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 */
157 abstract public int read(char cbuf[], int off, int len) throws IOException;
158
159 /** Maximum skip-buffer size */
160 private static final int maxSkipBufferSize = 8192;
161
162 /** Skip buffer, null until allocated */
163 private char skipBuffer[] = null;
164
165 /**
166 * Skips characters. This method will block until some characters are
167 * available, an I/O error occurs, or the end of the stream is reached.
168 *
169 * @param n The number of characters to skip
170 *
171 * @return The number of characters actually skipped
172 *
173 * @exception IllegalArgumentException If <code>n</code> is negative.
174 * @exception IOException If an I/O error occurs
175 */
176 public long skip(long n) throws IOException {
177 if (n < 0L)
178 throw new IllegalArgumentException("skip value is negative");
179 int nn = (int) Math.min(n, maxSkipBufferSize);
180 synchronized (lock) {
181 if ((skipBuffer == null) || (skipBuffer.length < nn))
182 skipBuffer = new char[nn];
183 long r = n;
184 while (r > 0) {
185 int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
186 if (nc == -1)
187 break;
188 r -= nc;
189 }
190 return n - r;
191 }
192 }
193
194 /**
195 * Tells whether this stream is ready to be read.
196 *
197 * @return True if the next read() is guaranteed not to block for input,
198 * false otherwise. Note that returning false does not guarantee that the
199 * next read will block.
200 *
201 * @exception IOException If an I/O error occurs
202 */
203 public boolean ready() throws IOException {
204 return false;
205 }
206
207 /**
208 * Tells whether this stream supports the mark() operation. The default
209 * implementation always returns false. Subclasses should override this
210 * method.
211 *
212 * @return true if and only if this stream supports the mark operation.
213 */
214 public boolean markSupported() {
215 return false;
216 }
217
218 /**
219 * Marks the present position in the stream. Subsequent calls to reset()
220 * will attempt to reposition the stream to this point. Not all
221 * character-input streams support the mark() operation.
222 *
223 * @param readAheadLimit Limit on the number of characters that may be
224 * read while still preserving the mark. After
225 * reading this many characters, attempting to
226 * reset the stream may fail.
227 *
228 * @exception IOException If the stream does not support mark(),
229 * or if some other I/O error occurs
230 */
231 public void mark(int readAheadLimit) throws IOException {
232 throw new IOException("mark() not supported");
233 }
234
235 /**
236 * Resets the stream. If the stream has been marked, then attempt to
237 * reposition it at the mark. If the stream has not been marked, then
238 * attempt to reset it in some way appropriate to the particular stream,
239 * for example by repositioning it to its starting point. Not all
240 * character-input streams support the reset() operation, and some support
241 * reset() without supporting mark().
242 *
243 * @exception IOException If the stream has not been marked,
244 * or if the mark has been invalidated,
245 * or if the stream does not support reset(),
246 * or if some other I/O error occurs
247 */
248 public void reset() throws IOException {
249 throw new IOException("reset() not supported");
250 }
251
252 /**
253 * Closes the stream and releases any system resources associated with
254 * it. Once the stream has been closed, further read(), ready(),
255 * mark(), reset(), or skip() invocations will throw an IOException.
256 * Closing a previously closed stream has no effect.
257 *
258 * @exception IOException If an I/O error occurs
259 */
260 abstract public void close() throws IOException;
261
262 }