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1   /*
2    * Copyright (c) 1994, 2010, 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>FilterInputStream</code> contains
30   * some other input stream, which it uses as
31   * its  basic source of data, possibly transforming
32   * the data along the way or providing  additional
33   * functionality. The class <code>FilterInputStream</code>
34   * itself simply overrides all  methods of
35   * <code>InputStream</code> with versions that
36   * pass all requests to the contained  input
37   * stream. Subclasses of <code>FilterInputStream</code>
38   * may further override some of  these methods
39   * and may also provide additional methods
40   * and fields.
41   *
42   * @author  Jonathan Payne
43   * @since   JDK1.0
44   */
45  public
46  class FilterInputStream extends InputStream {
47      /**
48       * The input stream to be filtered.
49       */
50      protected volatile InputStream in;
51  
52      /**
53       * Creates a <code>FilterInputStream</code>
54       * by assigning the  argument <code>in</code>
55       * to the field <code>this.in</code> so as
56       * to remember it for later use.
57       *
58       * @param   in   the underlying input stream, or <code>null</code> if
59       *          this instance is to be created without an underlying stream.
60       */
61      protected FilterInputStream(InputStream in) {
62          this.in = in;
63      }
64  
65      /**
66       * Reads the next byte of data from this input stream. The value
67       * byte is returned as an <code>int</code> in the range
68       * <code>0</code> to <code>255</code>. If no byte is available
69       * because the end of the stream has been reached, the value
70       * <code>-1</code> is returned. This method blocks until input data
71       * is available, the end of the stream is detected, or an exception
72       * is thrown.
73       * <p>
74       * This method
75       * simply performs <code>in.read()</code> and returns the result.
76       *
77       * @return     the next byte of data, or <code>-1</code> if the end of the
78       *             stream is reached.
79       * @exception  IOException  if an I/O error occurs.
80       * @see        java.io.FilterInputStream#in
81       */
82      public int read() throws IOException {
83          return in.read();
84      }
85  
86      /**
87       * Reads up to <code>byte.length</code> bytes of data from this
88       * input stream into an array of bytes. This method blocks until some
89       * input is available.
90       * <p>
91       * This method simply performs the call
92       * <code>read(b, 0, b.length)</code> and returns
93       * the  result. It is important that it does
94       * <i>not</i> do <code>in.read(b)</code> instead;
95       * certain subclasses of  <code>FilterInputStream</code>
96       * depend on the implementation strategy actually
97       * used.
98       *
99       * @param      b   the buffer into which the data is read.
100      * @return     the total number of bytes read into the buffer, or
101      *             <code>-1</code> if there is no more data because the end of
102      *             the stream has been reached.
103      * @exception  IOException  if an I/O error occurs.
104      * @see        java.io.FilterInputStream#read(byte[], int, int)
105      */
106     public int read(byte b[]) throws IOException {
107         return read(b, 0, b.length);
108     }
109 
110     /**
111      * Reads up to <code>len</code> bytes of data from this input stream
112      * into an array of bytes. If <code>len</code> is not zero, the method
113      * blocks until some input is available; otherwise, no
114      * bytes are read and <code>0</code> is returned.
115      * <p>
116      * This method simply performs <code>in.read(b, off, len)</code>
117      * and returns the result.
118      *
119      * @param      b     the buffer into which the data is read.
120      * @param      off   the start offset in the destination array <code>b</code>
121      * @param      len   the maximum number of bytes read.
122      * @return     the total number of bytes read into the buffer, or
123      *             <code>-1</code> if there is no more data because the end of
124      *             the stream has been reached.
125      * @exception  NullPointerException If <code>b</code> is <code>null</code>.
126      * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
127      * <code>len</code> is negative, or <code>len</code> is greater than
128      * <code>b.length - off</code>
129      * @exception  IOException  if an I/O error occurs.
130      * @see        java.io.FilterInputStream#in
131      */
132     public int read(byte b[], int off, int len) throws IOException {
133         return in.read(b, off, len);
134     }
135 
136     /**
137      * Skips over and discards <code>n</code> bytes of data from the
138      * input stream. The <code>skip</code> method may, for a variety of
139      * reasons, end up skipping over some smaller number of bytes,
140      * possibly <code>0</code>. The actual number of bytes skipped is
141      * returned.
142      * <p>
143      * This method simply performs <code>in.skip(n)</code>.
144      *
145      * @param      n   the number of bytes to be skipped.
146      * @return     the actual number of bytes skipped.
147      * @exception  IOException  if the stream does not support seek,
148      *                          or if some other I/O error occurs.
149      */
150     public long skip(long n) throws IOException {
151         return in.skip(n);
152     }
153 
154     /**
155      * Returns an estimate of the number of bytes that can be read (or
156      * skipped over) from this input stream without blocking by the next
157      * caller of a method for this input stream. The next caller might be
158      * the same thread or another thread.  A single read or skip of this
159      * many bytes will not block, but may read or skip fewer bytes.
160      * <p>
161      * This method returns the result of {@link #in in}.available().
162      *
163      * @return     an estimate of the number of bytes that can be read (or skipped
164      *             over) from this input stream without blocking.
165      * @exception  IOException  if an I/O error occurs.
166      */
167     public int available() throws IOException {
168         return in.available();
169     }
170 
171     /**
172      * Closes this input stream and releases any system resources
173      * associated with the stream.
174      * This
175      * method simply performs <code>in.close()</code>.
176      *
177      * @exception  IOException  if an I/O error occurs.
178      * @see        java.io.FilterInputStream#in
179      */
180     public void close() throws IOException {
181         in.close();
182     }
183 
184     /**
185      * Marks the current position in this input stream. A subsequent
186      * call to the <code>reset</code> method repositions this stream at
187      * the last marked position so that subsequent reads re-read the same bytes.
188      * <p>
189      * The <code>readlimit</code> argument tells this input stream to
190      * allow that many bytes to be read before the mark position gets
191      * invalidated.
192      * <p>
193      * This method simply performs <code>in.mark(readlimit)</code>.
194      *
195      * @param   readlimit   the maximum limit of bytes that can be read before
196      *                      the mark position becomes invalid.
197      * @see     java.io.FilterInputStream#in
198      * @see     java.io.FilterInputStream#reset()
199      */
200     public synchronized void mark(int readlimit) {
201         in.mark(readlimit);
202     }
203 
204     /**
205      * Repositions this stream to the position at the time the
206      * <code>mark</code> method was last called on this input stream.
207      * <p>
208      * This method
209      * simply performs <code>in.reset()</code>.
210      * <p>
211      * Stream marks are intended to be used in
212      * situations where you need to read ahead a little to see what's in
213      * the stream. Often this is most easily done by invoking some
214      * general parser. If the stream is of the type handled by the
215      * parse, it just chugs along happily. If the stream is not of
216      * that type, the parser should toss an exception when it fails.
217      * If this happens within readlimit bytes, it allows the outer
218      * code to reset the stream and try another parser.
219      *
220      * @exception  IOException  if the stream has not been marked or if the
221      *               mark has been invalidated.
222      * @see        java.io.FilterInputStream#in
223      * @see        java.io.FilterInputStream#mark(int)
224      */
225     public synchronized void reset() throws IOException {
226         in.reset();
227     }
228 
229     /**
230      * Tests if this input stream supports the <code>mark</code>
231      * and <code>reset</code> methods.
232      * This method
233      * simply performs <code>in.markSupported()</code>.
234      *
235      * @return  <code>true</code> if this stream type supports the
236      *          <code>mark</code> and <code>reset</code> method;
237      *          <code>false</code> otherwise.
238      * @see     java.io.FilterInputStream#in
239      * @see     java.io.InputStream#mark(int)
240      * @see     java.io.InputStream#reset()
241      */
242     public boolean markSupported() {
243         return in.markSupported();
244     }
245 }