mybatis-plus官網(wǎng)：https://mybatis.plus

springboot 2.1.7
maven 3.5.0
mysql 5.7.24
mybatis-plus 3.2.0

一、新建SpringBoot項目

在mybatis-plus官網(wǎng)上看到:

引入 MyBatis-Plus 之后請不要再次引入 MyBatis 以及 MyBatis-Spring柬赐，以避免因版本差異導(dǎo)致的問題兰迫。

因此我選擇了新建項目整合嘗試。

1.pom文件maven依賴如下所示：

<dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</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>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- mybatis-plus依賴 -->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.2.0</version>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus</artifactId>
            <version>3.2.0</version>
        </dependency>
    </dependencies>

2.application.yml配置文件如下所示：

#自定義項目端口號
server:
  port: 6000
  session-timeout: 30
  tomcat.max-threads: 0
  tomcat.uri-encoding: UTF-8

#mysql
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/demo
    username: root
    password: 123456

3.啟動類配置 MapperScan 注解

package com.liulin.demo;

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

@MapperScan("com.liulin.demo.mapper")
@SpringBootApplication
public class DemoApplication {

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

4.項目結(jié)構(gòu)

項目結(jié)構(gòu)

在使用maven等構(gòu)建工具時，默認會將源碼(java文件夾)編譯后再加上資源目錄（resources文件夾）的文件放到target目錄下作為最后運行的文件起胰，xml文件放到Java文件夾里升酣，編譯時會被maven忽略，因此常采用在resources下新建文件夾煞茫，用來存放mapper的xml文件帕涌。

二、代碼準備

1.表結(jié)構(gòu)
這里我使用了MP官網(wǎng)給的表续徽。

CREATE TABLE user (
  id BIGINT(20) NOT NULL COMMENT '主鍵ID',
  name VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
  age INT(11) NULL DEFAULT NULL COMMENT '年齡',
  email VARCHAR(50) NULL DEFAULT NULL COMMENT '郵箱',
  PRIMARY KEY (id)
);

其對應(yīng)的數(shù)據(jù)庫Data腳本:

INSERT INTO user (id, name, age, email) VALUES
(1, 'Jone', 18, 'test1@baomidou.com'),
(2, 'Jack', 20, 'test2@baomidou.com'),
(3, 'Tom', 28, 'test3@baomidou.com'),
(4, 'Sandy', 21, 'test4@baomidou.com'),
(5, 'Billie', 24, 'test5@baomidou.com'),
(6, 'JackSon', 27, 'test6@baomidou.com');

2.實體類

@Data
public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

3.DAO層

Mapper通用CRUD封裝BaseMapper接口蚓曼，自動解析實體表關(guān)系映射轉(zhuǎn)換為 Mybatis 內(nèi)部對象注入容器

package com.liulin.demo.mapper;

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

/**
 * Created by liulin on 2019-08-29 23:44
 */
public interface UserMapper extends BaseMapper<User> {
}

4.Service層

通用Service CRUD封裝IService接口
get 查詢單行
remove 刪除
list 查詢集合
page 分頁

(1) Service類

package com.liulin.demo.service;

import com.baomidou.mybatisplus.extension.service.IService;
import com.liulin.demo.entity.User;

/**
 * Created by liulin on 2019-09-02 23:48
 */
public interface UserService extends IService<User> {
}

(2) ServiceImpl類

package com.liulin.demo.service.impl;

import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.liulin.demo.entity.User;
import com.liulin.demo.mapper.UserMapper;
import com.liulin.demo.service.UserService;
import org.springframework.stereotype.Service;

/**
 * Created by liulin on 2019-09-02 23:57
 */
@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {
}

5.Controller層

package com.liulin.demo.controller;

import com.liulin.demo.entity.User;
import com.liulin.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * Created by liulin on 2019-09-03 14:43
 */
@RestController
@RequestMapping("/user")
public class UserController {
    
    @Autowired UserService userService;

    @PostMapping("/getUserInfo")
    public User getUserInfo(Integer userId) {
        User user = userService.getById(userId);
        return user;
    }
}

三、Postman調(diào)試

1.以getUserInfo方法為例

Postman（localhost:6000/user/getUserInfo?userId=1）輸出結(jié)果如下：

{
    "id":1,
    "name":"Jone",
    "age":18,
    "email":"test1@baomidou.com"
}

可以看到钦扭，Service纫版、Mapper一個方法都沒寫的情況下，從表里查出了userId為1的全部信息客情，省去了mybatis中xml的sql查詢那一步其弊，在官方給出的文檔中，可以看到基本上都是基于主鍵id返回單一實體或?qū)嶓wlist膀斋。

2.條件構(gòu)造器

(1)查詢年齡等于28的結(jié)果
因為表是自建梭伐，age=18的結(jié)果只有1條，所以這里使用的是IService的getOne方法概页，如果是多條結(jié)果的話籽御，該方法就會報錯。

@PostMapping("/getUserByAge")
public User getUserByAge(int age) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    //lambda寫法:
    queryWrapper.lambda().eq(User::getAge, age);
    User user = userService.getOne(queryWrapper);
    return user;
}

Postman（localhost:6000/user/getUserByAge?age=18）輸出結(jié)果如下：

{
    "id": 3,
    "name": "Tom",
    "age": 28,
    "email": "test3@baomidou.com"
}

(2)查詢年齡大于20小于25的結(jié)果

    @PostMapping("/getUserListByAgeLimit")
    public List<User> getUserListByAgeLimit() {
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.lambda().gt(User::getAge, 20);
        queryWrapper.lambda().lt(User::getAge, 25);
        List<User> userList = userService.list(queryWrapper);
        return userList;
    }

Postman（localhost:6000/user/getUserListByAgeLimit）輸出結(jié)果如下：

[
    {
        "id": 4,
        "name": "Sandy",
        "age": 21,
        "email": "test4@baomidou.com"
    },
    {
        "id": 5,
        "name": "Billie",
        "age": 24,
        "email": "test5@baomidou.com"
    }
]

(3)自定義sql
使用Wrapper構(gòu)造條件自定義sql子句,官網(wǎng)提供了兩種方案:

第一種：Mapper.java使用注解

package com.liulin.demo.mapper;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.baomidou.mybatisplus.core.toolkit.Constants;
import com.liulin.demo.entity.User;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

import java.util.List;

/**
 * Created by liulin on 2019-08-29 23:44
 */
public interface UserMapper extends BaseMapper<User> {

    @Select("select * from user ${ew.customSqlSegment} ")
    List<User> getUserListByCondition(@Param(Constants.WRAPPER) QueryWrapper<User> condition);
}

Service層

package com.liulin.demo.service;

import com.baomidou.mybatisplus.extension.service.IService;
import com.liulin.demo.entity.User;

import java.util.List;

/**
 * Created by liulin on 2019-09-02 23:48
 */
public interface UserService extends IService<User> {

    List<User> getUserListByCondition(String name);
    
}

ServiceImpl類

package com.liulin.demo.service.impl;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.liulin.demo.entity.User;
import com.liulin.demo.mapper.UserMapper;
import com.liulin.demo.service.UserService;
import org.springframework.stereotype.Service;

import java.util.List;

/**
 * Created by liulin on 2019-09-02 23:57
 */
@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {

    @Override
    public List<User> getUserListByCondition(String name) {
        QueryWrapper<User> condition = new QueryWrapper<>();
        //like模糊查詢且年齡小于25
        condition.lambda().like(User::getName, name).lt(User::getAge, 25);
        return baseMapper.getUserListByCondition(condition);
    }
}

Controller層

    @PostMapping("/getUserListBySql")
    public List<User> getUserListBySql(String name) {
        List<User> userList = userService.getUserListByCondition(name);
        return userList;
    }

Postman（localhost:6000/user/getUserListBySql?name=Jac）輸出結(jié)果如下：

[
    {
        "id": 2,
        "name": "Jack",
        "age": 20,
        "email": "test2@baomidou.com"
    }
]

第二種：Mapper.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.liulin.demo.mapper.UserMapper">
    
    <select id="getUserListByCondition" resultType="com.liulin.demo.entity.User">
        SELECT * FROM user where name = #{name}
    </select>
</mapper>

四、其他

1.mybatis-plus配置執(zhí)行sql輸出到控制臺
application.yml文件：

mybatis-plus:
  configuration:
    #控制臺打印完整帶參數(shù)SQL語句
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

有SQL執(zhí)行時技掏，控制臺輸出結(jié)果如下：

JDBC Connection [HikariProxyConnection@1882318550 wrapping com.mysql.cj.jdbc.ConnectionImpl@2022fa88] will not be managed by Spring
==>  Preparing: SELECT id,name,email,age FROM user WHERE (age = ?) 
==> Parameters: 28(Integer)
<==    Columns: id, name, email, age
<==        Row: 3, Tom, test3@baomidou.com, 28
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3291f605]

2.使用Mapper.xml形式時配置文件
application.yml文件

mybatis-plus:
  configuration:
    #控制臺打印完整帶參數(shù)SQL語句
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  #resources目錄下
  mapper-locations: classpath:/mapper/**.xml

總結(jié)：

1铃将、mybatis-plus是mybatis的增強版，在MyBatis的基礎(chǔ)上只做增強不做改變哑梳。
2劲阎、mybatis-plus官網(wǎng)條件構(gòu)造器一節(jié)中提供了eq、ne鸠真、like悯仙、isNull、having等拼接的方法吠卷，使用lambda寫法使之簡潔有效锡垄，單表操作的情況下，使用Mapper和Service封裝的CURD方法節(jié)約代碼量和工作量祭隔。
３货岭、在多表聯(lián)合復(fù)雜查詢的時候就需要在xml文件里寫sql語句。

以上就是SpringBoot整合mybatis-plus整合學(xué)習(xí)過程疾渴，關(guān)于mybatis-plus方法千贯，只學(xué)習(xí)了select的用法，其他增改刪后期還需結(jié)合官網(wǎng)加以實踐搞坝，熟練操作搔谴。