MP 自定义业务方法 （三）

一嘴一个橘子2026-04-28 17:17

目录

复制代码 
src/main
├── java/com/atguigu
│   ├── Main.java          # 启动类
│   ├── config/
│   │   └── MyBatisPlusConfig.java    # 配置类，配置分页
│   ├── common/
│   │   └── Result.java               # 全局统一返回
│   │   └── PageVO.java               # 自定义通用分页对象（只保留核心字段）
│   ├── pojo/                         # 数据库实体
│   │   ├── Employees.java
│   │   └── Departments.java
│   ├── dto/                          # 查询参数封装
│   │   └── EmpQueryDTO.java
│   ├── vo/                           # 视图对象（连表/返回前端）
│   │   └── EmpDepartmentsVO.java
│   ├── mapper/                       # Mapper接口
│   │   └── EmpMapper.java
│   ├── service/
│   │   ├── EmployeesService.java          # 业务接口
│   │   └── impl/
│   │       └── EmployeesServiceImpl.java  # 业务实现
│   └── controller/
│       └── EmpController.java       # 接口层
└── resources/                        # 资源目录（核心！）
    ├── mapper/
    │   └── xml/
    │       └── EmpMapper.xml        # XML SQL文件（放这里！）
    └── application.yml               # 配置文件

pom.xml

xml 复制代码 
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>  
  
    <parent> 
        <groupId>org.springframework.boot</groupId>  
        <artifactId>spring-boot-starter-parent</artifactId>  
        <version>3.0.5</version> 
    </parent>

    <groupId>com.atguigu</groupId>
    <artifactId>mp-project-testa</artifactId>
    <version>1.0-SNAPSHOT</version>
  
    <packaging>war</packaging>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>  
        <maven.compiler.target>17</maven.compiler.target>  
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> 
    </properties>

    <dependencies> 
        <dependency> 
            <groupId>org.springframework.boot</groupId>  
            <artifactId>spring-boot-starter</artifactId> 
        </dependency>
    
        <!-- 测试环境 -->  
        <dependency> 
            <groupId>org.springframework.boot</groupId>  
            <artifactId>spring-boot-starter-test</artifactId> 
        </dependency>
  
        <!-- mybatis-plus  -->  
        <dependency> 
            <groupId>com.baomidou</groupId>  
            <artifactId>mybatis-plus-boot-starter</artifactId>  
            <version>3.5.3.1</version> 
        </dependency>
    
        <!-- 数据库相关配置启动器 -->  
        <dependency> 
            <groupId>org.springframework.boot</groupId>  
            <artifactId>spring-boot-starter-jdbc</artifactId> 
        </dependency>
    
        <!-- druid启动器的依赖  -->  
        <dependency> 
            <groupId>com.alibaba</groupId>  
            <artifactId>druid-spring-boot-3-starter</artifactId>  
            <version>1.2.20</version> 
        </dependency>
  
        <!-- 驱动类-->  
        <dependency> 
            <groupId>mysql</groupId>  
            <artifactId>mysql-connector-java</artifactId>  
            <version>8.0.28</version> 
        </dependency>
    
        <dependency> 
            <groupId>org.projectlombok</groupId>  
            <artifactId>lombok</artifactId>  
            <version>1.18.28</version> 
        </dependency>
  
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

    <!-- SpringBoot应用打包插件 -->  
    <build> 
        <plugins> 
            <plugin> 
                <groupId>org.springframework.boot</groupId>  
                <artifactId>spring-boot-maven-plugin</artifactId> 
            </plugin> 
        </plugins> 
    </build> 
</project>

application.yml

yml 复制代码 
# 连接池配置
spring:
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    druid:
      url: jdbc:mysql:///atguigudb
      username: root
      password: root
      driver-class-name: com.mysql.cj.jdbc.Driver

mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl # 控制台输出sql语句
    map-underscore-to-camel-case: true
  mapper-locations: classpath*:/mapper/*.xml
  type-aliases-package: com.atguigu

配置类

java 复制代码 
package com.atguigu.config;

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MyBatisPlusConfig {

    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        // mysql分页插件
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }
}

通用类

统一返回格式

java 复制代码 
package com.atguigu.common;

import lombok.Data;

/*
* 全局统一返回结果
* */
@Data
public class Result<T> {
    private int code;
    private String msg;
    private T data;

    public static <T> Result<T> success(T data) {
        Result<T> result = new Result<T>();
        result.setData(data);
        result.setCode(200);
        result.setMsg("success");
        return result;
    }

    public static <T> Result<T> fail(String msg) {
        Result<T> result = new Result<T>();
        result.setCode(500);
        result.setMsg(msg);
        return result;
    }
}

自定义通用分页对象

java 复制代码 
package com.atguigu.common;

import lombok.Data;

import java.util.List;

/**
 * 自定义通用分页对象（只保留核心字段）
 */
@Data
public class PageVO<T> {
    // 数据列表
    private List<T> records;

    // 总条数
    private Long total;

    // 每页条数
    private Long size;

    // 当前页码
    private Long current;

    // 总页数
    private Long pages;

    /*
        首先，类上的<T>是 public class PageVO<T>，这个是属于实例的泛型，
        而，静态方法是属于类的，不属于实例，
        所以，静态方法用不了类上的<T>，必须自己声明一个<T>。

        说白了：
            作用：告诉编译器，这个静态方法是泛型方法，里面的 T 是方法自己的泛型类型，
                 和传入的 IPage<T>、返回的 PageVO<T>的 T 是同一个类型。

        当你调用：PageVO.restPage(IPage<Employees>) 时候
        编译器就会自动把 <T> 推断为 Employees，保证类型安全。
    */
    // 返回值类型：PageVO<T>，方法名：restPage
    public static <T> PageVO<T> restPage(com.baomidou.mybatisplus.core.metadata.IPage<T> page) {
        PageVO<T> pageVO = new PageVO<T>();
        pageVO.setRecords(page.getRecords());
        pageVO.setTotal(page.getTotal());
        pageVO.setSize(page.getSize());
        pageVO.setCurrent(page.getCurrent());
        pageVO.setPages(page.getPages());

        return pageVO;
    }
}

实体类

Employees.java

java 复制代码 
package com.atguigu.pojo;

import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;

@Data
@TableName("employees")
public class Employees {
	@TableId(value = "employee_id", type = IdType.AUTO)
    private Long employeeId;
    private String firstName;
    private String lastName;
    private String email;

    private Long departmentId;
}

Departments.java

java 复制代码 
package com.atguigu.pojo;

import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;

@Data
@TableName("departments")
public class Departments {
	@TableId(value = "department_id", type = IdType.AUTO)
    private Long departmentId;
    private String departmentName;
    private Integer managerId;
}

Mapper + XML

EmpMapper 接口

继承 MP 的 BaseMapper，自定义业务方法*

java 复制代码 
package com.atguigu.mapper;

import com.atguigu.dto.EmpQueryDTO;
import com.atguigu.pojo.Employees;
import com.atguigu.vo.EmpDepartmentsVO;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import org.apache.ibatis.annotations.Param;

public interface EmpMapper extends BaseMapper<Employees> {
    // 分页查询 - 单表
    IPage<Employees> selectEmpList(Page<Employees> page, @Param("query")EmpQueryDTO empQueryDTO);

    // 分页查询 - 多表
    IPage<EmpDepartmentsVO> selectEmpDepartmentList(Page<EmpDepartmentsVO> page, @Param("query")EmpQueryDTO empQueryDTO);
}

EmpMapper.xml

xml 复制代码 
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTO Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.atguigu.mapper.EmpMapper">
    <!-- 单表查询：数据库列名用下划线 -->
    <select id="selectEmpList" resultType="com.atguigu.pojo.Employees">
        select employee_id, first_name, last_name, email, department_id
        from employees
        <where>
            <if test="query.lastName != null and query.lastName != ''">
                and last_name like concat("%", #{query.lastName}, "%")
            </if>
            <if test="query.email != null and query.email != ''">
                and email like concat('%', #{query.email}, '%')
            </if>
        </where>
    </select>

    <!-- 多表查询：必须加表别名d.，列名用下划线 -->
    <select id="selectEmpDepartmentList" resultType="com.atguigu.vo.EmpDepartmentsVO">
        select
            e.employee_id, e.first_name, e.last_name, e.email,
            d.department_id, d.department_name
        from employees e
        left join departments d
        on e.department_id = d.department_id
        <where>
            <if test="query.lastName != null and query.lastName != ''">
                and e.last_name like concat("%", #{query.lastName}, "%")
            </if>
            <if test="query.email != null and query.email != ''">
                and e.email like concat('%', #{query.email}, '%')
            </if>
            <if test="query.departmentName != null and query.departmentName != ''">
                and d.department_name like concat('%', #{query.departmentName}, '%')
            </if>
        </where>
    </select>
</mapper>

查询DTO

java 复制代码 
package com.atguigu.dto;

import lombok.Data;

@Data
public class EmpQueryDTO {
    private String firstName;
    private String lastName;
    private String email;
    private String departmentName;

    private Integer pageNum = 1;   // 默认第1页
    private Integer pageSize = 10; // 默认每页10条
}

连表查询结果VO

java 复制代码 
package com.atguigu.vo;

import lombok.Data;

@Data
public class EmpDepartmentsVO {
    // employees表
    private Long employeeId;
    private String firstName;
    private String lastName;
    private String email;

    // departments表
    private Long departmentId;
    private String departmentName;
}

service

EmployeesService接口

java 复制代码 
package com.atguigu.service;

import com.atguigu.dto.EmpQueryDTO;
import com.atguigu.pojo.Employees;
import com.atguigu.vo.EmpDepartmentsVO;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.service.IService;

public interface EmployeesService extends IService<Employees> {
    IPage<Employees> getEmpList(EmpQueryDTO empQueryDTO);

    IPage<EmpDepartmentsVO> getEmpDepartmentList(EmpQueryDTO empQueryDTO);
}

EmployeesServiceImpl.java

java 复制代码 
package com.atguigu.service.impl;

import com.atguigu.dto.EmpQueryDTO;
import com.atguigu.mapper.EmpMapper;
import com.atguigu.pojo.Employees;
import com.atguigu.service.EmployeesService;
import com.atguigu.vo.EmpDepartmentsVO;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class EmployeesServiceImpl extends ServiceImpl<EmpMapper, Employees> implements EmployeesService {

    @Autowired
    private EmpMapper empMapper;

    @Override
    public IPage<Employees> getEmpList(EmpQueryDTO empQueryDTO) {
        Page<Employees> page = new Page<>(empQueryDTO.getPageNum(), empQueryDTO.getPageSize());
        return empMapper.selectEmpList(page, empQueryDTO);
    }

    @Override
    public IPage<EmpDepartmentsVO> getEmpDepartmentList(EmpQueryDTO empQueryDTO) {
        Page<EmpDepartmentsVO> page = new Page<>(empQueryDTO.getPageNum(), empQueryDTO.getPageSize());
        return empMapper.selectEmpDepartmentList(page, empQueryDTO);
    }
}

controller

java 复制代码 
package com.atguigu.controller;

import com.atguigu.common.PageVO;
import com.atguigu.common.Result;
import com.atguigu.dto.EmpQueryDTO;
import com.atguigu.pojo.Employees;
import com.atguigu.service.EmployeesService;
import com.atguigu.vo.EmpDepartmentsVO;
import com.baomidou.mybatisplus.core.metadata.IPage;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/emp")
public class EmpController {

    @Autowired
    private EmployeesService empService;

    @GetMapping("/list")
    public Result<PageVO<Employees>> getEmployeeList(EmpQueryDTO empQueryDTO) {
        IPage<Employees> page = empService.getEmpList(empQueryDTO);
        return Result.success(PageVO.restPage(page));
    }

    @GetMapping("/empDepartment/list")
    public Result<PageVO<EmpDepartmentsVO>> getEmpDepartmentList(EmpQueryDTO empQueryDTO) {
        IPage<EmpDepartmentsVO> page = empService.getEmpDepartmentList(empQueryDTO);
        return Result.success(PageVO.restPage(page));
    }
}

启动类

java 复制代码 
package com.atguigu;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@MapperScan("com.atguigu.mapper")
@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        SpringApplication.run(Main.class, args);
    }
}
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