org.apache.xmlgraphics.image.codec.util.MemoryCacheSeekableStream Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* $Id: MemoryCacheSeekableStream.java 1732018 2016-02-24 04:51:06Z gadams $ */
package org.apache.xmlgraphics.image.codec.util;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
/**
* A subclass of SeekableStream that may be used to wrap
* a regular InputStream. Seeking backwards is supported
* by means of an in-memory cache. For greater efficiency,
* FileCacheSeekableStream should be used in
* circumstances that allow the creation of a temporary file.
*
* The mark() and reset() methods are
* supported.
*
*
This class is not a committed part of the JAI API. It may
* be removed or changed in future releases of JAI.
*/
public final class MemoryCacheSeekableStream extends SeekableStream {
/** The source input stream. */
private InputStream src;
/** Position of first unread byte. */
private long pointer;
/** Log_2 of the sector size. */
private static final int SECTOR_SHIFT = 9;
/** The sector size. */
private static final int SECTOR_SIZE = 1 << SECTOR_SHIFT;
/** A mask to determine the offset within a sector. */
private static final int SECTOR_MASK = SECTOR_SIZE - 1;
/** A Vector of source sectors. */
private List data = new ArrayList();
/** Number of sectors stored. */
// int sectors = 0;
/** Number of bytes read. */
int length;
/** True if we've previously reached the end of the source stream */
boolean foundEOS;
/**
* Constructs a MemoryCacheSeekableStream that takes
* its source data from a regular InputStream.
* Seeking backwards is supported by means of an in-memory cache.
*/
public MemoryCacheSeekableStream(InputStream src) {
this.src = src;
}
/**
* Ensures that at least pos bytes are cached,
* or the end of the source is reached. The return value
* is equal to the smaller of pos and the
* length of the source stream.
*/
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 (foundEOS) {
return length;
}
int sector = (int)(pos >> SECTOR_SHIFT);
// First unread sector
int startSector = length >> SECTOR_SHIFT;
// Read sectors until the desired sector
for (int i = startSector; i <= sector; i++) {
byte[] buf = new byte[SECTOR_SIZE];
data.add(buf);
// Read up to SECTOR_SIZE bytes
int len = SECTOR_SIZE;
int off = 0;
while (len > 0) {
int nbytes = src.read(buf, off, len);
// Found the end-of-stream
if (nbytes == -1) {
foundEOS = true;
return length;
}
off += nbytes;
len -= nbytes;
// Record new data length
length += nbytes;
}
}
return length;
}
/**
* Returns true since all
* MemoryCacheSeekableStream 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 pos is less than
* 0 or if an I/O error occurs.
*/
public void seek(long pos) throws IOException {
if (pos < 0) {
throw new IOException(PropertyUtil.getString("MemoryCacheSeekableStream0"));
}
pointer = pos;
}
/**
* Reads the next byte of data from the input stream. The value byte is
* returned as an int in the range 0 to
* 255. If no byte is available because the end of the stream
* has been reached, the value -1 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 -1 if the end of the
* stream is reached.
*/
public int read() throws IOException {
long next = pointer + 1;
long pos = readUntil(next);
if (pos >= next) {
byte[] buf =
(byte[])data.get((int)(pointer >> SECTOR_SHIFT));
return buf[(int)(pointer++ & SECTOR_MASK)] & 0xff;
} else {
return -1;
}
}
/**
* Reads up to len bytes of data from the input stream into
* an array of bytes. An attempt is made to read as many as
* len bytes, but a smaller number may be read, possibly
* zero. The number of bytes actually read is returned as an integer.
*
*
This method blocks until input data is available, end of file is
* detected, or an exception is thrown.
*
*
If b is null, a
* NullPointerException is thrown.
*
*
If off is negative, or len is negative, or
* off+len is greater than the length of the array
* b, then an IndexOutOfBoundsException is
* thrown.
*
*
If len is zero, then no bytes are read and
* 0 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 -1 is returned; otherwise, at least one
* byte is read and stored into b.
*
*
The first byte read is stored into element b[off], the
* next one into b[off+1], and so on. The number of bytes read
* is, at most, equal to len. Let k be the number of
* bytes actually read; these bytes will be stored in elements
* b[off] through b[off+k-1],
* leaving elements b[off+k] through
* b[off+len-1] unaffected.
*
*
In every case, elements b[0] through
* b[off] and elements b[off+len] through
* b[b.length-1] are unaffected.
*
*
If the first byte cannot be read for any reason other than end of
* file, then an IOException is thrown. In particular, an
* IOException 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 b
* 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
* -1 if there is no more data because the end of
* the stream has been reached.
*/
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);
// End-of-stream
if (pos <= pointer) {
return -1;
}
byte[] buf = (byte[])data.get((int)(pointer >> SECTOR_SHIFT));
int nbytes = Math.min(len, SECTOR_SIZE - (int)(pointer & SECTOR_MASK));
System.arraycopy(buf, (int)(pointer & SECTOR_MASK),
b, off, nbytes);
pointer += nbytes;
return nbytes;
}
}