1 /*
2 * Copyright (c) 1996, 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 import java.util.Objects;
30
31 /**
32 * Abstract class for reading character streams. The only methods that a
33 * subclass must implement are read(char[], int, int) and close(). Most
34 * subclasses, however, will override some of the methods defined here in order
35 * to provide higher efficiency, additional functionality, or both.
36 *
37 *
38 * @see BufferedReader
39 * @see LineNumberReader
40 * @see CharArrayReader
41 * @see InputStreamReader
42 * @see FileReader
43 * @see FilterReader
44 * @see PushbackReader
45 * @see PipedReader
46 * @see StringReader
47 * @see Writer
48 *
49 * @author Mark Reinhold
50 * @since 1.1
51 */
52
53 public abstract class Reader implements Readable, Closeable {
54
55 private static final int TRANSFER_BUFFER_SIZE = 8192;
56
57 /**
58 * The object used to synchronize operations on this stream. For
59 * efficiency, a character-stream object may use an object other than
60 * itself to protect critical sections. A subclass should therefore use
61 * the object in this field rather than {@code this} or a synchronized
62 * method.
63 */
64 protected Object lock;
65
66 /**
67 * Creates a new character-stream reader whose critical sections will
68 * synchronize on the reader itself.
69 */
70 protected Reader() {
71 this.lock = this;
72 }
73
74 /**
75 * Creates a new character-stream reader whose critical sections will
76 * synchronize on the given object.
77 *
78 * @param lock The Object to synchronize on.
79 */
80 protected Reader(Object lock) {
81 if (lock == null) {
82 throw new NullPointerException();
83 }
84 this.lock = lock;
85 }
86
87 /**
88 * Attempts to read characters into the specified character buffer.
89 * The buffer is used as a repository of characters as-is: the only
90 * changes made are the results of a put operation. No flipping or
91 * rewinding of the buffer is performed.
92 *
93 * @param target the buffer to read characters into
94 * @return The number of characters added to the buffer, or
95 * -1 if this source of characters is at its end
96 * @throws IOException if an I/O error occurs
97 * @throws NullPointerException if target is null
98 * @throws java.nio.ReadOnlyBufferException if target is a read only buffer
99 * @since 1.5
100 */
101 public int read(java.nio.CharBuffer target) throws IOException {
102 int len = target.remaining();
103 char[] cbuf = new char[len];
104 int n = read(cbuf, 0, len);
105 if (n > 0)
106 target.put(cbuf, 0, n);
107 return n;
108 }
109
110 /**
111 * Reads a single character. This method will block until a character is
112 * available, an I/O error occurs, or the end of the stream is reached.
113 *
114 * <p> Subclasses that intend to support efficient single-character input
115 * should override this method.
116 *
117 * @return The character read, as an integer in the range 0 to 65535
118 * ({@code 0x00-0xffff}), or -1 if the end of the stream has
119 * been reached
120 *
121 * @exception IOException If an I/O error occurs
122 */
123 public int read() throws IOException {
124 char cb[] = new char[1];
125 if (read(cb, 0, 1) == -1)
126 return -1;
127 else
128 return cb[0];
129 }
130
131 /**
132 * Reads characters into an array. This method will block until some input
133 * is available, an I/O error occurs, or the end of the stream is reached.
134 *
135 * @param cbuf Destination buffer
136 *
137 * @return The number of characters read, or -1
138 * if the end of the stream
139 * has been reached
140 *
141 * @exception IOException If an I/O error occurs
142 */
143 public int read(char cbuf[]) throws IOException {
144 return read(cbuf, 0, cbuf.length);
145 }
146
147 /**
148 * Reads characters into a portion of an array. This method will block
149 * until some input is available, an I/O error occurs, or the end of the
150 * stream is reached.
151 *
152 * @param cbuf Destination buffer
153 * @param off Offset at which to start storing characters
154 * @param len Maximum number of characters to read
155 *
156 * @return The number of characters read, or -1 if the end of the
157 * stream has been reached
158 *
159 * @exception IOException If an I/O error occurs
160 * @exception IndexOutOfBoundsException
161 * If {@code off} is negative, or {@code len} is negative,
162 * or {@code len} is greater than {@code cbuf.length - off}
163 */
164 public abstract int read(char cbuf[], int off, int len) throws IOException;
165
166 /** Maximum skip-buffer size */
167 private static final int maxSkipBufferSize = 8192;
168
169 /** Skip buffer, null until allocated */
170 private char skipBuffer[] = null;
171
172 /**
173 * Skips characters. This method will block until some characters are
174 * available, an I/O error occurs, or the end of the stream is reached.
175 *
176 * @param n The number of characters to skip
177 *
178 * @return The number of characters actually skipped
179 *
180 * @exception IllegalArgumentException If <code>n</code> is negative.
181 * @exception IOException If an I/O error occurs
182 */
183 public long skip(long n) throws IOException {
184 if (n < 0L)
185 throw new IllegalArgumentException("skip value is negative");
186 int nn = (int) Math.min(n, maxSkipBufferSize);
187 synchronized (lock) {
188 if ((skipBuffer == null) || (skipBuffer.length < nn))
189 skipBuffer = new char[nn];
190 long r = n;
191 while (r > 0) {
192 int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
193 if (nc == -1)
194 break;
195 r -= nc;
196 }
197 return n - r;
198 }
199 }
200
201 /**
202 * Tells whether this stream is ready to be read.
203 *
204 * @return True if the next read() is guaranteed not to block for input,
205 * false otherwise. Note that returning false does not guarantee that the
206 * next read will block.
207 *
208 * @exception IOException If an I/O error occurs
209 */
210 public boolean ready() throws IOException {
211 return false;
212 }
213
214 /**
215 * Tells whether this stream supports the mark() operation. The default
216 * implementation always returns false. Subclasses should override this
217 * method.
218 *
219 * @return true if and only if this stream supports the mark operation.
220 */
221 public boolean markSupported() {
222 return false;
223 }
224
225 /**
226 * Marks the present position in the stream. Subsequent calls to reset()
227 * will attempt to reposition the stream to this point. Not all
228 * character-input streams support the mark() operation.
229 *
230 * @param readAheadLimit Limit on the number of characters that may be
231 * read while still preserving the mark. After
232 * reading this many characters, attempting to
233 * reset the stream may fail.
234 *
235 * @exception IOException If the stream does not support mark(),
236 * or if some other I/O error occurs
237 */
238 public void mark(int readAheadLimit) throws IOException {
239 throw new IOException("mark() not supported");
240 }
241
242 /**
243 * Resets the stream. If the stream has been marked, then attempt to
244 * reposition it at the mark. If the stream has not been marked, then
245 * attempt to reset it in some way appropriate to the particular stream,
246 * for example by repositioning it to its starting point. Not all
247 * character-input streams support the reset() operation, and some support
248 * reset() without supporting mark().
249 *
250 * @exception IOException If the stream has not been marked,
251 * or if the mark has been invalidated,
252 * or if the stream does not support reset(),
253 * or if some other I/O error occurs
254 */
255 public void reset() throws IOException {
256 throw new IOException("reset() not supported");
257 }
258
259 /**
260 * Closes the stream and releases any system resources associated with
261 * it. Once the stream has been closed, further read(), ready(),
262 * mark(), reset(), or skip() invocations will throw an IOException.
263 * Closing a previously closed stream has no effect.
264 *
265 * @exception IOException If an I/O error occurs
266 */
267 public abstract void close() throws IOException;
268
269 /**
270 * Reads all characters from this reader and writes the characters to the
271 * given writer in the order that they are read. On return, this reader
272 * will be at end of the stream. This method does not close either reader
273 * or writer.
274 * <p>
275 * This method may block indefinitely reading from the reader, or
276 * writing to the writer. The behavior for the case where the reader
277 * and/or writer is <i>asynchronously closed</i>, or the thread
278 * interrupted during the transfer, is highly reader and writer
279 * specific, and therefore not specified.
280 * <p>
281 * If an I/O error occurs reading from the reader or writing to the
282 * writer, then it may do so after some characters have been read or
283 * written. Consequently the reader may not be at end of the stream and
284 * one, or both, streams may be in an inconsistent state. It is strongly
285 * recommended that both streams be promptly closed if an I/O error occurs.
286 *
287 * @param out the writer, non-null
288 * @return the number of characters transferred
289 * @throws IOException if an I/O error occurs when reading or writing
290 * @throws NullPointerException if {@code out} is {@code null}
291 *
292 * @since 10
293 */
294 public long transferTo(Writer out) throws IOException {
295 Objects.requireNonNull(out, "out");
296 long transferred = 0;
297 char[] buffer = new char[TRANSFER_BUFFER_SIZE];
298 int nRead;
299 while ((nRead = read(buffer, 0, TRANSFER_BUFFER_SIZE)) >= 0) {
300 out.write(buffer, 0, nRead);
301 transferred += nRead;
302 }
303 return transferred;
304 }
305
306 }