/**
* 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.jena.riot.lang;
import java.security.MessageDigest ;
import java.security.NoSuchAlgorithmException ;
import java.util.UUID ;
import org.apache.jena.atlas.lib.Bytes ;
import org.apache.jena.atlas.lib.Cache ;
import org.apache.jena.atlas.lib.CacheFactory ;
import org.apache.jena.atlas.lib.InternalErrorException ;
import org.apache.jena.atlas.lib.cache.Getter ;
import com.hp.hpl.jena.graph.Node ;
import com.hp.hpl.jena.graph.NodeFactory ;
import com.hp.hpl.jena.rdf.model.AnonId ;
/** Allocate bnode labels using a per-run seed and the label presented.
* <p>
* This is the most scalable, always legal allocator.
* <p>
* New allocators must be created per parser run, or .reset() called.
* These are fed to a digest to gve a bit string, (currently MD5, to get a 128bit bit string)
* that is used to form a bNode AnonId of hex digits.
* <p>
* In addition there is a cache of label->node allocations,
* using the natural tendendency to locality in a database dump.
* (subject bNodes, bNodes in lists and other datavalues structures like
* unit values).
* <p>
* Not thread safe.
*/
public class BlankNodeAllocatorHash implements BlankNodeAllocator
{
private static String DigestAlgorithm = "MD5" ;
private static int CacheSize = 1000 ;
private MessageDigest mDigest ;
private byte[] seedBytes ;
private byte[] counterBytes = new byte[10] ; // long+2 bytes to distinguish from UTF-8 bytes.
private Cache<String, Node> cache ;
private long counter = 0 ;
public BlankNodeAllocatorHash()
{
reset() ;
try { mDigest = MessageDigest.getInstance(DigestAlgorithm) ; }
catch (NoSuchAlgorithmException e) { throw new InternalErrorException("failed to create message digest", e) ; }
Getter<String, Node> getter = new Getter<String, Node>() {
@Override public Node get(String key) { return alloc(key) ; }
} ;
Cache<String, Node> cache1 = CacheFactory.createCache(CacheSize) ;
cache = CacheFactory.createCacheWithGetter(cache1, getter) ;
}
@Override
public void reset()
{
UUID seed = UUID.randomUUID() ;
seedBytes = new byte[128/8] ;
Bytes.setLong(seed.getMostSignificantBits(), seedBytes, 0) ;
Bytes.setLong(seed.getLeastSignificantBits(), seedBytes, 8) ;
}
@Override
public Node alloc(String label)
{
return alloc(Bytes.string2bytes(label)) ;
}
@Override
public Node create()
{
counter++ ;
// Make illegal string bytes so can't clash with alloc(String)
counterBytes[0] = 0 ;
counterBytes[1] = 0 ;
Bytes.setLong(counter, counterBytes, 2) ;
return alloc(counterBytes) ;
}
private Node alloc(byte[] labelBytes)
{
mDigest.update(seedBytes) ;
mDigest.update(labelBytes) ;
byte[] bytes = mDigest.digest() ; // resets
String hexString = Bytes.asHexLC(bytes) ;
return NodeFactory.createAnon(new AnonId(hexString)) ;
}
}