arraycopy(buf, pos, b, off, avail);
181 pos += avail;
182 off += avail;
183 len -= avail;
184 }
185 if (len > 0) {
186 len = super.read(b, off, len);
187 if (len == -1) {
188 return avail == 0 ? -1 : avail;
189 }
190 return avail + len;
191 }
192 return avail;
193 }
194
195 /**
196 * Pushes back a byte by copying it to the front of the pushback buffer.
197 * After this method returns, the next byte to be read will have the value
198 * <code>(byte)b</code>.
199 *
200 * @param b the <code>int</code> value whose low-order
201 * byte is to be pushed back.
202 * @exception IOException If there is not enough room in the pushback
203 * buffer for the byte, or this input stream has been closed by
204 * invoking its {@link #close()} method.
205 */
206 public void unread(int b) throws IOException {
207 ensureOpen();
208 if (pos == 0) {
209 throw new IOException("Push back buffer is full");
210 }
211 buf[--pos] = (byte)b;
212 }
213
214 /**
215 * Pushes back a portion of an array of bytes by copying it to the front
216 * of the pushback buffer. After this method returns, the next byte to be
217 * read will have the value <code>b[off]</code>, the byte after that will
218 * have the value <code>b[off+1]</code>, and so forth.
219 *
220 * @param b the byte array to push back.
221 * @param off the start offset of the data.
222 * @param len the number of bytes to push back.
223 * @exception NullPointerException If <code>b</code> is <code>null</code>.
224 * @exception IOException If there is not enough room in the pushback
225 * buffer for the specified number of bytes,
226 * or this input stream has been closed by
227 * invoking its {@link #close()} method.
228 * @since 1.1
229 */
230 public void unread(byte[] b, int off, int len) throws IOException {
231 ensureOpen();
232 if (len > pos) {
233 throw new IOException("Push back buffer is full");
234 }
235 pos -= len;
236 System.arraycopy(b, off, buf, pos, len);
237 }
238
239 /**
240 * Pushes back an array of bytes by copying it to the front of the
241 * pushback buffer. After this method returns, the next byte to be read
242 * will have the value <code>b[0]</code>, the byte after that will have the
243 * value <code>b[1]</code>, and so forth.
244 *
245 * @param b the byte array to push back
246 * @exception NullPointerException If <code>b</code> is <code>null</code>.
247 * @exception IOException If there is not enough room in the pushback
248 * buffer for the specified number of bytes,
249 * or this input stream has been closed by
250 * invoking its {@link #close()} method.
251 * @since 1.1
252 */
253 public void unread(byte[] b) throws IOException {
254 unread(b, 0, b.length);
255 }
256
257 /**
258 * Returns an estimate of the number of bytes that can be read (or
259 * skipped over) from this input stream without blocking by the next
260 * invocation of a method for this input stream. The next invocation might be
261 * the same thread or another thread. A single read or skip of this
262 * many bytes will not block, but may read or skip fewer bytes.
263 *
264 * <p> The method returns the sum of the number of bytes that have been
265 * pushed back and the value returned by {@link
266 * java.io.FilterInputStream#available available}.
267 *
268 * @return the number of bytes that can be read (or skipped over) from
269 * the input stream without blocking.
270 * @exception IOException if this input stream has been closed by
271 * invoking its {@link #close()} method,
272 * or an I/O error occurs.
273 * @see java.io.FilterInputStream#in
274 * @see java.io.InputStream#available()
275 */
276 public int available() throws IOException {
277 ensureOpen();
278 int n = buf.length - pos;
279 int avail = super.available();
280 return n > (Integer.MAX_VALUE - avail)
281 ? Integer.MAX_VALUE
282 : n + avail;
283 }
284
285 /**
286 * Skips over and discards <code>n</code> bytes of data from this
287 * input stream. The <code>skip</code> method may, for a variety of
288 * reasons, end up skipping over some smaller number of bytes,
289 * possibly zero. If <code>n</code> is negative, no bytes are skipped.
290 *
291 * <p> The <code>skip</code> method of <code>PushbackInputStream</code>
292 * first skips over the bytes in the pushback buffer, if any. It then
293 * calls the <code>skip</code> method of the underlying input stream if
294 * more bytes need to be skipped. The actual number of bytes skipped
295 * is returned.
296 *
297 * @param n {@inheritDoc}
298 * @return {@inheritDoc}
299 * @throws IOException if the stream has been closed by
300 * invoking its {@link #close()} method,
301 * {@code in.skip(n)} throws an IOException,
302 * or an I/O error occurs.
303 * @see java.io.FilterInputStream#in
304 * @see java.io.InputStream#skip(long n)
305 * @since 1.2
306 */
307 public long skip(long n) throws IOException {
308 ensureOpen();
309 if (n <= 0) {
310 return 0;
311 }
312
313 long pskip = buf.length - pos;
314 if (pskip > 0) {
315 if (n < pskip) {
316 pskip = n;
317 }
318 pos += pskip;
319 n -= pskip;
320 }
321 if (n > 0) {
322 pskip += super.skip(n);
323 }
324 return pskip;
325 }
326
327 /**
328 * Tests if this input stream supports the <code>mark</code> and
329 * <code>reset</code> methods, which it does not.
330 *
331 * @return <code>false</code>, since this class does not support the
332 * <code>mark</code> and <code>reset</code> methods.
333 * @see java.io.InputStream#mark(int)
334 * @see java.io.InputStream#reset()
335 */
336 public boolean markSupported() {
337 return false;
338 }
339
340 /**
341 * Marks the current position in this input stream.
342 *
343 * <p> The <code>mark</code> method of <code>PushbackInputStream</code>
344 * does nothing.
345 *
346 * @param readlimit the maximum limit of bytes that can be read before
347 * the mark position becomes invalid.
348 * @see java.io.InputStream#reset()
349 */
350 public synchronized void mark(int readlimit) {
351 }
352
353 /**
354 * Repositions this stream to the position at the time the
355 * <code>mark</code> method was last called on this input stream.
356 *
357 * <p> The method <code>reset</code> for class
358 * <code>PushbackInputStream</code> does nothing except throw an
359 * <code>IOException</code>.
360 *
361 * @exception IOException if this method is invoked.
362 * @see java.io.InputStream#mark(int)
363 * @see java.io.IOException
364 */
365 public synchronized void reset() throws IOException {
366 throw new IOException("mark/reset not supported");
367 }
368
369 /**
370 * Closes this input stream and releases any system resources
371 * associated with the stream.
372 * Once the stream has been closed, further read(), unread(),
373 * available(), reset(), or skip() invocations will throw an IOException.
374 * Closing a previously closed stream has no effect.
375 *
376 * @exception IOException if an I/O error occurs.
377 */
378 public synchronized void close() throws IOException {
379 if (in == null)
380 return;
381 in.close();
382 in = null;
383 buf = null;
384 }
385 }