1 /*
2 * Copyright (c) 1994, 2013, 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.util.Objects;
29
30 /**
31 * This abstract class is the superclass of all classes representing
32 * an input stream of bytes.
33 *
34 * <p> Applications that need to define a subclass of <code>InputStream</code>
35 * must always provide a method that returns the next byte of input.
36 *
37 * @author Arthur van Hoff
38 * @see java.io.BufferedInputStream
39 * @see java.io.ByteArrayInputStream
40 * @see java.io.DataInputStream
41 * @see java.io.FilterInputStream
42 * @see java.io.InputStream#read()
43 * @see java.io.OutputStream
44 * @see java.io.PushbackInputStream
45 * @since 1.0
46 */
47 public abstract class InputStream implements Closeable {
48
49 // MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to
50 // use when skipping.
51 private static final int MAX_SKIP_BUFFER_SIZE = 2048;
52
53 /**
54 * Reads the next byte of data from the input stream. The value byte is
55 * returned as an <code>int</code> in the range <code>0</code> to
56 * <code>255</code>. If no byte is available because the end of the stream
57 * has been reached, the value <code>-1</code> is returned. This method
58 * blocks until input data is available, the end of the stream is detected,
59 * or an exception is thrown.
60 *
61 * <p> A subclass must provide an implementation of this method.
62 *
63 * @return the next byte of data, or <code>-1</code> if the end of the
64 * stream is reached.
65 * @exception IOException if an I/O error occurs.
66 */
67 public abstract int read() throws IOException;
68
69 /**
70 * Reads some number of bytes from the input stream and stores them into
71 * the buffer array <code>b</code>. The number of bytes actually read is
72 * returned as an integer. This method blocks until input data is
73 * available, end of file is detected, or an exception is thrown.
74 *
75 * <p> If the length of <code>b</code> is zero, then no bytes are read and
76 * <code>0</code> is returned; otherwise, there is an attempt to read at
77 * least one byte. If no byte is available because the stream is at the
78 * end of the file, the value <code>-1</code> is returned; otherwise, at
79 * least one byte is read and stored into <code>b</code>.
80 *
81 * <p> The first byte read is stored into element <code>b[0]</code>, the
82 * next one into <code>b[1]</code>, and so on. The number of bytes read is,
83 * at most, equal to the length of <code>b</code>. Let <i>k</i> be the
84 * number of bytes actually read; these bytes will be stored in elements
85 * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,
86 * leaving elements <code>b[</code><i>k</i><code>]</code> through
87 * <code>b[b.length-1]</code> unaffected.
88 *
89 * <p> The <code>read(b)</code> method for class <code>InputStream</code>
90 * has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>
91 *
92 * @param b the buffer into which the data is read.
93 * @return the total number of bytes read into the buffer, or
94 * <code>-1</code> if there is no more data because the end of
95 * the stream has been reached.
96 * @exception IOException If the first byte cannot be read for any reason
97 * other than the end of the file, if the input stream has been closed, or
98 * if some other I/O error occurs.
99 * @exception NullPointerException if <code>b</code> is <code>null</code>.
100 * @see java.io.InputStream#read(byte[], int, int)
101 */
102 public int read(byte b[]) throws IOException {
103 return read(b, 0, b.length);
104 }
105
106 /**
107 * Reads up to <code>len</code> bytes of data from the input stream into
108 * an array of bytes. An attempt is made to read as many as
109 * <code>len</code> bytes, but a smaller number may be read.
110 * The number of bytes actually read is returned as an integer.
111 *
112 * <p> This method blocks until input data is available, end of file is
113 * detected, or an exception is thrown.
114 *
115 * <p> If <code>len</code> is zero, then no bytes are read and
116 * <code>0</code> is returned; otherwise, there is an attempt to read at
117 * least one byte. If no byte is available because the stream is at end of
118 * file, the value <code>-1</code> is returned; otherwise, at least one
119 * byte is read and stored into <code>b</code>.
120 *
121 * <p> The first byte read is stored into element <code>b[off]</code>, the
122 * next one into <code>b[off+1]</code>, and so on. The number of bytes read
123 * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
124 * bytes actually read; these bytes will be stored in elements
125 * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
126 * leaving elements <code>b[off+</code><i>k</i><code>]</code> through
127 * <code>b[off+len-1]</code> unaffected.
128 *
129 * <p> In every case, elements <code>b[0]</code> through
130 * <code>b[off]</code> and elements <code>b[off+len]</code> through
131 * <code>b[b.length-1]</code> are unaffected.
132 *
133 * <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method
134 * for class <code>InputStream</code> simply calls the method
135 * <code>read()</code> repeatedly. If the first such call results in an
136 * <code>IOException</code>, that exception is returned from the call to
137 * the <code>read(b,</code> <code>off,</code> <code>len)</code> method. If
138 * any subsequent call to <code>read()</code> results in a
139 * <code>IOException</code>, the exception is caught and treated as if it
140 * were end of file; the bytes read up to that point are stored into
141 * <code>b</code> and the number of bytes read before the exception
142 * occurred is returned. The default implementation of this method blocks
143 * until the requested amount of input data <code>len</code> has been read,
144 * end of file is detected, or an exception is thrown. Subclasses are encouraged
145 * to provide a more efficient implementation of this method.
146 *
147 * @param b the buffer into which the data is read.
148 * @param off the start offset in array <code>b</code>
149 * at which the data is written.
150 * @param len the maximum number of bytes to read.
151 * @return the total number of bytes read into the buffer, or
152 * <code>-1</code> if there is no more data because the end of
153 * the stream has been reached.
154 * @exception IOException If the first byte cannot be read for any reason
155 * other than end of file, or if the input stream has been closed, or if
156 * some other I/O error occurs.
157 * @exception NullPointerException If <code>b</code> is <code>null</code>.
158 * @exception IndexOutOfBoundsException If <code>off</code> is negative,
159 * <code>len</code> is negative, or <code>len</code> is greater than
160 * <code>b.length - off</code>
161 * @see java.io.InputStream#read()
162 */
163 public int read(byte b[], int off, int len) throws IOException {
164 if (b == null) {
165 throw new NullPointerException();
166 } else if (off < 0 || len < 0 || len > b.length - off) {
167 throw new IndexOutOfBoundsException();
168 } else if (len == 0) {
169 return 0;
170 }
171
172 int c = read();
173 if (c == -1) {
174 return -1;
175 }
176 b[off] = (byte)c;
177
178 int i = 1;
179 try {
180 for (; i < len ; i++) {
181 c = read();
182 if (c == -1) {
183 break;
184 }
185 b[off + i] = (byte)c;
186 }
187 } catch (IOException ee) {
188 }
189 return i;
190 }
191
192 /**
193 * Skips over and discards <code>n</code> bytes of data from this input
194 * stream. The <code>skip</code> method may, for a variety of reasons, end
195 * up skipping over some smaller number of bytes, possibly <code>0</code>.
196 * This may result from any of a number of conditions; reaching end of file
197 * before <code>n</code> bytes have been skipped is only one possibility.
198 * The actual number of bytes skipped is returned. If {@code n} is
199 * negative, the {@code skip} method for class {@code InputStream} always
200 * returns 0, and no bytes are skipped. Subclasses may handle the negative
201 * value differently.
202 *
203 * <p> The <code>skip</code> method of this class creates a
204 * byte array and then repeatedly reads into it until <code>n</code> bytes
205 * have been read or the end of the stream has been reached. Subclasses are
206 * encouraged to provide a more efficient implementation of this method.
207 * For instance, the implementation may depend on the ability to seek.
208 *
209 * @param n the number of bytes to be skipped.
210 * @return the actual number of bytes skipped.
211 * @exception IOException if the stream does not support seek,
212 * or if some other I/O error occurs.
213 */
214 public long skip(long n) throws IOException {
215
216 long remaining = n;
217 int nr;
218
219 if (n <= 0) {
220 return 0;
221 }
222
223 int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
224 byte[] skipBuffer = new byte[size];
225 while (remaining > 0) {
226 nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
227 if (nr < 0) {
228 break;
229 }
230 remaining -= nr;
231 }
232
233 return n - remaining;
234 }
235
236 /**
237 * Returns an estimate of the number of bytes that can be read (or
238 * skipped over) from this input stream without blocking by the next
239 * invocation of a method for this input stream. The next invocation
240 * might be the same thread or another thread. A single read or skip of this
241 * many bytes will not block, but may read or skip fewer bytes.
242 *
243 * <p> Note that while some implementations of {@code InputStream} will return
244 * the total number of bytes in the stream, many will not. It is
245 * never correct to use the return value of this method to allocate
246 * a buffer intended to hold all data in this stream.
247 *
248 * <p> A subclass' implementation of this method may choose to throw an
249 * {@link IOException} if this input stream has been closed by
250 * invoking the {@link #close()} method.
251 *
252 * <p> The {@code available} method for class {@code InputStream} always
253 * returns {@code 0}.
254 *
255 * <p> This method should be overridden by subclasses.
256 *
257 * @return an estimate of the number of bytes that can be read (or skipped
258 * over) from this input stream without blocking or {@code 0} when
259 * it reaches the end of the input stream.
260 * @exception IOException if an I/O error occurs.
261 */
262 public int available() throws IOException {
263 return 0;
264 }
265
266 /**
267 * Closes this input stream and releases any system resources associated
268 * with the stream.
269 *
270 * <p> The <code>close</code> method of <code>InputStream</code> does
271 * nothing.
272 *
273 * @exception IOException if an I/O error occurs.
274 */
275 public void close() throws IOException {}
276
277 /**
278 * Marks the current position in this input stream. A subsequent call to
279 * the <code>reset</code> method repositions this stream at the last marked
280 * position so that subsequent reads re-read the same bytes.
281 *
282 * <p> The <code>readlimit</code> arguments tells this input stream to
283 * allow that many bytes to be read before the mark position gets
284 * invalidated.
285 *
286 * <p> The general contract of <code>mark</code> is that, if the method
287 * <code>markSupported</code> returns <code>true</code>, the stream somehow
288 * remembers all the bytes read after the call to <code>mark</code> and
289 * stands ready to supply those same bytes again if and whenever the method
290 * <code>reset</code> is called. However, the stream is not required to
291 * remember any data at all if more than <code>readlimit</code> bytes are
292 * read from the stream before <code>reset</code> is called.
293 *
294 * <p> Marking a closed stream should not have any effect on the stream.
295 *
296 * <p> The <code>mark</code> method of <code>InputStream</code> does
297 * nothing.
298 *
299 * @param readlimit the maximum limit of bytes that can be read before
300 * the mark position becomes invalid.
301 * @see java.io.InputStream#reset()
302 */
303 public synchronized void mark(int readlimit) {}
304
305 /**
306 * Repositions this stream to the position at the time the
307 * <code>mark</code> method was last called on this input stream.
308 *
309 * <p> The general contract of <code>reset</code> is:
310 *
311 * <ul>
312 * <li> If the method <code>markSupported</code> returns
313 * <code>true</code>, then:
314 *
315 * <ul><li> If the method <code>mark</code> has not been called since
316 * the stream was created, or the number of bytes read from the stream
317 * since <code>mark</code> was last called is larger than the argument
318 * to <code>mark</code> at that last call, then an
319 * <code>IOException</code> might be thrown.
320 *
321 * <li> If such an <code>IOException</code> is not thrown, then the
322 * stream is reset to a state such that all the bytes read since the
323 * most recent call to <code>mark</code> (or since the start of the
324 * file, if <code>mark</code> has not been called) will be resupplied
325 * to subsequent callers of the <code>read</code> method, followed by
326 * any bytes that otherwise would have been the next input data as of
327 * the time of the call to <code>reset</code>. </ul>
328 *
329 * <li> If the method <code>markSupported</code> returns
330 * <code>false</code>, then:
331 *
332 * <ul><li> The call to <code>reset</code> may throw an
333 * <code>IOException</code>.
334 *
335 * <li> If an <code>IOException</code> is not thrown, then the stream
336 * is reset to a fixed state that depends on the particular type of the
337 * input stream and how it was created. The bytes that will be supplied
338 * to subsequent callers of the <code>read</code> method depend on the
339 * particular type of the input stream. </ul></ul>
340 *
341 * <p>The method <code>reset</code> for class <code>InputStream</code>
342 * does nothing except throw an <code>IOException</code>.
343 *
344 * @exception IOException if this stream has not been marked or if the
345 * mark has been invalidated.
346 * @see java.io.InputStream#mark(int)
347 * @see java.io.IOException
348 */
349 public synchronized void reset() throws IOException {
350 throw new IOException("mark/reset not supported");
351 }
352
353 /**
354 * Tests if this input stream supports the <code>mark</code> and
355 * <code>reset</code> methods. Whether or not <code>mark</code> and
356 * <code>reset</code> are supported is an invariant property of a
357 * particular input stream instance. The <code>markSupported</code> method
358 * of <code>InputStream</code> returns <code>false</code>.
359 *
360 * @return <code>true</code> if this stream instance supports the mark
361 * and reset methods; <code>false</code> otherwise.
362 * @see java.io.InputStream#mark(int)
363 * @see java.io.InputStream#reset()
364 */
365 public boolean markSupported() {
366 return false;
367 }
368
369 /**
370 * Reads all bytes from this input stream and writes the bytes to the
371 * given output stream in the order that they are read. On return, this
372 * input stream will be at end of stream. This method does not close either
373 * stream.
374 * <p>
375 * This method may block indefinitely reading from the input stream, or
376 * writing to the output stream. The behavior for the case where the input
377 * and/or output stream is <i>asynchronously closed</i>, or the thread
378 * interrupted during the transfer, is highly input and output stream
379 * specific, and therefore not specified.
380 * <p>
381 * If an I/O error occurs reading from the input stream or writing to the
382 * output stream, then it may do so after some bytes have been read or
383 * written. Consequently the input stream may not be at end of stream and
384 * one, or both, streams may be in an inconsistent state. It is strongly
385 * recommended that both streams be promptly closed if an I/O error occurs.
386 *
387 * @param out the output stream, non-null
388 * @return the number of bytes transferred
389 * @throws IOException if an I/O error occurs when reading or writing
390 * @throws NullPointerException if {@code out} is {@code null}
391 *
392 * @since 1.9
393 */
394 public long transferTo(OutputStream out) throws IOException {
395 Objects.requireNonNull(out, "out");
396 int transferred = 0;
397 byte[] buffer = new byte[8192];
398 for (int read; (read = this.read(buffer, 0, buffer.length)) > -1;
399 transferred += read) {
400 out.write(buffer, 0, read);
401 }
402 return transferred;
403 }
404 }