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 /**
29 * This abstract class is the superclass of all classes representing
30 * an input stream of bytes.
31 *
32 * <p> Applications that need to define a subclass of <code>InputStream</code>
33 * must always provide a method that returns the next byte of input.
34 *
35 * @author Arthur van Hoff
36 * @see java.io.BufferedInputStream
37 * @see java.io.ByteArrayInputStream
38 * @see java.io.DataInputStream
39 * @see java.io.FilterInputStream
40 * @see java.io.InputStream#read()
41 * @see java.io.OutputStream
42 * @see java.io.PushbackInputStream
43 * @since JDK1.0
44 */
45 public abstract class InputStream implements Closeable {
46
47 // MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to
48 // use when skipping.
49 private static final int MAX_SKIP_BUFFER_SIZE = 2048;
50
51 /**
52 * Reads the next byte of data from the input stream. The value byte is
53 * returned as an <code>int</code> in the range <code>0</code> to
54 * <code>255</code>. If no byte is available because the end of the stream
55 * has been reached, the value <code>-1</code> is returned. This method
56 * blocks until input data is available, the end of the stream is detected,
57 * or an exception is thrown.
58 *
59 * <p> A subclass must provide an implementation of this method.
60 *
61 * @return the next byte of data, or <code>-1</code> if the end of the
62 * stream is reached.
63 * @exception IOException if an I/O error occurs.
64 */
65 public abstract int read() throws IOException;
66
67 /**
68 * Reads some number of bytes from the input stream and stores them into
69 * the buffer array <code>b</code>. The number of bytes actually read is
70 * returned as an integer. This method blocks until input data is
71 * available, end of file is detected, or an exception is thrown.
72 *
73 * <p> If the length of <code>b</code> is zero, then no bytes are read and
74 * <code>0</code> is returned; otherwise, there is an attempt to read at
75 * least one byte. If no byte is available because the stream is at the
76 * end of the file, the value <code>-1</code> is returned; otherwise, at
77 * least one byte is read and stored into <code>b</code>.
78 *
79 * <p> The first byte read is stored into element <code>b[0]</code>, the
80 * next one into <code>b[1]</code>, and so on. The number of bytes read is,
81 * at most, equal to the length of <code>b</code>. Let <i>k</i> be the
82 * number of bytes actually read; these bytes will be stored in elements
83 * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,
84 * leaving elements <code>b[</code><i>k</i><code>]</code> through
85 * <code>b[b.length-1]</code> unaffected.
86 *
87 * <p> The <code>read(b)</code> method for class <code>InputStream</code>
88 * has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>
89 *
90 * @param b the buffer into which the data is read.
91 * @return the total number of bytes read into the buffer, or
92 * <code>-1</code> if there is no more data because the end of
93 * the stream has been reached.
94 * @exception IOException If the first byte cannot be read for any reason
95 * other than the end of the file, if the input stream has been closed, or
96 * if some other I/O error occurs.
97 * @exception NullPointerException if <code>b</code> is <code>null</code>.
98 * @see java.io.InputStream#read(byte[], int, int)
99 */
100 public int read(byte b[]) throws IOException {
101 return read(b, 0, b.length);
102 }
103
104 /**
105 * Reads up to <code>len</code> bytes of data from the input stream into
106 * an array of bytes. An attempt is made to read as many as
107 * <code>len</code> bytes, but a smaller number may be read.
108 * The number of bytes actually read is returned as an integer.
109 *
110 * <p> This method blocks until input data is available, end of file is
111 * detected, or an exception is thrown.
112 *
113 * <p> If <code>len</code> is zero, then no bytes are read and
114 * <code>0</code> is returned; otherwise, there is an attempt to read at
115 * least one byte. If no byte is available because the stream is at end of
116 * file, the value <code>-1</code> is returned; otherwise, at least one
117 * byte is read and stored into <code>b</code>.
118 *
119 * <p> The first byte read is stored into element <code>b[off]</code>, the
120 * next one into <code>b[off+1]</code>, and so on. The number of bytes read
121 * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
122 * bytes actually read; these bytes will be stored in elements
123 * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
124 * leaving elements <code>b[off+</code><i>k</i><code>]</code> through
125 * <code>b[off+len-1]</code> unaffected.
126 *
127 * <p> In every case, elements <code>b[0]</code> through
128 * <code>b[off]</code> and elements <code>b[off+len]</code> through
129 * <code>b[b.length-1]</code> are unaffected.
130 *
131 * <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method
132 * for class <code>InputStream</code> simply calls the method
133 * <code>read()</code> repeatedly. If the first such call results in an
134 * <code>IOException</code>, that exception is returned from the call to
135 * the <code>read(b,</code> <code>off,</code> <code>len)</code> method. If
136 * any subsequent call to <code>read()</code> results in a
137 * <code>IOException</code>, the exception is caught and treated as if it
138 * were end of file; the bytes read up to that point are stored into
139 * <code>b</code> and the number of bytes read before the exception
140 * occurred is returned. The default implementation of this method blocks
141 * until the requested amount of input data <code>len</code> has been read,
142 * end of file is detected, or an exception is thrown. Subclasses are encouraged
143 * to provide a more efficient implementation of this method.
144 *
145 * @param b the buffer into which the data is read.
146 * @param off the start offset in array <code>b</code>
147 * at which the data is written.
148 * @param len the maximum number of bytes to read.
149 * @return the total number of bytes read into the buffer, or
150 * <code>-1</code> if there is no more data because the end of
151 * the stream has been reached.
152 * @exception IOException If the first byte cannot be read for any reason
153 * other than end of file, or if the input stream has been closed, or if
154 * some other I/O error occurs.
155 * @exception NullPointerException If <code>b</code> is <code>null</code>.
156 * @exception IndexOutOfBoundsException If <code>off</code> is negative,
157 * <code>len</code> is negative, or <code>len</code> is greater than
158 * <code>b.length - off</code>
159 * @see java.io.InputStream#read()
160 */
161 public int read(byte b[], int off, int len) throws IOException {
162 if (b == null) {
163 throw new NullPointerException();
164 } else if (off < 0 || len < 0 || len > b.length - off) {
165 throw new IndexOutOfBoundsException();
166 } else if (len == 0) {
167 return 0;
168 }
169
170 int c = read();
171 if (c == -1) {
172 return -1;
173 }
174 b[off] = (byte)c;
175
176 int i = 1;
177 try {
178 for (; i < len ; i++) {
179 c = read();
180 if (c == -1) {
181 break;
182 }
183 b[off + i] = (byte)c;
184 }
185 } catch (IOException ee) {
186 }
187 return i;
188 }
189
190 /**
191 * Skips over and discards <code>n</code> bytes of data from this input
192 * stream. The <code>skip</code> method may, for a variety of reasons, end
193 * up skipping over some smaller number of bytes, possibly <code>0</code>.
194 * This may result from any of a number of conditions; reaching end of file
195 * before <code>n</code> bytes have been skipped is only one possibility.
196 * The actual number of bytes skipped is returned. If {@code n} is
197 * negative, the {@code skip} method for class {@code InputStream} always
198 * returns 0, and no bytes are skipped. Subclasses may handle the negative
199 * value differently.
200 *
201 * <p> The <code>skip</code> method of this class creates a
202 * byte array and then repeatedly reads into it until <code>n</code> bytes
203 * have been read or the end of the stream has been reached. Subclasses are
204 * encouraged to provide a more efficient implementation of this method.
205 * For instance, the implementation may depend on the ability to seek.
206 *
207 * @param n the number of bytes to be skipped.
208 * @return the actual number of bytes skipped.
209 * @exception IOException if the stream does not support seek,
210 * or if some other I/O error occurs.
211 */
212 public long skip(long n) throws IOException {
213
214 long remaining = n;
215 int nr;
216
217 if (n <= 0) {
218 return 0;
219 }
220
221 int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
222 byte[] skipBuffer = new byte[size];
223 while (remaining > 0) {
224 nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
225 if (nr < 0) {
226 break;
227 }
228 remaining -= nr;
229 }
230
231 return n - remaining;
232 }
233
234 /**
235 * Returns an estimate of the number of bytes that can be read (or
236 * skipped over) from this input stream without blocking by the next
237 * invocation of a method for this input stream. The next invocation
238 * might be the same thread or another thread. A single read or skip of this
239 * many bytes will not block, but may read or skip fewer bytes.
240 *
241 * <p> Note that while some implementations of {@code InputStream} will return
242 * the total number of bytes in the stream, many will not. It is
243 * never correct to use the return value of this method to allocate
244 * a buffer intended to hold all data in this stream.
245 *
246 * <p> A subclass' implementation of this method may choose to throw an
247 * {@link IOException} if this input stream has been closed by
248 * invoking the {@link #close()} method.
249 *
250 * <p> The {@code available} method for class {@code InputStream} always
251 * returns {@code 0}.
252 *
253 * <p> This method should be overridden by subclasses.
254 *
255 * @return an estimate of the number of bytes that can be read (or skipped
256 * over) from this input stream without blocking or {@code 0} when
257 * it reaches the end of the input stream.
258 * @exception IOException if an I/O error occurs.
259 */
260 public int available() throws IOException {
261 return 0;
262 }
263
264 /**
265 * Closes this input stream and releases any system resources associated
266 * with the stream.
267 *
268 * <p> The <code>close</code> method of <code>InputStream</code> does
269 * nothing.
270 *
271 * @exception IOException if an I/O error occurs.
272 */
273 public void close() throws IOException {}
274
275 /**
276 * Marks the current position in this input stream. A subsequent call to
277 * the <code>reset</code> method repositions this stream at the last marked
278 * position so that subsequent reads re-read the same bytes.
279 *
280 * <p> The <code>readlimit</code> arguments tells this input stream to
281 * allow that many bytes to be read before the mark position gets
282 * invalidated.
283 *
284 * <p> The general contract of <code>mark</code> is that, if the method
285 * <code>markSupported</code> returns <code>true</code>, the stream somehow
286 * remembers all the bytes read after the call to <code>mark</code> and
287 * stands ready to supply those same bytes again if and whenever the method
288 * <code>reset</code> is called. However, the stream is not required to
289 * remember any data at all if more than <code>readlimit</code> bytes are
290 * read from the stream before <code>reset</code> is called.
291 *
292 * <p> Marking a closed stream should not have any effect on the stream.
293 *
294 * <p> The <code>mark</code> method of <code>InputStream</code> does
295 * nothing.
296 *
297 * @param readlimit the maximum limit of bytes that can be read before
298 * the mark position becomes invalid.
299 * @see java.io.InputStream#reset()
300 */
301 public synchronized void mark(int readlimit) {}
302
303 /**
304 * Repositions this stream to the position at the time the
305 * <code>mark</code> method was last called on this input stream.
306 *
307 * <p> The general contract of <code>reset</code> is:
308 *
309 * <ul>
310 * <li> If the method <code>markSupported</code> returns
311 * <code>true</code>, then:
312 *
313 * <ul><li> If the method <code>mark</code> has not been called since
314 * the stream was created, or the number of bytes read from the stream
315 * since <code>mark</code> was last called is larger than the argument
316 * to <code>mark</code> at that last call, then an
317 * <code>IOException</code> might be thrown.
318 *
319 * <li> If such an <code>IOException</code> is not thrown, then the
320 * stream is reset to a state such that all the bytes read since the
321 * most recent call to <code>mark</code> (or since the start of the
322 * file, if <code>mark</code> has not been called) will be resupplied
323 * to subsequent callers of the <code>read</code> method, followed by
324 * any bytes that otherwise would have been the next input data as of
325 * the time of the call to <code>reset</code>. </ul>
326 *
327 * <li> If the method <code>markSupported</code> returns
328 * <code>false</code>, then:
329 *
330 * <ul><li> The call to <code>reset</code> may throw an
331 * <code>IOException</code>.
332 *
333 * <li> If an <code>IOException</code> is not thrown, then the stream
334 * is reset to a fixed state that depends on the particular type of the
335 * input stream and how it was created. The bytes that will be supplied
336 * to subsequent callers of the <code>read</code> method depend on the
337 * particular type of the input stream. </ul></ul>
338 *
339 * <p>The method <code>reset</code> for class <code>InputStream</code>
340 * does nothing except throw an <code>IOException</code>.
341 *
342 * @exception IOException if this stream has not been marked or if the
343 * mark has been invalidated.
344 * @see java.io.InputStream#mark(int)
345 * @see java.io.IOException
346 */
347 public synchronized void reset() throws IOException {
348 throw new IOException("mark/reset not supported");
349 }
350
351 /**
352 * Tests if this input stream supports the <code>mark</code> and
353 * <code>reset</code> methods. Whether or not <code>mark</code> and
354 * <code>reset</code> are supported is an invariant property of a
355 * particular input stream instance. The <code>markSupported</code> method
356 * of <code>InputStream</code> returns <code>false</code>.
357 *
358 * @return <code>true</code> if this stream instance supports the mark
359 * and reset methods; <code>false</code> otherwise.
360 * @see java.io.InputStream#mark(int)
361 * @see java.io.InputStream#reset()
362 */
363 public boolean markSupported() {
364 return false;
365 }
366
367 }