Source Code Cross Referenced for BufferedInputStream.java in  » 6.0-JDK-Modules » j2me » java » io » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » 6.0 JDK Modules » j2me » java.io 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * @(#)BufferedInputStream.java	1.51 06/10/10
003:         *
004:         * Copyright  1990-2006 Sun Microsystems, Inc. All Rights Reserved.  
005:         * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
006:         *   
007:         * This program is free software; you can redistribute it and/or  
008:         * modify it under the terms of the GNU General Public License version  
009:         * 2 only, as published by the Free Software Foundation.   
010:         *   
011:         * This program is distributed in the hope that it will be useful, but  
012:         * WITHOUT ANY WARRANTY; without even the implied warranty of  
013:         * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
014:         * General Public License version 2 for more details (a copy is  
015:         * included at /legal/license.txt).   
016:         *   
017:         * You should have received a copy of the GNU General Public License  
018:         * version 2 along with this work; if not, write to the Free Software  
019:         * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
020:         * 02110-1301 USA   
021:         *   
022:         * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
023:         * Clara, CA 95054 or visit www.sun.com if you need additional  
024:         * information or have any questions. 
025:         *
026:         */
027:
028:        package java.io;
029:
030:        /**
031:         * A <code>BufferedInputStream</code> adds
032:         * functionality to another input stream-namely,
033:         * the ability to buffer the input and to
034:         * support the <code>mark</code> and <code>reset</code>
035:         * methods. When  the <code>BufferedInputStream</code>
036:         * is created, an internal buffer array is
037:         * created. As bytes  from the stream are read
038:         * or skipped, the internal buffer is refilled
039:         * as necessary  from the contained input stream,
040:         * many bytes at a time. The <code>mark</code>
041:         * operation  remembers a point in the input
042:         * stream and the <code>reset</code> operation
043:         * causes all the  bytes read since the most
044:         * recent <code>mark</code> operation to be
045:         * reread before new bytes are  taken from
046:         * the contained input stream.
047:         *
048:         * @version 1.44 11/09/00
049:         * @since   JDK1.0
050:         */
051:        public class BufferedInputStream extends FilterInputStream {
052:
053:            private static int defaultBufferSize = 2048;
054:
055:            /**
056:             * The internal buffer array where the data is stored. When necessary,
057:             * it may be replaced by another array of
058:             * a different size.
059:             */
060:            protected byte buf[];
061:
062:            /**
063:             * The index one greater than the index of the last valid byte in 
064:             * the buffer. 
065:             * This value is always
066:             * in the range <code>0</code> through <code>buf.length</code>;
067:             * elements <code>buf[0]</code>  through <code>buf[count-1]
068:             * </code>contain buffered input data obtained
069:             * from the underlying  input stream.
070:             */
071:            protected int count;
072:
073:            /**
074:             * The current position in the buffer. This is the index of the next 
075:             * character to be read from the <code>buf</code> array. 
076:             * <p>
077:             * This value is always in the range <code>0</code>
078:             * through <code>count</code>. If it is less
079:             * than <code>count</code>, then  <code>buf[pos]</code>
080:             * is the next byte to be supplied as input;
081:             * if it is equal to <code>count</code>, then
082:             * the  next <code>read</code> or <code>skip</code>
083:             * operation will require more bytes to be
084:             * read from the contained  input stream.
085:             *
086:             * @see     java.io.BufferedInputStream#buf
087:             */
088:            protected int pos;
089:
090:            /**
091:             * The value of the <code>pos</code> field at the time the last 
092:             * <code>mark</code> method was called.
093:             * <p>
094:             * This value is always
095:             * in the range <code>-1</code> through <code>pos</code>.
096:             * If there is no marked position in  the input
097:             * stream, this field is <code>-1</code>. If
098:             * there is a marked position in the input
099:             * stream,  then <code>buf[markpos]</code>
100:             * is the first byte to be supplied as input
101:             * after a <code>reset</code> operation. If
102:             * <code>markpos</code> is not <code>-1</code>,
103:             * then all bytes from positions <code>buf[markpos]</code>
104:             * through  <code>buf[pos-1]</code> must remain
105:             * in the buffer array (though they may be
106:             * moved to  another place in the buffer array,
107:             * with suitable adjustments to the values
108:             * of <code>count</code>,  <code>pos</code>,
109:             * and <code>markpos</code>); they may not
110:             * be discarded unless and until the difference
111:             * between <code>pos</code> and <code>markpos</code>
112:             * exceeds <code>marklimit</code>.
113:             *
114:             * @see     java.io.BufferedInputStream#mark(int)
115:             * @see     java.io.BufferedInputStream#pos
116:             */
117:            protected int markpos = -1;
118:
119:            /**
120:             * The maximum read ahead allowed after a call to the 
121:             * <code>mark</code> method before subsequent calls to the 
122:             * <code>reset</code> method fail. 
123:             * Whenever the difference between <code>pos</code>
124:             * and <code>markpos</code> exceeds <code>marklimit</code>,
125:             * then the  mark may be dropped by setting
126:             * <code>markpos</code> to <code>-1</code>.
127:             *
128:             * @see     java.io.BufferedInputStream#mark(int)
129:             * @see     java.io.BufferedInputStream#reset()
130:             */
131:            protected int marklimit;
132:
133:            /**
134:             * Check to make sure that this stream has not been closed
135:             */
136:            private void ensureOpen() throws IOException {
137:                if (in == null)
138:                    throw new IOException("Stream closed");
139:            }
140:
141:            /**
142:             * Creates a <code>BufferedInputStream</code>
143:             * and saves its  argument, the input stream
144:             * <code>in</code>, for later use. An internal
145:             * buffer array is created and  stored in <code>buf</code>.
146:             *
147:             * @param   in   the underlying input stream.
148:             */
149:            public BufferedInputStream(InputStream in) {
150:                this (in, defaultBufferSize);
151:            }
152:
153:            /**
154:             * Creates a <code>BufferedInputStream</code>
155:             * with the specified buffer size,
156:             * and saves its  argument, the input stream
157:             * <code>in</code>, for later use.  An internal
158:             * buffer array of length  <code>size</code>
159:             * is created and stored in <code>buf</code>.
160:             *
161:             * @param   in     the underlying input stream.
162:             * @param   size   the buffer size.
163:             * @exception IllegalArgumentException if size <= 0.
164:             */
165:            public BufferedInputStream(InputStream in, int size) {
166:                super (in);
167:                if (size <= 0) {
168:                    throw new IllegalArgumentException("Buffer size <= 0");
169:                }
170:                buf = new byte[size];
171:            }
172:
173:            /**
174:             * Fills the buffer with more data, taking into account
175:             * shuffling and dealing with marks.
176:             * Assumes that it is being called by a synchronized method.
177:             * This method also assumes that all data has already been read in,
178:             * hence pos > count.
179:             */
180:            private void fill() throws IOException {
181:                if (markpos < 0)
182:                    pos = 0; /* no mark: throw away the buffer */
183:                else if (pos >= buf.length) /* no room left in buffer */
184:                    if (markpos > 0) { /* can throw away early part of the buffer */
185:                        int sz = pos - markpos;
186:                        System.arraycopy(buf, markpos, buf, 0, sz);
187:                        pos = sz;
188:                        markpos = 0;
189:                    } else if (buf.length >= marklimit) {
190:                        markpos = -1; /* buffer got too big, invalidate mark */
191:                        pos = 0; /* drop buffer contents */
192:                    } else { /* grow buffer */
193:                        int nsz = pos * 2;
194:                        if (nsz > marklimit)
195:                            nsz = marklimit;
196:                        byte nbuf[] = new byte[nsz];
197:                        System.arraycopy(buf, 0, nbuf, 0, pos);
198:                        buf = nbuf;
199:                    }
200:                count = pos;
201:                int n = in.read(buf, pos, buf.length - pos);
202:                if (n > 0)
203:                    count = n + pos;
204:            }
205:
206:            /**
207:             * See
208:             * the general contract of the <code>read</code>
209:             * method of <code>InputStream</code>.
210:             *
211:             * @return     the next byte of data, or <code>-1</code> if the end of the
212:             *             stream is reached.
213:             * @exception  IOException  if an I/O error occurs.
214:             * @see        java.io.FilterInputStream#in
215:             */
216:            public synchronized int read() throws IOException {
217:                if (pos >= count) {
218:                    ensureOpen();
219:                    fill();
220:                    if (pos >= count)
221:                        return -1;
222:                }
223:                return buf[pos++] & 0xff;
224:            }
225:
226:            /**
227:             * Read characters into a portion of an array, reading from the underlying
228:             * stream at most once if necessary.
229:             */
230:            private int read1(byte[] b, int off, int len) throws IOException {
231:                int avail = count - pos;
232:                if (avail <= 0) {
233:                    /* If the requested length is at least as large as the buffer, and
234:                       if there is no mark/reset activity, do not bother to copy the
235:                       bytes into the local buffer.  In this way buffered streams will
236:                       cascade harmlessly. */
237:                    if (len >= buf.length && markpos < 0) {
238:                        return in.read(b, off, len);
239:                    }
240:                    fill();
241:                    avail = count - pos;
242:                    if (avail <= 0)
243:                        return -1;
244:                }
245:                int cnt = (avail < len) ? avail : len;
246:                System.arraycopy(buf, pos, b, off, cnt);
247:                pos += cnt;
248:                return cnt;
249:            }
250:
251:            /**
252:             * Reads bytes from this byte-input stream into the specified byte array,
253:             * starting at the given offset.
254:             *
255:             * <p> This method implements the general contract of the corresponding
256:             * <code>{@link InputStream#read(byte[], int, int) read}</code> method of
257:             * the <code>{@link InputStream}</code> class.  As an additional
258:             * convenience, it attempts to read as many bytes as possible by repeatedly
259:             * invoking the <code>read</code> method of the underlying stream.  This
260:             * iterated <code>read</code> continues until one of the following
261:             * conditions becomes true: <ul>
262:             *
263:             *   <li> The specified number of bytes have been read,
264:             *
265:             *   <li> The <code>read</code> method of the underlying stream returns
266:             *   <code>-1</code>, indicating end-of-file, or
267:             *
268:             *   <li> The <code>available</code> method of the underlying stream
269:             *   returns zero, indicating that further input requests would block.
270:             *
271:             * </ul> If the first <code>read</code> on the underlying stream returns
272:             * <code>-1</code> to indicate end-of-file then this method returns
273:             * <code>-1</code>.  Otherwise this method returns the number of bytes
274:             * actually read.
275:             *
276:             * <p> Subclasses of this class are encouraged, but not required, to
277:             * attempt to read as many bytes as possible in the same fashion.
278:             *
279:             * @param      b     destination buffer.
280:             * @param      off   offset at which to start storing bytes.
281:             * @param      len   maximum number of bytes to read.
282:             * @return     the number of bytes read, or <code>-1</code> if the end of
283:             *             the stream has been reached.
284:             * @exception  IOException  if an I/O error occurs.
285:             */
286:            public synchronized int read(byte b[], int off, int len)
287:                    throws IOException {
288:                ensureOpen();
289:                if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
290:                    throw new IndexOutOfBoundsException();
291:                } else if (len == 0) {
292:                    return 0;
293:                }
294:
295:                int n = read1(b, off, len);
296:                if (n <= 0)
297:                    return n;
298:                while ((n < len) && (in.available() > 0)) {
299:                    int n1 = read1(b, off + n, len - n);
300:                    if (n1 <= 0)
301:                        break;
302:                    n += n1;
303:                }
304:                return n;
305:            }
306:
307:            /**
308:             * See the general contract of the <code>skip</code>
309:             * method of <code>InputStream</code>.
310:             *
311:             * @param      n   the number of bytes to be skipped.
312:             * @return     the actual number of bytes skipped.
313:             * @exception  IOException  if an I/O error occurs.
314:             */
315:            public synchronized long skip(long n) throws IOException {
316:                ensureOpen();
317:                if (n <= 0) {
318:                    return 0;
319:                }
320:                long avail = count - pos;
321:
322:                if (avail <= 0) {
323:                    // If no mark position set then don't keep in buffer
324:                    if (markpos < 0)
325:                        return in.skip(n);
326:
327:                    // Fill in buffer to save bytes for reset
328:                    fill();
329:                    avail = count - pos;
330:                    if (avail <= 0)
331:                        return 0;
332:                }
333:
334:                long skipped = (avail < n) ? avail : n;
335:                pos += skipped;
336:                return skipped;
337:            }
338:
339:            /**
340:             * Returns the number of bytes that can be read from this input 
341:             * stream without blocking. 
342:             * <p>
343:             * The <code>available</code> method of 
344:             * <code>BufferedInputStream</code> returns the sum of the the number 
345:             * of bytes remaining to be read in the buffer 
346:             * (<code>count&nbsp;- pos</code>) 
347:             * and the result of calling the <code>available</code> method of the 
348:             * underlying input stream. 
349:             *
350:             * @return     the number of bytes that can be read from this input
351:             *             stream without blocking.
352:             * @exception  IOException  if an I/O error occurs.
353:             * @see        java.io.FilterInputStream#in
354:             */
355:            public synchronized int available() throws IOException {
356:                ensureOpen();
357:                return (count - pos) + in.available();
358:            }
359:
360:            /** 
361:             * See the general contract of the <code>mark</code>
362:             * method of <code>InputStream</code>.
363:             *
364:             * @param   readlimit   the maximum limit of bytes that can be read before
365:             *                      the mark position becomes invalid.
366:             * @see     java.io.BufferedInputStream#reset()
367:             */
368:            public synchronized void mark(int readlimit) {
369:                marklimit = readlimit;
370:                markpos = pos;
371:            }
372:
373:            /**
374:             * See the general contract of the <code>reset</code>
375:             * method of <code>InputStream</code>.
376:             * <p>
377:             * If <code>markpos</code> is <code>-1</code>
378:             * (no mark has been set or the mark has been
379:             * invalidated), an <code>IOException</code>
380:             * is thrown. Otherwise, <code>pos</code> is
381:             * set equal to <code>markpos</code>.
382:             *
383:             * @exception  IOException  if this stream has not been marked or
384:             *               if the mark has been invalidated.
385:             * @see        java.io.BufferedInputStream#mark(int)
386:             */
387:            public synchronized void reset() throws IOException {
388:                ensureOpen();
389:                if (markpos < 0)
390:                    throw new IOException("Resetting to invalid mark");
391:                pos = markpos;
392:            }
393:
394:            /**
395:             * Tests if this input stream supports the <code>mark</code> 
396:             * and <code>reset</code> methods. The <code>markSupported</code> 
397:             * method of <code>BufferedInputStream</code> returns 
398:             * <code>true</code>. 
399:             *
400:             * @return  a <code>boolean</code> indicating if this stream type supports
401:             *          the <code>mark</code> and <code>reset</code> methods.
402:             * @see     java.io.InputStream#mark(int)
403:             * @see     java.io.InputStream#reset()
404:             */
405:            public boolean markSupported() {
406:                return true;
407:            }
408:
409:            /**
410:             * Closes this input stream and releases any system resources 
411:             * associated with the stream. 
412:             *
413:             * @exception  IOException  if an I/O error occurs.
414:             */
415:            public void close() throws IOException {
416:                if (in == null)
417:                    return;
418:                in.close();
419:                in = null;
420:                buf = null;
421:                pos = count = 0;
422:            }
423:        }
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