1、数据库准备

1、192.168.8.162 test1主

2、192.168.8.134 test1从

3、192.168.8.176 test1从

2、上代码

1、pom.xml配置引入maven依赖

    <properties>
        <java.version>1.8</java.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <druid.version>1.1.9</druid.version>
        <mybatis-plus.version>3.1.1</mybatis-plus.version>
        <mybatis-plus-stater.version>3.1.2</mybatis-plus-stater.version>
        <lombok.version>1.16.18</lombok.version>
        <mybatisplus-spring-boot-starter.version>1.0.5</mybatisplus-spring-boot-starter.version>
    </properties>    

         <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>

        <!-- druid -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>${druid.version}</version>
        </dependency>
        <!-- Mybatis-plus -->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatisplus-spring-boot-starter</artifactId>
            <version>${mybatisplus-spring-boot-starter.version}</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.baomidou/mybatis-plus -->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>${mybatis-plus-stater.version}</version>
        </dependency>

        <dependency>
            <groupId>org.apache.shardingsphere</groupId>
            <artifactId>sharding-jdbc-spring-boot-starter</artifactId>
            <version>4.1.0</version>
        </dependency>

2、在application.yml中配置使用mybatis-plus及引用数据源

#### spring  ####
spring:
  # 配置说明地址 https://shardingsphere.apache.org/document/legacy/4.x/document/cn/manual/sharding-jdbc/configuration/config-spring-boot/#%E6%95%B0%E6%8D%AE%E5%88%86%E7%89%87
  shardingsphere:
    # 数据库
    datasource:
      # 数据库的别名
      names: ds0,ds1,ds2
      # 主库1 ,master数据库
      ds0:
        ###  数据源类别
        type: com.alibaba.druid.pool.DruidDataSource
        driverClassName: com.mysql.cj.jdbc.Driver
        url: jdbc:mysql://192.168.8.162:3306/test1?useUnicode=true&characterEncoding=utf8&zeroDateTimeBehavior=convertToNull&serverTimezone=GMT%2B8
        username: root
        password: root
      # 从库1 ,slave数据库
      ds1:
        ###  数据源类别
        type: com.alibaba.druid.pool.DruidDataSource
        driverClassName: com.mysql.cj.jdbc.Driver
        url: jdbc:mysql://192.168.8.134:3306/test1?useUnicode=true&characterEncoding=utf8&zeroDateTimeBehavior=convertToNull&serverTimezone=GMT%2B8
        username: root
        password: root
      # 从库2 ,slave数据库
      ds2:
        ###  数据源类别
        type: com.alibaba.druid.pool.DruidDataSource
        driverClassName: com.mysql.cj.jdbc.Driver
        url: jdbc:mysql://192.168.8.176:3306/test1?useUnicode=true&characterEncoding=utf8&zeroDateTimeBehavior=convertToNull&serverTimezone=GMT%2B8
        username: root
        password: root

    # *** 数据库分库分表配置 start
    masterslave:
      # 查询时的负载均衡算法，目前有2种算法，round_robin（轮询）和random（随机），
      # 算法接口是io.shardingjdbc.core.api.algorithm.masterslave.MasterSlaveLoadBalanceAlgorithm。
      # 实现类有RandomMasterSlaveLoadBalanceAlgorithm 和 RoundRobinMasterSlaveLoadBalanceAlgorithm。
      load-balance-algorithm-type: round_robin
      name: dataSource
      # 主数据源名称
      master-data-source-name: ds0
      # 从数据源名称，多个用逗号隔开
      slave-data-source-names: ds1,ds2
      # *** 数据库分库分表配置 end

    props:
      # 打印SQL
      sql:
        show: true
      check:
        table:
          metadata: true
          # 是否在启动时检查分表元数据一致性
          enabled: true
      query:
        with:
          cipher:
            column: true
#### mybatis-plus ###
mybatis-plus:
  # 如果是放在src/main/java目录下 classpath:/com/yourpackage/*/mapper/*Mapper.xml
  # 如果是放在resource目录 classpath:/mapper/*Mapper.xml
  mapper-locations: classpath:mapper/*.xml
  #实体扫描，多个package用逗号或者分号分隔
  type-aliases-package: com.demo.shardingjdbc.entity
  configuration:
    map-underscore-to-camel-case: true
    cache-enabled: false
  #主键类型  0:"数据库ID自增", 1:"用户输入ID",2:"全局唯一ID (数字类型唯一ID)", 3:"全局唯一ID UUID";
  global-config:
    db-config:
      id-type: auto
      #字段策略 0:"忽略判断",1:"非 NULL 判断"),2:"非空判断"
      field-strategy: not_empty
      #驼峰下划线转换
      column-underline: true
      #逻辑删除配置
      logic-delete-value: 0
      logic-not-delete-value: 1
      db-type: mysql
  #刷新mapper 调试神器
  refresh: false

3、mybatis-plus操作数据库配置

User.jar

package com.demo.shardingjdbc.entity;

import java.io.Serializable;

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableName;

import lombok.Data;

/**
 * @Description: (User)实体类
 */
@Data
@TableName("t_user")
public class User implements Serializable {

    private static final long serialVersionUID = 358157380505039579L;

    /**
     * 用户id
     */
    @TableField("id")
    private Integer id;

    /**
     * 用户名称
     */
    @TableField("name")
    private String name;


    /**
     * 性别
     */
    @TableField("sex")
    private String sex;


}

mybatis-plus配置MybatisPlusConfig

package com.demo.shardingjdbc.config;

import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.annotation.EnableTransactionManagement;

/**
 * @Description:
 */

//Spring boot方式
@EnableTransactionManagement
@Configuration
//扫描的mapper文件路径
@MapperScan(value = "com.demo.shardingjdbc.mapper")
public class MybatisPlusConfig {

    /**
     * 分页插件
     */
    @Bean
    public PaginationInterceptor paginationInterceptor() {
        return new PaginationInterceptor();
    }
}

mapper层

package com.demo.shardingjdbc.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.demo.shardingjdbc.entity.User;

/**
 * (T_User)表数据库访问层
 *
 */
public interface UserMapper extends BaseMapper<User> {

}

controller控制层

package com.demo.shardingjdbc.controller;

import java.util.List;

import org.apache.shardingsphere.api.hint.HintManager;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.demo.shardingjdbc.entity.User;
import com.demo.shardingjdbc.mapper.UserMapper;

import lombok.extern.slf4j.Slf4j;

/**
 * @ClassName TestController
 * @Description TestController
 * @Version
 */
@RestController
@Slf4j
public class TestController {

    /**
     * user mapper
     */
    @Autowired
    private UserMapper userMapper;

    /**
     * 用户列表
     */
    @RequestMapping("userList")
    public List<User> userList() {
        log.info("********TestController userList()");
        List<User> users = userMapper.selectList(null);
        return users;
    }

    /**
     * 用户列表,强制路由主库
     */
    @RequestMapping("userListDs0")
    public List<User> userListDs0() {
        log.info("********TestController userListDs0():强制路由主库");

        HintManager hintManager = HintManager.getInstance();
        hintManager.setDatabaseShardingValue("ds0");
        List<User> users = userMapper.selectList(null);

        //清除分片键值，分片键值保存在ThreadLocal中，所以需要在操作结束时调用hintManager.close()来清除ThreadLocal中的内容。hintManager实现了AutoCloseable接口，可推荐使用try with resource自动关闭。
        
          hintManager.close(); List<User> users1 = userMapper.selectList(null);
          users.addAll(users1);
         
        return users;
    }

    /**
     * 保存用户
     *
     * @return
     */
    @PostMapping("save")
    public int save(User user) {
        log.info("********save User");
        int insert = userMapper.insert(user);
        return insert;
    }
}

完成。用Sharding-JDBC实现了数据库的读写分离，对192.168.8.162 test1中t_user的操作，对92.168.8.134 test1，92.168.8.134 test1中t_user的查询。

读写分离的好处就是在并发量比较大的情况下，将查询数据库的压力分担到多个从库中，能够满足高并发的要求。如下图