org.jgrasstools.gears.io.disktree.DiskTreeReader Maven / Gradle / Ivy
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/*
* This file is part of JGrasstools (http://www.jgrasstools.org)
* (C) HydroloGIS - www.hydrologis.com
*
* JGrasstools is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see .
*/
package org.jgrasstools.gears.io.disktree;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.RandomAccessFile;
import com.vividsolutions.jts.JTSVersion;
import com.vividsolutions.jts.geom.Geometry;
import com.vividsolutions.jts.index.strtree.STRtree;
/**
* Reader for the Sort-Tile-Recursive disk index.
*
* @author Andrea Antonello (www.hydrologis.com)
* @see IDiskTree
*/
public class DiskTreeReader implements IDiskTree {
private final String path;
private STRtree indexObj;
private RandomAccessFile raf = null;
/**
* Constructor.
*
* @param path the path from which to read.
*/
public DiskTreeReader( String path ) {
this.path = path;
}
/**
* Reads the {@link STRtree} object from the file.
*
* @return the quadtree, holding envelops and geometry positions in the file.
* @throws Exception
*/
public STRtree readIndex() throws Exception {
File file = new File(path);
raf = new RandomAccessFile(file, "r");
raf.seek(6L);
checkVersions();
long position = INDEX_ADDRESS_POSITION;
raf.seek(position);
long indexAddress = raf.readLong();
position = INDEX_ADDRESS_POSITION + INDEX_ADDRESS_SIZE;
raf.seek(position);
long indexSize = raf.readLong();
raf.seek(indexAddress);
byte[] indexBytes = new byte[(int) indexSize];
int read = raf.read(indexBytes);
if (read != indexSize) {
throw new IOException();
}
ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(indexBytes));
indexObj = (STRtree) in.readObject();
return indexObj;
}
private void checkVersions() throws IOException {
int fileMajor = raf.readInt();
int fileMinor = raf.readInt();
int currMajor = JTSVersion.MAJOR;
int currMinor = JTSVersion.MINOR;
if (fileMajor != currMajor || fileMinor != currMinor) {
System.out
.println("Warning, the current used JTS version differs from the one used to create the file. Unexpected results may occurr.");
}
}
/**
* Reads a single geomtry, using the info from the quadtree read in {@link #readIndex()}.
*
* @param position the position of the geom to read.
* @param size the size of the geom to read.
* @return the read geometry.
* @throws Exception
*/
public Geometry pickGeometry( long position, long size ) throws Exception {
byte[] geomBytes = new byte[(int) size];
raf.seek(position);
raf.read(geomBytes);
ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(geomBytes));
return (Geometry) in.readObject();
}
/**
* Closes the filehandle.
*
* @throws IOException
*/
public void close() throws IOException {
raf.close();
}
}