你在使用 MyBatis 的過程中，是否有想過多個數據源應該如何配置，如何去實現？出于這個好奇心，我在 Druid Wiki 的數據庫多數據源中知曉 Spring 提供了對多數據源的支持，基于 Spring 提供的 AbstractRoutingDataSource，可以自己實現數據源的切換。

一、配置動態數據源

下面就如何配置動態數據源提供一個簡單的實現：

org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource，代碼如下：

public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean { @Nullable private Object defaultTargetDataSource; @Nullable private Map<Object, DataSource> resolvedDataSources; @Nullable private DataSource resolvedDefaultDataSource; @Override public Connection getConnection() throws SQLException { return determineTargetDataSource().getConnection(); } @Override public Connection getConnection(String username, String password) throws SQLException { return determineTargetDataSource().getConnection(username, password); } protected DataSource determineTargetDataSource() { Assert.notNull(this.resolvedDataSources, 'DataSource router not initialized'); // 確定當前要使用的數據源 Object lookupKey = determineCurrentLookupKey(); DataSource dataSource = this.resolvedDataSources.get(lookupKey); if (dataSource == null && (this.lenientFallback || lookupKey == null)) { dataSource = this.resolvedDefaultDataSource; } if (dataSource == null) { throw new IllegalStateException('Cannot determine target DataSource for lookup key [' + lookupKey + ']'); } return dataSource; } /** * Determine the current lookup key. This will typically be implemented to check a thread-bound transaction context. * <p> * Allows for arbitrary keys. The returned key needs to match the stored lookup key type, as resolved by the * {@link #resolveSpecifiedLookupKey} method. */ @Nullable protected abstract Object determineCurrentLookupKey(); // 省略相關代碼...}

重寫 AbstractRoutingDataSource 的 determineCurrentLookupKey() 方法，可以實現對多數據源的支持

思路：

重寫其 determineCurrentLookupKey() 方法，支持選擇不同的數據源 初始化多個 DataSource 數據源到 AbstractRoutingDataSource 的 resolvedDataSources 屬性中 然后通過 Spring AOP， 以自定義注解作為切點，根據不同的數據源的 Key 值，設置當前線程使用的數據源

接下來的實現方式是 Spring Boot 結合 Druid 配置動態數據源

（一）引入依賴

基于 3.繼承SpringBoot 中已添加的依賴再添加對AOP支持的依賴，如下：

<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-aop</artifactId></dependency>（二）開始實現

1. DataSourceContextHolder

DataSourceContextHolder 使用 ThreadLocal 存儲當前線程指定的數據源的 Key 值，代碼如下：

package cn.tzh.mybatis.config;import lombok.extern.slf4j.Slf4j;import java.util.HashSet;import java.util.Set;/** * @author tzh * @date 2021/1/4 11:42 */@Slf4jpublic class DataSourceContextHolder { /** * 線程本地變量 */ private static final ThreadLocal<String> DATASOURCE_KEY = new ThreadLocal<>(); /** * 配置的所有數據源的 Key 值 */ public static Set<Object> ALL_DATASOURCE_KEY = new HashSet<>(); /** * 設置當前線程的數據源的 Key * * @param dataSourceKey 數據源的 Key 值 */ public static void setDataSourceKey(String dataSourceKey) { if (ALL_DATASOURCE_KEY.contains(dataSourceKey)) { DATASOURCE_KEY.set(dataSourceKey); } else { log.warn('the datasource [{}] does not exist', dataSourceKey); } } /** * 獲取當前線程的數據源的 Key 值 * * @return 數據源的 Key 值 */ public static String getDataSourceKey() { return DATASOURCE_KEY.get(); } /** * 移除當前線程持有的數據源的 Key 值 */ public static void clear() { DATASOURCE_KEY.remove(); }}

2. MultipleDataSource

重寫其 AbstractRoutingDataSource 的 determineCurrentLookupKey() 方法，代碼如下：

package cn.tzh.mybatis.config;import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;/** * @author tzh * @date 2021/1/4 11:44 */public class MultipleDataSource extends AbstractRoutingDataSource { /** * 返回當前線程是有的數據源的 Key * * @return dataSourceKey */ @Override protected Object determineCurrentLookupKey() { return DataSourceContextHolder.getDataSourceKey(); }}

3. DataSourceAspect切面

使用 Spring AOP 功能，定義一個切面，用于設置當前需要使用的數據源，代碼如下：

package cn.tzh.mybatis.config;import lombok.extern.log4j.Log4j2;import org.aspectj.lang.JoinPoint;import org.aspectj.lang.annotation.After;import org.aspectj.lang.annotation.Aspect;import org.aspectj.lang.annotation.Before;import org.aspectj.lang.reflect.MethodSignature;import org.springframework.stereotype.Component;import java.lang.reflect.Method;/** * @author tzh * @date 2021/1/4 11:46 */@Aspect@Component@Log4j2public class DataSourceAspect { @Before('@annotation(cn.tzh.mybatis.config.TargetDataSource)') public void before(JoinPoint joinPoint) { MethodSignature methodSignature = (MethodSignature) joinPoint.getSignature(); Method method = methodSignature.getMethod(); if (method.isAnnotationPresent(TargetDataSource.class)) { TargetDataSource targetDataSource = method.getAnnotation(TargetDataSource.class); DataSourceContextHolder.setDataSourceKey(targetDataSource.value()); log.info('set the datasource of the current thread to [{}]', targetDataSource.value()); } else if (joinPoint.getTarget().getClass().isAnnotationPresent(TargetDataSource.class)) { TargetDataSource targetDataSource = joinPoint.getTarget().getClass().getAnnotation(TargetDataSource.class); DataSourceContextHolder.setDataSourceKey(targetDataSource.value()); log.info('set the datasource of the current thread to [{}]', targetDataSource.value()); } } @After('@annotation(cn.tzh.mybatis.config.TargetDataSource)') public void after() { DataSourceContextHolder.clear(); log.info('clear the datasource of the current thread'); }}

4. DruidConfig

Druid 配置類，代碼如下：

package cn.tzh.mybatis.config;import com.alibaba.druid.support.spring.stat.DruidStatInterceptor;import org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;/** * @author tzh * @date 2021/1/4 11:49 */@Configurationpublic class DruidConfig { @Bean(value = 'druid-stat-interceptor') public DruidStatInterceptor druidStatInterceptor() { return new DruidStatInterceptor(); } @Bean public BeanNameAutoProxyCreator beanNameAutoProxyCreator() { BeanNameAutoProxyCreator beanNameAutoProxyCreator = new BeanNameAutoProxyCreator(); beanNameAutoProxyCreator.setProxyTargetClass(true); // 設置要監控的bean的id beanNameAutoProxyCreator.setInterceptorNames('druid-stat-interceptor'); return beanNameAutoProxyCreator; }}

5. MultipleDataSourceConfig

MyBatis 的配置類，配置了 2 個數據源，代碼如下：

package cn.tzh.mybatis.config;import com.alibaba.druid.pool.DruidDataSource;import com.alibaba.druid.spring.boot.autoconfigure.DruidDataSourceBuilder;import org.apache.ibatis.mapping.DatabaseIdProvider;import org.apache.ibatis.plugin.Interceptor;import org.apache.ibatis.scripting.LanguageDriver;import org.apache.ibatis.session.ExecutorType;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.type.TypeHandler;import org.mybatis.spring.SqlSessionFactoryBean;import org.mybatis.spring.SqlSessionTemplate;import org.mybatis.spring.boot.autoconfigure.ConfigurationCustomizer;import org.mybatis.spring.boot.autoconfigure.MybatisProperties;import org.mybatis.spring.boot.autoconfigure.SpringBootVFS;import org.springframework.beans.BeanWrapperImpl;import org.springframework.beans.factory.ObjectProvider;import org.springframework.boot.context.properties.ConfigurationProperties;import org.springframework.boot.context.properties.EnableConfigurationProperties;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.core.io.ResourceLoader;import org.springframework.jdbc.datasource.DataSourceTransactionManager;import org.springframework.transaction.PlatformTransactionManager;import org.springframework.util.CollectionUtils;import org.springframework.util.ObjectUtils;import org.springframework.util.StringUtils;import javax.sql.DataSource;import java.beans.FeatureDescriptor;import java.util.*;import java.util.stream.Collectors;import java.util.stream.Stream;/** * @author tzh * @projectName code-demo * @title MultipleDataSourceConfig * @description * @date 2021/1/4 13:43 */@Configuration@EnableConfigurationProperties({MybatisProperties.class})public class MultipleDataSourceConfig { private final MybatisProperties properties; private final Interceptor[] interceptors; private final TypeHandler[] typeHandlers; private final LanguageDriver[] languageDrivers; private final ResourceLoader resourceLoader; private final DatabaseIdProvider databaseIdProvider; private final List<ConfigurationCustomizer> configurationCustomizers; public MultipleDataSourceConfig(MybatisProperties properties, ObjectProvider<Interceptor[]> interceptorsProvider, ObjectProvider<TypeHandler[]> typeHandlersProvider, ObjectProvider<LanguageDriver[]> languageDriversProvider, ResourceLoader resourceLoader, ObjectProvider<DatabaseIdProvider> databaseIdProvider, ObjectProvider<List<ConfigurationCustomizer>> configurationCustomizersProvider) { this.properties = properties; this.interceptors = (Interceptor[]) interceptorsProvider.getIfAvailable(); this.typeHandlers = (TypeHandler[]) typeHandlersProvider.getIfAvailable(); this.languageDrivers = (LanguageDriver[]) languageDriversProvider.getIfAvailable(); this.resourceLoader = resourceLoader; this.databaseIdProvider = (DatabaseIdProvider) databaseIdProvider.getIfAvailable(); this.configurationCustomizers = (List) configurationCustomizersProvider.getIfAvailable(); } @Bean(name = 'master', initMethod = 'init', destroyMethod = 'close') @ConfigurationProperties(prefix = 'spring.datasource.druid.master') public DruidDataSource master() { return DruidDataSourceBuilder.create().build(); } @Bean(name = 'slave', initMethod = 'init', destroyMethod = 'close') @ConfigurationProperties(prefix = 'spring.datasource.druid.slave') public DruidDataSource slave() { return DruidDataSourceBuilder.create().build(); } @Bean(name = 'dynamicDataSource') public DataSource dynamicDataSource() { MultipleDataSource dynamicRoutingDataSource = new MultipleDataSource(); Map<Object, Object> dataSources = new HashMap<>(); dataSources.put('master', master()); dataSources.put('slave', slave()); dynamicRoutingDataSource.setDefaultTargetDataSource(master()); dynamicRoutingDataSource.setTargetDataSources(dataSources); DataSourceContextHolder.ALL_DATASOURCE_KEY.addAll(dataSources.keySet()); return dynamicRoutingDataSource; } @Bean public SqlSessionFactory sqlSessionFactory() throws Exception { SqlSessionFactoryBean factory = new SqlSessionFactoryBean(); factory.setDataSource(dynamicDataSource()); factory.setVfs(SpringBootVFS.class); if (StringUtils.hasText(this.properties.getConfigLocation())) { factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation())); } this.applyConfiguration(factory); if (this.properties.getConfigurationProperties() != null) { factory.setConfigurationProperties(this.properties.getConfigurationProperties()); } if (!ObjectUtils.isEmpty(this.interceptors)) { factory.setPlugins(this.interceptors); } if (this.databaseIdProvider != null) { factory.setDatabaseIdProvider(this.databaseIdProvider); } if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) { factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage()); } if (this.properties.getTypeAliasesSuperType() != null) { factory.setTypeAliasesSuperType(this.properties.getTypeAliasesSuperType()); } if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) { factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage()); } if (!ObjectUtils.isEmpty(this.typeHandlers)) { factory.setTypeHandlers(this.typeHandlers); } if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) { factory.setMapperLocations(this.properties.resolveMapperLocations()); } Set<String> factoryPropertyNames = (Set) Stream.of((new BeanWrapperImpl(SqlSessionFactoryBean.class)).getPropertyDescriptors()).map(FeatureDescriptor::getName).collect(Collectors.toSet()); Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver(); if (factoryPropertyNames.contains('scriptingLanguageDrivers') && !ObjectUtils.isEmpty(this.languageDrivers)) { factory.setScriptingLanguageDrivers(this.languageDrivers); if (defaultLanguageDriver == null && this.languageDrivers.length == 1) { defaultLanguageDriver = this.languageDrivers[0].getClass(); } } if (factoryPropertyNames.contains('defaultScriptingLanguageDriver')) { factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver); } return factory.getObject(); } private void applyConfiguration(SqlSessionFactoryBean factory) { org.apache.ibatis.session.Configuration configuration = this.properties.getConfiguration(); if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) { configuration = new org.apache.ibatis.session.Configuration(); } if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) { Iterator var3 = this.configurationCustomizers.iterator(); while (var3.hasNext()) { ConfigurationCustomizer customizer = (ConfigurationCustomizer) var3.next(); customizer.customize(configuration); } } factory.setConfiguration(configuration); } @Bean public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) { ExecutorType executorType = this.properties.getExecutorType(); return executorType != null ? new SqlSessionTemplate(sqlSessionFactory, executorType) : new SqlSessionTemplate(sqlSessionFactory); } @Bean public PlatformTransactionManager masterTransactionManager() { // 配置事務管理器 return new DataSourceTransactionManager(dynamicDataSource()); }}

6. 添加配置

server: port: 9092 servlet: context-path: /mybatis-springboot-demo tomcat: accept-count: 200 min-spare-threads: 200spring: application: name: mybatis-springboot-demo profiles: active: test servlet: multipart: max-file-size: 100MB max-request-size: 100MB datasource: type: com.alibaba.druid.pool.DruidDataSource druid: master: driver-class-name: com.mysql.cj.jdbc.Driver url: jdbc:mysql://127.0.0.1:3306/mybatis-demo username: root password: root initial-size: 5 # 初始化時建立物理連接的個數 min-idle: 20 # 最小連接池數量 max-active: 20 # 最大連接池數量 slave: driver-class-name: com.mysql.cj.jdbc.Driver url: jdbc:mysql://127.0.0.1:3306/mybatis-demo1 username: root password: root initial-size: 5 # 初始化時建立物理連接的個數 min-idle: 20 # 最小連接池數量 max-active: 20 # 最大連接池數量mybatis: type-aliases-package: cn.tzh.mybatis.entity mapper-locations: classpath:cn/tzh/mybatis/mapper/*.xml config-location: classpath:mybatis-config.xmlpagehelper: helper-dialect: mysql reasonable: true # 分頁合理化參數 offset-as-page-num: true # 將 RowBounds 中的 offset 參數當成 pageNum 使用 supportMethodsArguments: true # 支持通過 Mapper 接口參數來傳遞分頁參數

其中分別定義了 master 和 slave 數據源的相關配置

這樣一來，在 DataSourceAspect 切面中根據自定義注解，設置 DataSourceContextHolder 當前線程所使用的數據源的 Key 值，MultipleDataSource 動態數據源則會根據該值設置需要使用的數據源，完成了動態數據源的切換

7. 使用示例

在 Mapper 接口上面添加自定義注解 @TargetDataSource，如下：

package cn.tzh.mybatis.mapper;import cn.tzh.mybatis.config.TargetDataSource;import cn.tzh.mybatis.entity.User;import org.apache.ibatis.annotations.Mapper;import org.apache.ibatis.annotations.Param;/** * @author tzh * @date 2020/12/28 14:29 */@Mapperpublic interface UserMapper { User selectUserOne(@Param('id') Long id); @TargetDataSource('slave') User selectUserTwo(@Param('id') Long id);} 總結

上面就如何配置動態數據源的實現方式僅提供一種思路，其中關于多事務方面并沒有實現，采用 Spring 提供的事務管理器，如果同一個方法中使用了多個數據源，并不支持多事務的，需要自己去實現（筆者能力有限），可以整合JAT組件，參考：SpringBoot2 整合JTA組件多數據源事務管理

分布式事務解決方案推薦使用 Seata 分布式服務框架

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