mybatis用spring的动态数据源实现读写分离

一、环境：

　　三个mysql数据库。一个master，两个slaver。master写数据，slaver读数据。

二、原理：

　　借助Spring的 AbstractRoutingDataSource 这个抽象实现。我们要实现 determineCurrentLookupKey()这个方法来动态的选择使用哪个数据源操着数据库

public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean {

    protected abstract Object determineCurrentLookupKey();

}

三、实现步骤：

1、添加spring，mybatis，mysql相关的pom依赖。

2、写jdbc.properties，定义三个数据库。

jdbc.driver=com.mysql.jdbc.Driver

#master库
master.jdbc.url=jdbc:mysql://127.0.0.1:3306/master?characterEncoding=utf8
master.jdbc.user=root
master.jdbc.password=tiger
#slave 一 库
slave.one.jdbc.url=jdbc:mysql://127.0.0.1:3306/slave-one?characterEncoding=utf8
slave.one.jdbc.user=root
slave.one.jdbc.password=tiger
#slave 二 库
slave.two.jdbc.url=jdbc:mysql://127.0.0.1:3306/slave-two?characterEncoding=utf8
slave.two.jdbc.user=root
slave.two.jdbc.password=tiger

3、配置三个数据源，分别写到三个配置文件中。

datasources-master.xml、datasource-slave-one.xml和datasource-slave-two.xml三个文件都一样，这里就写一个

<!--master数据源，支持读写-->
    <bean id="dataSourceMaster" class="com.alibaba.druid.pool.DruidDataSource"
          init-method="init" destroy-method="close">
        <property name="driverClassName" value="${jdbc.driver}"/>
        <property name="url" value="${master.jdbc.url}"/>
        <property name="username" value="${master.jdbc.user}"/>
        <property name="password" value="${master.jdbc.password}"/>

        <property name="filters" value="stat"/>

        <property name="maxActive" value="20"/>
        <property name="initialSize" value="1"/>
        <property name="maxWait" value="60000"/>
        <property name="minIdle" value="1"/>

        <property name="timeBetweenEvictionRunsMillis" value="60000"/>
        <property name="minEvictableIdleTimeMillis" value="300000"/>

        <property name="validationQuery" value="SELECT 'x'"/>
        <property name="testWhileIdle" value="true"/>
        <property name="testOnBorrow" value="false"/>
        <property name="testOnReturn" value="false"/>
    </bean>

4、写spring的配置文件applicationContext.xml。

    <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations">
            <list>
                <value>classpath*:jdbc.properties</value>
            </list>
        </property>
        <property name="fileEncoding" value="UTF-8" />
        <property name= "ignoreResourceNotFound" value="false"/>
    </bean>

    <context:component-scan base-package="org.hope.lee"/>

    <aop:aspectj-autoproxy/>

    <!--spring的路由来管理数据源-->
    <bean id="dynamicDataSource" class="org.hope.lee.utils.DynamicDataSource">
        <property name="targetDataSources">
            <map>
                <entry value-ref="dataSourceMaster" key="db_master"/>
                <entry value-ref="dataSourceSlaveOne" key="db_slave_one"/>
                <entry value-ref="dataSourceSlaveTwo" key="db_slave_two"/>
            </map>
        </property>
    </bean>

    <!--spring-mybatis整合-->
    <bean id="dynamicsqlSessionFactory"
          class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dynamicDataSource"/>
        <property name="mapperLocations">
            <array>
                <value>classpath:mappers/*Mapper.xml</value>
            </array>
        </property>
        <property name="configLocation" value="classpath:mybatis-config.xml"/>
        <property name="typeAliasesPackage" value="org.hope.lee.model"/>
    </bean>

    <!--自动扫描所有的Mapper接口与文件-->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="org.hope.lee.dao"></property>
        <property name="sqlSessionFactoryBeanName" value="dynamicsqlSessionFactory"></property>
    </bean>

    <!--配置事务-->
    <bean id="transactionManager"
          class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dynamicDataSource"/>
    </bean>
    <!--开启注解事务-->
    <tx:annotation-driven transaction-manager="transactionManager"/>

    <import resource="classpath:datasource-master.xml"/>
    <import resource="classpath:datasource-slave-one.xml"/>
    <import resource="classpath:datasource-slave-two.xml"/>

5、新建DBContextHolder，DBType为动态设置数据库的util

package org.hope.lee.utils;

public class DBType {
    public final static String DB_TYPE_MASTER = "db_master";

    public final static String DB_TYPE_SLAVE_ONE = "db_slave_one";

    public final static String DB_TYPE_SLAVE_TWO = "db_slave_two";
}

package org.hope.lee.utils;

public class DBContextHolder {

    private static ThreadLocal<String> contextHolder = new ThreadLocal<String>();

    public static String getDBType() {
        String db = contextHolder.get();
        if(db == null) {
            db = DBType.DB_TYPE_MASTER; //默认是master库
        }

        return db;
    }

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

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

}

6、继承Spring的 AbstractRoutingDataSource 来动态的进行数据库路由

package org.hope.lee.utils;

import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

public class DynamicDataSource extends AbstractRoutingDataSource {
    @Override
    protected Object determineCurrentLookupKey() {
        return DBContextHolder.getDBType();
    }
}

7、创建三个数据库master、slave-one、slave-two。三个库建同一张user表进行测试。

DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

8、写mybatis的dao层,service层,model层

package org.hope.lee.model;

public class User {
    private int id;
    private String name;

    setters()&getters()
}

package org.hope.lee.dao;

import org.hope.lee.model.User;
import org.springframework.stereotype.Repository;

@Repository
public interface UserMapper {
    void insert(User user);
    User selectOne(int id);
}

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

<mapper namespace="org.hope.lee.dao.UserMapper">
    <resultMap id="usersResultMap" type="User">
        <id column="id" property="id" javaType="Integer" />
        <result column="name" property="name" />
    </resultMap>

    <insert id="insert" useGeneratedKeys="true" parameterType="User">
        INSERT INTO `user`(name) VALUES(#{name, jdbcType=VARCHAR});
    </insert>

    <select id="selectOne" resultMap="usersResultMap" parameterType="int" >
        SELECT id, name FROM `user` WHERE id=#{id, jdbcType=INTEGER}
    </select>
</mapper>

package org.hope.lee.service;

import org.hope.lee.dao.UserMapper;
import org.hope.lee.model.User;
import org.hope.lee.utils.DBContextHolder;
import org.hope.lee.utils.DBType;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service("userService")
public class UserServiceImpl implements UserService {

    @Autowired
    private UserMapper userMapper;

    public void addUser(User user) {
        //设置数据库
        DBContextHolder.setDBType(DBType.DB_TYPE_MASTER);
        userMapper.insert(user);
    }

    public User getUserById(int id) {
       //设置数据库，单元测试的时候自己手动修改一下，看看效果       
　　　　DBContextHolder.setDBType(DBType.DB_TYPE_SLAVE_ONE);
       return userMapper.selectOne(id);
    }
}

9、单元测试。

import org.hope.lee.model.User;
import org.hope.lee.service.UserService;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"classpath*:applicationContext.xml"})
public class UserServiceTest {

    @Autowired
    private UserService userService;

    @Test
    public void addUserTest() {
        User user = new User();
        user.setName("马云");

        userService.addUser(user);
    }

    @Test
    public void getUserOneTest() {
        int id = 1;
        User u = userService.getUserById(id);
        System.out.println(u.getName());
    }
}

10、在service层修改 DBContextHolder.setDBType()来看看效果。

四、遇到的问题：

　　1、遇到Spring的PropertyPlaceholderConfigurer不起效果，在数据源配置的${jdbc.driver}中获取不到jdbc.properties中的值。

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
      <property name="locations">
          <list>
              <value>classpath*:jdbc.properties</value>
          </list>
      </property>
      <property name="fileEncoding" value="UTF-8" />
      <property name= "ignoreResourceNotFound" value="false"/>
</bean>

　　解决：

<!--
　　原来id的名称是sqlSessionFactory,但是在spring里使用org.mybatis.spring.mapper.MapperScannerConfigurer
   进行自动扫描的时候，设置了sqlSessionFactory 的话，他会优先于PropertyPlaceholderConfigurer执行。
   从而导致PropertyPlaceholderConfigurer失效，
   这时在xml中用${url}、${username}、${password}等这样之类的表达式，
   将无法获取到properties文件里的内容。
-->
    <bean id="dynamicsqlSessionFactory"
          class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dynamicDataSource"/>
        <property name="mapperLocations">
            <array>
                <value>classpath:mappers/*Mapper.xml</value>
            </array>
        </property>
        <property name="configLocation" value="classpath:mybatis-config.xml"/>
        <property name="typeAliasesPackage" value="org.hope.lee.model"/>
    </bean>

六、还有一种方式是使用mysql自带的replicationDriver来实现读写分离。大家自己也可以试试

　　　　　　http://blog.csdn.net/lixiucheng005/article/details/17391857

https://gitee.com/huayicompany/mybatis-learn/tree/master/separated-read-write

参考：

[1] 博客，http://blog.csdn.net/xtj332/article/details/43953699

[2] 博客，http://blog.csdn.net/keda8997110/article/details/16827215