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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   * A <code>PushbackInputStream</code> adds
30   * functionality to another input stream, namely
31   * the  ability to "push back" or "unread"
32   * one byte. This is useful in situations where
33   * it is  convenient for a fragment of code
34   * to read an indefinite number of data bytes
35   * that  are delimited by a particular byte
36   * value; after reading the terminating byte,
37   * the  code fragment can "unread" it, so that
38   * the next read operation on the input stream
39   * will reread the byte that was pushed back.
40   * For example, bytes representing the  characters
41   * constituting an identifier might be terminated
42   * by a byte representing an  operator character;
43   * a method whose job is to read just an identifier
44   * can read until it  sees the operator and
45   * then push the operator back to be re-read.
46   *
47   * @author  David Connelly
48   * @author  Jonathan Payne
49   * @since   JDK1.0
50   */
51  public
52  class PushbackInputStream extends FilterInputStream {
53      /**
54       * The pushback buffer.
55       * @since   JDK1.1
56       */
57      protected byte[] buf;
58  
59      /**
60       * The position within the pushback buffer from which the next byte will
61       * be read.  When the buffer is empty, <code>pos</code> is equal to
62       * <code>buf.length</code>; when the buffer is full, <code>pos</code> is
63       * equal to zero.
64       *
65       * @since   JDK1.1
66       */
67      protected int pos;
68  
69      /**
70       * Check to make sure that this stream has not been closed
71       */
72      private void ensureOpen() throws IOException {
73          if (in == null)
74              throw new IOException("Stream closed");
75      }
76  
77      /**
78       * Creates a <code>PushbackInputStream</code>
79       * with a pushback buffer of the specified <code>size</code>,
80       * and saves its  argument, the input stream
81       * <code>in</code>, for later use. Initially,
82       * there is no pushed-back byte  (the field
83       * <code>pushBack</code> is initialized to
84       * <code>-1</code>).
85       *
86       * @param  in    the input stream from which bytes will be read.
87       * @param  size  the size of the pushback buffer.
88       * @exception IllegalArgumentException if {@code size <= 0}
89       * @since  JDK1.1
90       */
91      public PushbackInputStream(InputStream in, int size) {
92          super(in);
93          if (size <= 0) {
94              throw new IllegalArgumentException("size <= 0");
95          }
96          this.buf = new byte[size];
97          this.pos = size;
98      }
99  
100     /**
101      * Creates a <code>PushbackInputStream</code>
102      * and saves its  argument, the input stream
103      * <code>in</code>, for later use. Initially,
104      * there is no pushed-back byte  (the field
105      * <code>pushBack</code> is initialized to
106      * <code>-1</code>).
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 IOException If there is not enough room in the pushback
224      *            buffer for the specified number of bytes,
225      *            or this input stream has been closed by
226      *            invoking its {@link #close()} method.
227      * @since     JDK1.1
228      */
229     public void unread(byte[] b, int off, int len) throws IOException {
230         ensureOpen();
231         if (len > pos) {
232             throw new IOException("Push back buffer is full");
233         }
234         pos -= len;
235         System.arraycopy(b, off, buf, pos, len);
236     }
237 
238     /**
239      * Pushes back an array of bytes by copying it to the front of the
240      * pushback buffer.  After this method returns, the next byte to be read
241      * will have the value <code>b[0]</code>, the byte after that will have the
242      * value <code>b[1]</code>, and so forth.
243      *
244      * @param b the byte array to push back
245      * @exception IOException If there is not enough room in the pushback
246      *            buffer for the specified number of bytes,
247      *            or this input stream has been closed by
248      *            invoking its {@link #close()} method.
249      * @since     JDK1.1
250      */
251     public void unread(byte[] b) throws IOException {
252         unread(b, 0, b.length);
253     }
254 
255     /**
256      * Returns an estimate of the number of bytes that can be read (or
257      * skipped over) from this input stream without blocking by the next
258      * invocation of a method for this input stream. The next invocation might be
259      * the same thread or another thread.  A single read or skip of this
260      * many bytes will not block, but may read or skip fewer bytes.
261      *
262      * <p> The method returns the sum of the number of bytes that have been
263      * pushed back and the value returned by {@link
264      * java.io.FilterInputStream#available available}.
265      *
266      * @return     the number of bytes that can be read (or skipped over) from
267      *             the input stream without blocking.
268      * @exception  IOException  if this input stream has been closed by
269      *             invoking its {@link #close()} method,
270      *             or an I/O error occurs.
271      * @see        java.io.FilterInputStream#in
272      * @see        java.io.InputStream#available()
273      */
274     public int available() throws IOException {
275         ensureOpen();
276         int n = buf.length - pos;
277         int avail = super.available();
278         return n > (Integer.MAX_VALUE - avail)
279                     ? Integer.MAX_VALUE
280                     : n + avail;
281     }
282 
283     /**
284      * Skips over and discards <code>n</code> bytes of data from this
285      * input stream. The <code>skip</code> method may, for a variety of
286      * reasons, end up skipping over some smaller number of bytes,
287      * possibly zero.  If <code>n</code> is negative, no bytes are skipped.
288      *
289      * <p> The <code>skip</code> method of <code>PushbackInputStream</code>
290      * first skips over the bytes in the pushback buffer, if any.  It then
291      * calls the <code>skip</code> method of the underlying input stream if
292      * more bytes need to be skipped.  The actual number of bytes skipped
293      * is returned.
294      *
295      * @param      n  {@inheritDoc}
296      * @return     {@inheritDoc}
297      * @exception  IOException  if the stream does not support seek,
298      *            or the stream has been closed by
299      *            invoking its {@link #close()} method,
300      *            or an I/O error occurs.
301      * @see        java.io.FilterInputStream#in
302      * @see        java.io.InputStream#skip(long n)
303      * @since      1.2
304      */
305     public long skip(long n) throws IOException {
306         ensureOpen();
307         if (n <= 0) {
308             return 0;
309         }
310 
311         long pskip = buf.length - pos;
312         if (pskip > 0) {
313             if (n < pskip) {
314                 pskip = n;
315             }
316             pos += pskip;
317             n -= pskip;
318         }
319         if (n > 0) {
320             pskip += super.skip(n);
321         }
322         return pskip;
323     }
324 
325     /**
326      * Tests if this input stream supports the <code>mark</code> and
327      * <code>reset</code> methods, which it does not.
328      *
329      * @return   <code>false</code>, since this class does not support the
330      *           <code>mark</code> and <code>reset</code> methods.
331      * @see     java.io.InputStream#mark(int)
332      * @see     java.io.InputStream#reset()
333      */
334     public boolean markSupported() {
335         return false;
336     }
337 
338     /**
339      * Marks the current position in this input stream.
340      *
341      * <p> The <code>mark</code> method of <code>PushbackInputStream</code>
342      * does nothing.
343      *
344      * @param   readlimit   the maximum limit of bytes that can be read before
345      *                      the mark position becomes invalid.
346      * @see     java.io.InputStream#reset()
347      */
348     public synchronized void mark(int readlimit) {
349     }
350 
351     /**
352      * Repositions this stream to the position at the time the
353      * <code>mark</code> method was last called on this input stream.
354      *
355      * <p> The method <code>reset</code> for class
356      * <code>PushbackInputStream</code> does nothing except throw an
357      * <code>IOException</code>.
358      *
359      * @exception  IOException  if this method is invoked.
360      * @see     java.io.InputStream#mark(int)
361      * @see     java.io.IOException
362      */
363     public synchronized void reset() throws IOException {
364         throw new IOException("mark/reset not supported");
365     }
366 
367     /**
368      * Closes this input stream and releases any system resources
369      * associated with the stream.
370      * Once the stream has been closed, further read(), unread(),
371      * available(), reset(), or skip() invocations will throw an IOException.
372      * Closing a previously closed stream has no effect.
373      *
374      * @exception  IOException  if an I/O error occurs.
375      */
376     public synchronized void close() throws IOException {
377         if (in == null)
378             return;
379         in.close();
380         in = null;
381         buf = null;
382     }
383 }