1 /*
2 * Copyright 1994-2006 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any 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 // SKIP_BUFFER_SIZE is used to determine the size of skipBuffer
48 private static final int SKIP_BUFFER_SIZE = 2048;
49 // skipBuffer is initialized in skip(long), if needed.
50 private static byte[] skipBuffer;
51
52 /**
53 * Reads the next byte of data from the input stream. The value byte is
54 * returned as an <code>int</code> in the range <code>0</code> to
55 * <code>255</code>. If no byte is available because the end of the stream
56 * has been reached, the value <code>-1</code> is returned. This method
57 * blocks until input data is available, the end of the stream is detected,
58 * or an exception is thrown.
59 *
60 * <p> A subclass must provide an implementation of this method.
61 *
62 * @return the next byte of data, or <code>-1</code> if the end of the
63 * stream is reached.
64 * @exception IOException if an I/O error occurs.
65 */
66 public abstract int read() throws IOException;
67
68 /**
69 * Reads some number of bytes from the input stream and stores them into
70 * the buffer array <code>b</code>. The number of bytes actually read is
71 * returned as an integer. This method blocks until input data is
72 * available, end of file is detected, or an exception is thrown.
73 *
74 * <p> If the length of <code>b</code> is zero, then no bytes are read and
75 * <code>0</code> is returned; otherwise, there is an attempt to read at
76 * least one byte. If no byte is available because the stream is at the
77 * end of the file, the value <code>-1</code> is returned; otherwise, at
78 * least one byte is read and stored into <code>b</code>.
79 *
80 * <p> The first byte read is stored into element <code>b[0]</code>, the
81 * next one into <code>b[1]</code>, and so on. The number of bytes read is,
82 * at most, equal to the length of <code>b</code>. Let <i>k</i> be the
83 * number of bytes actually read; these bytes will be stored in elements
84 * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,
85 * leaving elements <code>b[</code><i>k</i><code>]</code> through
86 * <code>b[b.length-1]</code> unaffected.
87 *
88 * <p> The <code>read(b)</code> method for class <code>InputStream</code>
89 * has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>
90 *
91 * @param b the buffer into which the data is read.
92 * @return the total number of bytes read into the buffer, or
93 * <code>-1</code> is there is no more data because the end of
94 * the stream has been reached.
95 * @exception IOException If the first byte cannot be read for any reason
96 * other than the end of the file, if the input stream has been closed, or
97 * if some other I/O error occurs.
98 * @exception NullPointerException if <code>b</code> is <code>null</code>.
99 * @see java.io.InputStream#read(byte[], int, int)
100 */
101 public int read(byte b[]) throws IOException {
102 return read(b, 0, b.length);
103 }
104
105 /**
106 * Reads up to <code>len</code> bytes of data from the input stream into
107 * an array of bytes. An attempt is made to read as many as
108 * <code>len</code> bytes, but a smaller number may be read.
109 * The number of bytes actually read is returned as an integer.
110 *
111 * <p> This method blocks until input data is available, end of file is
112 * detected, or an exception is thrown.
113 *
114 * <p> If <code>len</code> is zero, then no bytes are read and
115 * <code>0</code> is returned; otherwise, there is an attempt to read at
116 * least one byte. If no byte is available because the stream is at end of
117 * file, the value <code>-1</code> is returned; otherwise, at least one
118 * byte is read and stored into <code>b</code>.
119 *
120 * <p> The first byte read is stored into element <code>b[off]</code>, the
121 * next one into <code>b[off+1]</code>, and so on. The number of bytes read
122 * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
123 * bytes actually read; these bytes will be stored in elements
124 * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
125 * leaving elements <code>b[off+</code><i>k</i><code>]</code> through
126 * <code>b[off+len-1]</code> unaffected.
127 *
128 * <p> In every case, elements <code>b[0]</code> through
129 * <code>b[off]</code> and elements <code>b[off+len]</code> through
130 * <code>b[b.length-1]</code> are unaffected.
131 *
132 * <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method
133 * for class <code>InputStream</code> simply calls the method
134 * <code>read()</code> repeatedly. If the first such call results in an
135 * <code>IOException</code>, that exception is returned from the call to
136 * the <code>read(b,</code> <code>off,</code> <code>len)</code> method. If
137 * any subsequent call to <code>read()</code> results in a
138 * <code>IOException</code>, the exception is caught and treated as if it
139 * were end of file; the bytes read up to that point are stored into
140 * <code>b</code> and the number of bytes read before the exception
141 * occurred is returned. The default implementation of this method blocks
142 * until the requested amount of input data <code>len</code> has been read,
143 * end of file is detected, or an exception is thrown. Subclasses are encouraged
144 * to provide a more efficient implementation of this method.
145 *
146 * @param b the buffer into which the data is read.
147 * @param off the start offset in array <code>b</code>
148 * at which the data is written.
149 * @param len the maximum number of bytes to read.
150 * @return the total number of bytes read into the buffer, or
151 * <code>-1</code> if there is no more data because the end of
152 * the stream has been reached.
153 * @exception IOException If the first byte cannot be read for any reason
154 * other than end of file, or if the input stream has been closed, or if
155 * some other I/O error occurs.
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 * @see java.io.InputStream#read()
161 */
162 public int read(byte b[], int off, int len) throws IOException {
163 if (b == null) {
164 throw new NullPointerException();
165 } else if (off < 0 || len < 0 || len > b.length - off) {
166 throw new IndexOutOfBoundsException();
167 } else if (len == 0) {
168 return 0;
169 }
170
171 int c = read();
172 if (c == -1) {
173 return -1;
174 }
175 b[off] = (byte)c;
176
177 int i = 1;
178 try {
179 for (; i < len ; i++) {
180 c = read();
181 if (c == -1) {
182 break;
183 }
184 b[off + i] = (byte)c;
185 }
186 } catch (IOException ee) {
187 }
188 return i;
189 }
190
191 /**
192 * Skips over and discards <code>n</code> bytes of data from this input
193 * stream. The <code>skip</code> method may, for a variety of reasons, end
194 * up skipping over some smaller number of bytes, possibly <code>0</code>.
195 * This may result from any of a number of conditions; reaching end of file
196 * before <code>n</code> bytes have been skipped is only one possibility.
197 * The actual number of bytes skipped is returned. If <code>n</code> is
198 * negative, no bytes are skipped.
199 *
200 * <p> The <code>skip</code> method of this class creates a
201 * byte array and then repeatedly reads into it until <code>n</code> bytes
202 * have been read or the end of the stream has been reached. Subclasses are
203 * encouraged to provide a more efficient implementation of this method.
204 * For instance, the implementation may depend on the ability to seek.
205 *
206 * @param n the number of bytes to be skipped.
207 * @return the actual number of bytes skipped.
208 * @exception IOException if the stream does not support seek,
209 * or if some other I/O error occurs.
210 */
211 public long skip(long n) throws IOException {
212
213 long remaining = n;
214 int nr;
215 if (skipBuffer == null)
216 skipBuffer = new byte[SKIP_BUFFER_SIZE];
217
218 byte[] localSkipBuffer = skipBuffer;
219
220 if (n <= 0) {
221 return 0;
222 }
223
224 while (remaining > 0) {
225 nr = read(localSkipBuffer, 0,
226 (int) Math.min(SKIP_BUFFER_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 * <p><ul>
312 *
313 * <li> If the method <code>markSupported</code> returns
314 * <code>true</code>, then:
315 *
316 * <ul><li> If the method <code>mark</code> has not been called since
317 * the stream was created, or the number of bytes read from the stream
318 * since <code>mark</code> was last called is larger than the argument
319 * to <code>mark</code> at that last call, then an
320 * <code>IOException</code> might be thrown.
321 *
322 * <li> If such an <code>IOException</code> is not thrown, then the
323 * stream is reset to a state such that all the bytes read since the
324 * most recent call to <code>mark</code> (or since the start of the
325 * file, if <code>mark</code> has not been called) will be resupplied
326 * to subsequent callers of the <code>read</code> method, followed by
327 * any bytes that otherwise would have been the next input data as of
328 * the time of the call to <code>reset</code>. </ul>
329 *
330 * <li> If the method <code>markSupported</code> returns
331 * <code>false</code>, then:
332 *
333 * <ul><li> The call to <code>reset</code> may throw an
334 * <code>IOException</code>.
335 *
336 * <li> If an <code>IOException</code> is not thrown, then the stream
337 * is reset to a fixed state that depends on the particular type of the
338 * input stream and how it was created. The bytes that will be supplied
339 * to subsequent callers of the <code>read</code> method depend on the
340 * particular type of the input stream. </ul></ul>
341 *
342 * <p>The method <code>reset</code> for class <code>InputStream</code>
343 * does nothing except throw an <code>IOException</code>.
344 *
345 * @exception IOException if this stream has not been marked or if the
346 * mark has been invalidated.
347 * @see java.io.InputStream#mark(int)
348 * @see java.io.IOException
349 */
350 public synchronized void reset() throws IOException {
351 throw new IOException("mark/reset not supported");
352 }
353
354 /**
355 * Tests if this input stream supports the <code>mark</code> and
356 * <code>reset</code> methods. Whether or not <code>mark</code> and
357 * <code>reset</code> are supported is an invariant property of a
358 * particular input stream instance. The <code>markSupported</code> method
359 * of <code>InputStream</code> returns <code>false</code>.
360 *
361 * @return <code>true</code> if this stream instance supports the mark
362 * and reset methods; <code>false</code> otherwise.
363 * @see java.io.InputStream#mark(int)
364 * @see java.io.InputStream#reset()
365 */
366 public boolean markSupported() {
367 return false;
368 }
369
370 }