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The Apache PDFBox library is an open source Java tool for working with PDF documents.
/*
* 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.
*/
package org.apache.pdfbox.io;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.util.LinkedHashMap;
import java.util.Map;
/**
* Provides {@link InputStream} access to portions of a file combined with
* buffered reading of content. Start of next bytes to read can be set via seek
* method.
*
* File is accessed via {@link RandomAccessFile} and is read in byte chunks
* which are cached.
*
* @author Timo Boehme (timo.boehme at ontochem com)
*/
public class RandomAccessBufferedFileInputStream
extends InputStream implements RandomAccessRead
{
private int pageSizeShift = 12;
private int pageSize = 1 << pageSizeShift;
private long pageOffsetMask = -1L << pageSizeShift;
private int maxCachedPages = 1000;
private byte[] lastRemovedCachePage = null;
/** Create a LRU page cache. */
private final LinkedHashMap pageCache =
new LinkedHashMap( maxCachedPages, 0.75f, true )
{
private static final long serialVersionUID = -6302488539257741101L;
@Override
protected boolean removeEldestEntry( Map.Entry _eldest )
{
final boolean doRemove = size() > maxCachedPages;
if (doRemove)
{
lastRemovedCachePage = _eldest.getValue();
}
return doRemove;
}
};
private long curPageOffset = -1;
private byte[] curPage = new byte[pageSize];
private int offsetWithinPage = 0;
private final RandomAccessFile raFile;
private final long fileLength;
private long fileOffset = 0;
// ------------------------------------------------------------------------
/** Create input stream instance for given file. */
public RandomAccessBufferedFileInputStream( File _file )
throws FileNotFoundException, IOException
{
raFile = new RandomAccessFile(_file, "r");
fileLength = _file.length();
seek(0);
}
// ------------------------------------------------------------------------
/**
* Returns offset in file at which next byte would be read.
*
* @deprecated use {@link #getPosition()} instead
*/
public long getFilePointer()
{
return fileOffset;
}
// ------------------------------------------------------------------------
/** Returns offset in file at which next byte would be read. */
public long getPosition()
{
return fileOffset;
}
// ------------------------------------------------------------------------
/**
* Seeks to new position. If new position is outside of current page the new
* page is either taken from cache or read from file and added to cache.
*/
public void seek( final long newOffset ) throws IOException
{
final long newPageOffset = newOffset & pageOffsetMask;
if ( newPageOffset != curPageOffset )
{
byte[] newPage = pageCache.get( newPageOffset );
if ( newPage == null )
{
raFile.seek( newPageOffset );
newPage = readPage();
pageCache.put( newPageOffset, newPage );
}
curPageOffset = newPageOffset;
curPage = newPage;
}
offsetWithinPage = (int) ( newOffset - curPageOffset );
fileOffset = newOffset;
}
// ------------------------------------------------------------------------
/**
* Reads a page with data from current file position. If we have a
* previously removed page from cache the buffer of this page is reused.
* Otherwise a new byte buffer is created.
*/
private final byte[] readPage() throws IOException
{
byte[] page;
if ( lastRemovedCachePage != null )
{
page = lastRemovedCachePage;
lastRemovedCachePage = null;
}
else
{
page = new byte[pageSize];
}
int readBytes = 0;
while ( readBytes < pageSize )
{
int curBytesRead = raFile.read( page, readBytes, pageSize - readBytes);
if (curBytesRead < 0)
{
// EOF
break;
}
readBytes += curBytesRead;
}
return page;
}
// ------------------------------------------------------------------------
@Override
public int read() throws IOException
{
if ( fileOffset >= fileLength )
{
return -1;
}
if ( offsetWithinPage == pageSize )
{
seek( fileOffset );
}
fileOffset++;
return curPage[offsetWithinPage++] & 0xff;
}
// ------------------------------------------------------------------------
@Override
public int read( byte[] b, int off, int len ) throws IOException
{
if ( fileOffset >= fileLength )
{
return -1;
}
if ( offsetWithinPage == pageSize )
{
seek( fileOffset );
}
int commonLen = Math.min( pageSize - offsetWithinPage, len );
if ( ( fileLength - fileOffset ) < pageSize )
commonLen = Math.min( commonLen, (int) ( fileLength - fileOffset ) );
System.arraycopy( curPage, offsetWithinPage, b, off, commonLen );
offsetWithinPage += commonLen;
fileOffset += commonLen;
return commonLen;
}
// ------------------------------------------------------------------------
@Override
public int available() throws IOException
{
return (int) Math.min( fileLength - fileOffset, Integer.MAX_VALUE );
}
// ------------------------------------------------------------------------
@Override
public long skip( long n ) throws IOException
{
// test if we have to reduce skip count because of EOF
long toSkip = n;
if ( fileLength - fileOffset < toSkip )
{
toSkip = fileLength - fileOffset;
}
if ( ( toSkip < pageSize ) && ( ( offsetWithinPage + toSkip ) <= pageSize ) )
{
// we can skip within current page
offsetWithinPage += toSkip;
fileOffset += toSkip;
}
else
{
// seek to the page we will get after skipping
seek( fileOffset + toSkip );
}
return toSkip;
}
// ------------------------------------------------------------------------
public long length() throws IOException
{
return fileLength;
}
// ------------------------------------------------------------------------
@Override
public void close() throws IOException
{
raFile.close();
pageCache.clear();
}
}