使用MyBatis

1、创建数据库、表

CREATE DATABASE mybatis;
USE mybatis;
CREATE TABLE `book` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(45) DEFAULT NULL,
  `author` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

2、新建SpringBoot项目

使用Spring Initializer：

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填写项目相关信息：

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添加部分依赖：

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项目保存路径等信息：

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项目结构：

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自动导入依赖：

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手动添加druid数据源（pom.xml）：

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.1.21</version>
</dependency>

3、MyBatis基础配置

数据库连接信息（application.yaml）：

spring:
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    url: jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC
    username: root
    password: root

MyBatis基本配置：
- 开启实体类与数据库名字按驼峰式相互匹配。
- 配置Mapper.xml文件所在的目录。
```
mybatis:
configuration:
  map-underscore-to-camel-case: true
mapper-locations: classpath:/mapper/*.xml
```

在启动类中，配置MapperScan，扫描该包下的所有接口作为DAO：

package com.xianhuii;

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

@MapperScan("com.xianhuii.mapper")
@SpringBootApplication
public class SpringbootMybatisApplication {

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

4、实体类

  package com.xianhuii.entity;

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

  @Data
  @AllArgsConstructor
  @NoArgsConstructor
  public class Book {
      private Integer id;
      private String name;
      private String author;
  }

5、DAO

Mapper接口：

package com.xianhuii.mapper;

import com.xianhuii.entity.Book;

import java.util.List;

public interface BookMapper {
    Integer addBook(Book book);

    Integer deleteBookById(Integer id);

    Integer updateBookById(Book book);

    Book getBookById(Integer id);

    List<Book> getAllBooks();
}

Mapper配置文件：

<?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.xianhuii.mapper.BookMapper">

    <!--Integer addBook(Book book)-->
    <insert id="addBook" parameterType="com.xianhuii.entity.Book">
        insert into book (name, author) values (#{name}, #{author})
    </insert>

    <!--Integer deleteBookById(Integer id)-->
    <delete id="deleteBookById" parameterType="int">
        delete from book where id = #{id}
    </delete>

    <!--Integer updateBookById(Book book)-->
    <update id="updateBookById" parameterType="com.xianhuii.entity.Book">
        update book set name = #{name}, author = #{author} where id = #{id}
    </update>

    <!--Book getBookById(Integer id)-->
    <select id="getBookById" parameterType="int" resultType="com.xianhuii.entity.Book">
        select * from book where id = #{id}
    </select>

    <!--List<Book> getAllBooks()-->
    <select id="getAllBooks" resultType="com.xianhuii.entity.Book">
        select * from book
    </select>
</mapper>

6、测试

  package com.xianhuii.mapper;

  import com.xianhuii.SpringbootMybatisApplication;
  import com.xianhuii.entity.Book;
  import org.junit.jupiter.api.Test;
  import org.springframework.beans.factory.annotation.Autowired;
  import org.springframework.boot.test.context.SpringBootTest;

  import javax.annotation.security.RunAs;

  import java.util.Iterator;
  import java.util.List;

  import static org.junit.jupiter.api.Assertions.*;
  // 不加这个注解会报：java.lang.NullPointerException
  @SpringBootTest(classes = SpringbootMybatisApplication.class)
  class BookMapperTest {
      @Autowired
      private BookMapper bookMapper;

      @Test
      void addBook() {
          Book book1 = new Book(null, "三国演义", "罗贯中");
          Book book2 = new Book(null, "水浒传", "施耐庵");
          Book book3 = new Book(null, "西游记", "吴承恩");
          Book book4 = new Book(null, "红楼梦", "曹雪芹");
          bookMapper.addBook(book1);
          bookMapper.addBook(book2);
          bookMapper.addBook(book3);
          bookMapper.addBook(book4);
      }

      @Test
      void deleteBookById() {
          System.out.println(bookMapper.deleteBookById(1));
      }

      @Test
      void updateBookById() {
          Book book = new Book(2, "水浒传2", "施耐庵2");
          System.out.println(bookMapper.updateBookById(book));
      }

      @Test
      void getBookById() {
          Book book = bookMapper.getBookById(1);
          System.out.println(book.getId() + "-" + book.getName() + "-" + book.getAuthor());
      }

      @Test
      void getAllBooks() {
          List<Book> books = bookMapper.getAllBooks();
          Iterator<Book> iterator = books.iterator();
          while (iterator.hasNext()) {
              Book book = iterator.next();
              System.out.println(book.getId() + "-" + book.getName() + "-" + book.getAuthor());
          }
      }
  }