你在使用 MyBatis 的过程中，是否有想过多个数据源应该如何配置，如何去实现？出于这个好奇心，我在 Druid Wiki 的数据库多数据源中知晓 Spring 提供了对多数据源的支持，基于 Spring 提供的 AbstractRoutingDataSource，可以自己实现数据源的切换。
下面就如何配置动态数据源提供一个简单的实现：
org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource，代码如下：
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");
// 确定当前要使用的数据源
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();
// 省略相关代码...
}
重写 AbstractRoutingDataSource 的 determineCurrentLookupKey() 方法，可以实现对多数据源的支持
思路：
接下来的实现方式是 Spring Boot 结合 Druid 配置动态数据源
基于 3.继承SpringBoot 中已添加的依赖再添加对AOP支持的依赖，如下：
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-aop</artifactId> </dependency>
1. DataSourceContextHolder
DataSourceContextHolder 使用 ThreadLocal 存储当前线程指定的数据源的 Key 值，代码如下：
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
*/
@Slf4j
public class DataSourceContextHolder {
/**
* 线程本地变量
*/
private static final ThreadLocal<String> DATASOURCE_KEY = new ThreadLocal<>();
/**
* 配置的所有数据源的 Key 值
*/
public static Set<Object> ALL_DATASOURCE_KEY = new HashSet<>();
/**
* 设置当前线程的数据源的 Key
*
* @param dataSourceKey 数据源的 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);
}
}
/**
* 获取当前线程的数据源的 Key 值
*
* @return 数据源的 Key 值
*/
public static String getDataSourceKey() {
return DATASOURCE_KEY.get();
}
/**
* 移除当前线程持有的数据源的 Key 值
*/
public static void clear() {
DATASOURCE_KEY.remove();
}
}
2. MultipleDataSource
重写其 AbstractRoutingDataSource 的 determineCurrentLookupKey() 方法，代码如下：
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 {
/**
* 返回当前线程是有的数据源的 Key
*
* @return dataSourceKey
*/
@Override
protected Object determineCurrentLookupKey() {
return DataSourceContextHolder.getDataSourceKey();
}
}
3. DataSourceAspect切面
使用 Spring AOP 功能，定义一个切面，用于设置当前需要使用的数据源，代码如下：
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
@Log4j2
public 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 配置类，代码如下：
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
*/
@Configuration
public class DruidConfig {
@Bean(value = "druid-stat-interceptor")
public DruidStatInterceptor druidStatInterceptor() {
return new DruidStatInterceptor();
}
@Bean
public BeanNameAutoProxyCreator beanNameAutoProxyCreator() {
BeanNameAutoProxyCreator beanNameAutoProxyCreator = new BeanNameAutoProxyCreator();
beanNameAutoProxyCreator.setProxyTargetClass(true);
// 设置要监控的bean的id
beanNameAutoProxyCreator.setInterceptorNames("druid-stat-interceptor");
return beanNameAutoProxyCreator;
}
}
5. MultipleDataSourceConfig
MyBatis 的配置类，配置了 2 个数据源，代码如下：
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() {
// 配置事务管理器
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: 200 spring: 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 # 初始化时建立物理连接的个数 min-idle: 20 # 最小连接池数量 max-active: 20 # 最大连接池数量 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 # 初始化时建立物理连接的个数 min-idle: 20 # 最小连接池数量 max-active: 20 # 最大连接池数量 mybatis: type-aliases-package: cn.tzh.mybatis.entity mapper-locations: classpath:cn/tzh/mybatis/mapper/*.xml config-location: classpath:mybatis-config.xml pagehelper: helper-dialect: mysql reasonable: true # 分页合理化参数 offset-as-page-num: true # 将 RowBounds 中的 offset 参数当成 pageNum 使用 supportMethodsArguments: true # 支持通过 Mapper 接口参数来传递分页参数
其中分别定义了 master 和 slave 数据源的相关配置
这样一来，在 DataSourceAspect 切面中根据自定义注解，设置 DataSourceContextHolder 当前线程所使用的数据源的 Key 值，MultipleDataSource 动态数据源则会根据该值设置需要使用的数据源，完成了动态数据源的切换
7. 使用示例
在 Mapper 接口上面添加自定义注解 @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
*/
@Mapper
public interface UserMapper {
User selectUserOne(@Param("id") Long id);
@TargetDataSource("slave")
User selectUserTwo(@Param("id") Long id);
}
上面就如何配置动态数据源的实现方式仅提供一种思路，其中关于多事务方面并没有实现，采用 Spring 提供的事务管理器，如果同一个方法中使用了多个数据源，并不支持多事务的，需要自己去实现（笔者能力有限），可以整合JAT组件，参考：SpringBoot2 整合JTA组件多数据源事务管理
分布式事务解决方案推荐使用 Seata 分布式服务框架
