1 /*
2 * Copyright (c) 1996, 2005, 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 whose source is a string.
31 *
32 * @author Mark Reinhold
33 * @since JDK1.1
34 */
35
36 public class StringReader extends Reader {
37
38 private String str;
39 private int length;
40 private int next = 0;
41 private int mark = 0;
42
43 /**
44 * Creates a new string reader.
45 *
46 * @param s String providing the character stream.
47 */
48 public StringReader(String s) {
49 this.str = s;
50 this.length = s.length();
51 }
52
53 /** Check to make sure that the stream has not been closed */
54 private void ensureOpen() throws IOException {
55 if (str == null)
56 throw new IOException("Stream closed");
57 }
58
59 /**
60 * Reads a single character.
61 *
62 * @return The character read, or -1 if the end of the stream has been
63 * reached
64 *
65 * @exception IOException If an I/O error occurs
66 */
67 public int read() throws IOException {
68 synchronized (lock) {
69 ensureOpen();
70 if (next >= length)
71 return -1;
72 return str.charAt(next++);
73 }
74 }
75
76 /**
77 * Reads characters into a portion of an array.
78 *
79 * @param cbuf Destination buffer
80 * @param off Offset at which to start writing characters
81 * @param len Maximum number of characters to read
82 *
83 * @return The number of characters read, or -1 if the end of the
84 * stream has been reached
85 *
86 * @exception IOException If an I/O error occurs
87 */
88 public int read(char cbuf[], int off, int len) throws IOException {
89 synchronized (lock) {
90 ensureOpen();
91 if ((off < 0) || (off > cbuf.length) || (len < 0) ||
92 ((off + len) > cbuf.length) || ((off + len) < 0)) {
93 throw new IndexOutOfBoundsException();
94 } else if (len == 0) {
95 return 0;
96 }
97 if (next >= length)
98 return -1;
99 int n = Math.min(length - next, len);
100 str.getChars(next, next + n, cbuf, off);
101 next += n;
102 return n;
103 }
104 }
105
106 /**
107 * Skips the specified number of characters in the stream. Returns
108 * the number of characters that were skipped.
109 *
110 * <p>The <code>ns</code> parameter may be negative, even though the
111 * <code>skip</code> method of the {@link Reader} superclass throws
112 * an exception in this case. Negative values of <code>ns</code> cause the
113 * stream to skip backwards. Negative return values indicate a skip
114 * backwards. It is not possible to skip backwards past the beginning of
115 * the string.
116 *
117 * <p>If the entire string has been read or skipped, then this method has
118 * no effect and always returns 0.
119 *
120 * @exception IOException If an I/O error occurs
121 */
122 public long skip(long ns) throws IOException {
123 synchronized (lock) {
124 ensureOpen();
125 if (next >= length)
126 return 0;
127 // Bound skip by beginning and end of the source
128 long n = Math.min(length - next, ns);
129 n = Math.max(-next, n);
130 next += n;
131 return n;
132 }
133 }
134
135 /**
136 * Tells whether this stream is ready to be read.
137 *
138 * @return True if the next read() is guaranteed not to block for input
139 *
140 * @exception IOException If the stream is closed
141 */
142 public boolean ready() throws IOException {
143 synchronized (lock) {
144 ensureOpen();
145 return true;
146 }
147 }
148
149 /**
150 * Tells whether this stream supports the mark() operation, which it does.
151 */
152 public boolean markSupported() {
153 return true;
154 }
155
156 /**
157 * Marks the present position in the stream. Subsequent calls to reset()
158 * will reposition the stream to this point.
159 *
160 * @param readAheadLimit Limit on the number of characters that may be
161 * read while still preserving the mark. Because
162 * the stream's input comes from a string, there
163 * is no actual limit, so this argument must not
164 * be negative, but is otherwise ignored.
165 *
166 * @exception IllegalArgumentException If readAheadLimit is < 0
167 * @exception IOException If an I/O error occurs
168 */
169 public void mark(int readAheadLimit) throws IOException {
170 if (readAheadLimit < 0){
171 throw new IllegalArgumentException("Read-ahead limit < 0");
172 }
173 synchronized (lock) {
174 ensureOpen();
175 mark = next;
176 }
177 }
178
179 /**
180 * Resets the stream to the most recent mark, or to the beginning of the
181 * string if it has never been marked.
182 *
183 * @exception IOException If an I/O error occurs
184 */
185 public void reset() throws IOException {
186 synchronized (lock) {
187 ensureOpen();
188 next = mark;
189 }
190 }
191
192 /**
193 * Closes the stream and releases any system resources associated with
194 * it. Once the stream has been closed, further read(),
195 * ready(), mark(), or reset() invocations will throw an IOException.
196 * Closing a previously closed stream has no effect.
197 */
198 public void close() {
199 str = null;
200 }
201 }