spring-boot集成mybatis

官方文档 http://mybatis.org/spring-boot-starter/

入门

mybatis-spring-boot-starter起步依赖提供了集成mybatis的简便方式

添加maven依赖

<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.2.0</version>
</dependency>

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

配置

配置数据源相关信息

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

mybatis中的相关配置

mybatis:
  # config-location: classpath:mybatis.xml # mybatis全局配置文件路径
  mapper-locations: classpath:com/lyp/mapper/*.xml # mapper映射文件路径
  type-aliases-package: com.lyp.entity # 实体类支持使用别名
  onfiguration:
    map-underscore-to-camel-case:  true # 下划线连接的数据列映射到驼峰命名

如果使用基于注解的mybatis配置方式，那么上面的配置不需要。

使用

使用方式与直接使用mybatis一样

数据库如下

drop table if exists `employees`;
CREATE TABLE `employees`
(
    `emp_no`     int(11)     NOT NULL,
    `birth_date` date        NOT NULL,
    `first_name` varchar(14) NOT NULL,
    `last_name`  varchar(16) NOT NULL,
    `gender`     char(1)     NOT NULL,
    `hire_date`  date        NOT NULL,
    PRIMARY KEY (`emp_no`)
);

INSERT INTO employees VALUES(10001,'1953-09-02','Georgi','Facello','M','1986-06-26');
INSERT INTO employees VALUES(10002,'1964-06-02','Bezalel','Simmel','F','1985-11-21');
INSERT INTO employees VALUES(10003,'1959-12-03','Parto','Bamford','M','1986-08-28');
INSERT INTO employees VALUES(10004,'1954-05-01','Chirstian','Koblick','M','1986-12-01');
INSERT INTO employees VALUES(10005,'1955-01-21','Kyoichi','Maliniak','M','1989-09-12');
INSERT INTO employees VALUES(10006,'1953-04-20','Anneke','Preusig','F','1989-06-02');
INSERT INTO employees VALUES(10007,'1957-05-23','Tzvetan','Zielinski','F','1989-02-10');
INSERT INTO employees VALUES(10008,'1958-02-19','Saniya','Kalloufi','M','1994-09-15');
INSERT INTO employees VALUES(10009,'1952-04-19','Sumant','Peac','F','1985-02-18');
INSERT INTO employees VALUES(10010,'1963-06-01','Duangkaew','Piveteau','F','1989-08-24');
INSERT INTO employees VALUES(10011,'1953-11-07','Mary','Sluis','F','1990-01-22');

1.定义实体类

com.lyp.entity.Employee

@Data
public class Employee
{
    private int number; // 员工编号
    private Date birthday; // 出生日期
    private String firstName;
    private String lastName;
    private String gender; // 性别
    private Date hireDay; // 雇佣日期
}

2.定义Mapper接口,使用注解@Mapper标记

com.lyp.mapper.EmployeeMapper

@Mapper
public interface EmployeeMapper
{
    List<Employee> findAll();
}

支持使用注解配置，而不需要像之前一样创建xml映射文件

@Mapper
public interface EmployeeMapper
{
    @Select("select emp_no number,birth_date birthday, first_name firstName, last_name lastName, gender, hire_date hireDay from employees")
    List<Employee> findAll();
}

虽然无需创建xml配置文件，但是sql放到java代码中？真的好丑。。。

(可选)3.配置mapper xml映射文件

注意：xml映射文件的路径要与对应的mapper接口包名对应，同时必须与配置中的mapper-locations相同

com/lyp/mapper/EmployeeMapper.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="com.lyp.mapper.EmployeeMapper">
    <select id="findAll" resultType="Employee">
        select emp_no number, birth_date birthday, first_name firstName, last_name lastName, gender, hire_date hireDay
               from employees;
    </select>
</mapper>

对于类字段名与表列名不一致的情况，除了直接使用别名外，mybatis还可以使用 resultMap 指定转换规则

<mapper namespace="com.lyp.mapper.EmployeeMapper">
    <resultMap id="employeeResultMap" type="employee">
        <result property="number" column="emp_no"/>
        <result property="birthday" column="birth_date"/>
        <result property="firstName" column="first_name"/>
        <result property="lastName" column="last_name"/>
        <result property="gender" column="gender"/>
        <result property="hireDay" column="hire_date"/>
    </resultMap>
    
    <select id="findAll" resultMap="employeeResultMap">
        select * from employees;
    </select>
</mapper>

4.执行crud

com.lyp.controller.MyController

@RestController
public class MyController
{
    private final EmployeeMapper employeeMapper;

    @Autowired
    public MyController(EmployeeMapper employeeMapper)
    {
        this.employeeMapper = employeeMapper;
    }

    @GetMapping("/employees")
    public Object showAllEmployees()
    {
        List<Employee> employees = employeeMapper.findAll();
        return employees;
    }
}

修改数据源

spring-boot jdbc默认使用Hikari作为数据源，如果要使用其它数据源，需要进行配置。

配置Druid数据源

官网文档

• https://github.com/alibaba/druid/wiki/
• https://hub.fastgit.org/alibaba/druid/tree/master/druid-spring-boot-starter

添加maven依赖

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid-spring-boot-starter</artifactId>
    <version>1.2.6</version>
</dependency>

添加了起步依赖，druid就自动生效。

druid提供的配置项以 spring.datasource.druid 开头，具体见文档。