1 /*
2 * Copyright (c) 1994, 2017, 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 1.0
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>b.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 * @throws IOException if {@code in.skip(n)} throws an IOException.
148 */
149 public long skip(long n) throws IOException {
150 return in.skip(n);
151 }
152
153 /**
154 * Returns an estimate of the number of bytes that can be read (or
155 * skipped over) from this input stream without blocking by the next
156 * caller of a method for this input stream. The next caller might be
157 * the same thread or another thread. A single read or skip of this
158 * many bytes will not block, but may read or skip fewer bytes.
159 * <p>
160 * This method returns the result of {@link #in in}.available().
161 *
162 * @return an estimate of the number of bytes that can be read (or skipped
163 * over) from this input stream without blocking.
164 * @exception IOException if an I/O error occurs.
165 */
166 public int available() throws IOException {
167 return in.available();
168 }
169
170 /**
171 * Closes this input stream and releases any system resources
172 * associated with the stream.
173 * This
174 * method simply performs <code>in.close()</code>.
175 *
176 * @exception IOException if an I/O error occurs.
177 * @see java.io.FilterInputStream#in
178 */
179 public void close() throws IOException {
180 in.close();
181 }
182
183 /**
184 * Marks the current position in this input stream. A subsequent
185 * call to the <code>reset</code> method repositions this stream at
186 * the last marked position so that subsequent reads re-read the same bytes.
187 * <p>
188 * The <code>readlimit</code> argument tells this input stream to
189 * allow that many bytes to be read before the mark position gets
190 * invalidated.
191 * <p>
192 * This method simply performs <code>in.mark(readlimit)</code>.
193 *
194 * @param readlimit the maximum limit of bytes that can be read before
195 * the mark position becomes invalid.
196 * @see java.io.FilterInputStream#in
197 * @see java.io.FilterInputStream#reset()
198 */
199 public synchronized void mark(int readlimit) {
200 in.mark(readlimit);
201 }
202
203 /**
204 * Repositions this stream to the position at the time the
205 * <code>mark</code> method was last called on this input stream.
206 * <p>
207 * This method
208 * simply performs <code>in.reset()</code>.
209 * <p>
210 * Stream marks are intended to be used in
211 * situations where you need to read ahead a little to see what's in
212 * the stream. Often this is most easily done by invoking some
213 * general parser. If the stream is of the type handled by the
214 * parse, it just chugs along happily. If the stream is not of
215 * that type, the parser should toss an exception when it fails.
216 * If this happens within readlimit bytes, it allows the outer
217 * code to reset the stream and try another parser.
218 *
219 * @exception IOException if the stream has not been marked or if the
220 * mark has been invalidated.
221 * @see java.io.FilterInputStream#in
222 * @see java.io.FilterInputStream#mark(int)
223 */
224 public synchronized void reset() throws IOException {
225 in.reset();
226 }
227
228 /**
229 * Tests if this input stream supports the <code>mark</code>
230 * and <code>reset</code> methods.
231 * This method
232 * simply performs <code>in.markSupported()</code>.
233 *
234 * @return <code>true</code> if this stream type supports the
235 * <code>mark</code> and <code>reset</code> method;
236 * <code>false</code> otherwise.
237 * @see java.io.FilterInputStream#in
238 * @see java.io.InputStream#mark(int)
239 * @see java.io.InputStream#reset()
240 */
241 public boolean markSupported() {
242 return in.markSupported();
243 }
244 }
245