View Javadoc
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>ByteArrayInputStream</code> contains
30   * an internal buffer that contains bytes that
31   * may be read from the stream. An internal
32   * counter keeps track of the next byte to
33   * be supplied by the <code>read</code> method.
34   * <p>
35   * Closing a <tt>ByteArrayInputStream</tt> has no effect. The methods in
36   * this class can be called after the stream has been closed without
37   * generating an <tt>IOException</tt>.
38   *
39   * @author  Arthur van Hoff
40   * @see     java.io.StringBufferInputStream
41   * @since   JDK1.0
42   */
43  public
44  class ByteArrayInputStream extends InputStream {
45  
46      /**
47       * An array of bytes that was provided
48       * by the creator of the stream. Elements <code>buf[0]</code>
49       * through <code>buf[count-1]</code> are the
50       * only bytes that can ever be read from the
51       * stream;  element <code>buf[pos]</code> is
52       * the next byte to be read.
53       */
54      protected byte buf[];
55  
56      /**
57       * The index of the next character to read from the input stream buffer.
58       * This value should always be nonnegative
59       * and not larger than the value of <code>count</code>.
60       * The next byte to be read from the input stream buffer
61       * will be <code>buf[pos]</code>.
62       */
63      protected int pos;
64  
65      /**
66       * The currently marked position in the stream.
67       * ByteArrayInputStream objects are marked at position zero by
68       * default when constructed.  They may be marked at another
69       * position within the buffer by the <code>mark()</code> method.
70       * The current buffer position is set to this point by the
71       * <code>reset()</code> method.
72       * <p>
73       * If no mark has been set, then the value of mark is the offset
74       * passed to the constructor (or 0 if the offset was not supplied).
75       *
76       * @since   JDK1.1
77       */
78      protected int mark = 0;
79  
80      /**
81       * The index one greater than the last valid character in the input
82       * stream buffer.
83       * This value should always be nonnegative
84       * and not larger than the length of <code>buf</code>.
85       * It  is one greater than the position of
86       * the last byte within <code>buf</code> that
87       * can ever be read  from the input stream buffer.
88       */
89      protected int count;
90  
91      /**
92       * Creates a <code>ByteArrayInputStream</code>
93       * so that it  uses <code>buf</code> as its
94       * buffer array.
95       * The buffer array is not copied.
96       * The initial value of <code>pos</code>
97       * is <code>0</code> and the initial value
98       * of  <code>count</code> is the length of
99       * <code>buf</code>.
100      *
101      * @param   buf   the input buffer.
102      */
103     public ByteArrayInputStream(byte buf[]) {
104         this.buf = buf;
105         this.pos = 0;
106         this.count = buf.length;
107     }
108 
109     /**
110      * Creates <code>ByteArrayInputStream</code>
111      * that uses <code>buf</code> as its
112      * buffer array. The initial value of <code>pos</code>
113      * is <code>offset</code> and the initial value
114      * of <code>count</code> is the minimum of <code>offset+length</code>
115      * and <code>buf.length</code>.
116      * The buffer array is not copied. The buffer's mark is
117      * set to the specified offset.
118      *
119      * @param   buf      the input buffer.
120      * @param   offset   the offset in the buffer of the first byte to read.
121      * @param   length   the maximum number of bytes to read from the buffer.
122      */
123     public ByteArrayInputStream(byte buf[], int offset, int length) {
124         this.buf = buf;
125         this.pos = offset;
126         this.count = Math.min(offset + length, buf.length);
127         this.mark = offset;
128     }
129 
130     /**
131      * Reads the next byte of data from this input stream. The value
132      * byte is returned as an <code>int</code> in the range
133      * <code>0</code> to <code>255</code>. If no byte is available
134      * because the end of the stream has been reached, the value
135      * <code>-1</code> is returned.
136      * <p>
137      * This <code>read</code> method
138      * cannot block.
139      *
140      * @return  the next byte of data, or <code>-1</code> if the end of the
141      *          stream has been reached.
142      */
143     public synchronized int read() {
144         return (pos < count) ? (buf[pos++] & 0xff) : -1;
145     }
146 
147     /**
148      * Reads up to <code>len</code> bytes of data into an array of bytes
149      * from this input stream.
150      * If <code>pos</code> equals <code>count</code>,
151      * then <code>-1</code> is returned to indicate
152      * end of file. Otherwise, the  number <code>k</code>
153      * of bytes read is equal to the smaller of
154      * <code>len</code> and <code>count-pos</code>.
155      * If <code>k</code> is positive, then bytes
156      * <code>buf[pos]</code> through <code>buf[pos+k-1]</code>
157      * are copied into <code>b[off]</code>  through
158      * <code>b[off+k-1]</code> in the manner performed
159      * by <code>System.arraycopy</code>. The
160      * value <code>k</code> is added into <code>pos</code>
161      * and <code>k</code> is returned.
162      * <p>
163      * This <code>read</code> method cannot block.
164      *
165      * @param   b     the buffer into which the data is read.
166      * @param   off   the start offset in the destination array <code>b</code>
167      * @param   len   the maximum number of bytes read.
168      * @return  the total number of bytes read into the buffer, or
169      *          <code>-1</code> if there is no more data because the end of
170      *          the stream has been reached.
171      * @exception  NullPointerException If <code>b</code> is <code>null</code>.
172      * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
173      * <code>len</code> is negative, or <code>len</code> is greater than
174      * <code>b.length - off</code>
175      */
176     public synchronized int read(byte b[], int off, int len) {
177         if (b == null) {
178             throw new NullPointerException();
179         } else if (off < 0 || len < 0 || len > b.length - off) {
180             throw new IndexOutOfBoundsException();
181         }
182 
183         if (pos >= count) {
184             return -1;
185         }
186 
187         int avail = count - pos;
188         if (len > avail) {
189             len = avail;
190         }
191         if (len <= 0) {
192             return 0;
193         }
194         System.arraycopy(buf, pos, b, off, len);
195         pos += len;
196         return len;
197     }
198 
199     /**
200      * Skips <code>n</code> bytes of input from this input stream. Fewer
201      * bytes might be skipped if the end of the input stream is reached.
202      * The actual number <code>k</code>
203      * of bytes to be skipped is equal to the smaller
204      * of <code>n</code> and  <code>count-pos</code>.
205      * The value <code>k</code> is added into <code>pos</code>
206      * and <code>k</code> is returned.
207      *
208      * @param   n   the number of bytes to be skipped.
209      * @return  the actual number of bytes skipped.
210      */
211     public synchronized long skip(long n) {
212         long k = count - pos;
213         if (n < k) {
214             k = n < 0 ? 0 : n;
215         }
216 
217         pos += k;
218         return k;
219     }
220 
221     /**
222      * Returns the number of remaining bytes that can be read (or skipped over)
223      * from this input stream.
224      * <p>
225      * The value returned is <code>count&nbsp;- pos</code>,
226      * which is the number of bytes remaining to be read from the input buffer.
227      *
228      * @return  the number of remaining bytes that can be read (or skipped
229      *          over) from this input stream without blocking.
230      */
231     public synchronized int available() {
232         return count - pos;
233     }
234 
235     /**
236      * Tests if this <code>InputStream</code> supports mark/reset. The
237      * <code>markSupported</code> method of <code>ByteArrayInputStream</code>
238      * always returns <code>true</code>.
239      *
240      * @since   JDK1.1
241      */
242     public boolean markSupported() {
243         return true;
244     }
245 
246     /**
247      * Set the current marked position in the stream.
248      * ByteArrayInputStream objects are marked at position zero by
249      * default when constructed.  They may be marked at another
250      * position within the buffer by this method.
251      * <p>
252      * If no mark has been set, then the value of the mark is the
253      * offset passed to the constructor (or 0 if the offset was not
254      * supplied).
255      *
256      * <p> Note: The <code>readAheadLimit</code> for this class
257      *  has no meaning.
258      *
259      * @since   JDK1.1
260      */
261     public void mark(int readAheadLimit) {
262         mark = pos;
263     }
264 
265     /**
266      * Resets the buffer to the marked position.  The marked position
267      * is 0 unless another position was marked or an offset was specified
268      * in the constructor.
269      */
270     public synchronized void reset() {
271         pos = mark;
272     }
273 
274     /**
275      * Closing a <tt>ByteArrayInputStream</tt> has no effect. The methods in
276      * this class can be called after the stream has been closed without
277      * generating an <tt>IOException</tt>.
278      */
279     public void close() throws IOException {
280     }
281 
282 }