Spring+iBatis多数据源的动态配置方案

在仅使用ibatis时，多数据源简直就是梦魇，每多一个数据源就需要多一份sql-map-config配置文件。

采用spring的AbstractRoutingDataSource就可以简单的解决这个问题。

AbstractRoutingDataSource实现了javax.sql.DataSource接口，因此可以理解为一个虚拟的动态DataSource，在需要的时候根据上下文Context动态决定使用哪个数据源。

下面是一个完整的配置：

<beans xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:aop="http://www.springframework.org/schema/aop"
        xmlns:tx="http://www.springframework.org/schema/tx"
        xmlns:jee="http://www.springframework.org/schema/jee"
        xsi:schemaLocation="
            http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
            http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd
            http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd
            http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-2.5.xsd">


    <!-- ========================= GENERAL DEFINITIONS ========================= -->
    <jee:jndi-lookup id="ds0" jndi-name="jdbc/ds0"/>
    <jee:jndi-lookup id="ds1" jndi-name="jdbc/ds1"/>
    <jee:jndi-lookup id="ds2" jndi-name="jdbc/ds2"/>

    <bean id="dataSource" class="com.xxx.xxx.util.DynamicDataSource">
            <property name="targetDataSources">
               <map key-type="java.lang.String">
                  <entry key="0" value-ref="ds0"/>
                  <entry key="1" value-ref="ds1"/>
                  <entry key="2" value-ref="ds2"/>
               </map>
            </property>
            <property name="defaultTargetDataSource" ref="1"/>
    </bean>
        <!-- SqlMap setup for iBATIS Database Layer -->
    <bean id="sqlMapClient" class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
        <property name="dataSource" ref="dataSource"/>
        <property name="configLocation" value="classpath:com/xxx/xxx/dao/sqlmap/sql-map-config.xml"/>
    </bean>
        <bean id="testDAO" class="com.xxx.xxx.dao.impl.TestDAO">
        <property name="sqlMapClient" ref="sqlMapClient"/>
    </bean>
        <bean id="testService" class="com.xxx.xxx.service.impl.TestService">
        <property name="testDAO" ref="testDAO"/>
    </bean>
</beans>

其核心是DynamicDataSource，代码如下

package com.xxx.xxx.util;

import org.apache.log4j.Logger;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

public class DynamicDataSource extends AbstractRoutingDataSource {

    static Logger log = Logger.getLogger("DynamicDataSource");
    @Override
    protected Object determineCurrentLookupKey() {
        // TODO Auto-generated method stub
        return DbContextHolder.getDbType();
    }

}

上下文DbContextHolder为一线程安全的ThreadLocal，如下

package com.xxx.xxx.util;

public class DbContextHolder {
    private static final ThreadLocal contextHolder = new ThreadLocal();

    public static void setDbType(String dbType) {
        contextHolder.set(dbType);
    }

    public static String getDbType() {
        return (String) contextHolder.get();
    }

    public static void clearDbType() {
        contextHolder.remove();
    }
}

sql-map-config.xml如下

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE sqlMapConfig PUBLIC "-//iBATIS.com//DTD SQL Map Config 2.0//EN"
        "http://www.ibatis.com/dtd/sql-map-config-2.dtd">

<sqlMapConfig>

    <sqlMap resource="com/xxx/xxx/dao/sqlmap/Object.xml"/>

</sqlMapConfig>

这样在调用service之前只需要设置一下上下文即可调用相应的数据源，如下：

DbContextHolder.setDbType("2");
//execute services
//.........

dao如下

package com.xxx.xxx.dao.impl;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.log4j.Logger;
import org.springframework.orm.ibatis.support.SqlMapClientDaoSupport;

import com.xxx.xxx.vo.TestObj;

public class TestDAO extends SqlMapClientDaoSupport implements ITestDAO {

    static Logger log = Logger.getLogger(TestDAO.class);

    public TestObj getTestObj(String objID) throws Exception {
        return (TestObj) getSqlMapClientTemplate().queryForObject("getTestObj", objID);
    }
}