org.apache.xmlgraphics.image.codec.util.FileCacheSeekableStream Maven / Gradle / Ivy
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/*
* 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: FileCacheSeekableStream.java 1732018 2016-02-24 04:51:06Z gadams $ */
package org.apache.xmlgraphics.image.codec.util;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
/**
* A subclass of SeekableStream that may be used to wrap
* a regular InputStream. 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
* MemoryCacheSeekableStream class may be used instead.
*
* 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 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;
/** Next byte to be read. */
private long pointer;
/** True if we've encountered the end of the source stream. */
private boolean foundEOF;
/**
* Constructs a MemoryCacheSeekableStream that takes
* its source data from a regular InputStream.
* Seeking backwards is supported by means of an file cache.
*
*
An IOException 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 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 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, 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 true since all
* FileCacheSeekableStream 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("FileCacheSeekableStream0"));
}
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.
* @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 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.
* @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(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();
}
}