Day57——SpringBoot2.x整合MyBatis

一. 问题背景

前面学习了Day56——SpringBoot2.x整合Druid&配置数据源监控，今天来学习整合MyBatis

二. 整合MyBatis

2.1 搭建环境

首先搭建好druid数据源，这个步骤与Day56——SpringBoot2.x整合Druid&配置数据源监控一样，步骤如下：

引入依赖：

 
 <dependency>
      <groupId>com.alibabagroupId>
      <artifactId>druid-spring-boot-starterartifactId>
      <version>1.1.17version>
  dependency>

配置Druid：
创建application.yaml，在druid属性以下的属性，都是druid-starter依赖所需要配置的。 schema属性以及initialization-mode属性是创建表时要用到的，因此创建完表后应该将schema和initialization-mode 注释掉如下：

spring:
  datasource:
    #   数据源基本配置
    username: root
    password: 123456
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://192.168.32.103:3306/mybatis
    type: com.alibaba.druid.pool.DruidDataSource
    #首次运行完创建表后，应该将schema和initialization-mode注释掉
#    # 指定sql脚本文件路径
#    schema:
#      - classpath:sql/department.sql
#      - classpath:sql/employee.sql
#    #设置SpringBoot启动后执行脚本文件
#    initialization-mode: always
    druid:
      initial-size: 5
      max-active: 20
      min-idle: 5
      max-wait: 60000
      pool-prepared-statements: true
      max-pool-prepared-statement-per-connection-size: 20
      validation-query: SELECT 1 FROM DUAL
      test-on-borrow: false
      test-on-return: false
      test-while-idle: true
      time-between-eviction-runs-millis: 60000
      min-evictable-idle-time-millis: 300000
      filter:
        stat:
          enabled: true
          db-type: mysql
          log-slow-sql: true
          slow-sql-millis: 2000
        wall:
          enabled: true
        slf4j:
          enabled: true
      keep-alive: true
      # 监控过滤器
      web-stat-filter:
        enabled: true
        exclusions:
          - "*.js"
          - "*.gif"
          - "*.jpg"
          - "*.png"
          - "*.css"
          - "*.ico"
          - "/druid/*"
      #exclusions可以是list格式配置，也可以是String格式
      #        exclusions: "*.js,*.gif,*.jpg,*.png,*.css,*.ico,/druid/*"
      # druid 监控页面
      stat-view-servlet:
        enabled: true
        url-pattern: /druid/*
        reset-enable: false
        login-username: admin
        login-password: 123456
        #拒绝本机连接（自行修改自己的本机连接）
        deny: 192.168.32.103

配置Druid数据源：

@Configuration
public class DruidConfig {

    @Bean
    @Primary
    @ConfigurationProperties(prefix = "spring.datasource.druid")
    public DruidDataSource druidDataSource(){
        return DruidDataSourceBuilder.create().build();
    }
}

引入两个sql脚本：

department.sql

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for department
-- ----------------------------
DROP TABLE IF EXISTS `department`;
CREATE TABLE `department` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `departmentName` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

employee.sql

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for employee
-- ----------------------------
DROP TABLE IF EXISTS `employee`;
CREATE TABLE `employee` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `lastName` varchar(255) DEFAULT NULL,
  `email` varchar(255) DEFAULT NULL,
  `gender` int(2) DEFAULT NULL,
  `d_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

首次运行完创建完表后，将yaml文件中的schema属性以及initialization-mode属性注释掉，然后创建Bean：
Employee.java

package com.atguigu.springboot.bean;

public class Employee {

    private Integer id;
    private String lastname;
    private Integer gender;
    private String email;
    private Integer dId;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastname() {
        return lastname;
    }

    public void setLastname(String lastname) {
        this.lastname = lastname;
    }

    public Integer getGender() {
        return gender;
    }

    public void setGender(Integer gender) {
        this.gender = gender;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public Integer getdId() {
        return dId;
    }

    public void setdId(Integer dId) {
        this.dId = dId;
    }
}

Department.java

package com.atguigu.springboot.bean;

public class Department {

    private Integer id;
    private String departmentName;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getDepartmentName() {
        return departmentName;
    }

    public void setDepartmentName(String departmentName) {
        this.departmentName = departmentName;
    }
}

至此搭建环境完成

2.2 注解版MyBatis

2.2.1 步骤

使用注解配置mybatis非常简单，只需创建interface并加上@Mapper注释即可，步骤如下：

首先创建一个interface：
DepartmentMapper.java

//指定这是一个操作数据库的mapper
@Mapper
public interface DepartmentMapper {

    @Select("select * from department where id = #{id}")
    public Department getDeptById(Integer id);

    @Delete("delete from department where id = #{id}")
    public int deleteDeptById(Integer id);

    @Options(useGeneratedKeys = true,keyProperty = "id")//插入后返回主键
    @Insert("insert into department(department_name) values(#{departmentName})")
    public int insertDept(Department department);

    @Update("update department set department_name = #{departmentName} where id = #{id}")
    public int updateDept(Department department);
}

解释： 所有的增删改查只需使用@Insert、@Delete、@Update、@Select书写sql语句，如果插入数据后需要返回主键，只需使用@Option(useGeneratedKeys=true, keyProperty="id")。

为了方便讲述，这里不再创建Service这些，直接创建Controller：
DeptController.java

@RestController
public class DeptController {

    @Autowired
    DepartmentMapper departmentMapper;

    @GetMapping("/dept/{id}")
    public Department getDepartment(@PathVariable("id") Integer id){
        return departmentMapper.getDeptById(id);
    }

    @GetMapping("/dept")
    public Department insertDept(Department department){
        departmentMapper.insertDept(department);
        return department;
    }
}

至此就完成了整合MyBatis。

测试：

2.2.2 配置驼峰命名

2.2.2.1 问题背景

假如将数据库字段名改成有下划线的格式，比如将departmentName改成department_name，执行sql语句还成功吗？

修改sql语句对应的数据库字段名为下划线格式，如下：

@Options(useGeneratedKeys = true,keyProperty = "id")//插入后返回主键
@Insert("insert into department(department_name) values(#{departmentName})")
public int insertDept(Department department);

@Update("update department set department_name = #{departmentName} where id = #{id}")
public int updateDept(Department department);

2.2.2.2 解决方案

只需创建一个配置类，并注册一个ConfigurationCustomizer到容器中，重写customize()方法，在方法里面开启驼峰命名规则，如下：

@Configuration
public class MyBatisConfig {

    @Bean
    public ConfigurationCustomizer configurationCustomizer(){
        return new ConfigurationCustomizer() {
            @Override
            public void customize(org.apache.ibatis.session.Configuration configuration) {
                configuration.setMapUnderscoreToCamelCase(true);//开启驼峰命名法
            }
        };
    }
}

2.2.2.3 原理

按2下shift搜索并打开MyBatisAutoConfiguration，有一个注册SqlSessionFactory的方法，如下：

@Bean
    @ConditionalOnMissingBean
    public SqlSessionFactory sqlSessionFactory(DataSource dataSource) 
                                                     throws Exception {
        ...
        this.applyConfiguration(factory);//关键方法
        ...
}

applyConfiguration()方法非常关键，如下:

private void applyConfiguration(SqlSessionFactoryBean factory) {
    if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
            Iterator var3 = this.configurationCustomizers.iterator();

            while(var3.hasNext()) {
                //拿到的ConfigurationCustomizer并调用它的customize()方法
                ConfigurationCustomizer customizer = (ConfigurationCustomizer)var3.next();
                customizer.customize(configuration);
            }
        }
}

解释： 可以看到，注册SqlSessionFactory的时候，会拿到的ConfigurationCustomizer并调用它的customize()方法

2.2.3 指定扫描mapper包

情景： 一个一个地给每个Mapper加@Mapper注解很繁琐，我们可以使用@MapperScan(basicPackage="xxx")指定mapper包的路径。

步骤：
在主配置类上加上@MapperScan(value = "com.atguigu.springboot.mapper")，如下：

@MapperScan(value = "com.atguigu.springboot.mapper")
@SpringBootApplication
public class SpringBoot06DataMybatisApplication {

2.3 配置版MyBatis

2.3.1 步骤

首先创建EmployeeMapper.java，如下：

//@Mapper或者@MapperScan将接口扫描到容器中
//@Mapper
public interface EmployeeMapper {

    public Employee getEmpById(Integer id);

    public void insertEmp(Employee employee);
}

创建EmployeeMapper.xml，如下：

<mapper namespace="com.atguigu.springboot.mapper.EmployeeMapper">
    
    <select id="getEmpById" resultType="com.atguigu.springboot.bean.Employee">
        SELECT * FROM employee WHERE id=#{id}
    select>

    <insert id="insertEmp">
        INSERT INTO employee(lastName,email,gender,d_id)
        VALUES (#{lastName},#{email},#{gender},#{dId})
    insert>
mapper>

创建mybatis-config.xml，如下：

<configuration>
    
    <settings>
        
    settings>

configuration>

以上两个mybatis的xml文件模板可以去mybatis官方文档查看，如下：

指定mybatis的xml映射文件以及全局配置文件的位置：

mybatis:
  # 指定全局配置文件位置
  config-location: classpath:mybatis/mybatis-config.xml
  # 指定sql映射文件位置
  mapper-locations: classpath:mybatis/mapper/*.xml

创建controller，如下：

@RestController
public class DeptController {

    @Autowired
    EmployeeMapper employeeMapper;

    @GetMapping("/emp/{id}")
    public Employee getEmpById(@PathVariable("id") Integer id){
        return employeeMapper.getEmpById(id);
    }
}

给数据表employee添加数据：

测试：

2.3.2 报错Invalid statment xxx not found

如果所有的配置无误但就是报错，而且是Invalid statement xxx not found，那么可以看看proeprties文件是否也配置了mybatis相关的配置，详情看：SpringBoot整合Mybatis启动报错Invalid Statement xxx not found