1 /*
2 * Copyright (c) 1994, 2019, 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 if (in == null) {
63 throw new NullPointerException();
64 }
65 this.in = in;
66 }
67
68 /**
69 * Reads the next byte of data from this input stream. The value
70 * byte is returned as an <code>int</code> in the range
71 * <code>0</code> to <code>255</code>. If no byte is available
72 * because the end of the stream has been reached, the value
73 * <code>-1</code> is returned. This method blocks until input data
74 * is available, the end of the stream is detected, or an exception
75 * is thrown.
76 * <p>
77 * This method
78 * simply performs <code>in.read()</code> and returns the result.
79 *
80 * @return the next byte of data, or <code>-1</code> if the end of the
81 * stream is reached.
82 * @exception IOException if an I/O error occurs.
83 * @see java.io.FilterInputStream#in
84 */
85 public int read() throws IOException {
86 return in.read();
87 }
88
89 /**
90 * Reads up to <code>b.length</code> bytes of data from this
91 * input stream into an array of bytes. This method blocks until some
92 * input is available.
93 * <p>
94 * This method simply performs the call
95 * <code>read(b, 0, b.length)</code> and returns
96 * the result. It is important that it does
97 * <i>not</i> do <code>in.read(b)</code> instead;
98 * certain subclasses of <code>FilterInputStream</code>
99 * depend on the implementation strategy actually
100 * used.
101 *
102 * @param b the buffer into which the data is read.
103 * @return the total number of bytes read into the buffer, or
104 * <code>-1</code> if there is no more data because the end of
105 * the stream has been reached.
106 * @exception IOException if an I/O error occurs.
107 * @see java.io.FilterInputStream#read(byte[], int, int)
108 */
109 public int read(byte b[]) throws IOException {
110 return read(b, 0, b.length);
111 }
112
113 /**
114 * Reads up to <code>len</code> bytes of data from this input stream
115 * into an array of bytes. If <code>len</code> is not zero, the method
116 * blocks until some input is available; otherwise, no
117 * bytes are read and <code>0</code> is returned.
118 * <p>
119 * This method simply performs <code>in.read(b, off, len)</code>
120 * and returns the result.
121 *
122 * @param b the buffer into which the data is read.
123 * @param off the start offset in the destination array <code>b</code>
124 * @param len the maximum number of bytes read.
125 * @return the total number of bytes read into the buffer, or
126 * <code>-1</code> if there is no more data because the end of
127 * the stream has been reached.
128 * @exception NullPointerException If <code>b</code> is <code>null</code>.
129 * @exception IndexOutOfBoundsException If <code>off</code> is negative,
130 * <code>len</code> is negative, or <code>len</code> is greater than
131 * <code>b.length - off</code>
132 * @exception IOException if an I/O error occurs.
133 * @see java.io.FilterInputStream#in
134 */
135 public int read(byte b[], int off, int len) throws IOException {
136 return in.read(b, off, len);
137 }
138
139 /**
140 * Skips over and discards <code>n</code> bytes of data from the
141 * input stream. The <code>skip</code> method may, for a variety of
142 * reasons, end up skipping over some smaller number of bytes,
143 * possibly <code>0</code>. The actual number of bytes skipped is
144 * returned.
145 * <p>
146 * This method simply performs <code>in.skip(n)</code>.
147 *
148 * @param n the number of bytes to be skipped.
149 * @return the actual number of bytes skipped.
150 * @throws IOException if {@code in.skip(n)} throws an IOException.
151 */
152 public long skip(long n) throws IOException {
153 return in.skip(n);
154 }
155
156 /**
157 * Returns an estimate of the number of bytes that can be read (or
158 * skipped over) from this input stream without blocking by the next
159 * caller of a method for this input stream. The next caller might be
160 * the same thread or another thread. A single read or skip of this
161 * many bytes will not block, but may read or skip fewer bytes.
162 * <p>
163 * This method returns the result of {@link #in in}.available().
164 *
165 * @return an estimate of the number of bytes that can be read (or skipped
166 * over) from this input stream without blocking.
167 * @exception IOException if an I/O error occurs.
168 */
169 public int available() throws IOException {
170 return in.available();
171 }
172
173 /**
174 * Closes this input stream and releases any system resources
175 * associated with the stream.
176 * This
177 * method simply performs <code>in.close()</code>.
178 *
179 * @exception IOException if an I/O error occurs.
180 * @see java.io.FilterInputStream#in
181 */
182 public void close() throws IOException {
183 in.close();
184 }
185
186 /**
187 * Marks the current position in this input stream. A subsequent
188 * call to the <code>reset</code> method repositions this stream at
189 * the last marked position so that subsequent reads re-read the same bytes.
190 * <p>
191 * The <code>readlimit</code> argument tells this input stream to
192 * allow that many bytes to be read before the mark position gets
193 * invalidated.
194 * <p>
195 * This method simply performs <code>in.mark(readlimit)</code>.
196 *
197 * @param readlimit the maximum limit of bytes that can be read before
198 * the mark position becomes invalid.
199 * @see java.io.FilterInputStream#in
200 * @see java.io.FilterInputStream#reset()
201 */
202 public synchronized void mark(int readlimit) {
203 in.mark(readlimit);
204 }
205
206 /**
207 * Repositions this stream to the position at the time the
208 * <code>mark</code> method was last called on this input stream.
209 * <p>
210 * This method
211 * simply performs <code>in.reset()</code>.
212 * <p>
213 * Stream marks are intended to be used in
214 * situations where you need to read ahead a little to see what's in
215 * the stream. Often this is most easily done by invoking some
216 * general parser. If the stream is of the type handled by the
217 * parse, it just chugs along happily. If the stream is not of
218 * that type, the parser should toss an exception when it fails.
219 * If this happens within readlimit bytes, it allows the outer
220 * code to reset the stream and try another parser.
221 *
222 * @exception IOException if the stream has not been marked or if the
223 * mark has been invalidated.
224 * @see java.io.FilterInputStream#in
225 * @see java.io.FilterInputStream#mark(int)
226 */
227 public synchronized void reset() throws IOException {
228 in.reset();
229 }
230
231 /**
232 * Tests if this input stream supports the <code>mark</code>
233 * and <code>reset</code> methods.
234 * This method
235 * simply performs <code>in.markSupported()</code>.
236 *
237 * @return <code>true</code> if this stream type supports the
238 * <code>mark</code> and <code>reset</code> method;
239 * <code>false</code> otherwise.
240 * @see java.io.FilterInputStream#in
241 * @see java.io.InputStream#mark(int)
242 * @see java.io.InputStream#reset()
243 */
244 public boolean markSupported() {
245 return in.markSupported();
246 }
247 }