Sharding-JDBC（二）2.0.3版本实践

目录

　　一、Sharding-JDBC依赖

　　二、分片策略

　　　　1. 标准分片策略

　　　　2. 复合分片策略

　　　　3. Inline表达式分片策略

　　　　4. 通过Hint而非SQL解析的方式分片的策略

　　　　5. 不分片的策略

　　三、分片键

　　四、分片算法

　　　　1. 精确分片算法

　　　　2. 范围分片算法

　　　　3. 复合分片算法

　　　　4. Hint分片算法

　　五、代码实践

上一篇博文以Sharding-JDBC为契机，了解了ShardingSphere大家族的全貌概览，以及Sharding-JDBC的角色定位。

Sharding-JDBC定位为轻量级Java框架，在Java的JDBC层提供的额外服务。 它使用客户端直连数据库，以jar包形式提供服务，无需额外部署和依赖，可理解为增强版的JDBC驱动，完全兼容JDBC和各种ORM框架。

Sharding-JDBC目前已经迭代到4.0.0版本，并且进入了Apache孵化器，但Sharding-JDBC各个大版本之间不支持向下兼容（这里主要描述的是2.x到4.x），大版本和大版本之间犹如断层，如果涉及到升级，就需要改动代码，并且2.x到4.x多多少少都有点BUG，导致在业务系统引进Sharding-JDBC的过程略显艰难。

接下来将介绍Sharding-JDBC的2.0.3版本，以及它的长处和短板。

一、Sharding-JDBC依赖

<!-- sharding-jdbc-core -->
<dependency>
    <groupId>io.shardingjdbc</groupId>
    <artifactId>sharding-jdbc-core</artifactId>
    <version>2.0.3</version>
</dependency>
<!-- sharding-jdbc-spring-namespace -->
<dependency>
    <groupId>io.shardingjdbc</groupId>
    <artifactId>sharding-jdbc-core-spring-namespace</artifactId>
    <version>2.0.3</version>
</dependency>

Sharding-JDBC没有将Spring Schema上传至公网，需引入namespace依赖包。

二、分片策略

包含分片键和分片算法，由于分片算法的独立性，将其独立抽离。真正可用于分片操作的是分片键 + 分片算法，也就是分片策略。目前提供5种分片策略：标准分片策略、复合分片策略、Inline表达式分片策略、通过Hint而非SQL解析的方式分片的策略和不分片的策略。

1. 标准分片策略

对应StandardShardingStrategy。提供对SQL语句中的=、IN和BETWEEN AND的分片操作支持。StandardShardingStrategy只支持单分片键，提供PreciseShardingAlgorithm和RangeShardingAlgorithm两个分片算法。PreciseShardingAlgorithm是必选的，用于处理=和IN的分片。RangeShardingAlgorithm是可选的，用于处理BETWEEN AND分片，如果不配置RangeShardingAlgorithm，SQL中的BETWEEN AND将按照全库路由处理。

2. 复合分片策略

对应ComplexShardingStrategy。复合分片策略。提供对SQL语句中的=、IN和BETWEEN AND的分片操作支持。ComplexShardingStrategy支持多分片键，由于多分片键之间的关系复杂，因此并未进行过多的封装，而是直接将分片键值组合以及分片操作符透传至分片算法，完全由应用开发者实现，提供最大的灵活度。

3. Inline表达式分片策略

对应InlineShardingStrategy。使用Groovy的表达式，提供对SQL语句中的=和IN的分片操作支持，只支持单分片键。对于简单的分片算法，可以通过简单的配置使用，从而避免繁琐的Java代码开发，如  t_user_$->{u_id % 8}  表示t_user表根据u_id模8，而分成8张表，表名称为 t_user_0 到 t_user_7 。

4. 通过Hint而非SQL解析的方式分片的策略

对应HintShardingStrategy。通过Hint而非SQL解析的方式分片的策略。

5. 不分片的策略

对应NoneShardingStrategy。不分片的策略。

标准分片策略、复合分片策略和Inline表达式分片策略要求分片键（即分片字段）必须存在于SQL中和数据表结构中，否则无法正确分片；相反，若分片键不存在于SQL中和数据表结构中，则可以使用Hint方式进行强制路由。

三、分片键

用于分片的数据库字段，是将数据库(表)水平拆分的关键字段。例：将订单表中的订单主键的尾数取模分片，则订单主键为分片字段。 SQL中如果无分片字段，将执行全路由，性能较差。 除了对单分片字段的支持，ShardingSphere也支持根据多个字段进行分片。

四、分片算法

通过分片算法将数据分片，支持通过=、IN和BETWEEN AND分片。分片算法需要应用方开发者自行实现，可实现的灵活度非常高。

目前提供4种分片算法。由于分片算法和业务实现紧密相关，因此并未提供内置分片算法，而是通过分片策略将各种场景提炼出来，提供更高层级的抽象，并提供接口让应用开发者自行实现分片算法。

1. 精确分片算法

对应PreciseShardingAlgorithm，用于处理使用单一键作为分片键的=与IN进行分片的场景。需要配合StandardShardingStrategy使用。

2. 范围分片算法

对应RangeShardingAlgorithm，用于处理使用单一键作为分片键的BETWEEN AND进行分片的场景。需要配合StandardShardingStrategy使用。

3. 复合分片算法

对应ComplexKeysShardingAlgorithm，用于处理使用多键作为分片键进行分片的场景，包含多个分片键的逻辑较复杂，需要应用开发者自行处理其中的复杂度。需要配合ComplexShardingStrategy使用。

4. Hint分片算法

对应HintShardingAlgorithm，用于处理使用Hint行分片的场景。需要配合HintShardingStrategy使用。

五、代码实践

在正式介绍代码之前，有必要先描述下业务背景，便于理解代码的用途。

数据表结构：

CREATE TABLE `settlement_20180403` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `pay_serial_number` varchar(32) DEFAULT NULL COMMENT '支付流水号',
  `user_mobile` varchar(15) DEFAULT NULL COMMENT '用户手机号',
  `money` int(10) DEFAULT '0' COMMENT '支付或退款金额, 单位: 分',
  `operate_tm` timestamp NULL DEFAULT NULL COMMENT '操作时间',
  `refund` tinyint(1) DEFAULT NULL COMMENT '是否退款 1: 是 2: 否',
  `remark` varchar(32) DEFAULT NULL COMMENT '备注',
  PRIMARY KEY (`id`),
  UNIQUE KEY `PAY_SERIAL_NUM_UNIQUE` (`pay_serial_number`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

表结构中比较有趣的字段是 pay_serial_number ，以 232042018040353088 为例， pay_serial_number 由三部分组成：前5位是固定编码，样例中是23204，中间8位是日期，包含年月日，样例中是20180403，最后5位是随机数，样例中是53088，以上三部分组成了支付流水号。

随着业务量逐渐扩增， settlement 表数据量急剧，需要以时间作为分表条件水平切分数据，分表字段则为 pay_serial_number ，其中的日期则为分表条件。接下来的代码都是以此业务背景展开。

如下代码配置了标准分片策略中的精确分片算法PreciseShardingAlgorithm和Hint分片算法HintShardingAlgorithm。

XML配置：

<?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:tx="http://www.springframework.org/schema/tx"
       xmlns:sharding="http://shardingjdbc.io/schema/shardingjdbc/sharding"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans.xsd
                           http://www.springframework.org/schema/tx
                           http://www.springframework.org/schema/tx/spring-tx.xsd
                           http://shardingjdbc.io/schema/shardingjdbc/sharding
                           http://shardingjdbc.io/schema/shardingjdbc/sharding/sharding.xsd">

    <!-- 标准分片策略 -->
    <sharding:standard-strategy id="settlementTableShardingStandardStrategy" sharding-column="pay_serial_number"
                                precise-algorithm-class="org.cellphone.finance.repo.sharding.PreciseTableShardingAlgorithm"/>

    <!-- 基于暗示(Hint)的数据分片策略 -->
    <sharding:hint-strategy id="settlementTableShardingHintStrategy"
                            algorithm-class="org.cellphone.finance.repo.sharding.HintTableShardingAlgorithm"/>

    <!-- 加了分库分表插件，spring boot 启动会实例化两个dataSource，不知是否正常？ -->
    <sharding:data-source id="shardingDataSource">
        <!-- dataSource是数据库连接池 -->
        <sharding:sharding-rule data-source-names="dataSource">
            <sharding:table-rules>
                <sharding:table-rule logic-table="settlement"
                                     table-strategy-ref="settlementTableShardingStandardStrategy"/>
                <!-- logic-table 一定要和SQL中的表名以及HintManager中配置的logicTable一致，否则无法找到对应的table rule -->
                <sharding:table-rule logic-table="settlement_hint"
                                     table-strategy-ref="settlementTableShardingHintStrategy"/>
            </sharding:table-rules>
        </sharding:sharding-rule>
        <sharding:props>
            <prop key="sql.show">true</prop>
        </sharding:props>
    </sharding:data-source>

    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="shardingDataSource"/>
    </bean>
    <tx:annotation-driven/>
</beans>

 精确分片算法：

package org.cellphone.finance.repo.sharding;

import com.google.common.collect.Lists;
import io.shardingjdbc.core.api.algorithm.sharding.PreciseShardingValue;
import io.shardingjdbc.core.api.algorithm.sharding.standard.PreciseShardingAlgorithm;
import org.apache.commons.collections.CollectionUtils;
import org.cellphone.common.constant.CommonConst;

import java.util.Collection;

/**
 * 精确分片算法，属于标准分片算法，用于处理=和IN的分片
 * <p>
 * 使用精确分片算法的前提：分片字段必须存在与SQL中、数据库表结构中，否则无法使用精确分片算法
 * <p>
 * 此分片算法应用于SETTLEMENT数据表，这里是按天分表
 * <p>
 * 特别说明：Sharding Jdbc版本：2.0.3
 * <p>
 * Created by on 2018/4/9.
 */
public class PreciseTableShardingAlgorithm implements PreciseShardingAlgorithm<String> {

    /**
     * 精确分片算法
     *
     * @param availableTargetNames 目标数据源名称或数据表名称，注意：是逻辑数据源名或逻辑数据表名，来自SQL
     * @param shardingValue        分片值，来自SQL中分片字段对应的值
     * @return 真实数据源名称或数据表名称
     */
    @Override
    public String doSharding(final Collection<String> availableTargetNames, final PreciseShardingValue<String> shardingValue) {
        // 默认数据表名称，有可能数据库中不存在这张表
        String tableName = "settlement";

        // 逻辑表名为空，返回默认表名
        if (CollectionUtils.isEmpty(availableTargetNames))
            return tableName;

        // availableTargetNames来自SQL，只有一个元素
        tableName = Lists.newArrayList(availableTargetNames).get(0);

        String paySerialNumber = shardingValue.getValue();
        String suffix = paySerialNumber.substring(5, 13);
        return tableName + CommonConst.UNDERLINE + suffix;
    }
}

上面说过，精确分片算法可以很完美的支持SQL语句中的=和IN的分片操作，因此PreciseTableShardingAlgorithm可以很好的支持简单的INSERT、UPDATE、DELETE和SELECT操作。

但如果要通过 pay_serial_number 查询数据就行不通了，因为分片键并不直接存在与SQL中和数据表结构中，而是间接存在于 pay_serial_number 中的时间数据，因此，就需要通过Hint方式来进行分片才能定位到真实的数据表。

Hint分片算法：

package org.cellphone.finance.repo.sharding;

import com.google.common.collect.Lists;
import io.shardingjdbc.core.api.algorithm.sharding.ListShardingValue;
import io.shardingjdbc.core.api.algorithm.sharding.ShardingValue;
import io.shardingjdbc.core.api.algorithm.sharding.hint.HintShardingAlgorithm;
import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.time.DateFormatUtils;
import org.apache.commons.lang3.time.DateUtils;
import org.cellphone.common.constant.CommonConst;
import org.cellphone.common.constant.DateConst;

import java.text.ParseException;
import java.util.*;

/**
 * Created by on 2019/4/27.
 */
public class HintTableShardingAlgorithm implements HintShardingAlgorithm {

    @Override
    public Collection<String> doSharding(Collection<String> availableTargetNames, ShardingValue shardingValue) {
        // 数据表名称列表
        List<String> tableNames = new ArrayList<>();

        // 逻辑表名为空
        if (CollectionUtils.isEmpty(availableTargetNames))
            return tableNames;

        // availableTargetNames来自SQL，只有一个元素
        String tableName = Lists.newArrayList(availableTargetNames).get(0);
        tableName = tableName.replace("_hint", StringUtils.EMPTY);

        ListShardingValue<String> listShardingValue = (ListShardingValue<String>) shardingValue;
        List<String> list = Lists.newArrayList(listShardingValue.getValues());

        Date startTm, endTm;

        try {
            startTm = DateUtils.parseDate(list.get(0), DateConst.DATE_FORMAT_NORMAL);
            endTm   = DateUtils.parseDate(list.get(1), DateConst.DATE_FORMAT_NORMAL);
        } catch (ParseException e) {
            return tableNames;
        }

        Calendar calendar = Calendar.getInstance();
        while (startTm.getTime() <= endTm.getTime()) {
            String suffix = DateFormatUtils.format(startTm, DateConst.DATE_FORMAT_YYYY_MM_DD);
            tableNames.add(tableName + CommonConst.UNDERLINE + suffix);

            calendar.setTime(startTm);
            calendar.add(Calendar.DATE, 1);
            startTm = calendar.getTime();
        }

        return tableNames;
    }
}

与Hint分片算法对应的Java查询方法 settlementMapper.selectByExample(example) ：

public List<Settlement> querySettlements(SettlementExample example, String startTime, String endTime) {
    HintManager hintManager = HintManager.getInstance();
    // logicTable必须和XML中的logic-table以及SQL中的逻辑表名称一致
    hintManager.addTableShardingValue("settlement_hint", "start_time", startTime);
    hintManager.addTableShardingValue("settlement_hint", "end_time", endTime);
    List<Settlement> settlements = settlementMapper.selectByExample(example);
    hintManager.close();
    return settlements;
}

以及该查询方法对应的SQL语句：

select * from settlement_hint t where t.pay_serial_number = ?

 单元测试代码：

@Test
public void test004QuerySettlements() throws ParseException {
    String startTime = "2018-04-03 00:00:00", endTime = "2018-04-05 00:00:00";

    SettlementExample example = new SettlementExample();
    SettlementExample.Criteria criteria = example.createCriteria();
    criteria.andPaySerialNumberEqualTo("232042018040353088");

    List<Settlement> settlements = repository.querySettlements(example, startTime, endTime);

    Assert.assertEquals("136********", settlements.get(0).getUserMobile());
}

 经过上述一波代码后，原以为单元测试可以完美通过，但天有不测风云，月有阴晴圆缺，单元测试竟然失败了，报错日志提示数据表不存在：

org.springframework.jdbc.BadSqlGrammarException: 
### Error querying database.  Cause: java.sql.SQLSyntaxErrorException: Table 'warehouse.settlement_hint' doesn't exist
### The error may exist in file [D:programsIdeaProjectswarehousewarehouse-financewarehouse-finance-service	argetclassesmapperSettlementMapper.xml]
### The error may involve org.cellphone.finance.repo.mapper.SettlementMapper.selectByExample-Inline
### The error occurred while setting parameters
### SQL: select           id, pay_serial_number, user_mobile,  money, operate_tm,  refund, remark         from settlement_hint    WHERE (  pay_serial_number = ? )
### Cause: java.sql.SQLSyntaxErrorException: Table 'warehouse.settlement_hint' doesn't exist
; bad SQL grammar []; nested exception is java.sql.SQLSyntaxErrorException: Table 'warehouse.settlement_hint' doesn't exist

    at org.springframework.jdbc.support.SQLErrorCodeSQLExceptionTranslator.doTranslate(SQLErrorCodeSQLExceptionTranslator.java:234)
    at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:72)
    at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:73)
    at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:446)
    at com.sun.proxy.$Proxy94.selectList(Unknown Source)
    at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:230)
    at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:139)
    at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:76)
    at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
    at com.sun.proxy.$Proxy95.selectByExample(Unknown Source)
    at org.cellphone.finance.repo.SettlementRepository.querySettlements(SettlementRepository.java:62)
    at org.cellphone.finance.repo.SettlementRepository$$FastClassBySpringCGLIB$$c5ad592f.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:746)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)
    at org.cellphone.finance.repo.SettlementRepository$$EnhancerBySpringCGLIB$$9133dcc1.querySettlements(<generated>)
    at org.cellphone.finance.SettlementRepositoryTest.test004QuerySettlements(SettlementRepositoryTest.java:89)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:73)
    at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:83)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: java.sql.SQLSyntaxErrorException: Table 'warehouse.settlement_hint' doesn't exist
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:120)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:975)
    at com.mysql.cj.jdbc.ClientPreparedStatement.execute(ClientPreparedStatement.java:392)
    at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3409)
    at com.alibaba.druid.filter.FilterEventAdapter.preparedStatement_execute(FilterEventAdapter.java:440)
    at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3407)
    at com.alibaba.druid.proxy.jdbc.PreparedStatementProxyImpl.execute(PreparedStatementProxyImpl.java:167)
    at com.alibaba.druid.pool.DruidPooledPreparedStatement.execute(DruidPooledPreparedStatement.java:498)
    at io.shardingjdbc.core.executor.type.prepared.PreparedStatementExecutor$3.execute(PreparedStatementExecutor.java:101)
    at io.shardingjdbc.core.executor.type.prepared.PreparedStatementExecutor$3.execute(PreparedStatementExecutor.java:97)
    at io.shardingjdbc.core.executor.ExecutorEngine.executeInternal(ExecutorEngine.java:187)
    at io.shardingjdbc.core.executor.ExecutorEngine.syncExecute(ExecutorEngine.java:167)
    at io.shardingjdbc.core.executor.ExecutorEngine.execute(ExecutorEngine.java:131)
    at io.shardingjdbc.core.executor.ExecutorEngine.executePreparedStatement(ExecutorEngine.java:98)
    at io.shardingjdbc.core.executor.type.prepared.PreparedStatementExecutor.execute(PreparedStatementExecutor.java:97)
    at io.shardingjdbc.core.jdbc.core.statement.ShardingPreparedStatement.execute(ShardingPreparedStatement.java:141)
    at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:63)
    at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79)
    at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63)
    at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:326)
    at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
    at com.github.pagehelper.PageInterceptor.intercept(PageInterceptor.java:108)
    at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61)
    at com.sun.proxy.$Proxy117.query(Unknown Source)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433)
    ... 46 more 

抛出错误堆栈后，很纳闷为何没有将逻辑表名 settlement_hint 转换为真实表名 settlement_20180403 ，于是就跟踪了Sharding-JDBC源码。

经过DEBUG，得知所有JDBC操作都会调用 io.shardingjdbc.core.routing.type.simple.SimpleRoutingEngine#route 方法：

/*
 * Copyright 1999-2015 dangdang.com.
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * </p>
 */

package io.shardingjdbc.core.routing.type.simple;

import io.shardingjdbc.core.api.algorithm.sharding.ShardingValue;
import io.shardingjdbc.core.hint.HintManagerHolder;
import io.shardingjdbc.core.hint.ShardingKey;
import io.shardingjdbc.core.parsing.parser.context.condition.Column;
import io.shardingjdbc.core.parsing.parser.context.condition.Condition;
import io.shardingjdbc.core.parsing.parser.sql.SQLStatement;
import io.shardingjdbc.core.routing.strategy.ShardingStrategy;
import io.shardingjdbc.core.routing.type.RoutingEngine;
import io.shardingjdbc.core.routing.type.RoutingResult;
import io.shardingjdbc.core.routing.type.TableUnit;
import io.shardingjdbc.core.rule.DataNode;
import io.shardingjdbc.core.rule.ShardingRule;
import io.shardingjdbc.core.rule.TableRule;
import com.google.common.base.Optional;
import com.google.common.base.Preconditions;
import lombok.RequiredArgsConstructor;

import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedList;
import java.util.List;

/**
 * Simple routing engine.
 *
 * @author zhangliang
 */
@RequiredArgsConstructor
public final class SimpleRoutingEngine implements RoutingEngine {

    private final ShardingRule shardingRule;

    private final List<Object> parameters;

    private final String logicTableName;

    private final SQLStatement sqlStatement;

    /**
     * Sharding-JDBC路由方法，所有JDBC操作都会调用此方法，路由到真实表
     *
     * @return
     */
    @Override
    public RoutingResult route() {
        // 从XML中根据逻辑表名获取配置的数据表规则
        TableRule tableRule = shardingRule.getTableRule(logicTableName);
        // 获取数据源分片值，分片值来自逻辑SQL中的数据，由于XML只配置了单个数据源，暂时不深入分析此环节
        List<ShardingValue> databaseShardingValues = getDatabaseShardingValues(tableRule);
        // 获取数据表分片值，分片值来自逻辑SQL中的数据，重点分析这部分代码
        List<ShardingValue> tableShardingValues = getTableShardingValues(tableRule);
        // 计算需要路由的真实数据源
        Collection<String> routedDataSources = routeDataSources(tableRule, databaseShardingValues);
        Collection<DataNode> routedDataNodes = new LinkedList<>();
        for (String each : routedDataSources) {
            // routeTables方法计算需要路由的真实数据表，重点分析这部分代码
            routedDataNodes.addAll(routeTables(tableRule, each, tableShardingValues));
        }
        // 产生路由结果
        return generateRoutingResult(routedDataNodes);
    }

    private List<ShardingValue> getDatabaseShardingValues(final TableRule tableRule) {
        ShardingStrategy strategy = shardingRule.getDatabaseShardingStrategy(tableRule);
        return HintManagerHolder.isUseShardingHint() ? getDatabaseShardingValuesFromHint(strategy.getShardingColumns()) : getShardingValues(strategy.getShardingColumns());
    }

    /**
     * 获取数据表分片值
     * 分片值由上面提到的querySettlements通过hintManager传入
     *
     * @param tableRule 数据表规则，从XML文件中获取
     * @return 分片值列表
     */
    private List<ShardingValue> getTableShardingValues(final TableRule tableRule) {
        // 从XML文件中获取数据表规则
        ShardingStrategy strategy = shardingRule.getTableShardingStrategy(tableRule);
        /*
         * 判断是否使用了Hint分片算法：
         * 1. 是：根据ShardingStrategy中拿到的shardingColumns来获取shardingValues，问题就出在这里！！！
         * 2. 否：从SQL中根据shardingColumns来获取shardingValues
         */
        return HintManagerHolder.isUseShardingHint() ? getTableShardingValuesFromHint(strategy.getShardingColumns()) : getShardingValues(strategy.getShardingColumns());
    }

    private List<ShardingValue> getDatabaseShardingValuesFromHint(final Collection<String> shardingColumns) {
        List<ShardingValue> result = new ArrayList<>(shardingColumns.size());
        for (String each : shardingColumns) {
            Optional<ShardingValue> shardingValue = HintManagerHolder.getDatabaseShardingValue(new ShardingKey(logicTableName, each));
            if (shardingValue.isPresent()) {
                result.add(shardingValue.get());
            }
        }
        return result;
    }

    /**
     * 从Hint分片算法中获取shardingValues
     *
     * @param shardingColumns 分片键
     * @return 分片值列表
     */
    private List<ShardingValue> getTableShardingValuesFromHint(final Collection<String> shardingColumns) {
        List<ShardingValue> result = new ArrayList<>(shardingColumns.size());
        for (String each : shardingColumns) {
            // 从HintManagerHolder获取sharding values
            Optional<ShardingValue> shardingValue = HintManagerHolder.getTableShardingValue(new ShardingKey(logicTableName, each));
            if (shardingValue.isPresent()) {
                result.add(shardingValue.get());
            }
        }
        return result;
    }

    private List<ShardingValue> getShardingValues(final Collection<String> shardingColumns) {
        List<ShardingValue> result = new ArrayList<>(shardingColumns.size());
        for (String each : shardingColumns) {
            Optional<Condition> condition = sqlStatement.getConditions().find(new Column(each, logicTableName));
            if (condition.isPresent()) {
                result.add(condition.get().getShardingValue(parameters));
            }
        }
        return result;
    }

    private Collection<String> routeDataSources(final TableRule tableRule, final List<ShardingValue> databaseShardingValues) {
        Collection<String> availableTargetDatabases = tableRule.getActualDatasourceNames();
        if (databaseShardingValues.isEmpty()) {
            return availableTargetDatabases;
        }
        Collection<String> result = shardingRule.getDatabaseShardingStrategy(tableRule).doSharding(availableTargetDatabases, databaseShardingValues);
        Preconditions.checkState(!result.isEmpty(), "no database route info");
        return result;
    }

    /**
     * 计算需要路由的真实数据表
     *
     * @param tableRule           数据表规则，从XML中获取
     * @param routedDataSource    需要路由的数据源
     * @param tableShardingValues 数据表分片值
     * @return 需要路由的真实数据节点
     */
    private Collection<DataNode> routeTables(final TableRule tableRule, final String routedDataSource, final List<ShardingValue> tableShardingValues) {
        // 所有的真实数据表名，在XML中可以显式配置，也可以省略
        Collection<String> availableTargetTables = tableRule.getActualTableNames(routedDataSource);
        /*
         * table sharding values是否为空：
         * 1. 是：路由到所有真实表
         * 2. 否：路由到自定义的分表策略算法定义的数据表
         *
         * 问题就出在这里：tableShardingValues.isEmpty()为true，导致无法使用自定义分表策略算法
         */
        Collection<String> routedTables = tableShardingValues.isEmpty() ? availableTargetTables
                : shardingRule.getTableShardingStrategy(tableRule).doSharding(availableTargetTables, tableShardingValues);
        Preconditions.checkState(!routedTables.isEmpty(), "no table route info");
        Collection<DataNode> result = new LinkedList<>();
        for (String each : routedTables) {
            result.add(new DataNode(routedDataSource, each));
        }
        return result;
    }

    private RoutingResult generateRoutingResult(final Collection<DataNode> routedDataNodes) {
        RoutingResult result = new RoutingResult();
        for (DataNode each : routedDataNodes) {
            result.getTableUnits().getTableUnits().add(new TableUnit(each.getDataSourceName(), logicTableName, each.getTableName()));
        }
        return result;
    }
}

 上述代码中， getTableShardingValuesFromHint 返回的 List<ShardingValue> 为空，原因是 getTableShardingValuesFromHint 的入参 strategy.getShardingColumns() 为空列表，而此参数来自Sharding-JDBC的默认实现HintShardingStrategy：

/*
 * Copyright 1999-2015 dangdang.com.
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * </p>
 */

package io.shardingjdbc.core.routing.strategy.hint;

import io.shardingjdbc.core.api.algorithm.sharding.hint.HintShardingAlgorithm;
import io.shardingjdbc.core.api.algorithm.sharding.ShardingValue;
import io.shardingjdbc.core.routing.strategy.ShardingStrategy;
import lombok.Getter;

import java.util.Collection;
import java.util.TreeSet;

/**
 * Hint sharding strategy.
 
 * final类，无法继承此类来重定义内部逻辑
 * 
 * 
 * @author zhangliang
 */
public final class HintShardingStrategy implements ShardingStrategy {
    /**
     * 没有提供Setter方法和可以配置的入口，无法设置shardingColumns，这是2.0.3版本的BUG
     * 
     * github issue: https://github.com/apache/incubator-shardingsphere/issues/1980
     */
    @Getter
    private final Collection<String> shardingColumns;
    
    private final HintShardingAlgorithm shardingAlgorithm;
    
    public HintShardingStrategy(final HintShardingAlgorithm shardingAlgorithm) {
        this.shardingColumns = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
        this.shardingAlgorithm = shardingAlgorithm;
    }
    
    @Override
    public Collection<String> doSharding(final Collection<String> availableTargetNames, final Collection<ShardingValue> shardingValues) {
        Collection<String> shardingResult = shardingAlgorithm.doSharding(availableTargetNames, shardingValues.iterator().next());
        Collection<String> result = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
        result.addAll(shardingResult);
        return result;
    }
}

跟踪到此，Hint分片算法无法使用的原因一路了然，这是Sharding-JDBC 2.0.3版本的BUG，但在后续版本4.x中得到了修复。