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本篇文章讲解如何在ssm（spring、springmvc、mybatis）结构的程序上集成sharding-jdbc（版本为1.5.4.1）进行分库分表；
假设分库分表行为如下：

• 将auth_user表分到4个库（user_0~user_3）中；
• 其他表不进行分库分表，保留在default_db库中；

1. POM配置

以spring配置文件为例，新增如下POM配置：

<dependency>
    <groupId>com.dangdang</groupId>
    <artifactId>sharding-jdbc-core</artifactId>
    <version>1.5.4.1</version>
</dependency>

<dependency>
    <groupId>com.dangdang</groupId>
    <artifactId>sharding-jdbc-config-spring</artifactId>
    <version>1.5.4.1</version>
</dependency>

此次集成sharding-jdbc以1.5.4.1版本为例，如果是2.x版本的sharding-jdbc，那么需要将坐标<groupId>com.dangdang</groupId>修改为<groupId>io.shardingjdbc</groupId>；另外，如果是yaml配置，那么需要将坐标<artifactId>sharding-jdbc-config-spring</artifactId>修改为<artifactId>sharding-jdbc-config-yaml</artifactId>；

2. 配置数据源

spring-datasource.xml配置所有需要的数据源如下--auth_user分库分表后需要的4个库user_0~user_3，以及不分库分表的默认库default_db：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <!-- 配置数据源 -->
    <bean id="sj_ds_0" class="com.alibaba.druid.pool.DruidDataSource"
          init-method="init" destroy-method="close">
        <property name="url" value="${sj_user_0.url}" />
        <property name="username" value="${sj_user_0.username}" />
        <property name="password" value="${sj_user_0.password}" />
        <!--druid配置优化可以放在这里-->
    </bean>

    <!-- 配置数据源 -->
    <bean id="sj_ds_1" class="com.alibaba.druid.pool.DruidDataSource"
          init-method="init" destroy-method="close">
        <property name="url" value="${sj_user_1.url}" />
        <property name="username" value="${sj_user_1.username}" />
        <property name="password" value="${sj_user_1.password}" />
        <!--druid配置优化可以放在这里-->
    </bean>

    <!-- 配置数据源 -->
    <bean id="sj_ds_2" class="com.alibaba.druid.pool.DruidDataSource"
          init-method="init" destroy-method="close">
        <property name="url" value="${sj_user_2.url}" />
        <property name="username" value="${sj_user_2.username}" />
        <property name="password" value="${sj_user_2.password}" />
        <!--druid配置优化可以放在这里-->
    </bean>

    <!-- 配置数据源 -->
    <bean id="sj_ds_3" class="com.alibaba.druid.pool.DruidDataSource"
          init-method="init" destroy-method="close">
        <property name="url" value="${sj_user_3.url}" />
        <property name="username" value="${sj_user_3.username}" />
        <property name="password" value="${sj_user_3.password}" />
        <!--druid配置优化可以放在这里-->
    </bean>

    <!-- 配置数据源 -->
    <bean id="sj_ds_default" class="com.alibaba.druid.pool.DruidDataSource"
          init-method="init" destroy-method="close">
        <property name="url" value="${sj_default.url}" />
        <property name="username" value="${sj_default.username}" />
        <property name="password" value="${sj_default.password}" />
        <!--druid配置优化可以放在这里-->
    </bean>
</beans>

properties配置文件内容如下：

sj_user_0.driver=com.mysql.jdbc.Driver
sj_user_0.url=jdbc:mysql://localhost:3306/user_0
sj_user_0.username=root
sj_user_0.password=RootAfei_1

sj_user_1.driver=com.mysql.jdbc.Driver
sj_user_1.url=jdbc:mysql://localhost:3306/user_1
sj_user_1.username=root
sj_user_1.password=RootAfei_1

sj_user_2.driver=com.mysql.jdbc.Driver
sj_user_2.url=jdbc:mysql://localhost:3306/user_2
sj_user_2.username=root
sj_user_2.password=RootAfei_1

sj_user_3.driver=com.mysql.jdbc.Driver
sj_user_3.url=jdbc:mysql://localhost:3306/user_3
sj_user_3.username=root
sj_user_3.password=RootAfei_1

sj_default.driver=com.mysql.jdbc.Driver
sj_default.url=jdbc:mysql://localhost:3306/default_db
sj_default.username=root
sj_default.password=RootAfei_1

3. 集成sharding数据源

spring-sharding.xml配置如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:rdb="http://www.dangdang.com/schema/ddframe/rdb"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                        http://www.springframework.org/schema/beans/spring-beans.xsd
                        http://www.dangdang.com/schema/ddframe/rdb
                        http://www.dangdang.com/schema/ddframe/rdb/rdb.xsd">

    <!--数据库sharding策略：以id列进行sharding，sharding逻辑在AuthUserDatabaseShardingAlgorithm中-->
    <rdb:strategy id="databaseStrategy" sharding-columns="id"
                  algorithm-class="com.crt.fin.ospsso.service.shardingjdbc.AuthUserDatabaseShardingAlgorithm" />
    <!--auth_user表sharding策略:无 -->

    <!--定义sharding数据源-->
    <rdb:data-source id="shardingDataSource">
        <!--default-data-source指定默认数据源, 即没有在<rdb:table-rules>申明的logic-table表,
        即不需要分库分表的表, 全部走默认数据源-->
        <rdb:sharding-rule data-sources="sj_ds_0,sj_ds_1,sj_ds_2,sj_ds_3,sj_ds_default"
                           default-data-source="sj_ds_default">
            <rdb:table-rules>
                <!--auth_user只分库不分表, actual-tables的值一定要加上:sj_ds_${0..3}.,
                否则会遍历data-sources, 而sj_ds_default中并没有auth_user表 -->
                <rdb:table-rule logic-table="auth_user" actual-tables="sj_ds_${0..3}.auth_user"
                                database-strategy="databaseStrategy"/>
            </rdb:table-rules>
            <rdb:default-database-strategy sharding-columns="none" algorithm-class="com.dangdang.ddframe.rdb.sharding.api.strategy.database.NoneDatabaseShardingAlgorithm"/>
            <rdb:default-table-strategy sharding-columns="none" algorithm-class="com.dangdang.ddframe.rdb.sharding.api.strategy.table.NoneTableShardingAlgorithm"/>
        </rdb:sharding-rule>
        <rdb:props>
            <prop key="sql.show">true</prop>
            <prop key="executor.size">2</prop>
        </rdb:props>
    </rdb:data-source>

    <!-- 配置sqlSessionFactory -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <!---datasource交给sharding-jdbc托管-->
        <property name="dataSource" ref="shardingDataSource"/>
        <property name="mapperLocations" value="classpath*:mybatis/*Mapper.xml"/>
    </bean>

    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.crt.fin.ospsso.dal.mapper"/>
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
    </bean>

</beans>

说明：spring-sharding.xml配置的分库分表规则：auth_user表分到id为sj_ds_${0..3}的四个库中，表名保持不变；其他表在id为sj_ds_default库中，不分库也不分表；集成sharding-jdbc的核心就是将SqlSessionFactoryBean需要的dataSource属性修改为shardingDataSource，把数据源交给sharding-jdbc处理；

分库逻辑AuthUserDatabaseShardingAlgorithm的代码很简单，源码如下：

/**
 * @author wangzhenfei9
 * @version 1.0.0
 * @since 2018年02月08日
 */
public class AuthUserDatabaseShardingAlgorithm implements SingleKeyDatabaseShardingAlgorithm<Long> {

    private final Logger logger = LoggerFactory.getLogger(this.getClass());

    private static final int SHARDING_NUMBER = 4;

    @Override
    public String doEqualSharding(final Collection<String> availableTargetNames, final ShardingValue<Long> shardingValue) {
        for (String each : availableTargetNames) {
            if (each.endsWith(shardingValue.getValue() % SHARDING_NUMBER + "")) {
                logger.debug("the target database name: {}", each);
                return each;
            }
        }
        throw new UnsupportedOperationException();
    }

    @Override
    public Collection<String> doInSharding(final Collection<String> availableTargetNames, final ShardingValue<Long> shardingValue) {
        Collection<String> result = new LinkedHashSet<>(availableTargetNames.size());
        Collection<Long> values = shardingValue.getValues();
        for (Long value : values) {
            for (String each : availableTargetNames) {
                if (each.endsWith(value % SHARDING_NUMBER + "")) {
                    result.add(each);
                }
            }
        }
        return result;
    }

    @Override
    public Collection<String> doBetweenSharding(final Collection<String> availableTargetNames, final ShardingValue<Long> shardingValue) {
        Collection<String> result = new LinkedHashSet<>(availableTargetNames.size());
        Range<Long> range = shardingValue.getValueRange();
        for (Long value = range.lowerEndpoint(); value <= range.upperEndpoint(); value++) {
            for (String each : availableTargetNames) {
                if (each.endsWith(value % SHARDING_NUMBER + "")) {
                    result.add(each);
                }
            }
        }
        return result;
    }
}

这段代码参考sharding-jdbc源码中DatabaseShardingAlgorithm.java接口的实现即可，例如ModuloDatabaseShardingAlgorithm.java；

4. 注意事项

无法识别sharding-jdbc分库分表规则inline-expression问题，例如：
<rdb:table-rule logic-table="auth_user" actual-tables="sj_ds_${0..3}.auth_user" database-strategy="databaseStrategy"/>

1. 根本原因：
   根本原因是spring把${}当做占位符，${0..3}这种表达式，spring会尝试去properties文件中找key为0..3的属性。但是这里是sharding-jdbc分库分表规则的inline表达式，需要spring忽略这种行为。否则会抛出异常:
   java.lang.IllegalArgumentException: Could not resolve placeholder '0..3' in value "sj_ds_${0..3}.auth_user"

2. 解决办法：
   配置: <property name="ignoreUnresolvablePlaceholders" value="true"/>
   或者: <context:property-placeholder ****** ignore-unresolvable="true" />

5. Main测试

Main.java用来测试分库分表是否OK，其源码如下：

/**
 * @author wangzhenfei9
 * @version 1.0.0
 * @since 2018年02月08日
 */
public class Main {

    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext(
                "/META-INF/spring/spring-*.xml");

        // auth_user有进行分库，
        AuthUserMapper authUserMapper = context.getBean(AuthUserMapper.class);
        AuthUser authUser = authUserMapper.selectByPrimaryKey(7L);
        System.out.println("-----> The auth user: "+JSON.toJSONString(authUser));

        // user_permission没有分库分表
        UserPermissionMapper userPermissionMapper = context.getBean(UserPermissionMapper.class);
        UserPermission userPermission = userPermissionMapper.selectPermissionByUsername("wangzhenfei", "FINANCE_WALLET");
        System.out.println("-----< The user permission: "+JSON.toJSONString(userPermission));
    }

}

AuthUserMapper.selectByPrimaryKey()和UserPermissionMapper.selectPermissionByUsername()的代码和没有分库分表的代码完全一样；

6. 遗留问题

Main方法测试，或者启动服务后的调用测试都没有问题，但是通过junit测试用例访问就会抛出异常，作为一个待解决的遗留问题：

org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'javax.sql.DataSource' available: expected single matching bean but found 6: sj_ds_0,sj_ds_1,sj_ds_2,sj_ds_3,sj_ds_default,shardingDataSource