1 /*
2 * Copyright (c) 1996, 2015, 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 * A character-stream reader that allows characters to be pushed back into the
31 * stream.
32 *
33 * @author Mark Reinhold
34 * @since 1.1
35 */
36
37 public class PushbackReader extends FilterReader {
38
39 /** Pushback buffer */
40 private char[] buf;
41
42 /** Current position in buffer */
43 private int pos;
44
45 /**
46 * Creates a new pushback reader with a pushback buffer of the given size.
47 *
48 * @param in The reader from which characters will be read
49 * @param size The size of the pushback buffer
50 * @exception IllegalArgumentException if {@code size <= 0}
51 */
52 public PushbackReader(Reader in, int size) {
53 super(in);
54 if (size <= 0) {
55 throw new IllegalArgumentException("size <= 0");
56 }
57 this.buf = new char[size];
58 this.pos = size;
59 }
60
61 /**
62 * Creates a new pushback reader with a one-character pushback buffer.
63 *
64 * @param in The reader from which characters will be read
65 */
66 public PushbackReader(Reader in) {
67 this(in, 1);
68 }
69
70 /** Checks to make sure that the stream has not been closed. */
71 private void ensureOpen() throws IOException {
72 if (buf == null)
73 throw new IOException("Stream closed");
74 }
75
76 /**
77 * Reads a single character.
78 *
79 * @return The character read, or -1 if the end of the stream has been
80 * reached
81 *
82 * @exception IOException If an I/O error occurs
83 */
84 public int read() throws IOException {
85 synchronized (lock) {
86 ensureOpen();
87 if (pos < buf.length)
88 return buf[pos++];
89 else
90 return super.read();
91 }
92 }
93
94 /**
95 * Reads characters into a portion of an array.
96 *
97 * @param cbuf Destination buffer
98 * @param off Offset at which to start writing characters
99 * @param len Maximum number of characters to read
100 *
101 * @return The number of characters read, or -1 if the end of the
102 * stream has been reached
103 *
104 * @exception IOException If an I/O error occurs
105 * @exception IndexOutOfBoundsException {@inheritDoc}
106 */
107 public int read(char[] cbuf, int off, int len) throws IOException {
108 synchronized (lock) {
109 ensureOpen();
110 try {
111 if (len <= 0) {
112 if (len < 0) {
113 throw new IndexOutOfBoundsException();
114 } else if ((off < 0) || (off > cbuf.length)) {
115 throw new IndexOutOfBoundsException();
116 }
117 return 0;
118 }
119 int avail = buf.length - pos;
120 if (avail > 0) {
121 if (len < avail)
122 avail = len;
123 System.arraycopy(buf, pos, cbuf, off, avail);
124 pos += avail;
125 off += avail;
126 len -= avail;
127 }
128 if (len > 0) {
129 len = super.read(cbuf, off, len);
130 if (len == -1) {
131 return (avail == 0) ? -1 : avail;
132 }
133 return avail + len;
134 }
135 return avail;
136 } catch (ArrayIndexOutOfBoundsException e) {
137 throw new IndexOutOfBoundsException();
138 }
139 }
140 }
141
142 /**
143 * Pushes back a single character by copying it to the front of the
144 * pushback buffer. After this method returns, the next character to be read
145 * will have the value <code>(char)c</code>.
146 *
147 * @param c The int value representing a character to be pushed back
148 *
149 * @exception IOException If the pushback buffer is full,
150 * or if some other I/O error occurs
151 */
152 public void unread(int c) throws IOException {
153 synchronized (lock) {
154 ensureOpen();
155 if (pos == 0)
156 throw new IOException("Pushback buffer overflow");
157 buf[--pos] = (char) c;
158 }
159 }
160
161 /**
162 * Pushes back a portion of an array of characters by copying it to the
163 * front of the pushback buffer. After this method returns, the next
164 * character to be read will have the value <code>cbuf[off]</code>, the
165 * character after that will have the value <code>cbuf[off+1]</code>, and
166 * so forth.
167 *
168 * @param cbuf Character array
169 * @param off Offset of first character to push back
170 * @param len Number of characters to push back
171 *
172 * @exception IOException If there is insufficient room in the pushback
173 * buffer, or if some other I/O error occurs
174 */
175 public void unread(char[] cbuf, int off, int len) throws IOException {
176 synchronized (lock) {
177 ensureOpen();
178 if (len > pos)
179 throw new IOException("Pushback buffer overflow");
180 pos -= len;
181 System.arraycopy(cbuf, off, buf, pos, len);
182 }
183 }
184
185 /**
186 * Pushes back an array of characters by copying it to the front of the
187 * pushback buffer. After this method returns, the next character to be
188 * read will have the value <code>cbuf[0]</code>, the character after that
189 * will have the value <code>cbuf[1]</code>, and so forth.
190 *
191 * @param cbuf Character array to push back
192 *
193 * @exception IOException If there is insufficient room in the pushback
194 * buffer, or if some other I/O error occurs
195 */
196 public void unread(char[] cbuf) throws IOException {
197 unread(cbuf, 0, cbuf.length);
198 }
199
200 /**
201 * Tells whether this stream is ready to be read.
202 *
203 * @exception IOException If an I/O error occurs
204 */
205 public boolean ready() throws IOException {
206 synchronized (lock) {
207 ensureOpen();
208 return (pos < buf.length) || super.ready();
209 }
210 }
211
212 /**
213 * Marks the present position in the stream. The <code>mark</code>
214 * for class <code>PushbackReader</code> always throws an exception.
215 *
216 * @exception IOException Always, since mark is not supported
217 */
218 public void mark(int readAheadLimit) throws IOException {
219 throw new IOException("mark/reset not supported");
220 }
221
222 /**
223 * Resets the stream. The <code>reset</code> method of
224 * <code>PushbackReader</code> always throws an exception.
225 *
226 * @exception IOException Always, since reset is not supported
227 */
228 public void reset() throws IOException {
229 throw new IOException("mark/reset not supported");
230 }
231
232 /**
233 * Tells whether this stream supports the mark() operation, which it does
234 * not.
235 */
236 public boolean markSupported() {
237 return false;
238 }
239
240 /**
241 * Closes the stream and releases any system resources associated with
242 * it. Once the stream has been closed, further read(),
243 * unread(), ready(), or skip() invocations will throw an IOException.
244 * Closing a previously closed stream has no effect. This method will block
245 * while there is another thread blocking on the reader.
246 *
247 * @exception IOException If an I/O error occurs
248 */
249 public void close() throws IOException {
250 synchronized (lock) {
251 super.close();
252 buf = null;
253 }
254 }
255
256 /**
257 * Skips characters. This method will block until some characters are
258 * available, an I/O error occurs, or the end of the stream is reached.
259 *
260 * @param n The number of characters to skip
261 *
262 * @return The number of characters actually skipped
263 *
264 * @exception IllegalArgumentException If <code>n</code> is negative.
265 * @exception IOException If an I/O error occurs
266 */
267 public long skip(long n) throws IOException {
268 if (n < 0L)
269 throw new IllegalArgumentException("skip value is negative");
270 synchronized (lock) {
271 ensureOpen();
272 int avail = buf.length - pos;
273 if (avail > 0) {
274 if (n <= avail) {
275 pos += n;
276 return n;
277 } else {
278 pos = buf.length;
279 n -= avail;
280 }
281 }
282 return avail + super.skip(n);
283 }
284 }
285 }