1 /* PushbackInputStream.java -- An input stream that can unread bytes
2 Copyright (C) 1998, 1999, 2001, 2002, 2005 Free Software Foundation, Inc.
4 This file is part of GNU Classpath.
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14 General Public License for more details.
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18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
21 Linking this library statically or dynamically with other modules is
22 making a combined work based on this library. Thus, the terms and
23 conditions of the GNU General Public License cover the whole
26 As a special exception, the copyright holders of this library give you
27 permission to link this library with independent modules to produce an
28 executable, regardless of the license terms of these independent
29 modules, and to copy and distribute the resulting executable under
30 terms of your choice, provided that you also meet, for each linked
31 independent module, the terms and conditions of the license of that
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35 obligated to do so. If you do not wish to do so, delete this
36 exception statement from your version. */
41 * This subclass of <code>FilterInputStream</code> provides the ability to
42 * unread data from a stream. It maintains an internal buffer of unread data
43 * that is supplied to the next read operation. This is conceptually similar to
44 * mark/reset functionality, except that in this case the position to reset the
45 * stream to does not need to be known in advance.
47 * The default pushback buffer size one byte, but this can be overridden by the
48 * creator of the stream.
51 * @author Aaron M. Renn (arenn@urbanophile.com)
52 * @author Warren Levy (warrenl@cygnus.com)
55 public class PushbackInputStream extends FilterInputStream {
57 * This is the default buffer size
60 private static final int DEFAULT_BUFFER_SIZE = 1;
63 * This is the buffer that is used to store the pushed back data
69 * This is the position in the buffer from which the next byte will be read.
70 * Bytes are stored in reverse order in the buffer, starting from
71 * <code>buf[buf.length - 1]</code> to <code>buf[0]</code>. Thus when
72 * <code>pos</code> is 0 the buffer is full and <code>buf.length</code> when
79 * This method initializes a <code>PushbackInputStream</code> to read from the
80 * specified subordinate <code>InputStream</code> with a default pushback
84 * The subordinate stream to read from
86 public PushbackInputStream(InputStream in) {
87 this(in, DEFAULT_BUFFER_SIZE);
91 * This method initializes a <code>PushbackInputStream</code> to read from the
92 * specified subordinate <code>InputStream</code> with the specified buffer
96 * The subordinate <code>InputStream</code> to read from
98 * The pushback buffer size to use
100 public PushbackInputStream(InputStream in, int size) {
103 throw new IllegalArgumentException();
104 buf = new byte[size];
109 * This method returns the number of bytes that can be read from this stream
110 * before a read can block. A return of 0 indicates that blocking might (or
111 * might not) occur on the very next read attempt.
113 * This method will return the number of bytes available from the pushback
114 * buffer plus the number of bytes available from the underlying stream.
116 * @return The number of bytes that can be read before blocking could occur
118 * @exception IOException
121 public int available() throws IOException {
123 return (buf.length - pos) + super.available();
124 } catch (NullPointerException npe) {
125 throw new IOException("Stream closed");
130 * This method closes the stream and releases any associated resources.
132 * @exception IOException
133 * If an error occurs.
135 public synchronized void close() throws IOException {
141 * This method returns <code>false</code> to indicate that it does not support
142 * mark/reset functionality.
144 * @return This method returns <code>false</code> to indicate that this class
145 * does not support mark/reset functionality
147 public boolean markSupported() {
152 * This method always throws an IOException in this class because mark/reset
153 * functionality is not supported.
155 * @exception IOException
156 * Always thrown for this class
158 public void reset() throws IOException {
159 throw new IOException("Mark not supported in this class");
163 * This method reads an unsigned byte from the input stream and returns it as
164 * an int in the range of 0-255. This method also will return -1 if the end of
165 * the stream has been reached. The byte returned will be read from the
166 * pushback buffer, unless the buffer is empty, in which case the byte will be
167 * read from the underlying stream.
169 * This method will block until the byte can be read.
171 * @return The byte read or -1 if end of stream
173 * @exception IOException
176 public synchronized int read() throws IOException {
177 if (pos < buf.length)
178 return ((int) buf[pos++]) & 0xFF;
184 * This method read bytes from a stream and stores them into a caller supplied
185 * buffer. It starts storing the data at index <code>offset</code> into the
186 * buffer and attempts to read <code>len</code> bytes. This method can return
187 * before reading the number of bytes requested. The actual number of bytes
188 * read is returned as an int. A -1 is returned to indicate the end of the
191 * This method will block until some data can be read.
193 * This method first reads bytes from the pushback buffer in order to satisfy
194 * the read request. If the pushback buffer cannot provide all of the bytes
195 * requested, the remaining bytes are read from the underlying stream.
198 * The array into which the bytes read should be stored
200 * The offset into the array to start storing bytes
202 * The requested number of bytes to read
204 * @return The actual number of bytes read, or -1 if end of stream.
206 * @exception IOException
207 * If an error occurs.
210 public synchronized int read(byte[] b, int off, int len) throws IOException {
211 int numBytes = Math.min(buf.length - pos, len);
215 System.arraycopy(buf, pos, b, off, numBytes);
222 len = super.read(b, off, len);
223 if (len == -1) // EOF
224 return numBytes > 0 ? numBytes : -1;
231 * This method pushes a single byte of data into the pushback buffer. The byte
232 * pushed back is the one that will be returned as the first byte of the next
235 * If the pushback buffer is full, this method throws an exception.
237 * The argument to this method is an <code>int</code>. Only the low eight bits
238 * of this value are pushed back.
241 * The byte to be pushed back, passed as an int
243 * @exception IOException
244 * If the pushback buffer is full.
246 public synchronized void unread(int b) throws IOException {
248 throw new IOException("Insufficient space in pushback buffer");
250 buf[--pos] = (byte) b;
254 * This method pushes all of the bytes in the passed byte array into the
255 * pushback bfer. These bytes are pushed in reverse order so that the next
256 * byte read from the stream after this operation will be <code>b[0]</code>
257 * followed by <code>b[1]</code>, etc.
259 * If the pushback buffer cannot hold all of the requested bytes, an exception
263 * The byte array to be pushed back
265 * @exception IOException
266 * If the pushback buffer is full
268 public synchronized void unread(byte[] b) throws IOException {
269 unread(b, 0, b.length);
273 * This method pushed back bytes from the passed in array into the pushback
274 * buffer. The bytes from <code>b[offset]</code> to
275 * <code>b[offset + len]</code> are pushed in reverse order so that the next
276 * byte read from the stream after this operation will be
277 * <code>b[offset]</code> followed by <code>b[offset + 1]</code>, etc.
279 * If the pushback buffer cannot hold all of the requested bytes, an exception
283 * The byte array to be pushed back
285 * The index into the array where the bytes to be push start
287 * The number of bytes to be pushed.
289 * @exception IOException
290 * If the pushback buffer is full
292 public synchronized void unread(byte[] b, int off, int len) throws IOException {
294 throw new IOException("Insufficient space in pushback buffer");
296 // Note the order that these bytes are being added is the opposite
297 // of what would be done if they were added to the buffer one at a time.
298 // See the Java Class Libraries book p. 1390.
299 System.arraycopy(b, off, buf, pos - len, len);
301 // Don't put this into the arraycopy above, an exception might be thrown
302 // and in that case we don't want to modify pos.
307 * This method skips the specified number of bytes in the stream. It returns
308 * the actual number of bytes skipped, which may be less than the requested
311 * This method first discards bytes from the buffer, then calls the
312 * <code>skip</code> method on the underlying <code>InputStream</code> to skip
313 * additional bytes if necessary.
316 * The requested number of bytes to skip
318 * @return The actual number of bytes skipped.
320 * @exception IOException
325 public synchronized long skip(long n) throws IOException {
326 final long origN = n;
329 int numread = (int) Math.min((long) (buf.length - pos), n);