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25 
26 package java.io;
27 
28 
29 /**
30  * A character stream whose source is a string.
31  *
32  * @author      Mark Reinhold
33  * @since       1.1
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      */
StringReader(String s)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 */
ensureOpen()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      */
read()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      * @exception  IndexOutOfBoundsException {@inheritDoc}
88      */
read(char cbuf[], int off, int len)89     public int read(char cbuf[], int off, int len) throws IOException {
90         synchronized (lock) {
91             ensureOpen();
92             if ((off < 0) || (off > cbuf.length) || (len < 0) ||
93                 ((off + len) > cbuf.length) || ((off + len) < 0)) {
94                 throw new IndexOutOfBoundsException();
95             } else if (len == 0) {
96                 return 0;
97             }
98             if (next >= length)
99                 return -1;
100             int n = Math.min(length - next, len);
101             str.getChars(next, next + n, cbuf, off);
102             next += n;
103             return n;
104         }
105     }
106 
107     /**
108      * Skips the specified number of characters in the stream. Returns
109      * the number of characters that were skipped.
110      *
111      * <p>The <code>ns</code> parameter may be negative, even though the
112      * <code>skip</code> method of the {@link Reader} superclass throws
113      * an exception in this case. Negative values of <code>ns</code> cause the
114      * stream to skip backwards. Negative return values indicate a skip
115      * backwards. It is not possible to skip backwards past the beginning of
116      * the string.
117      *
118      * <p>If the entire string has been read or skipped, then this method has
119      * no effect and always returns 0.
120      *
121      * @exception  IOException  If an I/O error occurs
122      */
skip(long ns)123     public long skip(long ns) throws IOException {
124         synchronized (lock) {
125             ensureOpen();
126             if (next >= length)
127                 return 0;
128             // Bound skip by beginning and end of the source
129             long n = Math.min(length - next, ns);
130             n = Math.max(-next, n);
131             next += n;
132             return n;
133         }
134     }
135 
136     /**
137      * Tells whether this stream is ready to be read.
138      *
139      * @return True if the next read() is guaranteed not to block for input
140      *
141      * @exception  IOException  If the stream is closed
142      */
ready()143     public boolean ready() throws IOException {
144         synchronized (lock) {
145             ensureOpen();
146             return true;
147         }
148     }
149 
150     /**
151      * Tells whether this stream supports the mark() operation, which it does.
152      */
markSupported()153     public boolean markSupported() {
154         return true;
155     }
156 
157     /**
158      * Marks the present position in the stream.  Subsequent calls to reset()
159      * will reposition the stream to this point.
160      *
161      * @param  readAheadLimit  Limit on the number of characters that may be
162      *                         read while still preserving the mark.  Because
163      *                         the stream's input comes from a string, there
164      *                         is no actual limit, so this argument must not
165      *                         be negative, but is otherwise ignored.
166      *
167      * @exception  IllegalArgumentException  If {@code readAheadLimit < 0}
168      * @exception  IOException  If an I/O error occurs
169      */
mark(int readAheadLimit)170     public void mark(int readAheadLimit) throws IOException {
171         if (readAheadLimit < 0){
172             throw new IllegalArgumentException("Read-ahead limit < 0");
173         }
174         synchronized (lock) {
175             ensureOpen();
176             mark = next;
177         }
178     }
179 
180     /**
181      * Resets the stream to the most recent mark, or to the beginning of the
182      * string if it has never been marked.
183      *
184      * @exception  IOException  If an I/O error occurs
185      */
reset()186     public void reset() throws IOException {
187         synchronized (lock) {
188             ensureOpen();
189             next = mark;
190         }
191     }
192 
193     /**
194      * Closes the stream and releases any system resources associated with
195      * it. Once the stream has been closed, further read(),
196      * ready(), mark(), or reset() invocations will throw an IOException.
197      * Closing a previously closed stream has no effect. This method will block
198      * while there is another thread blocking on the reader.
199      */
close()200     public void close() {
201         synchronized (lock) {
202             str = null;
203         }
204     }
205 }
206