Spring Boot MyBatis 动态数据源切换、多数据源，读写分离

蔚落 2022-01-26 08:27 403阅读 0赞

转自： [https://blog.csdn.net/u013360850/article/details/78861442][https_blog.csdn.net_u013360850_article_details_78861442]

Spring Boot + Mybatis多数据源和动态数据源配置:  [https://blog.csdn.net/neosmith/article/details/61202084][https_blog.csdn.net_neosmith_article_details_61202084]

mybatis连接多个数据源成功案例: [https://blog.csdn.net/tan554334064/article/details/52188885][https_blog.csdn.net_tan554334064_article_details_52188885]

Spring Boot MyBatis 动态数据源切换、多数据源，读写分离: [https://blog.csdn.net/u013360850/article/details/78861442][https_blog.csdn.net_u013360850_article_details_78861442]

项目地址 https://github.com/helloworlde/SpringBoot-DynamicDataSource  
本项目使用 Spring Boot 和 MyBatis 实现多数据源，动态数据源的切换；有多种不同的实现方式，在学习的过程中发现没有文章将这些方式和常见的问题集中处理，所以将常用的方式和常见的问题都写在了在本项目的不同分支上：

master: 使用了多数据源的 RESTful API 接口，使用 Druid 实现了 DAO 层数据源动态切换和只读数据源负载均衡  
dev: 最简单的切面和注解方式实现的动态数据源切换  
druid: 通过切面和注解方式实现的使用 Druid 连接池的动态数据源切换  
aspect\_dao: 通过切面实现的 DAO 层的动态数据源切换  
roundrobin: 通过切面使用轮询方式实现的只读数据源负载均衡  
hikari: 升级到SpringBoot 2.0, 数据源使用 Hikari  
以上分支都是基于 dev 分支修改或扩充而来，基本涵盖了常用的多数据源动态切换的方式，基本的原理都一样，都是通过切面根据不同的条件在执行数据库操作前切换数据源

在使用的过程中基本踩遍了所有动态数据源切换的坑，将常见的一些坑和解决方法写在了 Issues 里面  
该项目使用了一个可写数据源和多个只读数据源，为了减少数据库压力，使用轮循的方式选择只读数据源；考虑到在一个 Service 中同时会有读和写的操作，所以本应用使用 AOP 切面通过 DAO 层的方法名切换只读数据源；但这种方式要求数据源主从一致，并且应当避免在同一个 Service 方法中写入后立即查询，如果必须在执行写入操作后立即读取，应当在 Service 方法上添加 @Transactional 注解以保证使用主数据源

需要注意的是，使用 DAO 层切面后不应该在 Service 类层面上加 @Transactional 注解，而应该添加在方法上，这也是 Spring 推荐的做法

动态切换数据源依赖 configuration 包下的4个类来实现，分别是：

DataSourceRoutingDataSource.java  
DataSourceConfigurer.java  
DynamicDataSourceContextHolder.java  
DynamicDataSourceAspect.java  
添加依赖  
dependencies \{  
    compile('org.mybatis.spring.boot:mybatis-spring-boot-starter:1.3.1')  
    compile('org.springframework.boot:spring-boot-starter-web')  
    compile('org.springframework.boot:spring-boot-starter-aop')  
    compile('com.alibaba:druid-spring-boot-starter:1.1.6')  
    runtime('mysql:mysql-connector-java')  
    testCompile('org.springframework.boot:spring-boot-starter-test')  
\}

创建数据库及表  
分别创建数据库product\_master, product\_slave\_alpha, product\_slave\_beta, product\_slave\_gamma  
在以上数据库中分别创建表 product，并插入不同数据  
DROP DATABASE IF EXISTS product\_master;  
CREATE DATABASE product\_master;  
CREATE TABLE product\_master.product(  
  id INT PRIMARY KEY AUTO\_INCREMENT,  
  name VARCHAR(50) NOT NULL,  
  price DOUBLE(10,2) NOT NULL DEFAULT 0);  
INSERT INTO product\_master.product (name, price) VALUES('master', '1');

DROP DATABASE IF EXISTS product\_slave\_alpha;  
CREATE DATABASE product\_slave\_alpha;  
CREATE TABLE product\_slave\_alpha.product(  
  id INT PRIMARY KEY AUTO\_INCREMENT,  
  name VARCHAR(50) NOT NULL,  
  price DOUBLE(10,2) NOT NULL DEFAULT 0);  
INSERT INTO product\_slave\_alpha.product (name, price) VALUES('slaveAlpha', '1');

DROP DATABASE IF EXISTS product\_slave\_beta;  
CREATE DATABASE product\_slave\_beta;  
CREATE TABLE product\_slave\_beta.product(  
  id INT PRIMARY KEY AUTO\_INCREMENT,  
  name VARCHAR(50) NOT NULL,  
  price DOUBLE(10,2) NOT NULL DEFAULT 0);  
INSERT INTO product\_slave\_beta.product (name, price) VALUES('slaveBeta', '1');

DROP DATABASE IF EXISTS product\_slave\_gamma;  
CREATE DATABASE product\_slave\_gamma;  
CREATE TABLE product\_slave\_gamma.product(  
  id INT PRIMARY KEY AUTO\_INCREMENT,  
  name VARCHAR(50) NOT NULL,  
  price DOUBLE(10,2) NOT NULL DEFAULT 0);  
INSERT INTO product\_slave\_gamma.product (name, price) VALUES('slaveGamma', '1');

配置数据源  
application.properties  
\# Master datasource config  
spring.datasource.druid.master.name=master  
spring.datasource.druid.master.driver-class-name=com.mysql.jdbc.Driver  
spring.datasource.druid.master.url=jdbc:mysql://localhost/product\_master?useSSL=false  
spring.datasource.druid.master.port=3306  
spring.datasource.druid.master.username=root  
spring.datasource.druid.master.password=123456

\# SlaveAlpha datasource config  
spring.datasource.druid.slave-alpha.name=SlaveAlpha  
spring.datasource.druid.slave-alpha.driver-class-name=com.mysql.jdbc.Driver  
spring.datasource.druid.slave-alpha.url=jdbc:mysql://localhost/product\_slave\_alpha?useSSL=false  
spring.datasource.druid.slave-alpha.port=3306  
spring.datasource.druid.slave-alpha.username=root  
spring.datasource.druid.slave-alpha.password=123456

\# SlaveBeta datasource config  
spring.datasource.druid.slave-beta.name=SlaveBeta  
spring.datasource.druid.slave-beta.driver-class-name=com.mysql.jdbc.Driver  
spring.datasource.druid.slave-beta.url=jdbc:mysql://localhost/product\_slave\_beta?useSSL=false  
spring.datasource.druid.slave-beta.port=3306  
spring.datasource.druid.slave-beta.username=root  
spring.datasource.druid.slave-beta.password=123456

\# SlaveGamma datasource config  
spring.datasource.druid.slave-gamma.name=SlaveGamma  
spring.datasource.druid.slave-gamma.driver-class-name=com.mysql.jdbc.Driver  
spring.datasource.druid.slave-gamma.url=jdbc:mysql://localhost/product\_slave\_gamma?useSSL=false  
spring.datasource.druid.slave-gamma.port=3306  
spring.datasource.druid.slave-gamma.username=root  
spring.datasource.druid.slave-gamma.password=123456

\# Druid dataSource config  
spring.datasource.type=com.alibaba.druid.pool.DruidDataSource  
spring.datasource.druid.initial-size=5  
spring.datasource.druid.max-active=20  
spring.datasource.druid.min-idle=5  
spring.datasource.druid.max-wait=60000  
spring.datasource.druid.pool-prepared-statements=false  
spring.datasource.druid.validation-query=SELECT 1  
spring.datasource.druid.validation-query-timeout=30000  
spring.datasource.druid.test-on-borrow=false  
spring.datasource.druid.test-on-return=false  
spring.datasource.druid.test-while-idle=true  
\#spring.datasource.druid.time-between-eviction-runs-millis=  
\#spring.datasource.druid.min-evictable-idle-time-millis=  
\#spring.datasource.druid.max-evictable-idle-time-millis=10000

\# Druid stat filter config  
spring.datasource.druid.filters=stat,wall,log4j  
spring.datasource.druid.web-stat-filter.enabled=true  
spring.datasource.druid.web-stat-filter.url-pattern=/\*  
spring.datasource.druid.web-stat-filter.exclusions=\*.js,\*.gif,\*.jpg,\*.png,\*.css,\*.ico,/druid/\*  
spring.datasource.druid.web-stat-filter.session-stat-enable=true  
spring.datasource.druid.web-stat-filter.session-stat-max-count=10  
spring.datasource.druid.web-stat-filter.principal-session-name=user  
\#spring.datasource.druid.web-stat-filter.principal-cookie-name=  
spring.datasource.druid.web-stat-filter.profile-enable=true  
spring.datasource.druid.filter.stat.db-type=mysql  
spring.datasource.druid.filter.stat.log-slow-sql=true  
spring.datasource.druid.filter.stat.slow-sql-millis=1000  
spring.datasource.druid.filter.stat.merge-sql=true  
spring.datasource.druid.filter.wall.enabled=true  
spring.datasource.druid.filter.wall.config.delete-allow=true  
spring.datasource.druid.filter.wall.config.drop-table-allow=false  
spring.datasource.druid.filter.slf4j.enabled=true  
\# Druid manage page config  
spring.datasource.druid.stat-view-servlet.enabled=true  
spring.datasource.druid.stat-view-servlet.url-pattern=/druid/\*  
spring.datasource.druid.stat-view-servlet.reset-enable=true  
spring.datasource.druid.stat-view-servlet.login-username=admin  
spring.datasource.druid.stat-view-servlet.login-password=admin  
\#spring.datasource.druid.stat-view-servlet.allow=  
\#spring.datasource.druid.stat-view-servlet.deny=  
spring.datasource.druid.use-global-data-source-stat=true  
\# Druid AOP config  
spring.datasource.druid.aop-patterns=cn.com.hellowood.dynamicdatasource.service.\*  
spring.aop.proxy-target-class=true

\# MyBatis config  
mybatis.type-aliases-package=cn.com.hellowood.dynamicdatasource.mapper  
mybatis.mapper-locations=mappers/\*\*Mapper.xml  
server.port=9999  
  
配置数据源  
DataSourceKey.java  
package cn.com.hellowood.dynamicdatasource.common;

public enum DataSourceKey \{  
    master,  
    slaveAlpha,  
    slaveBeta,  
    slaveGamma  
\}

DataSourceRoutingDataSource.java  
该类继承自 AbstractRoutingDataSource 类，在访问数据库时会调用该类的 determineCurrentLookupKey() 方法获取数据库实例的 key

package cn.com.hellowood.dynamicdatasource.configuration;

import org.slf4j.Logger;  
import org.slf4j.LoggerFactory;  
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

public class DynamicRoutingDataSource extends AbstractRoutingDataSource \{

private final Logger logger = LoggerFactory.getLogger(getClass());

@Override  
    protected Object determineCurrentLookupKey() \{  
        logger.info("Current DataSource is \[\{\}\]", DynamicDataSourceContextHolder.getDataSourceKey());  
        return DynamicDataSourceContextHolder.getDataSourceKey();  
    \}  
\}

DataSourceConfigurer.java  
数据源配置类，在该类中生成多个数据源实例并将其注入到 ApplicationContext 中

package cn.com.hellowood.dynamicdatasource.configuration;

import org.mybatis.spring.SqlSessionFactoryBean;  
import org.springframework.boot.autoconfigure.jdbc.DataSourceBuilder;  
import org.springframework.boot.context.properties.ConfigurationProperties;  
import org.springframework.context.annotation.Bean;  
import org.springframework.context.annotation.Configuration;  
import org.springframework.context.annotation.Primary;

import javax.sql.DataSource;  
import java.util.HashMap;  
import java.util.Map;

@Configuration  
public class DataSourceConfigurer \{

/\*\*  
     \* master DataSource  
     \* @Primary 注解用于标识默认使用的 DataSource Bean，因为有5个 DataSource Bean，该注解可用于 master  
     \* 或 slave DataSource Bean, 但不能用于 dynamicDataSource Bean, 否则会产生循环调用   
     \*   
     \* @ConfigurationProperties 注解用于从 application.properties 文件中读取配置，为 Bean 设置属性   
     \* @return data source  
     \*/  
    @Bean("master")  
    @Primary  
    @ConfigurationProperties(prefix = "spring.datasource.druid.master")  
    public DataSource master() \{  
        return DruidDataSourceBuilder.create().build();  
    \}

/\*\*  
     \* Slave alpha data source.  
     \*  
     \* @return the data source  
     \*/  
    @Bean("slaveAlpha")  
    @ConfigurationProperties(prefix = "spring.datasource.druid.slave-alpha")  
    public DataSource slaveAlpha() \{  
        return DruidDataSourceBuilder.create().build();  
    \}

/\*\*  
     \* Slave beta data source.  
     \*  
     \* @return the data source  
     \*/  
    @Bean("slaveBeta")  
    @ConfigurationProperties(prefix = "spring.datasource.druid.slave-beta")  
    public DataSource slaveBeta() \{  
        return DruidDataSourceBuilder.create().build();  
    \}

/\*\*  
     \* Slave gamma data source.  
     \*  
     \* @return the data source  
     \*/  
    @Bean("slaveGamma")  
    @ConfigurationProperties(prefix = "spring.datasource.druid.slave-gamma")  
    public DataSource slaveGamma() \{  
        return DruidDataSourceBuilder.create().build();  
    \}

/\*\*  
     \* Dynamic data source.  
     \*  
     \* @return the data source  
     \*/  
    @Bean("dynamicDataSource")  
    public DataSource dynamicDataSource() \{  
        DynamicRoutingDataSource dynamicRoutingDataSource = new DynamicRoutingDataSource();  
        Map<Object, Object> dataSourceMap = new HashMap<>(4);  
        dataSourceMap.put(DataSourceKey.master.name(), master());  
        dataSourceMap.put(DataSourceKey.slaveAlpha.name(), slaveAlpha());  
        dataSourceMap.put(DataSourceKey.slaveBeta.name(), slaveBeta());  
        dataSourceMap.put(DataSourceKey.slaveGamma.name(), slaveGamma());

// 将 master 数据源作为默认指定的数据源  
        dynamicRoutingDataSource.setDefaultTargetDataSource(master());  
        // 将 master 和 slave 数据源作为指定的数据源  
        dynamicRoutingDataSource.setTargetDataSources(dataSourceMap);

// 将数据源的 key 放到数据源上下文的 key 集合中，用于切换时判断数据源是否有效  
        DynamicDataSourceContextHolder.dataSourceKeys.addAll(dataSourceMap.keySet());

// 将 Slave 数据源的 key 放在集合中，用于轮循  
        DynamicDataSourceContextHolder.slaveDataSourceKeys.addAll(dataSourceMap.keySet());  
        DynamicDataSourceContextHolder.slaveDataSourceKeys.remove(DataSourceKey.master.name());  
        return dynamicRoutingDataSource;  
    \}     
      
    /\*\*  
     \* 配置 SqlSessionFactoryBean  
     \* @ConfigurationProperties 在这里是为了将 MyBatis 的 mapper 位置和持久层接口的别名设置到   
     \* Bean 的属性中，如果没有使用 \*.xml 则可以不用该配置，否则将会产生 invalid bond statement 异常  
     \*   
     \* @return the sql session factory bean  
     \*/  
    @Bean  
    @ConfigurationProperties(prefix = "mybatis")  
    public SqlSessionFactoryBean sqlSessionFactoryBean() \{  
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();  
        // 配置数据源，此处配置为关键配置，如果没有将 dynamicDataSource 作为数据源则不能实现切换  
        sqlSessionFactoryBean.setDataSource(dynamicDataSource());  
        return sqlSessionFactoryBean;  
    \}  
      
    /\*\*  
     \* 注入 DataSourceTransactionManager 用于事务管理  
     \*/  
    @Bean  
    public PlatformTransactionManager transactionManager() \{  
        return new DataSourceTransactionManager(dynamicDataSource());  
    \}  
      
\}

DynamicDataSourceContextHolder.java  
该类为数据源上下文配置，用于切换数据源

package cn.com.hellowood.dynamicdatasource.configuration;

import cn.com.hellowood.dynamicdatasource.common.DataSourceKey;  
import org.slf4j.Logger;  
import org.slf4j.LoggerFactory;

import java.util.ArrayList;  
import java.util.List;  
import java.util.concurrent.locks.Lock;  
import java.util.concurrent.locks.ReentrantLock;

public class DynamicDataSourceContextHolder \{

private static final Logger logger = LoggerFactory.getLogger(DynamicDataSourceContextHolder.class);

/\*\*  
     \* 用于在切换数据源时保证不会被其他线程修改  
     \*/  
    private static Lock lock = new ReentrantLock();

/\*\*  
     \* 用于轮循的计数器  
     \*/  
    private static int counter = 0;

/\*\*  
     \* Maintain variable for every thread, to avoid effect other thread  
     \*/  
    private static final ThreadLocal<Object> CONTEXT\_HOLDER = ThreadLocal.withInitial(DataSourceKey.master);

/\*\*  
     \* All DataSource List  
     \*/  
    public static List<Object> dataSourceKeys = new ArrayList<>();

/\*\*  
     \* The constant slaveDataSourceKeys.  
     \*/  
    public static List<Object> slaveDataSourceKeys = new ArrayList<>();

/\*\*  
     \* To switch DataSource  
     \*  
     \* @param key the key  
     \*/  
    public static void setDataSourceKey(String key) \{  
        CONTEXT\_HOLDER.set(key);  
    \}

/\*\*  
     \* Use master data source.  
     \*/  
    public static void useMasterDataSource() \{  
        CONTEXT\_HOLDER.set(DataSourceKey.master);  
    \}

/\*\*  
     \* 当使用只读数据源时通过轮循方式选择要使用的数据源  
     \*/  
    public static void useSlaveDataSource() \{  
        lock.lock();

try \{  
            int datasourceKeyIndex = counter % slaveDataSourceKeys.size();  
            CONTEXT\_HOLDER.set(String.valueOf(slaveDataSourceKeys.get(datasourceKeyIndex)));  
            counter++;  
        \} catch (Exception e) \{  
            logger.error("Switch slave datasource failed, error message is \{\}", e.getMessage());  
            useMasterDataSource();  
            e.printStackTrace();  
        \} finally \{  
            lock.unlock();  
        \}  
    \}

/\*\*  
     \* Get current DataSource  
     \*  
     \* @return data source key  
     \*/  
    public static String getDataSourceKey() \{  
        return CONTEXT\_HOLDER.get();  
    \}

/\*\*  
     \* To set DataSource as default  
     \*/  
    public static void clearDataSourceKey() \{  
        CONTEXT\_HOLDER.remove();  
    \}

/\*\*  
     \* Check if give DataSource is in current DataSource list  
     \*  
     \* @param key the key  
     \* @return boolean boolean  
     \*/  
    public static boolean containDataSourceKey(String key) \{  
        return dataSourceKeys.contains(key);  
    \}  
\}

DynamicDataSourceAspect.java  
动态数据源切换的切面，切 DAO 层，通过 DAO 层方法名判断使用哪个数据源，实现数据源切换

package cn.com.hellowood.dynamicdatasource.configuration;

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.annotation.Pointcut;  
import org.slf4j.Logger;  
import org.slf4j.LoggerFactory;  
import org.springframework.stereotype.Component;

@Aspect  
@Component  
public class DynamicDataSourceAspect \{  
    private static final Logger logger = LoggerFactory.getLogger(DynamicDataSourceAspect.class);

private final String\[\] QUERY\_PREFIX = \{"select"\};

@Pointcut("execution( \* cn.com.hellowood.dynamicdatasource.mapper.\*.\*(..))")  
    public void daoAspect() \{  
    \}

@Before("daoAspect()")  
    public void switchDataSource(JoinPoint point) \{  
        Boolean isQueryMethod = isQueryMethod(point.getSignature().getName());  
        if (isQueryMethod) \{  
            DynamicDataSourceContextHolder.useSlaveDataSource();  
            logger.info("Switch DataSource to \[\{\}\] in Method \[\{\}\]",  
                    DynamicDataSourceContextHolder.getDataSourceKey(), point.getSignature());  
        \}  
    \}

@After("daoAspect()")  
    public void restoreDataSource(JoinPoint point) \{  
        DynamicDataSourceContextHolder.clearDataSourceKey();  
        logger.info("Restore DataSource to \[\{\}\] in Method \[\{\}\]",  
                DynamicDataSourceContextHolder.getDataSourceKey(), point.getSignature());  
    \}

private Boolean isQueryMethod(String methodName) \{  
        for (String prefix : QUERY\_PREFIX) \{  
            if (methodName.startsWith(prefix)) \{  
                return true;  
            \}  
        \}  
        return false;  
    \}

配置 Product REST API 接口  
ProductController.java  
package cn.com.hellowood.dynamicdatasource.controller;

import cn.com.hellowood.dynamicdatasource.common.CommonResponse;  
import cn.com.hellowood.dynamicdatasource.common.ResponseUtil;  
import cn.com.hellowood.dynamicdatasource.modal.Product;  
import cn.com.hellowood.dynamicdatasource.service.ProductService;  
import cn.com.hellowood.dynamicdatasource.utils.ServiceException;  
import org.springframework.beans.factory.annotation.Autowired;  
import org.springframework.web.bind.annotation.\*;

@RestController  
@RequestMapping("/product")  
public class ProductController \{

@Autowired  
    private ProductService productService;

@GetMapping("/\{id\}")  
    public CommonResponse getProduct(@PathVariable("id") Long productId) throws ServiceException \{  
        return ResponseUtil.generateResponse(productService.select(productId));  
    \}

@GetMapping  
    public CommonResponse getAllProduct() \{  
        return ResponseUtil.generateResponse(productService.getAllProduct());  
    \}

@PutMapping("/\{id\}")  
    public CommonResponse updateProduct(@PathVariable("id") Long productId, @RequestBody Product newProduct) throws ServiceException \{  
        return ResponseUtil.generateResponse(productService.update(productId, newProduct));  
    \}

@DeleteMapping("/\{id\}")  
    public CommonResponse deleteProduct(@PathVariable("id") long productId) throws ServiceException \{  
        return ResponseUtil.generateResponse(productService.delete(productId));  
    \}

@PostMapping  
    public CommonResponse addProduct(@RequestBody Product newProduct) throws ServiceException \{  
        return ResponseUtil.generateResponse(productService.add(newProduct));  
    \}  
\}

ProductService.java  
package cn.com.hellowood.dynamicdatasource.service;

import cn.com.hellowood.dynamicdatasource.mapper.ProductDao;  
import cn.com.hellowood.dynamicdatasource.modal.Product;  
import cn.com.hellowood.dynamicdatasource.utils.ServiceException;  
import org.springframework.beans.factory.annotation.Autowired;  
import org.springframework.dao.DataAccessException;  
import org.springframework.stereotype.Service;  
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

@Service  
public class ProductService \{

@Autowired  
    private ProductDao productDao;

public Product select(long productId) throws ServiceException \{  
        Product product = productDao.select(productId);  
        if (product == null) \{  
            throw new ServiceException("Product:" + productId + " not found");  
        \}  
        return product;  
    \}

@Transactional(rollbackFor = DataAccessException.class)  
    public Product update(long productId, Product newProduct) throws ServiceException \{

if (productDao.update(newProduct) <= 0) \{  
            throw new ServiceException("Update product:" + productId + "failed");  
        \}  
        return newProduct;  
    \}

@Transactional(rollbackFor = DataAccessException.class)  
    public boolean add(Product newProduct) throws ServiceException \{  
        Integer num = productDao.insert(newProduct);  
        if (num <= 0) \{  
            throw new ServiceException("Add product failed");  
        \}  
        return true;  
    \}

@Transactional(rollbackFor = DataAccessException.class)  
    public boolean delete(long productId) throws ServiceException \{  
        Integer num = productDao.delete(productId);  
        if (num <= 0) \{  
            throw new ServiceException("Delete product:" + productId + "failed");  
        \}  
        return true;  
    \}

public List<Product> getAllProduct() \{  
        return productDao.getAllProduct();  
    \}  
\}

ProductDao.java  
package cn.com.hellowood.dynamicdatasource.mapper;

import cn.com.hellowood.dynamicdatasource.modal.Product;  
import org.apache.ibatis.annotations.Mapper;  
import org.apache.ibatis.annotations.Param;

import java.util.List;

@Mapper  
public interface ProductDao \{  
    Product select(@Param("id") long id);

Integer update(Product product);

Integer insert(Product product);

Integer delete(long productId);

List<Product> getAllProduct();  
\}

ProductMapper.xml  
启动项目，此时访问 /product/1 会返回 product\_master 数据库中 product 表中的所有数据，多次访问 /product 会分别返回 product\_slave\_alpha、product\_slave\_beta、product\_slave\_gamma 数据库中 product 表中的数据，同时也可以在看到切换数据源的 log，说明动态切换数据源是有效的

注意  
在该应用中因为使用了 DAO 层的切面切换数据源，所以 @Transactional 注解不能加在类上，只能用于方法；有 @Trasactional注解的方法无法切换数据源  
\---------------------   
作者：呜呜呜啦啦啦   
来源：CSDN   
原文：https://blog.csdn.net/u013360850/article/details/78861442   
版权声明：本文为博主原创文章，转载请附上博文链接！

[https_blog.csdn.net_u013360850_article_details_78861442]: https://blog.csdn.net/u013360850/article/details/78861442
[https_blog.csdn.net_neosmith_article_details_61202084]: https://blog.csdn.net/neosmith/article/details/61202084
[https_blog.csdn.net_tan554334064_article_details_52188885]: https://blog.csdn.net/tan554334064/article/details/52188885