在Idea中创建SpringBoot项目，勾选需要的依赖

可以在创建时勾选,也可以在创建项目时手动添加依赖

手动添加JSON数据处理的包

        
        <dependency>
            <groupId>com.fasterxml.jackson.coregroupId>
            <artifactId>jackson-databindartifactId>
            <version>2.10.0version>
        dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.coregroupId>
            <artifactId>jackson-coreartifactId>
            <version>2.10.0version>
        dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.coregroupId>
            <artifactId>jackson-annotationsartifactId>
            <version>2.10.0version>
        dependency>
        <dependency>
            <groupId>jakarta.annotationgroupId>
            <artifactId>jakarta.annotation-apiartifactId>
            <version>1.3.5version>
        dependency>

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加入c3p0的依赖

 <dependency>
            <groupId>com.mchangegroupId>
            <artifactId>c3p0artifactId>
            <version>0.9.5.2version>
        dependency>
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在配置文件中配置数据源等配置

这里使用yml格式

server:
  port: 端口号
  servlet:
    context-path: /自定义地址名
spring:
  datasource:
    type: com.mchange.v2.c3p0.ComboPooledDataSource
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/数据库名?useSSL=false&serverTimezone=GMT%2B8&allowPublicKeyRetrieval=true
    username: 用户名
    password: "密码"
    maxPoolSize: 20
    minPoolSize: 2
    initialPoolSize: 5
mybatis:
  type-aliases-package: 实体类地址
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根据MySQL表创建实体类

package pringbootmybatis.demo.entity;

import lombok.Data;

import java.util.Date;

/**
 * @author Una
 * @date 2022/8/22 13:27
 * @description:
 */

@Data
@ToString
public class Book {
    private Integer bookId;
    private String bookName;
    private String bookAuthor;
    private Date bookDate;
    private Integer bookPrice;

    public Book() {
    }

    public Book(Integer bookId, String bookName, String bookAuthor, Date bookDate, Integer bookPrice) {
        this.bookId = bookId;
        this.bookName = bookName;
        this.bookAuthor = bookAuthor;
        this.bookDate = bookDate;
        this.bookPrice = bookPrice;
    }
}
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创建对应方法的接口，在接口中实现结果集的映射

在BookMapper中，创建findAll()方法对应"select * from book"；因为实体类属性名与表中列名有区别，则使用**@Results进行映射；使用@Mapper**标注整个类，将其标注为映射文件

package pringbootmybatis.demo.mapper;

import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import pringbootmybatis.demo.entity.Book;

import java.util.List;

/**
 * @author Una
 * @date 2022/8/22 13:30
 * @description:
 */

@Mapper
public interface BookMapper {
    @Select("select * from book")
    @Results({
            @Result(id = true,property = "bookId",column = "book_id"),
            @Result(property = "bookName",column = "book_name"),
            @Result(property = "bookAuthor",column = "book_author"),
            @Result(property = "bookDate",column = "book_date"),
            @Result(property = "bookPrice", column = "book_price")
    })
    public List<Book> findAll();
}
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在服务层创建接口

package pringbootmybatis.demo.service;

import pringbootmybatis.demo.entity.Book;

import java.util.List;

/**
 * @author Una
 * @date 2022/8/22 13:47
 * @description:
 */

public interface BookService {
    public List<Book> getBooks();
}
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实现接口

使用**@Service**标注类，将其标注为服务层
使用 @Autowired自动注入
重写getBooks()，接收findAll()方法

package pringbootmybatis.demo.service.impl;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import pringbootmybatis.demo.entity.Book;
import pringbootmybatis.demo.mapper.BookMapper;
import pringbootmybatis.demo.service.BookService;

import java.util.List;

/**
 * @author Una
 * @date 2022/8/22 13:40
 * @description:
 */

@Service
public class BookServiceImpl implements BookService {
    @Autowired
    private BookMapper bookMapper;

    @Override
    public List<Book> getBooks() {
        return bookMapper.findAll();
    }
}
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编写Controller控制器

使用@RestController将类标注为Controller
使用 @Autowired自动注入
使用@GetMapping

package pringbootmybatis.demo.controller;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import pringbootmybatis.demo.entity.Book;
import pringbootmybatis.demo.service.BookService;

import java.util.List;

/**
 * @author Una
 * @date 2022/8/22 13:49
 * @description:
 */


@RestController
public class BookController {
    @Autowired
    private BookService bookService;
    @GetMapping("/all")
    public String books() throws JsonProcessingException {
        List<Book> list=bookService.getBooks();
        ObjectMapper objectMapper=new ObjectMapper();
        String books=objectMapper.writeValueAsString(list);
        return books;
    }
}
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测试