连接多个数据库其实也很简单，只是在连接一个数据库的基础上，添加多一个访问的数据源而已，详情请往下看，这里以连接两个数据库为例，更多的连接，请阅览后参考写法继续添加即可！

一：更改application.yml

spring:
  datasource:
# 配置多个数据源
    one:
      type: com.alibaba.druid.pool.DruidDataSource
      username: root
      password: root
      jdbc-url: jdbc:mysql://localhost:3306/business?useSSL=true&userUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
      driver-class-name: com.mysql.cj.jdbc.Driver  #数据库链接驱动

    two:
      type: com.alibaba.druid.pool.DruidDataSource
      username: root
      password: root
      jdbc-url: jdbc:mysql://localhost:3306/test?useSSL=true&userUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
      driver-class-name: com.mysql.cj.jdbc.Driver  #数据库链接驱动

需要注意：

  连接多个数据库时，url要更改为jdbc-url，否则会报错。

报错内容：

java.lang.IllegalArgumentException: jdbcUrl is required with driverClassName

二：添加两个配置类

（1）DataSourceOneConfig

package com.example.business.config;


import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.SqlSessionTemplate;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.jdbc.DataSourceBuilder;
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 tk.mybatis.spring.annotation.MapperScan;

import javax.sql.DataSource;

@Configuration
@MapperScan(basePackages = "com.example.business.mapper.basemapper", sqlSessionTemplateRef = "db1SqlSessionTemplate")
public class DataSourceOneConfig {
    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.one")
    @Primary
    public DataSource db1DataSource() {
        return DataSourceBuilder.create().build();
    }

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

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

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

（2）DataSourceTwoConfig

package com.example.business.config;

import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.SqlSessionTemplate;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.jdbc.DataSourceBuilder;
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 tk.mybatis.spring.annotation.MapperScan;

import javax.sql.DataSource;

@Configuration
@MapperScan(basePackages = "com.example.business.mapper.test", sqlSessionTemplateRef = "db2SqlSessionTemplate")
public class DataSourceTwoConfig {

    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.two")
    public DataSource db2DataSource() {
        return DataSourceBuilder.create().build();
    }

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

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

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

需要注意：

（1） basePackages

@MapperScan(basePackages = "com.example.business.mapper.test", sqlSessionTemplateRef = "db2SqlSessionTemplate")

  basePackages 里面是你的mapper存放的位置，由于这里连接的是两个数据库，所有这里两个值不能一样，即第一个和第二个数据库的mapper应该放在两个不同的目录下。否则启动会报找不到表的错误。

（2）如果启动类添加了@MapperScan，需要去掉。

package com.example.business;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class BusinessApplication {

    public static void main(String[] args) {
        SpringApplication.run(BusinessApplication.class, args);

    }

}

三：测试连接效果

（1）新建Bean

package com.example.business.bean;

import lombok.Data;
import tk.mybatis.mapper.annotation.KeySql;

import javax.persistence.Column;
import javax.persistence.Id;
import javax.persistence.Table;

@Data
@Table(name = "user")
public class User {
    @Id//主键
    @KeySql(useGeneratedKeys = true)//自动生成主键
    private Integer id;

    @Column(name = "name")
    private String name;

    @Column(name = "password")
    private String password;
}

（2）新建Mapper

package com.example.business.mapper.test;

import com.example.business.bean.User;
import com.example.business.mapper.BaseMapper;
import org.springframework.stereotype.Repository;

@Repository
public interface UserMapper extends BaseMapper<User> {

}

（3）新建Service

package com.example.business.service;

import com.example.business.bean.User;

import java.util.List;

public interface TestService {
    public List<User> selectUserAll();
}

（4）新建ServiceImpl

package com.example.business.serviceImpl;

import com.example.business.bean.User;
import com.example.business.mapper.test.UserMapper;
import com.example.business.service.TestService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
@Slf4j
public class TestServiceImpl implements TestService {

    @Autowired
    UserMapper userMapper;

    @Override
    public List<User> selectUserAll() {
        return userMapper.selectAll();
    }
}

（5）新建Controller

  由于我前面第一个已经测试通过，没问题，所以这里只测试第二个数据库。

package com.example.business.controller;

import com.example.business.service.TestService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping(value = "/SimRecommendController")
public class SimRecommendController {

    private Object result;

    @Autowired
    private TestService testService;

    @RequestMapping(value = "/selectUserAll")
    public Object selectUserAll() {
        result = testService.selectUserAll();
        return result;
    }
}

  经过访问，完美连接！

PS：项目目录结构图：

  目录结构并没有强制限制，按照你自己的项目目录来就可以了，只要注意mapper要区分两个数据库的mapper，要放在不同目录下就可以！