Mybatis + SpringBoot 入门级实战（基础篇）

这篇文章中，笔者将要介绍SpringBoot+Mybatis进行简单的查询

使用的是maven建项目，数据库使用的Mysql：
添加SpringBoot相关依赖：

        <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>
        </dependency>

添加Mybatis相关依赖：

        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>1.3.2</version>
        </dependency>

添加Mysql 相关依赖：

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>6.0.6</version>
        </dependency>

添加Mybatis-SpringBoot 依赖：

        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>1.3.2</version>
        </dependency>

spring-boot 所做的事情是：
在jdbc上进行了一层包装
当程序开始运行时候，它会做如下几件事情：

1. 获取mybatis_config.xml文件，并通过它，获得所有的mapper文件路径
2. 扫描所有的类：
   获取其中的@Service @Controller @Component标识的类，自动生成一个相应的bean。
   获取其中的@Mapper 标识的接口类，找到其对应的mapper文件，自动生成一个相应的bean，mapper 接口类所有的抽象方法在mapper文件中都有相应id标识的sql语句

和单独使用Mybatis不同在于，不再需要mybatis配置文件了：

配置SpringBoot资源文件

Application.yml

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

到这里，我们有几种方法
第一种：映射的简单形式（不需要配置映射文件）
第二种：配置映射文件，并且建立Mapper接口类
第三种：配置映射文件，不建立Mapper接口类，自己封装一个类

第一种：

package demo.mappers;

import demo.domain.User;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

@Mapper
public interface UserMapper {
    @Select("select * from User where userId = #{id}")
    User queryById(@Param("id") Integer id);
}

第二种和第三种都需要UserMapper.xml:

一定需要注意的是，资源mapper文件的路径一定要和mapper抽象类的路径形式完全相同，名称完全相同，不然，程序无法找到相应的映射文件

UserMapper.xml

<?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="demo.mappers.UserMapper">
    <select id="queryById" resultType="demo.domain.User">
        SELECT * FROM User WHERE userId = #{id}
    </select>

</mapper>

这里的namespace是这个mapper文件所对应的mapper类的路径
“queryById” 对应了mapper类中的抽象方法

第二种：

package demo.mappers;

import demo.domain.User;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;

@Mapper
public interface UserMapper {
    User queryById(@Param("id") Integer id);
}

第三种：
建立一个类，比如叫：UserDao.java

package demo.dao;

import demo.domain.User;
import org.apache.ibatis.session.SqlSession;
import org.springframework.stereotype.Component;

@Component
public class UserDao {

    private final SqlSession sqlSession;

    public UserDao(SqlSession sqlSession){
        this.sqlSession = sqlSession;
    }

    public User selectUserById(int id){
        return this.sqlSession.selectOne("queryById", 1);
    }
}

第一二种运行：

package demo;

import demo.dao.UserDao;
import demo.mappers.UserMapper;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;

@SpringBootApplication
public class Application implements CommandLineRunner{
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    private final UserMapper userMapper;

    public Application(UserMapper userMapper){
        this.userMapper = userMapper;
    }

    @Override
    @SuppressWarnings("squid:S106")
    public void run(String... args) throws Exception {
        System.out.println(this.userMapper.queryById(1));
    }

}

第三种运行：

package demo;

import demo.dao.UserDao;
import demo.mappers.UserMapper;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;

@SpringBootApplication
public class Application implements CommandLineRunner{
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    private final UserDao userDao;

    public Application(UserDao userDao){
        this.userDao = userDao;
    }

    @Override
    @SuppressWarnings("squid:S106")
    public void run(String... args) throws Exception {
        System.out.println(this.userDao.selectUserById(1));
    }

}

运行结果相同

---

以上是简单使用，如果想要做的更加完整
需要一个service:

package db.java.service;


import db.java.domain.User;
import db.java.mappers.UserMapper;
import org.springframework.stereotype.Service;


import javax.annotation.Resource;
import java.util.List;

@Service
public class UserServiceImpl implements UserService {

    @Resource
    UserMapper userMapper;

    @Override
    public User queryById(Integer userId) {
        return userMapper.queryById(userId);
    }

    @Override
    public List<User> queryByName(String userName) {
        return null;
    }

    @Override
    public int add(User user) {
        return 0;
    }

    @Override
    public int update(User user) {
        return 0;
    }

    @Override
    public int deleteById(Integer userId) {
        return 0;
    }
}

简单起见，只处理了queryById()方法

需要一个controller

package admin_api.java.web;

import db.java.domain.User;
import db.java.service.UserServiceImpl;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/admin/user")  //整个类是用于处理/admin/user/..的
public class AdminUserController{
    private final Log logger = LogFactory.getLog(AdminUserController.class);

    @Autowired
    UserServiceImpl userService;

    @RequestMapping(value = "/query", method = RequestMethod.GET)
    public User query(Integer id){
        return userService.queryById(id);
    }
}

Application:

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

运行
postman中发出get请求，localhost:8080/admin/user/query?id=1
得到数据库中查询结果：

{
    "userId": 1,
    "nickName": "Alice",
    "passWord": "234",
    "email": "111@qq.com",
    "phoneNum": "112334",
    "gender": "female",
    "creditScore": 10
}