mybatis如何配置使用多個數據源？

一、資料庫連線properties配置檔案，兩個資料來源的地址：

hd.jdbc.driverClassName=com.mysql.jdbc.Driver
hd.jdbc.url=jdbc:mysql://127.0.0.1::3306/hd?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true
hd.jdbc.username=root
hd.jdbc.password=root

ho.jdbc.driverClassName=com.mysql.jdbc.Driver
ho.jdbc
 
.url=jdbc:mysql://127.0.0.1:3306/ho?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true
ho.jdbc.username=root
ho.jdbc.password=root

二、mybatis配置檔案，配置兩個environment：

<?xml version="1.0" encoding="UTF-8"?> 
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-config.dtd">
 

<configuration>
    <properties resource="mybatis/jdbc.properties"/>
    <environments default="HO">
        <environment id="HD">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="${hd.jdbc.driverClassName}"
 
 />
                <property name="url" value="${hd.jdbc.url}" />
                <property name="username" value="${hd.jdbc.username}" />
                <property name="password" value="${hd.jdbc.password}" />
            </dataSource>
        </environment>
        <environment id="HO">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="${ho.jdbc.driverClassName}" />
                <property name="url" value="${ho.jdbc.url}" />
                <property name="username" value="${ho.jdbc.username}" />
                <property name="password" value="${ho.jdbc.password}" />
            </dataSource>
        </environment>
    </environments>
</configuration>

三、獲取SqlSessionFactory，獲取Mapper代理，便於在執行完Mapper方法後關閉SqlSession。
SqlSessionFactory的獲取

/**
 * 根據mybatis.xml中配置的不同的environment建立對應的SqlSessionFactory
 * @author boyce
 * @version 2014-3-27
 */
public final class DataSourceSqlSessionFactory {
    private static final String CONFIGURATION_PATH = "mybatis/mybatis.xml";

    private static final Map<DataSourceEnvironment, SqlSessionFactory> SQLSESSIONFACTORYS 
        = new HashMap<DataSourceEnvironment, SqlSessionFactory>();

    /**
     * 根據指定的DataSourceEnvironment獲取對應的SqlSessionFactory
     * @param environment 資料來源environment
     * @return SqlSessionFactory
     */
    public static SqlSessionFactory getSqlSessionFactory(DataSourceEnvironment environment) {

        SqlSessionFactory sqlSessionFactory = SQLSESSIONFACTORYS.get(environment);
        if (ObjectUtils.isNotNull(sqlSessionFactory))
            return sqlSessionFactory;
        else {
            InputStream inputStream = null;
            try {
                inputStream = Resources.getResourceAsStream(CONFIGURATION_PATH);
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream, environment.name());

                logger.info("Get {} SqlSessionFactory successfully.", environment.name());
            } catch (IOException e) {
                logger.warn("Get {} SqlSessionFactory error.", environment.name());
                logger.error(e.getMessage(), e);
            }
            finally {
                IOUtils.closeQuietly(inputStream);
            }

            SQLSESSIONFACTORYS.put(environment, sqlSessionFactory);
            return sqlSessionFactory;
        }
    }

    /**
     * 配置到Configuration.xml檔案中的資料來源的environment的列舉描述
     * @author boyce
     * @version 2014-3-27
     */
    public static enum DataSourceEnvironment {
        HD,
        HO;
    }
}

定義一個統一的Mapper標識介面，每一個具體的Mapper介面繼承該介面：

/**
 * Mapper Interface
 * @author boyce
 * @version 2014-3-28
 */
public interface Mapper {
}

定義一個Mapper代理工廠：

/**
 * Mapper Factory
 * @author boyce
 * @version 2014-3-28
 */
public final class MapperFactory {
    private static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(MapperFactory.class);
    /**
     * Create a mapper of environment by Mapper class
     * @param clazz Mapper class 
     * @param environment A datasource environment
     * @return a Mapper instance
     */
    @SuppressWarnings("unchecked")
    public static <T> T createMapper(Class<? extends Mapper> clazz, DataSourceEnvironment environment) {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory(environment);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        Mapper mapper = sqlSession.getMapper(clazz);
        return (T)MapperProxy.bind(mapper, sqlSession);
    }

    /**
     * Mapper Proxy 
     * executing mapper method and close sqlsession
     * @author boyce
     * @version 2014-4-9
     */
    private static class MapperProxy implements InvocationHandler {
        private Mapper mapper;
        private SqlSession sqlSession;

        private MapperProxy(Mapper mapper, SqlSession sqlSession) {
            this.mapper = mapper;
            this.sqlSession = sqlSession;
        }

        @SuppressWarnings("unchecked")
        private static Mapper bind(Mapper mapper, SqlSession sqlSession) {
            return (Mapper) Proxy.newProxyInstance(mapper.getClass().getClassLoader(),
                    mapper.getClass().getInterfaces(), new MapperProxy(mapper, sqlSession));
        }

        /**
         * execute mapper method and finally close sqlSession
         */
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            Object object = null;
            try {
                object = method.invoke(mapper, args);
            } catch(Exception e) {
                e.printStackTrace();
                logger.error(e.getMessage(), e);
            } finally {
                sqlSession.close();
            }
            return object;
        }
    }

    //Get a SqlSessionFactory of environment
    private static SqlSessionFactory getSqlSessionFactory(DataSourceEnvironment environment) {
        return DataSourceSqlSessionFactory.getSqlSessionFactory(environment);
    }

大功告成，客戶端使用：

UserMapper mapper = MapperFactory.createMapper(UserMapper.class, DataSourceEnvironment.HD);
User user = mapper.getUserById(162L);
System.out.println(user);

OK，到此基本上所有的工作就完成了，以上的方式就可以支援多個數據源了。
但是程式碼還不夠優雅，以上程式碼我們發現DataSourceEnvironment這個列舉變數在客戶端，MapperFactory以及DataSourceEnvironment
中傳來傳去，我們應該儘量減少一個類對外界類的耦合，也就是不符合Java程式設計原則中的迪米特法則。
好了，那我們來改良一下。
將MapperFactory設計成列舉策略模式：

/**
 * Mapper Creator
 * @author boyce
 * @version 2014-3-28
 */
public enum MapperFactory {

    HD {
        private SqlSessionFactory sqlSessionFactory;

        @Override
        public <T> T createMapper(Class<? extends Mapper> clazz) {
            return createMapper(clazz, this);
        }

        @Override
        protected void createSqlSessionFactory() {
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream, this.name());
        }

        @Override
        public SqlSessionFactory getSqlSessionFactory() {
            return sqlSessionFactory;
        }

    },
    HO {
        private SqlSessionFactory sqlSessionFactory;
        @Override
        public <T> T createMapper(Class<? extends Mapper> clazz) {
            return createMapper(clazz, this);
        }

        @Override
        protected void createSqlSessionFactory() {
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream, this.name());
        }

        @Override
        public SqlSessionFactory getSqlSessionFactory() {
            return sqlSessionFactory;
        }
    };

    /**
     * Create a mapper of environment by Mapper class
     * @param clazz Mapper class 
     * @param environment A datasource environment
     * @return a Mapper instance
     */
    public abstract <T> T createMapper(Class<? extends Mapper> clazz);

    /**
     * Create SqlSessionFactory of environment
     */
    protected abstract void createSqlSessionFactory();

    /**
     * get SqlSessionFactory
     */
    public abstract SqlSessionFactory getSqlSessionFactory();

    private static InputStream inputStream = null;
    static {
        try {
            inputStream = Resources.getResourceAsStream("mybatis/mybatis.xml");
            HO.createSqlSessionFactory();
            HD.createSqlSessionFactory();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            IOUtils.closeQuietly(inputStream);
        }
    }

    @SuppressWarnings("unchecked")
    private static <T> T createMapper(Class<? extends Mapper> clazz, MapperFactory MapperFactory) {
        SqlSession sqlSession = MapperFactory.getSqlSessionFactory().openSession();
        Mapper mapper = sqlSession.getMapper(clazz);
        return (T)MapperProxy.bind(mapper, sqlSession);
    }

    /**
     * Mapper Proxy 
     * executing mapper method and close sqlsession
     * @author boyce
     * @version 2014-4-9
     */
    private static class MapperProxy implements InvocationHandler {
        private Mapper mapper;
        private SqlSession sqlSession;

        private MapperProxy(Mapper mapper, SqlSession sqlSession) {
            this.mapper = mapper;
            this.sqlSession = sqlSession;
        }

        private static Mapper bind(Mapper mapper, SqlSession sqlSession) {
            return (Mapper) Proxy.newProxyInstance(mapper.getClass().getClassLoader(),
                    mapper.getClass().getInterfaces(), new MapperProxy(mapper, sqlSession));
        }

        /**
         * execute mapper method and finally close sqlSession
         */
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            Object object = null;
            try {
                object = method.invoke(mapper, args);
            } catch(Exception e) {
                e.printStackTrace();
            } finally {
                sqlSession.close();
            }
            return object;
        }
    }

}

客戶端使用場景：

UserMapper mapper = MapperFactory.HO.createMapper(UserMapper.class);
User user = mapper.getUserById(162L);
System.out.println(user);

=============以下非轉摘，個人經驗================

可改進的地方

1、MapperProxy中針對每一次的呼叫都進行close，比較浪費，可以考慮threadlocal來設定
2、對於複雜的事務可以採用如下方法進行控制：

SqlSession sqlSession = MapperFactory.xxxSqlSessionFactory().openSession(false);
//根據業務需要來獲得對應的session,手動控制事務
try{
    //業務操作1
    //業務操作2
    sqlSession.commit();
}catch(Exception ex){
    sqlSession.rollback();
    isSucess = false;
}finally{
    if (sqlSession != null) {
        sqlSession.close();
    }
}

3、每個db都在配置檔案中，如果涉及到分庫和分分表，建議在負載均衡類中啟動，從資料庫彙總獲得對應的分庫策略，然後將SqlSessionFactory()設定完成