一、先修改配置文件

spring: 
	datasource:
	    name: druidDataSource
	    type: com.alibaba.druid.pool.DruidDataSource
	    driver-class-name: com.mysql.cj.jdbc.Driver
	    druid:
	      #数据库1
	      db1:
	        url: jdbc:mysql://localhost:3306/mysql?serverTimezone=UTC&characterEncoding=UTF-8&useSSL=false&allowMultiQueries=true
	        username: root
	        password: root
	      #数据源2
	      db2:
	        # 数据源2开关、默认关闭
	        enable: false
	        url: jdbc:mysql://localhost:3306/nacos_config?serverTimezone=UTC&characterEncoding=UTF-8&useSSL=false&allowMultiQueries=true
	        username: root
	        password: root

二、添加配置类（根据生效位置配置）

1. DB1Config.java(数据源1)

import com.alibaba.druid.pool.DruidDataSource;
import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.SqlSessionTemplate;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;

import javax.sql.DataSource;

/**
 * @Author liull
 * @DATE 2022/6/21 13:22
 **/
@Slf4j
@Configuration
@MapperScan(value = {"xxx.xxx.xxx.db1.dao"}, sqlSessionTemplateRef = "db1SqlSessionTemplate")
public class DB1Config {
    @Value("${spring.datasource.druid.db1.url}")
    private String url;
    @Value("${spring.datasource.druid.db1.username}")
    private String username;
    @Value("${spring.datasource.druid.db1.password}")
    private String password;
    @Value("${spring.datasource.driver-class-name}")
    private String driverClassName;

    @Bean("db1DataSource")
    @Primary
    public DruidDataSource dataSource() {
        DruidDataSource datasource = new DruidDataSource();
        datasource.setUrl(this.url);
        datasource.setUsername(username);
        datasource.setPassword(password);
        datasource.setDriverClassName(driverClassName);
        log.info("db1 init");
        return datasource;
    }

    @Bean("db1SqlSessionFactory")
    @Primary
    public SqlSessionFactory sqlSessionFactory(@Qualifier("db1DataSource") DataSource dataSource) throws Exception {
        SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
        sessionFactory.setDataSource(dataSource);
        sessionFactory.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*Mapper.xml"));
        return sessionFactory.getObject();
    }

    @Bean("db1TransactionManager")
    @Primary
    public DataSourceTransactionManager transactionManager(@Qualifier("db1DataSource") DataSource dataSource) {
        return new DataSourceTransactionManager(dataSource);
    }

    @Bean("db1SqlSessionTemplate")
    @Primary
    public SqlSessionTemplate sqlSessionTemplate(@Qualifier("db1SqlSessionFactory") SqlSessionFactory sqlSessionFactory) throws Exception {
        return new SqlSessionTemplate(sqlSessionFactory);
    }
}

2. DB2Config.java（数据源2）

import com.alibaba.druid.pool.DruidDataSource;
import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.SqlSessionTemplate;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;

import javax.sql.DataSource;

/**
 * @Author liull
 * @DATE 2022/6/21 13:32
 **/
@Slf4j
@Configuration
// 修改包扫描路径
@MapperScan(value = "xxx.xxx.xxx.db2.dao", sqlSessionTemplateRef = "db2SqlSessionTemplate")
public class DB2Config {
    @Value("${spring.datasource.druid.db2.url}")
    private String url;
    @Value("${spring.datasource.druid.db2.username}")
    private String username;
    @Value("${spring.datasource.druid.db2.password}")
    private String password;
    @Value("${spring.datasource.driver-class-name}")
    private String driverClassName;

    @Bean("db2DataSource")
    @Qualifier("db2DataSource")
    public DruidDataSource dataSource() {
        DruidDataSource datasource = new DruidDataSource();
        datasource.setUrl(this.url);
        datasource.setUsername(username);
        datasource.setPassword(password);
        datasource.setDriverClassName(driverClassName);
        log.info("db2 init");
        return datasource;
    }

    @Bean("db2SqlSessionFactory")
    @Qualifier("db2DataSource")
    public SqlSessionFactory sqlSessionFactory(@Qualifier("db2DataSource") DataSource dataSource) throws Exception {
        SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
        sessionFactory.setDataSource(dataSource);
        sessionFactory.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/db2/*Mapper.xml"));
        return sessionFactory.getObject();
    }

    @Bean("db2TransactionManager")
    @Qualifier("db2DataSource")
    public DataSourceTransactionManager transactionManager(@Qualifier("db2DataSource") DataSource dataSource) {
        return new DataSourceTransactionManager(dataSource);
    }

    @Bean("db2SqlSessionTemplate")
    @Qualifier("db2DataSource")
    public SqlSessionTemplate sqlSessionTemplate(@Qualifier("db2SqlSessionFactory") SqlSessionFactory sqlSessionFactory) throws Exception {
        return new SqlSessionTemplate(sqlSessionFactory);
    }
}

三、注意事项

1. 注意包扫描路径，建议两种数据源持久层分包写（dao.dao1,dao.dao2）

2. 注意两个配置文件：

Ⅰ）定义不同的sqlSessionTemplateRef

Ⅱ）注意默认的数据源@Primary

3. 注意静态文件路径，建议两种数据源分包写(mapper.db1,mapper.db2)

四、特别提示

1. 多数据源配置几乎相同，只是换了不同的名字，由连接一个数据库变为连接两个数据库，在配置类中设置对应的包扫描路径和静态文件路径。

2. 某些技术贴分享需要先修改启动类上面的注解，比如多数据源配置起数据库名（如下图），需要将@SpringBootApplication()修改为@SpringBootApplication(exclude={DataSourceAutoConfiguration.calss})，并且去掉@MapperScan()，为了让系统关闭自动扫描，这个视情节而定，不修改目前没有遇到问题。
   

3. 如果大家遇到什么问题，欢迎评论讨论，如有错误之处，敬请留言。