Sharding-JDBC（二）2.0.3版本实践
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Sharding-JDBC（二）2.0.3版本实践
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目錄
一、Sharding-JDBC依賴
二、分片策略
1. 標準分片策略
2. 復合分片策略
3. Inline表達式分片策略
4. 通過Hint而非SQL解析的方式分片的策略
5. 不分片的策略
三、分片鍵
四、分片算法
1. 精確分片算法
2. 范圍分片算法
3. 復合分片算法
4. Hint分片算法
五、代碼實踐
?
上一篇博文以Sharding-JDBC為契機，了解了ShardingSphere大家族的全貌概覽，以及Sharding-JDBC的角色定位。
Sharding-JDBC定位為輕量級Java框架，在Java的JDBC層提供的額外服務。 它使用客戶端直連數據庫，以jar包形式提供服務，無需額外部署和依賴，可理解為增強版的JDBC驅動，完全兼容JDBC和各種ORM框架。
Sharding-JDBC目前已經迭代到4.0.0版本，并且進入了Apache孵化器，但Sharding-JDBC各個大版本之間不支持向下兼容（這里主要描述的是2.x到4.x），大版本和大版本之間猶如斷層，如果涉及到升級，就需要改動代碼，并且2.x到4.x多多少少都有點BUG，導致在業務系統引進Sharding-JDBC的過程略顯艱難。
接下來將介紹Sharding-JDBC的2.0.3版本，以及它的長處和短板。
一、Sharding-JDBC依賴
<!-- 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沒有將Spring Schema上傳至公網，需引入namespace依賴包。
二、分片策略
包含分片鍵和分片算法，由于分片算法的獨立性，將其獨立抽離。真正可用于分片操作的是分片鍵 + 分片算法，也就是分片策略。目前提供5種分片策略：標準分片策略、復合分片策略、Inline表達式分片策略、通過Hint而非SQL解析的方式分片的策略和不分片的策略。
1. 標準分片策略
對應StandardShardingStrategy。提供對SQL語句中的=、IN和BETWEEN AND的分片操作支持。StandardShardingStrategy只支持單分片鍵，提供PreciseShardingAlgorithm和RangeShardingAlgorithm兩個分片算法。PreciseShardingAlgorithm是必選的，用于處理=和IN的分片。RangeShardingAlgorithm是可選的，用于處理BETWEEN AND分片，如果不配置RangeShardingAlgorithm，SQL中的BETWEEN AND將按照全庫路由處理。
2.?復合分片策略
對應ComplexShardingStrategy。復合分片策略。提供對SQL語句中的=、IN和BETWEEN AND的分片操作支持。ComplexShardingStrategy支持多分片鍵，由于多分片鍵之間的關系復雜，因此并未進行過多的封裝，而是直接將分片鍵值組合以及分片操作符透傳至分片算法，完全由應用開發者實現，提供最大的靈活度。
3.?Inline表達式分片策略
對應InlineShardingStrategy。使用Groovy的表達式，提供對SQL語句中的=和IN的分片操作支持，只支持單分片鍵。對于簡單的分片算法，可以通過簡單的配置使用，從而避免繁瑣的Java代碼開發，如??t_user_$->{u_id % 8}??表示t_user表根據u_id模8，而分成8張表，表名稱為?t_user_0?到?t_user_7?。
4.?通過Hint而非SQL解析的方式分片的策略
對應HintShardingStrategy。通過Hint而非SQL解析的方式分片的策略。
5.?不分片的策略
對應NoneShardingStrategy。不分片的策略。
標準分片策略、復合分片策略和Inline表達式分片策略要求分片鍵（即分片字段）必須存在于SQL中和數據表結構中，否則無法正確分片；相反，若分片鍵不存在于SQL中和數據表結構中，則可以使用Hint方式進行強制路由。
三、分片鍵
用于分片的數據庫字段，是將數據庫(表)水平拆分的關鍵字段。例：將訂單表中的訂單主鍵的尾數取模分片，則訂單主鍵為分片字段。 SQL中如果無分片字段，將執行全路由，性能較差。 除了對單分片字段的支持，ShardingSphere也支持根據多個字段進行分片。
四、分片算法
通過分片算法將數據分片，支持通過=、IN和BETWEEN AND分片。分片算法需要應用方開發者自行實現，可實現的靈活度非常高。
目前提供4種分片算法。由于分片算法和業務實現緊密相關，因此并未提供內置分片算法，而是通過分片策略將各種場景提煉出來，提供更高層級的抽象，并提供接口讓應用開發者自行實現分片算法。
1. 精確分片算法
對應PreciseShardingAlgorithm，用于處理使用單一鍵作為分片鍵的=與IN進行分片的場景。需要配合StandardShardingStrategy使用。
2. 范圍分片算法
對應RangeShardingAlgorithm，用于處理使用單一鍵作為分片鍵的BETWEEN AND進行分片的場景。需要配合StandardShardingStrategy使用。
3. 復合分片算法
對應ComplexKeysShardingAlgorithm，用于處理使用多鍵作為分片鍵進行分片的場景，包含多個分片鍵的邏輯較復雜，需要應用開發者自行處理其中的復雜度。需要配合ComplexShardingStrategy使用。
4. Hint分片算法
對應HintShardingAlgorithm，用于處理使用Hint行分片的場景。需要配合HintShardingStrategy使用。
五、代碼實踐
在正式介紹代碼之前，有必要先描述下業務背景，便于理解代碼的用途。
數據表結構：
CREATE TABLE `settlement_20180403` (`id` bigint(20) NOT NULL AUTO_INCREMENT,`pay_serial_number` varchar(32) DEFAULT NULL COMMENT '支付流水號',`user_mobile` varchar(15) DEFAULT NULL COMMENT '用戶手機號',`money` int(10) DEFAULT '0' COMMENT '支付或退款金額, 單位: 分',`operate_tm` timestamp NULL DEFAULT NULL COMMENT '操作時間',`refund` tinyint(1) DEFAULT NULL COMMENT '是否退款 1: 是 2: 否',`remark` varchar(32) DEFAULT NULL COMMENT '備注',PRIMARY KEY (`id`),UNIQUE KEY `PAY_SERIAL_NUM_UNIQUE` (`pay_serial_number`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;表結構中比較有趣的字段是?pay_serial_number?，以?232042018040353088?為例，?pay_serial_number?由三部分組成：前5位是固定編碼，樣例中是23204，中間8位是日期，包含年月日，樣例中是20180403，最后5位是隨機數，樣例中是53088，以上三部分組成了支付流水號。
隨著業務量逐漸擴增，?settlement?表數據量急劇，需要以時間作為分表條件水平切分數據，分表字段則為?pay_serial_number?，其中的日期則為分表條件。接下來的代碼都是以此業務背景展開。
如下代碼配置了標準分片策略中的精確分片算法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/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/txhttp://www.springframework.org/schema/tx/spring-tx.xsdhttp://shardingjdbc.io/schema/shardingjdbc/shardinghttp://shardingjdbc.io/schema/shardingjdbc/sharding/sharding.xsd"><!-- 標準分片策略 --><sharding:standard-strategy id="settlementTableShardingStandardStrategy" sharding-column="pay_serial_number"precise-algorithm-class="org.cellphone.finance.repo.sharding.PreciseTableShardingAlgorithm"/><!-- 基于暗示(Hint)的數據分片策略 --><sharding:hint-strategy id="settlementTableShardingHintStrategy"algorithm-class="org.cellphone.finance.repo.sharding.HintTableShardingAlgorithm"/><!-- 加了分庫分表插件，spring boot 啟動會實例化兩個dataSource，不知是否正常？ --><sharding:data-source id="shardingDataSource"><!-- dataSource是數據庫連接池 --><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，否則無法找到對應的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>?精確分片算法：
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;/*** 精確分片算法，屬于標準分片算法，用于處理=和IN的分片* <p>* 使用精確分片算法的前提：分片字段必須存在與SQL中、數據庫表結構中，否則無法使用精確分片算法* <p>* 此分片算法應用于SETTLEMENT數據表，這里是按天分表* <p>* 特別說明：Sharding Jdbc版本：2.0.3* <p>* Created by on 2018/4/9.*/ public class PreciseTableShardingAlgorithm implements PreciseShardingAlgorithm<String> {/*** 精確分片算法** @param availableTargetNames 目標數據源名稱或數據表名稱，注意：是邏輯數據源名或邏輯數據表名，來自SQL* @param shardingValue 分片值，來自SQL中分片字段對應的值* @return 真實數據源名稱或數據表名稱*/@Overridepublic String doSharding(final Collection<String> availableTargetNames, final PreciseShardingValue<String> shardingValue) {// 默認數據表名稱，有可能數據庫中不存在這張表String tableName = "settlement";// 邏輯表名為空，返回默認表名if (CollectionUtils.isEmpty(availableTargetNames))return tableName;// availableTargetNames來自SQL，只有一個元素tableName = Lists.newArrayList(availableTargetNames).get(0);String paySerialNumber = shardingValue.getValue();String suffix = paySerialNumber.substring(5, 13);return tableName + CommonConst.UNDERLINE + suffix;} }上面說過，精確分片算法可以很完美的支持SQL語句中的=和IN的分片操作，因此PreciseTableShardingAlgorithm可以很好的支持簡單的INSERT、UPDATE、DELETE和SELECT操作。
但如果要通過?pay_serial_number?查詢數據就行不通了，因為分片鍵并不直接存在與SQL中和數據表結構中，而是間接存在于?pay_serial_number?中的時間數據，因此，就需要通過Hint方式來進行分片才能定位到真實的數據表。
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 {@Overridepublic Collection<String> doSharding(Collection<String> availableTargetNames, ShardingValue shardingValue) {// 數據表名稱列表List<String> tableNames = new ArrayList<>();// 邏輯表名為空if (CollectionUtils.isEmpty(availableTargetNames))return tableNames;// availableTargetNames來自SQL，只有一個元素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;} }與Hint分片算法對應的Java查詢方法?settlementMapper.selectByExample(example)?：
public List<Settlement> querySettlements(SettlementExample example, String startTime, String endTime) {HintManager hintManager = HintManager.getInstance();// logicTable必須和XML中的logic-table以及SQL中的邏輯表名稱一致hintManager.addTableShardingValue("settlement_hint", "start_time", startTime);hintManager.addTableShardingValue("settlement_hint", "end_time", endTime);List<Settlement> settlements = settlementMapper.selectByExample(example);hintManager.close();return settlements; }以及該查詢方法對應的SQL語句：
select * from settlement_hint t where t.pay_serial_number = ??單元測試代碼：
@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()); }?經過上述一波代碼后，原以為單元測試可以完美通過，但天有不測風云，月有陰晴圓缺，單元測試竟然失敗了，報錯日志提示數據表不存在：
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 existat 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 existat 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拋出錯誤堆棧后，很納悶為何沒有將邏輯表名?settlement_hint?轉換為真實表名?settlement_20180403?，于是就跟蹤了Sharding-JDBC源碼。
經過DEBUG，得知所有JDBC操作都會調用?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操作都會調用此方法，路由到真實表** @return*/@Overridepublic RoutingResult route() {// 從XML中根據邏輯表名獲取配置的數據表規則TableRule tableRule = shardingRule.getTableRule(logicTableName);// 獲取數據源分片值，分片值來自邏輯SQL中的數據，由于XML只配置了單個數據源，暫時不深入分析此環節List<ShardingValue> databaseShardingValues = getDatabaseShardingValues(tableRule);// 獲取數據表分片值，分片值來自邏輯SQL中的數據，重點分析這部分代碼List<ShardingValue> tableShardingValues = getTableShardingValues(tableRule);// 計算需要路由的真實數據源Collection<String> routedDataSources = routeDataSources(tableRule, databaseShardingValues);Collection<DataNode> routedDataNodes = new LinkedList<>();for (String each : routedDataSources) {// routeTables方法計算需要路由的真實數據表，重點分析這部分代碼routedDataNodes.addAll(routeTables(tableRule, each, tableShardingValues));}// 產生路由結果return generateRoutingResult(routedDataNodes);}private List<ShardingValue> getDatabaseShardingValues(final TableRule tableRule) {ShardingStrategy strategy = shardingRule.getDatabaseShardingStrategy(tableRule);return HintManagerHolder.isUseShardingHint() ? getDatabaseShardingValuesFromHint(strategy.getShardingColumns()) : getShardingValues(strategy.getShardingColumns());}/*** 獲取數據表分片值* 分片值由上面提到的querySettlements通過hintManager傳入** @param tableRule 數據表規則，從XML文件中獲取* @return 分片值列表*/private List<ShardingValue> getTableShardingValues(final TableRule tableRule) {// 從XML文件中獲取數據表規則ShardingStrategy strategy = shardingRule.getTableShardingStrategy(tableRule);/** 判斷是否使用了Hint分片算法：* 1. 是：根據ShardingStrategy中拿到的shardingColumns來獲取shardingValues，問題就出在這里！！！* 2. 否：從SQL中根據shardingColumns來獲取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;}/*** 從Hint分片算法中獲取shardingValues** @param shardingColumns 分片鍵* @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) {// 從HintManagerHolder獲取sharding valuesOptional<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;}/*** 計算需要路由的真實數據表** @param tableRule 數據表規則，從XML中獲取* @param routedDataSource 需要路由的數據源* @param tableShardingValues 數據表分片值* @return 需要路由的真實數據節點*/private Collection<DataNode> routeTables(final TableRule tableRule, final String routedDataSource, final List<ShardingValue> tableShardingValues) {// 所有的真實數據表名，在XML中可以顯式配置，也可以省略Collection<String> availableTargetTables = tableRule.getActualTableNames(routedDataSource);/** table sharding values是否為空：* 1. 是：路由到所有真實表* 2. 否：路由到自定義的分表策略算法定義的數據表** 問題就出在這里：tableShardingValues.isEmpty()為true，導致無法使用自定義分表策略算法*/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;} }?上述代碼中，?getTableShardingValuesFromHint?返回的?List<ShardingValue>?為空，原因是?getTableShardingValuesFromHint?的入參?strategy.getShardingColumns()?為空列表，而此參數來自Sharding-JDBC的默認實現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類，無法繼承此類來重定義內部邏輯* * * @author zhangliang*/ public final class HintShardingStrategy implements ShardingStrategy {/*** 沒有提供Setter方法和可以配置的入口，無法設置shardingColumns，這是2.0.3版本的BUG* * github issue: https://github.com/apache/incubator-shardingsphere/issues/1980*/@Getterprivate final Collection<String> shardingColumns;private final HintShardingAlgorithm shardingAlgorithm;public HintShardingStrategy(final HintShardingAlgorithm shardingAlgorithm) {this.shardingColumns = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);this.shardingAlgorithm = shardingAlgorithm;}@Overridepublic 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;} }跟蹤到此，Hint分片算法無法使用的原因一路了然，這是Sharding-JDBC 2.0.3版本的BUG，但在后續版本4.x中得到了修復。
總結
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