FileCacheSeekableStream.java
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- /*
- * Copyright (c) 2001 Sun Microsystems, Inc. All Rights Reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are met:
- *
- * -Redistributions of source code must retain the above copyright notice, this
- * list of conditions and the following disclaimer.
- *
- * -Redistribution in binary form must reproduct the above copyright notice,
- * this list of conditions and the following disclaimer in the documentation
- * and/or other materials provided with the distribution.
- *
- * Neither the name of Sun Microsystems, Inc. or the names of contributors may
- * be used to endorse or promote products derived from this software without
- * specific prior written permission.
- *
- * This software is provided "AS IS," without a warranty of any kind. ALL
- * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING ANY
- * IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR
- * NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE
- * LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING
- * OR DISTRIBUTING THE SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS
- * LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT,
- * INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER
- * CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF THE USE OF
- * OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN ADVISED OF THE
- * POSSIBILITY OF SUCH DAMAGES.
- *
- * You acknowledge that Software is not designed,licensed or intended for use in
- * the design, construction, operation or maintenance of any nuclear facility.
- */
- import java.io.File;
- import java.io.FileInputStream;
- import java.io.InputStream;
- import java.io.IOException;
- import java.io.RandomAccessFile;
- /**
- * A subclass of <code>SeekableStream</code> that may be used to wrap
- * a regular <code>InputStream</code>. Seeking backwards is supported
- * by means of a file cache. In circumstances that do not allow the
- * creation of a temporary file (for example, due to security
- * consideration or the absence of local disk), the
- * <code>MemoryCacheSeekableStream</code> class may be used instead.
- *
- * <p> The <code>mark()</code> and <code>reset()</code> methods are
- * supported.
- *
- * <p><b> This class is not a committed part of the JAI API. It may
- * be removed or changed in future releases of JAI.</b>
- */
- public final class FileCacheSeekableStream extends SeekableStream {
- /** The source stream. */
- private InputStream stream;
- /** The cache File. */
- private File cacheFile;
- /** The cache as a RandomAcessFile. */
- private RandomAccessFile cache;
- /** The length of the read buffer. */
- private int bufLen = 1024;
- /** The read buffer. */
- private byte[] buf = new byte[bufLen];
- /** Number of bytes in the cache. */
- private long length = 0;
- /** Next byte to be read. */
- private long pointer = 0;
- /** True if we've encountered the end of the source stream. */
- private boolean foundEOF = false;
- /**
- * Constructs a <code>MemoryCacheSeekableStream</code> that takes
- * its source data from a regular <code>InputStream</code>.
- * Seeking backwards is supported by means of an file cache.
- *
- * <p> An <code>IOException</code> will be thrown if the
- * attempt to create the cache file fails for any reason.
- */
- public FileCacheSeekableStream(InputStream stream)
- throws IOException {
- this.stream = stream;
- this.cacheFile = File.createTempFile("jai-FCSS-", ".tmp");
- cacheFile.deleteOnExit();
- this.cache = new RandomAccessFile(cacheFile, "rw");
- }
- /**
- * Ensures that at least <code>pos</code> bytes are cached,
- * or the end of the source is reached. The return value
- * is equal to the smaller of <code>pos</code> and the
- * length of the source file.
- */
- private long readUntil(long pos) throws IOException {
- // We've already got enough data cached
- if (pos < length) {
- return pos;
- }
- // pos >= length but length isn't getting any bigger, so return it
- if (foundEOF) {
- return length;
- }
- long len = pos - length;
- cache.seek(length);
- while (len > 0) {
- // Copy a buffer's worth of data from the source to the cache
- // bufLen will always fit into an int so this is safe
- int nbytes = stream.read(buf, 0, (int)Math.min(len, (long)bufLen));
- if (nbytes == -1) {
- foundEOF = true;
- return length;
- }
- cache.setLength(cache.length() + nbytes);
- cache.write(buf, 0, nbytes);
- len -= nbytes;
- length += nbytes;
- }
- return pos;
- }
- /**
- * Returns <code>true</code> since all
- * <code>FileCacheSeekableStream</code> instances support seeking
- * backwards.
- */
- public boolean canSeekBackwards() {
- return true;
- }
- /**
- * Returns the current offset in this file.
- *
- * @return the offset from the beginning of the file, in bytes,
- * at which the next read occurs.
- */
- public long getFilePointer() {
- return pointer;
- }
- /**
- * Sets the file-pointer offset, measured from the beginning of this
- * file, at which the next read occurs.
- *
- * @param pos the offset position, measured in bytes from the
- * beginning of the file, at which to set the file
- * pointer.
- * @exception IOException if <code>pos</code> is less than
- * <code>0</code> or if an I/O error occurs.
- */
- public void seek(long pos) throws IOException {
- if (pos < 0) {
- throw new IOException(JaiI18N.getString("FileCacheSeekableStream0"));
- }
- pointer = pos;
- }
- /**
- * Reads the next byte of data from the input stream. The value byte is
- * returned as an <code>int</code> in the range <code>0</code> to
- * <code>255</code>. If no byte is available because the end of the stream
- * has been reached, the value <code>-1</code> is returned. This method
- * blocks until input data is available, the end of the stream is detected,
- * or an exception is thrown.
- *
- * @return the next byte of data, or <code>-1</code> if the end of the
- * stream is reached.
- * @exception IOException if an I/O error occurs.
- */
- public int read() throws IOException {
- long next = pointer + 1;
- long pos = readUntil(next);
- if (pos >= next) {
- cache.seek(pointer++);
- return cache.read();
- } else {
- return -1;
- }
- }
- /**
- * Reads up to <code>len</code> bytes of data from the input stream into
- * an array of bytes. An attempt is made to read as many as
- * <code>len</code> bytes, but a smaller number may be read, possibly
- * zero. The number of bytes actually read is returned as an integer.
- *
- * <p> This method blocks until input data is available, end of file is
- * detected, or an exception is thrown.
- *
- * <p> If <code>b</code> is <code>null</code>, a
- * <code>NullPointerException</code> is thrown.
- *
- * <p> If <code>off</code> is negative, or <code>len</code> is negative, or
- * <code>off+len</code> is greater than the length of the array
- * <code>b</code>, then an <code>IndexOutOfBoundsException</code> is
- * thrown.
- *
- * <p> If <code>len</code> is zero, then no bytes are read and
- * <code>0</code> is returned; otherwise, there is an attempt to read at
- * least one byte. If no byte is available because the stream is at end of
- * file, the value <code>-1</code> is returned; otherwise, at least one
- * byte is read and stored into <code>b</code>.
- *
- * <p> The first byte read is stored into element <code>b[off]</code>, the
- * next one into <code>b[off+1]</code>, and so on. The number of bytes read
- * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
- * bytes actually read; these bytes will be stored in elements
- * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
- * leaving elements <code>b[off+</code><i>k</i><code>]</code> through
- * <code>b[off+len-1]</code> unaffected.
- *
- * <p> In every case, elements <code>b[0]</code> through
- * <code>b[off]</code> and elements <code>b[off+len]</code> through
- * <code>b[b.length-1]</code> are unaffected.
- *
- * <p> If the first byte cannot be read for any reason other than end of
- * file, then an <code>IOException</code> is thrown. In particular, an
- * <code>IOException</code> is thrown if the input stream has been closed.
- *
- * @param b the buffer into which the data is read.
- * @param off the start offset in array <code>b</code>
- * at which the data is written.
- * @param len the maximum number of bytes to read.
- * @return the total number of bytes read into the buffer, or
- * <code>-1</code> if there is no more data because the end of
- * the stream has been reached.
- * @exception IOException if an I/O error occurs.
- */
- public int read(byte[] b, int off, int len) throws IOException {
- if (b == null) {
- throw new NullPointerException();
- }
- if ((off < 0) || (len < 0) || (off + len > b.length)) {
- throw new IndexOutOfBoundsException();
- }
- if (len == 0) {
- return 0;
- }
- long pos = readUntil(pointer + len);
- // len will always fit into an int so this is safe
- len = (int)Math.min((long)len, pos - pointer);
- if (len > 0) {
- cache.seek(pointer);
- cache.readFully(b, off, len);
- pointer += len;
- return len;
- } else {
- return -1;
- }
- }
-
- /**
- * Closes this stream and releases any system resources
- * associated with the stream.
- *
- * @throws IOException if an I/O error occurs.
- */
- public void close() throws IOException {
- super.close();
- cache.close();
- cacheFile.delete();
- }
- }