1 /*
2 * Copyright (c) 1996, 2012, 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 /**
30 * Abstract class for reading character streams. The only methods that a
31 * subclass must implement are read(char[], int, int) and close(). Most
32 * subclasses, however, will override some of the methods defined here in order
33 * to provide higher efficiency, additional functionality, or both.
34 *
35 *
36 * @see BufferedReader
37 * @see LineNumberReader
38 * @see CharArrayReader
39 * @see InputStreamReader
40 * @see FileReader
41 * @see FilterReader
42 * @see PushbackReader
43 * @see PipedReader
44 * @see StringReader
45 * @see Writer
46 *
47 * @author Mark Reinhold
48 * @since 1.1
49 */
50
51 public abstract class Reader implements Readable, Closeable {
52
53 /**
54 * The object used to synchronize operations on this stream. For
55 * efficiency, a character-stream object may use an object other than
56 * itself to protect critical sections. A subclass should therefore use
57 * the object in this field rather than <tt>this</tt> or a synchronized
58 * method.
59 */
60 protected Object lock;
61
62 /**
63 * Creates a new character-stream reader whose critical sections will
64 * synchronize on the reader itself.
65 */
66 protected Reader() {
67 this.lock = this;
68 }
69
70 /**
71 * Creates a new character-stream reader whose critical sections will
72 * synchronize on the given object.
73 *
74 * @param lock The Object to synchronize on.
75 */
76 protected Reader(Object lock) {
77 if (lock == null) {
78 throw new NullPointerException();
79 }
80 this.lock = lock;
81 }
82
83 /**
84 * Attempts to read characters into the specified character buffer.
85 * The buffer is used as a repository of characters as-is: the only
86 * changes made are the results of a put operation. No flipping or
87 * rewinding of the buffer is performed.
88 *
89 * @param target the buffer to read characters into
90 * @return The number of characters added to the buffer, or
91 * -1 if this source of characters is at its end
92 * @throws IOException if an I/O error occurs
93 * @throws NullPointerException if target is null
94 * @throws java.nio.ReadOnlyBufferException if target is a read only buffer
95 * @since 1.5
96 */
97 public int read(java.nio.CharBuffer target) throws IOException {
98 int len = target.remaining();
99 char[] cbuf = new char[len];
100 int n = read(cbuf, 0, len);
101 if (n > 0)
102 target.put(cbuf, 0, n);
103 return n;
104 }
105
106 /**
107 * Reads a single character. This method will block until a character is
108 * available, an I/O error occurs, or the end of the stream is reached.
109 *
110 * <p> Subclasses that intend to support efficient single-character input
111 * should override this method.
112 *
113 * @return The character read, as an integer in the range 0 to 65535
114 * (<tt>0x00-0xffff</tt>), or -1 if the end of the stream has
115 * been reached
116 *
117 * @exception IOException If an I/O error occurs
118 */
119 public int read() throws IOException {
120 char cb[] = new char[1];
121 if (read(cb, 0, 1) == -1)
122 return -1;
123 else
124 return cb[0];
125 }
126
127 /**
128 * Reads characters into an array. This method will block until some input
129 * is available, an I/O error occurs, or the end of the stream is reached.
130 *
131 * @param cbuf Destination buffer
132 *
133 * @return The number of characters read, or -1
134 * if the end of the stream
135 * has been reached
136 *
137 * @exception IOException If an I/O error occurs
138 */
139 public int read(char cbuf[]) throws IOException {
140 return read(cbuf, 0, cbuf.length);
141 }
142
143 /**
144 * Reads characters into a portion of an array. This method will block
145 * until some input is available, an I/O error occurs, or the end of the
146 * stream is reached.
147 *
148 * @param cbuf Destination buffer
149 * @param off Offset at which to start storing characters
150 * @param len Maximum number of characters to read
151 *
152 * @return The number of characters read, or -1 if the end of the
153 * stream has been reached
154 *
155 * @exception IOException If an I/O error occurs
156 * @exception IndexOutOfBoundsException
157 * If {@code off} is negative, or {@code len} is negative,
158 * or {@code off+len} is negative or greater than the length
159 * of the given array
160 */
161 abstract public int read(char cbuf[], int off, int len) throws IOException;
162
163 /** Maximum skip-buffer size */
164 private static final int maxSkipBufferSize = 8192;
165
166 /** Skip buffer, null until allocated */
167 private char skipBuffer[] = null;
168
169 /**
170 * Skips characters. This method will block until some characters are
171 * available, an I/O error occurs, or the end of the stream is reached.
172 *
173 * @param n The number of characters to skip
174 *
175 * @return The number of characters actually skipped
176 *
177 * @exception IllegalArgumentException If <code>n</code> is negative.
178 * @exception IOException If an I/O error occurs
179 */
180 public long skip(long n) throws IOException {
181 if (n < 0L)
182 throw new IllegalArgumentException("skip value is negative");
183 int nn = (int) Math.min(n, maxSkipBufferSize);
184 synchronized (lock) {
185 if ((skipBuffer == null) || (skipBuffer.length < nn))
186 skipBuffer = new char[nn];
187 long r = n;
188 while (r > 0) {
189 int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
190 if (nc == -1)
191 break;
192 r -= nc;
193 }
194 return n - r;
195 }
196 }
197
198 /**
199 * Tells whether this stream is ready to be read.
200 *
201 * @return True if the next read() is guaranteed not to block for input,
202 * false otherwise. Note that returning false does not guarantee that the
203 * next read will block.
204 *
205 * @exception IOException If an I/O error occurs
206 */
207 public boolean ready() throws IOException {
208 return false;
209 }
210
211 /**
212 * Tells whether this stream supports the mark() operation. The default
213 * implementation always returns false. Subclasses should override this
214 * method.
215 *
216 * @return true if and only if this stream supports the mark operation.
217 */
218 public boolean markSupported() {
219 return false;
220 }
221
222 /**
223 * Marks the present position in the stream. Subsequent calls to reset()
224 * will attempt to reposition the stream to this point. Not all
225 * character-input streams support the mark() operation.
226 *
227 * @param readAheadLimit Limit on the number of characters that may be
228 * read while still preserving the mark. After
229 * reading this many characters, attempting to
230 * reset the stream may fail.
231 *
232 * @exception IOException If the stream does not support mark(),
233 * or if some other I/O error occurs
234 */
235 public void mark(int readAheadLimit) throws IOException {
236 throw new IOException("mark() not supported");
237 }
238
239 /**
240 * Resets the stream. If the stream has been marked, then attempt to
241 * reposition it at the mark. If the stream has not been marked, then
242 * attempt to reset it in some way appropriate to the particular stream,
243 * for example by repositioning it to its starting point. Not all
244 * character-input streams support the reset() operation, and some support
245 * reset() without supporting mark().
246 *
247 * @exception IOException If the stream has not been marked,
248 * or if the mark has been invalidated,
249 * or if the stream does not support reset(),
250 * or if some other I/O error occurs
251 */
252 public void reset() throws IOException {
253 throw new IOException("reset() not supported");
254 }
255
256 /**
257 * Closes the stream and releases any system resources associated with
258 * it. Once the stream has been closed, further read(), ready(),
259 * mark(), reset(), or skip() invocations will throw an IOException.
260 * Closing a previously closed stream has no effect.
261 *
262 * @exception IOException If an I/O error occurs
263 */
264 abstract public void close() throws IOException;
265
266 }