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/*
Copyright (c) 2013, 2014, Oracle and/or its affiliates. All rights reserved.
The MySQL Connector/J is licensed under the terms of the GPLv2
<http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most MySQL Connectors.
There are special exceptions to the terms and conditions of the GPLv2 as it is applied to
this software, see the FOSS License Exception
<http://www.mysql.com/about/legal/licensing/foss-exception.html>.
This program 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; version 2
of the License.
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, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth
Floor, Boston, MA 02110-1301 USA
*/
package com.mysql.fabric;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;
/**
* A shard mapping with ranges defined by hashing key values. Lookups work essentially
* the same as in {@link RangeShardMapping} but strings are compared as opposed to ints.
*/
public class HashShardMapping extends ShardMapping {
private static class ReverseShardIndexSorter implements Comparator<ShardIndex> {
public int compare(ShardIndex i1, ShardIndex i2) {
return i2.getBound().compareTo(i1.getBound());
}
// singleton instance
public static final ReverseShardIndexSorter instance = new ReverseShardIndexSorter();
}
private static final MessageDigest md5Hasher;
static {
try {
md5Hasher = MessageDigest.getInstance("MD5");
} catch (java.security.NoSuchAlgorithmException ex) {
throw new ExceptionInInitializerError(ex);
}
}
public HashShardMapping(int mappingId, ShardingType shardingType, String globalGroupName, Set<ShardTable> shardTables, Set<ShardIndex> shardIndices) {
super(mappingId, shardingType, globalGroupName, shardTables, new TreeSet<ShardIndex>(ReverseShardIndexSorter.instance));
this.shardIndices.addAll(shardIndices);
}
@Override
protected ShardIndex getShardIndexForKey(String stringKey) {
String hashedKey = new BigInteger(/* unsigned/positive */1, md5Hasher.digest(stringKey.getBytes())).toString(16).toUpperCase();
// pad out to 32 digits
for (int i = 0; i < (32 - hashedKey.length()); ++i) {
hashedKey = "0" + hashedKey;
}
for (ShardIndex i : this.shardIndices) {
if (i.getBound().compareTo(hashedKey) <= 0) {
return i;
}
}
// default to the first (highest) bound,
// implementing wrapping
return this.shardIndices.iterator().next();
}
}