准备
1. 以Hibernate Shards 数据的水平、垂直切割（一）- Hibernate测试环境的项目为基础
2. Hibernate Shards使用了commons logging，下载个项目最新的release版本。这里用的版本为1.1.1
3. 在Hibernate Shards 数据的水平、垂直切割（一）- Hibernate测试环境中，我们在mysql中建立了一个hbshards数据库，为了测试shards再建立一个hbshards2的数据库，contact表的结构一样
4. 将Hibernate Shards发布包中的hibernate-shards.jar放到lib目录
    项目引用添加hibernate-shards.jar
    将commons logging发布包中的commons-logging-1.1.1.jar放到lib目录
    CLASSPATH中添加hibernate-shards.jar、commons-logging-1.1.1.jar

Hibernate Shards测试项目
出于结构上的简单考虑，定义一个ShardableEntity的接口，让ContactEntity实现这个接口:

public interface ShardableEntity {public String getIdentifier();
}
public class ContactEntity implements ShardableEntity {public String getIdentifier(){return this._id;}//other code omitted is the same with previous post
}

映射文件ContactEntity.hbm.xml与上一篇文章中的一样
因为我们需要将contact的数据以切片的形式存入2个数据库中，因此需要配置这2个数据库的信息。Hibernate Shards通过定义2个hibernate的配置文件解决这个问题:
shard0.hibernate.cfg.xml:

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory><property name="connection.driver_class">com.mysql.jdbc.Driver</property><property name="connection.url">jdbc:mysql://localhost/hbshards</property><property name="connection.username">root</property><property name="connection.password">dev</property><property name="connection.pool_size">10</property><property name="show_sql">true</property><property name="dialect">org.hibernate.dialect.MySQLInnoDBDialect</property><property name="hbm2ddl.auto">validate</property><property name="hibernate.connection.shard_id">0</property><property name="hibernate.shard.enable_cross_shard_relationship_checks">false</property><mapping resource="ContactEntity.hbm.xml" />
</session-factory>
</hibernate-configuration>

shard1.hibernate.cfg.xml:

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory><property name="connection.driver_class">com.mysql.jdbc.Driver</property><property name="connection.url">jdbc:mysql://localhost/hbshards2</property><property name="connection.username">root</property><property name="connection.password">dev</property><property name="dialect">org.hibernate.dialect.MySQLInnoDBDialect</property><property name="hibernate.connection.shard_id">1</property><property name="hibernate.shard.enable_cross_shard_relationship_checks">false</property>
</session-factory>
</hibernate-configuration>

其中shard0.hibernate.cfg.xml作为主要的配置文件，针对每个shard创建的SessionFactory对象，除了数据库连接信息的配置之外，都来自shard0.hibernate.cfg.xml
针对其他每个shard创建的SessionFactory，数据库连接信息从相应的配置文件（例如shard1.hibernate.cfg.xml）中读取，读取的内容包括connection.url、connection.username、connection.password、connection.datasource。为了hibernate加载其他shard的配置文件时不抛异常，在其他shard的配置文件中我们还是把必要的配置属性写上去了
hibernate.connection.shard_id属性为每个shard定义一个id，必须有一个shard_id为0的shard，其他的shard_id可以定义为任意整数

我们假定contact的id都是由数字组成的一个8位长度的字符串
对contact的切割策略简单定义为: contact id第一个字符为0-4的存入shard0中，为5-9的存入shard1中
为了实现这一策略，我们需要实现hibernate shards的2个接口
ShardResolutionStrategy接口的实现:

import java.util.List;
import java.util.ArrayList;
import org.hibernate.shards.strategy.resolution.ShardResolutionStrategy;
import org.hibernate.shards.strategy.selection.ShardResolutionStrategyData;
import org.hibernate.shards.ShardId;
/** a simple ShardResolutionStrategy implementation for our ContactEntity*/
public class MyShardResolutionStrategy implements ShardResolutionStrategy {private List<ShardId> _shardIds;public MyShardResolutionStrategy(List<ShardId> shardIds){this._shardIds = shardIds;}public List selectShardIdsFromShardResolutionStrategyData(ShardResolutionStrategyData arg0){List ids = new ArrayList();String id = (String)arg0.getId();if(id==null || id.isEmpty()) ids.add(this._shardIds.get(0));else{//our shard selection is identified by the //first char(number) in contact id//0-4 => shards0, 5-9 => shards1Integer i = new Integer(id.substring(0, 1));ids.add(this._shardIds.get(i/5));}return ids;}
}

ShardSelectionStrategy接口的实现:

import java.util.List;
import org.hibernate.shards.ShardId;
import org.hibernate.shards.strategy.selection.ShardSelectionStrategy;
/** a simple ShardSelectionStrategy implementation for our ContactEntity*/
public class MyShardSelectionStrategy implements ShardSelectionStrategy {private List<ShardId> _shardIds;public MyShardSelectionStrategy(List<ShardId> shardIds){this._shardIds=shardIds;}public ShardId selectShardIdForNewObject(Object obj) {if(obj instanceof ShardableEntity) {String id = ((ShardableEntity)obj).getIdentifier();if(id==null || id.isEmpty()) return this._shardIds.get(0);Integer i = new Integer(id.substring(0, 1));//our shard selection is identified by the //first char(number) in contact id//0-4 => shards0, 5-9 => shards1return this._shardIds.get(i/5);}//for non-shardable entities we just use shard0return this._shardIds.get(0);}
}

接下来就是怎么使用hibernate shards的测试代码了:

import java.util.Iterator;
import java.util.List;
import java.util.ArrayList;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.shards.*;
import org.hibernate.shards.cfg.*;
import org.hibernate.shards.strategy.*;
import org.hibernate.shards.strategy.access.*;
import org.hibernate.shards.strategy.resolution.*;
import org.hibernate.shards.strategy.selection.*;

public class Main {public static void main(String[] args) {HibernateShardsTest(args);}private static SessionFactory createSessionFactory() {//加载主配置文件，为每个shard创建SessionFactory对象时将//以他作为原型Configuration prototypeCfg = new Configuration().configure("shard0.hibernate.cfg.xml");//每个shard的配置文件List<ShardConfiguration> shardCfgs = new ArrayList<ShardConfiguration>();shardCfgs.add(buildShardConfig("shard0.hibernate.cfg.xml"));shardCfgs.add(buildShardConfig("shard1.hibernate.cfg.xml"));//数据切片策略的工厂对象ShardStrategyFactory strategyFactory = buildShardStrategyFactory();ShardedConfiguration shardedConfig = new ShardedConfiguration(prototypeCfg, shardCfgs, strategyFactory);//返回一个ShardedSessionFactory对象return shardedConfig.buildShardedSessionFactory();}private static ShardStrategyFactory buildShardStrategyFactory() {ShardStrategyFactory factory = new ShardStrategyFactory() {//测试用的自定义数据切片策略的工厂类public ShardStrategy newShardStrategy(List<ShardId> shardIds) {ShardSelectionStrategy ss = new MyShardSelectionStrategy(shardIds);ShardResolutionStrategy rs = new MyShardResolutionStrategy(shardIds);ShardAccessStrategy as = new SequentialShardAccessStrategy();return new ShardStrategyImpl(ss, rs, as);}};return factory;}private static ShardConfiguration buildShardConfig(String configFile) {Configuration config = new Configuration().configure(configFile);return new ConfigurationToShardConfigurationAdapter(config);}private static void HibernateShardsTest(String[] args){String loginId = "RicCC@cnblogs.com";String password = "123";if(args!=null && args.length==2){loginId = args[0];password = args[1];}SessionFactory factory = null;try{factory = createSessionFactory();ShardsTestCreate(factory);ShardsTestLogin(factory, loginId, password);ShardsTestDelete(factory);}catch(Exception e){System.out.println(e.getMessage());e.printStackTrace();}finally{if(factory!=null) factory.close();}}private static void ShardsTestCreate(SessionFactory factory){Session session = null;Transaction transaction = null;System.out.println("===Create Contacts===");try{session = factory.openSession();transaction = session.beginTransaction();            session.save(new ContactEntity("01111111","RicCC@cnblogs.com", "123", "Richie", "RicCC@cnblogs.com"));session.save(new ContactEntity("91111111","a@cnblogs.com", "123", "AAA", "a@cnblogs.com"));session.save(new ContactEntity("81111111","b@cnblogs.com", "123", "BBB", "b@cnblogs.com"));session.save(new ContactEntity("31111111","c@cnblogs.com", "123", "CCC", "c@cnblogs.com"));transaction.commit();}catch(Exception e){if(transaction!=null) transaction.rollback();System.out.println(e.getMessage());e.printStackTrace();}finally{if(session!=null) session.close();}}private static void ShardsTestLogin(SessionFactory factory, String loginId, String password){Session session = null;ContactEntity c = null;System.out.println("\n===Login Test===");try{session = factory.openSession();List contacts = session.createQuery("from ContactEntity where LoginId=:loginId").setString("loginId", loginId).list();if(contacts.isEmpty())System.out.println("Contact \"" + loginId + "\" not found!");else{c = (ContactEntity)contacts.get(0);if(c.getPassword().equals(password))System.out.println("Contact \"" + loginId + "\" login successful");else System.out.println("Password is incorrect (should be: "+ c.getPassword() + ", but is: " + password + ")");}System.out.println("\n===Get Contact by Id===");c = (ContactEntity)session.get(ContactEntity.class, "81111111");System.out.println(c.toString());c = (ContactEntity)session.get(ContactEntity.class, "31111111");System.out.println(c.toString());}catch(Exception e){System.out.println(e.getMessage());e.printStackTrace();}finally{if(session!=null) session.close();}}private static void ShardsTestDelete(SessionFactory factory){Session session = null;Transaction transaction = null;System.out.println("\n===Delete Contacts===");try{session = factory.openSession();transaction = session.beginTransaction();List contacts = session.createQuery("from ContactEntity").list();Iterator it = contacts.iterator();while(it.hasNext()){session.delete(it.next());}transaction.commit();}catch(Exception e){if(transaction!=null) transaction.rollback();System.out.println(e.getMessage());e.printStackTrace();}finally{if(session!=null) session.close();}}
}

项目结构图:
    

运行测试
用Eclipse编译class文件，将生成的所有class文件以及相关的配置、映射文件 拷贝到lib目录中，运行Main.class结果如下:
D:\Work\research\Java\Hibernate-Test\lib>java Main
===Create Contacts===
Hibernate: insert into CONTACT (EMAIL, NAME, LOGIN_ID, PASSWORD, ID) values (?,?, ?, ?, ?)
Hibernate: insert into CONTACT (EMAIL, NAME, LOGIN_ID, PASSWORD, ID) values (?,?, ?, ?, ?)
Hibernate: insert into CONTACT (EMAIL, NAME, LOGIN_ID, PASSWORD, ID) values (?,?, ?, ?, ?)
Hibernate: insert into CONTACT (EMAIL, NAME, LOGIN_ID, PASSWORD, ID) values (?,?, ?, ?, ?)

===Login Test===
Hibernate: select contactent0_.ID as ID0_, contactent0_.EMAIL as EMAIL0_, contactent0_.NAME as NAME0_, contactent0_.LOGIN_ID as LOGIN4_0_, contactent0_.PASSWORD as PASSWORD0_ from CONTACT contactent0_ where contactent0_.LOGIN_ID=?
Hibernate: select contactent0_.ID as ID0_, contactent0_.EMAIL as EMAIL0_, contactent0_.NAME as NAME0_, contactent0_.LOGIN_ID as LOGIN4_0_, contactent0_.PASSWORD as PASSWORD0_ from CONTACT contactent0_ where contactent0_.LOGIN_ID=?
Contact "RicCC@cnblogs.com" login successful

===Get Contact by Id===
Hibernate: select contactent0_.ID as ID0_0_, contactent0_.EMAIL as EMAIL0_0_, contactent0_.NAME as NAME0_0_, contactent0_.LOGIN_ID as LOGIN4_0_0_, contactent0_.PASSWORD as PASSWORD0_0_ from CONTACT contactent0_ where contactent0_.ID=?
{ Id="81111111", LoginId="b@cnblogs.com", Name="BBB", EMail="b@cnblogs.com" }
Hibernate: select contactent0_.ID as ID0_0_, contactent0_.EMAIL as EMAIL0_0_, contactent0_.NAME as NAME0_0_, contactent0_.LOGIN_ID as LOGIN4_0_0_, contactent0_.PASSWORD as PASSWORD0_0_ from CONTACT contactent0_ where contactent0_.ID=?
{ Id="31111111", LoginId="c@cnblogs.com", Name="CCC", EMail="c@cnblogs.com" }

===Delete Contacts===
Hibernate: select contactent0_.ID as ID0_, contactent0_.EMAIL as EMAIL0_, contactent0_.NAME as NAME0_, contactent0_.LOGIN_ID as LOGIN4_0_, contactent0_.PASSWORD as PASSWORD0_ from CONTACT contactent0_
Hibernate: select contactent0_.ID as ID0_, contactent0_.EMAIL as EMAIL0_, contactent0_.NAME as NAME0_, contactent0_.LOGIN_ID as LOGIN4_0_, contactent0_.PASSWORD as PASSWORD0_ from CONTACT contactent0_
Hibernate: delete from CONTACT where ID=?
Hibernate: delete from CONTACT where ID=?
Hibernate: delete from CONTACT where ID=?
Hibernate: delete from CONTACT where ID=?

1. 通过id加载实体的时候，hibernate shards使用ShardSelectionStrategy来决定应当从哪个shard加载数据
2. 新增数据的时候，hibernate shards使用ShardResolutionStrategy来决定应当将数据insert到哪个shard中
    这里为什么不能使用ShardSelectionStrategy呢？因为与id的生成机制相关，比如说可以让数据库来生成id（hibernate中的native方式），例如自增id，在shard的应用场景下可以简单的给每个shard一个起止范围，只是在insert数据的时候必须通过特定的算法决定将数据insert到哪个shard中，这样的情况下ShardSelectionStrategy是无法运用的。而对于assigned等类似的id生成机制，还是可以运用ShardSelectionStrategy策略的
3. 执行hql或者Criteria查询的时候，则使用ShardAccessStrategy从shard中查询数据
    上面示例中的buildShardStrategyFactory方法中，我们使用了hibernate shards项目提供的SequentialShardAccessStrategy策略，这个策略在所有shards中逐个执行查询语句，然后对各个结果进行合并

基于上面几点，我们可以对上面测试运行后的输出做出解释了:
两个使用了hql的地方，都产生了两次sql查询，这是因为使用了SequentialShardAccessStrategy缘故，他从我们定义的两个shard中分别执行sql查询，合并结果集返回给调用者

把测试代码中的删除语句注释掉，运行测试后查询数据库，可以确认数据都是正确的insert在相应的shard中的

总结
上面演示了hibernate shards的基本用法，总体来看使用上非常简单，只需要针对实施shard的实体使用hibernate shards提供的ShardedSessionFactory即可
使用hibernate shards也存在一些限制，但大部分都是使用shards后的一些设计要求，或者是目前的it技术背景下对shards设计上的约束，在后面一篇中再详细整理一下这方面内容
文中使用的测试项目源文件在这里: 下载。引用到的jar文件需要从相关项目网站去下载