Source Code Cross Referenced for MemoryCacheSeekableStream.java in  » 6.0-JDK-Modules » Java-Advanced-Imaging » com » sun » media » jai » codec » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » 6.0 JDK Modules » Java Advanced Imaging » com.sun.media.jai.codec 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * $RCSfile: MemoryCacheSeekableStream.java,v $
003:         *
004:         * Copyright (c) 2005 Sun Microsystems, Inc. All rights reserved.
005:         *
006:         * Use is subject to license terms.
007:         *
008:         * $Revision: 1.2 $
009:         * $Date: 2005/11/17 00:47:30 $
010:         * $State: Exp $
011:         */
012:        package com.sun.media.jai.codec;
013:
014:        import java.io.InputStream;
015:        import java.io.IOException;
016:        import java.util.Vector;
017:
018:        /**
019:         * A subclass of <code>SeekableStream</code> that may be used to wrap
020:         * a regular <code>InputStream</code>.  Seeking backwards is supported
021:         * by means of an in-memory cache.  For greater efficiency,
022:         * <code>FileCacheSeekableStream</code> should be used in
023:         * circumstances that allow the creation of a temporary file.
024:         *
025:         * <p> The <code>mark()</code> and <code>reset()</code> methods are
026:         * supported.
027:         *
028:         * <p><b> This class is not a committed part of the JAI API.  It may
029:         * be removed or changed in future releases of JAI.</b>
030:         */
031:        public final class MemoryCacheSeekableStream extends SeekableStream {
032:
033:            /** The source input stream. */
034:            private InputStream src;
035:
036:            /** Position of first unread byte. */
037:            private long pointer = 0;
038:
039:            /** Log_2 of the sector size. */
040:            private static final int SECTOR_SHIFT = 9;
041:
042:            /** The sector size. */
043:            private static final int SECTOR_SIZE = 1 << SECTOR_SHIFT;
044:
045:            /** A mask to determine the offset within a sector. */
046:            private static final int SECTOR_MASK = SECTOR_SIZE - 1;
047:
048:            /** A Vector of source sectors. */
049:            private Vector data = new Vector();
050:
051:            /** Number of sectors stored. */
052:            int sectors = 0;
053:
054:            /** Number of bytes read. */
055:            int length = 0;
056:
057:            /** True if we've previously reached the end of the source stream */
058:            boolean foundEOS = false;
059:
060:            /**
061:             * Constructs a <code>MemoryCacheSeekableStream</code> that takes
062:             * its source data from a regular <code>InputStream</code>.
063:             * Seeking backwards is supported by means of an in-memory cache.
064:             */
065:            public MemoryCacheSeekableStream(InputStream src) {
066:                this .src = src;
067:            }
068:
069:            /** Forwards the request to the real <code>InputStream</code>. */
070:            public final int available() throws IOException {
071:                return src.available();
072:            }
073:
074:            /**
075:             * Ensures that at least <code>pos</code> bytes are cached,
076:             * or the end of the source is reached.  The return value
077:             * is equal to the smaller of <code>pos</code> and the
078:             * length of the source stream.
079:             */
080:            private long readUntil(long pos) throws IOException {
081:                // We've already got enough data cached
082:                if (pos < length) {
083:                    return pos;
084:                }
085:                // pos >= length but length isn't getting any bigger, so return it
086:                if (foundEOS) {
087:                    return length;
088:                }
089:
090:                int sector = (int) (pos >> SECTOR_SHIFT);
091:
092:                // First unread sector
093:                int startSector = length >> SECTOR_SHIFT;
094:
095:                // Read sectors until the desired sector
096:                for (int i = startSector; i <= sector; i++) {
097:                    byte[] buf = new byte[SECTOR_SIZE];
098:                    data.addElement(buf);
099:
100:                    // Read up to SECTOR_SIZE bytes
101:                    int len = SECTOR_SIZE;
102:                    int off = 0;
103:                    while (len > 0) {
104:                        int nbytes = src.read(buf, off, len);
105:                        // Found the end-of-stream
106:                        if (nbytes == -1) {
107:                            foundEOS = true;
108:                            return length;
109:                        }
110:                        off += nbytes;
111:                        len -= nbytes;
112:
113:                        // Record new data length
114:                        length += nbytes;
115:                    }
116:                }
117:
118:                return length;
119:            }
120:
121:            /**
122:             * Returns <code>true</code> since all
123:             * <code>MemoryCacheSeekableStream</code> instances support seeking
124:             * backwards.
125:             */
126:            public boolean canSeekBackwards() {
127:                return true;
128:            }
129:
130:            /**
131:             * Returns the current offset in this file. 
132:             *
133:             * @return     the offset from the beginning of the file, in bytes,
134:             *             at which the next read occurs.
135:             */
136:            public long getFilePointer() {
137:                return pointer;
138:            }
139:
140:            /**
141:             * Sets the file-pointer offset, measured from the beginning of this 
142:             * file, at which the next read occurs.
143:             *
144:             * @param      pos   the offset position, measured in bytes from the 
145:             *                   beginning of the file, at which to set the file 
146:             *                   pointer.
147:             * @exception  IOException  if <code>pos</code> is less than 
148:             *                          <code>0</code> or if an I/O error occurs.
149:             */
150:            public void seek(long pos) throws IOException {
151:                if (pos < 0) {
152:                    throw new IOException(JaiI18N
153:                            .getString("MemoryCacheSeekableStream0"));
154:                }
155:                pointer = pos;
156:            }
157:
158:            /**
159:             * Reads the next byte of data from the input stream. The value byte is
160:             * returned as an <code>int</code> in the range <code>0</code> to
161:             * <code>255</code>. If no byte is available because the end of the stream
162:             * has been reached, the value <code>-1</code> is returned. This method
163:             * blocks until input data is available, the end of the stream is detected,
164:             * or an exception is thrown.
165:             *
166:             * @return     the next byte of data, or <code>-1</code> if the end of the
167:             *             stream is reached.
168:             */
169:            public int read() throws IOException {
170:                long next = pointer + 1;
171:                long pos = readUntil(next);
172:                if (pos >= next) {
173:                    byte[] buf = (byte[]) data
174:                            .elementAt((int) (pointer >> SECTOR_SHIFT));
175:                    return buf[(int) (pointer++ & SECTOR_MASK)] & 0xff;
176:                } else {
177:                    return -1;
178:                }
179:            }
180:
181:            /**
182:             * Reads up to <code>len</code> bytes of data from the input stream into
183:             * an array of bytes.  An attempt is made to read as many as
184:             * <code>len</code> bytes, but a smaller number may be read, possibly
185:             * zero. The number of bytes actually read is returned as an integer.
186:             *
187:             * <p> This method blocks until input data is available, end of file is
188:             * detected, or an exception is thrown.
189:             *
190:             * <p> If <code>b</code> is <code>null</code>, a
191:             * <code>NullPointerException</code> is thrown.
192:             *
193:             * <p> If <code>off</code> is negative, or <code>len</code> is negative, or
194:             * <code>off+len</code> is greater than the length of the array
195:             * <code>b</code>, then an <code>IndexOutOfBoundsException</code> is
196:             * thrown.
197:             *
198:             * <p> If <code>len</code> is zero, then no bytes are read and
199:             * <code>0</code> is returned; otherwise, there is an attempt to read at
200:             * least one byte. If no byte is available because the stream is at end of
201:             * file, the value <code>-1</code> is returned; otherwise, at least one
202:             * byte is read and stored into <code>b</code>.
203:             *
204:             * <p> The first byte read is stored into element <code>b[off]</code>, the
205:             * next one into <code>b[off+1]</code>, and so on. The number of bytes read
206:             * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
207:             * bytes actually read; these bytes will be stored in elements
208:             * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
209:             * leaving elements <code>b[off+</code><i>k</i><code>]</code> through
210:             * <code>b[off+len-1]</code> unaffected.
211:             *
212:             * <p> In every case, elements <code>b[0]</code> through
213:             * <code>b[off]</code> and elements <code>b[off+len]</code> through
214:             * <code>b[b.length-1]</code> are unaffected.
215:             *
216:             * <p> If the first byte cannot be read for any reason other than end of
217:             * file, then an <code>IOException</code> is thrown. In particular, an
218:             * <code>IOException</code> is thrown if the input stream has been closed.
219:             *
220:             * @param      b     the buffer into which the data is read.
221:             * @param      off   the start offset in array <code>b</code>
222:             *                   at which the data is written.
223:             * @param      len   the maximum number of bytes to read.
224:             * @return     the total number of bytes read into the buffer, or
225:             *             <code>-1</code> if there is no more data because the end of
226:             *             the stream has been reached.
227:             */
228:            public int read(byte[] b, int off, int len) throws IOException {
229:                if (b == null) {
230:                    throw new NullPointerException();
231:                }
232:                if ((off < 0) || (len < 0) || (off + len > b.length)) {
233:                    throw new IndexOutOfBoundsException();
234:                }
235:                if (len == 0) {
236:                    return 0;
237:                }
238:
239:                long pos = readUntil(pointer + len);
240:                // End-of-stream
241:                if (pos <= pointer) {
242:                    return -1;
243:                }
244:
245:                byte[] buf = (byte[]) data
246:                        .elementAt((int) (pointer >> SECTOR_SHIFT));
247:                int nbytes = Math.min((int) (pos < pointer + len ? pos
248:                        - pointer : len), SECTOR_SIZE
249:                        - (int) (pointer & SECTOR_MASK));
250:                System.arraycopy(buf, (int) (pointer & SECTOR_MASK), b, off,
251:                        nbytes);
252:                pointer += nbytes;
253:                return nbytes;
254:            }
255:        }
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