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、实际操作
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版本了，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，就需要改动代码了，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
Sharding-JDBC提供的分片策略有5种：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
标准分片策略。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
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Sharding-JDBC并未做过多的封装，而是直接将分片键值组合以及分片操作符交于算法接口，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
Inline表达式分片策略。使用Groovy的Inline表达式，提供对SQL语句中的=和IN的分片操作支持。InlineShardingStrategy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：tuser${user_id % 8} 表示t_user表按照user_id按8取模分成8个表，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
5. 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，否则无法正确路由；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、实际操作
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。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。
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 001157 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=, IN和BETWEEN AND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 查询数据就有点麻烦了，因为分片键并不存在与SQL中和数据表结构中，而是存在于 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 XiaofengWu 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中的表名一致
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("13691695897", 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:\programs\IdeaProjects\warehouse\warehouse-finance\warehouse-finance-service\target\classes\mapper\SettlementMapper.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。
经过调试，确定所有JDBC产生的SQL都会透传到此方法：
/*
* 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产生的SQL都会透传到此方法，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
* 也不允许自行实例化此类
*
* @author zhangliang
*/
public final class HintShardingStrategy implements ShardingStrategy {
/**
* 没有提供可以配置的入口，无法指定shardingColumns，这是2.0.3版本的BUG
*
*
*/
@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3.x中得到了修复，下期将介绍Sharding-JDBC 3.1.0版本的使用。