001/* 002 * HA-JDBC: High-Availability JDBC 003 * Copyright (C) 2012 Paul Ferraro 004 * 005 * This program is free software: you can redistribute it and/or modify 006 * it under the terms of the GNU Lesser General Public License as published by 007 * the Free Software Foundation, either version 3 of the License, or 008 * (at your option) any later version. 009 * 010 * This program is distributed in the hope that it will be useful, 011 * but WITHOUT ANY WARRANTY; without even the implied warranty of 012 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 013 * GNU Lesser General Public License for more details. 014 * 015 * You should have received a copy of the GNU Lesser General Public License 016 * along with this program. If not, see <http://www.gnu.org/licenses/>. 017 */ 018package net.sf.hajdbc.balancer.random; 019 020import java.util.ArrayList; 021import java.util.Collections; 022import java.util.List; 023import java.util.Random; 024import java.util.Set; 025 026import net.sf.hajdbc.Database; 027import net.sf.hajdbc.balancer.AbstractSetBalancer; 028 029/** 030 * Balancer implementation whose {@link #next()} implementation returns a random database. 031 * The probability that a given database will be returned is: <em>weight / total-weight</em>. 032 * 033 * @author Paul Ferraro 034 * @param <D> either java.sql.Driver or javax.sql.DataSource 035 */ 036public class RandomBalancer<P, D extends Database<P>> extends AbstractSetBalancer<P, D> 037{ 038 private volatile List<D> databaseList; 039 040 private Random random = new Random(); 041 042 /** 043 * Constructs a new RandomBalancer 044 * @param databases 045 */ 046 public RandomBalancer(Set<D> databases) 047 { 048 super(databases); 049 050 int total = 0; 051 052 for (D database: databases) 053 { 054 total += database.getWeight(); 055 } 056 057 List<D> list = new ArrayList<D>(total); 058 059 for (D database: databases) 060 { 061 int weight = database.getWeight(); 062 for (int i = 0; i < weight; ++i) 063 { 064 list.add(database); 065 } 066 } 067 068 this.databaseList = list; 069 } 070 071 /** 072 * {@inheritDoc} 073 * @see net.sf.hajdbc.balancer.Balancer#next() 074 */ 075 @Override 076 public D next() 077 { 078 List<D> list = this.databaseList; 079 080 return !list.isEmpty() ? list.get(this.random.nextInt(list.size())) : this.primary(); 081 } 082 083 /** 084 * {@inheritDoc} 085 * @see net.sf.hajdbc.balancer.AbstractSetBalancer#added(net.sf.hajdbc.Database) 086 */ 087 @Override 088 protected void added(D database) 089 { 090 int weight = database.getWeight(); 091 092 if (weight > 0) 093 { 094 List<D> list = new ArrayList<D>(this.databaseList.size() + weight); 095 096 list.addAll(this.databaseList); 097 098 for (int i = 0; i < weight; ++i) 099 { 100 list.add(database); 101 } 102 103 this.databaseList = list; 104 } 105 } 106 107 /** 108 * {@inheritDoc} 109 * @see net.sf.hajdbc.balancer.AbstractSetBalancer#removed(net.sf.hajdbc.Database) 110 */ 111 @Override 112 protected void removed(D database) 113 { 114 int weight = database.getWeight(); 115 116 if (weight > 0) 117 { 118 List<D> list = new ArrayList<D>(this.databaseList.size() - weight); 119 120 int index = this.databaseList.indexOf(database); 121 122 list.addAll(this.databaseList.subList(0, index)); 123 list.addAll(this.databaseList.subList(index + weight, this.databaseList.size())); 124 125 this.databaseList = list; 126 } 127 } 128 129 /** 130 * {@inheritDoc} 131 * @see net.sf.hajdbc.balancer.AbstractSetBalancer#cleared() 132 */ 133 @Override 134 protected void cleared() 135 { 136 this.databaseList = Collections.emptyList(); 137 } 138}