<?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 https://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>2.4.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>studentmybatisspring</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>studentmybatisspring</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.20</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.4</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

2.4 项目配置文件application.yml

application.yml

server:
  port: 8080

spring:
  datasource:
    url: jdbc:mysql://124.70.87.136:3306/chen?useUnicode=true&characterEncoding=UTF-8
    username: root
    password: 123456
    driver-class-name: com.mysql.cj.jdbc.Driver

logging:
  level:
    com.example.studentmybatisspring.mapper: debug

里面包含项目端口信息

数据库连接信息

以及开启查看执行sql的日志。

这里设置查看日志，我们一般只设置查看对应包的日志。这里是想要查看的包名。

这个mapper就是我们mabits里面的mapper。

当我们启动项目，触发相应的sql时，就会显示对应的sql日志。

2.5 实例层entity

存放的是我们需要的实例。

ResultMsg，我们用来封装接口的返回结果。

package com.example.studentmybatisspring.entity;


import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class ResultMsg<T> {
    public static final String SUCCESS_NO = "200";
    public static final String SUCCESS_SUCCESS = "success";

    private String no;
    private String msg;
    private T data;

    public ResultMsg(String no, String msg) {
        this.no = no;
        this.msg = msg;
    }

    public static <T> ResultMsg<T> success(T data){
        return new ResultMsg(SUCCESS_NO,SUCCESS_SUCCESS,data);
    }

    public static <T> ResultMsg<T> error(String no,String msg){
        return new ResultMsg(no,msg);
    }
}

MyStudent，是数据库里MyStudent表对应的实例。

数据库的表：

对应表的实例MyStudent

package com.example.studentmybatisspring.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class MyStudent {
    private long id;
    private String name;
    private int age;

    public MyStudent(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public MyStudent(String name) {
        this.name = name;
    }
}

2.6 mybatis的mapper层

接口：MyStudentMapper

package com.example.studentmybatisspring.mapper;

import com.example.studentmybatisspring.entity.MyStudent;
import org.apache.ibatis.annotations.Select;
import org.springframework.stereotype.Repository;

import java.util.List;

@Repository
public interface MyStudentMapper {

    @Select("select * from MyStudent where name = #{name}")
    List<MyStudent> findByName(String name);
}

接口：MyStudentMapper中，包含sql语句，以及sql语句对应的方法。

2.7 spring boot service 层

service接口

package com.example.studentmybatisspring.service;

import com.example.studentmybatisspring.entity.MyStudent;

import java.util.List;

public interface MyStudentService {
    List<MyStudent> findByName(String name);

}

service实现类

package com.example.studentmybatisspring.service.impl;

import com.example.studentmybatisspring.entity.MyStudent;
import com.example.studentmybatisspring.mapper.MyStudentMapper;
import com.example.studentmybatisspring.service.MyStudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class MyStudentServiceImpl implements MyStudentService {

    @Autowired
    private MyStudentMapper myStudentMapper;

    @Override
    public List<MyStudent> findByName(String name) {
        return myStudentMapper.findByName(name);
    }


}

我们在spring boot service 实现类中，注入了mybatis 的 mapper接口。

2.8 controller层

MyStudentController

package com.example.studentmybatisspring.controller;

import com.example.studentmybatisspring.entity.MyStudent;
import com.example.studentmybatisspring.entity.ResultMsg;
import com.example.studentmybatisspring.service.MyStudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
@RequestMapping("/chen")
public class MyStudentController {
    @Autowired
    private MyStudentService myStudentService;

    @RequestMapping("/findByName")
    public ResultMsg<List<MyStudent>> findByName(String name){
        List<MyStudent> byName = myStudentService.findByName(name);
        return ResultMsg.success(byName);
    }
}

2.9 应用启动层StudentmybatisspringApplication

我们需要在项目启动层，增加mapper的扫描。

相对于单纯的mybatis 使用，spring boot 应用mybatis 缺少了mybatis 的总配置文件。

这里填写包名。@MapperScan(basePackages =

package com.example.studentmybatisspring;

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

@SpringBootApplication
@MapperScan(basePackages = "com.example.studentmybatisspring.mapper")
public class StudentmybatisspringApplication {

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

}

在浏览器里访问：

在控制台显示sql日志

三、数据库字段名称与java实体类字段名称不一致

同一个表，数据库的字段名称，与java实体类字段名称不一致。

如数据库中，字段名称为user_id

但是在java项目中，实体类的名称为驼峰格式，userId。

我们需要在application.yml，开启驼峰命名的映射。