第六章：（3）数据访问之整合MyBatis

一、搭建开发环境

　　1、依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</dependency>
<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.2.0</version>
</dependency>

　　依赖关系：

　　2、使用 Druid 数据源

　　　　（1）添加依赖

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.1.8</version>
</dependency>

　　　　（2）配置文件

spring:
  datasource:
    username: root
    password: '123456'
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/mybatis
    type: com.alibaba.druid.pool.DruidDataSource

#   数据源其他配置
    initialSize: 5
    minIdle: 5
    maxActive: 20
    maxWait: 60000
    timeBetweenEvictionRunsMillis: 60000
    minEvictableIdleTimeMillis: 300000
    validationQuery: SELECT 1 FROM DUAL
    testWhileIdle: true
    testOnBorrow: false
    testOnReturn: false
    poolPreparedStatements: true
    #   配置监控统计拦截的filters，去掉后监控界面sql无法统计，'wall'用于防火墙
    filters: stat,wall,log4j
    maxPoolPreparedStatementPerConnectionSize: 20
    useGlobalDataSourceStat: true
    connectionProperties: druid.stat.mergeSql=true;druid.stat.slowSqlMillis=500

　　　　（3）配置类

@Configuration
public class DruidConfig {

    @ConfigurationProperties(prefix = "spring.datasource")
    @Bean
    public DataSource druid() {
        return new DruidDataSource();
    }

    //配置Druid的监控
    //1、配置一个管理后台的Servlet
    @Bean
    public ServletRegistrationBean statViewServlet() {
        ServletRegistrationBean bean = new ServletRegistrationBean(new StatViewServlet(),
                "/druid/*");
        Map<String, String> initParams = new HashMap<>();
        initParams.put("loginUsername", "admin");
        initParams.put("loginPassword", "admin");
        initParams.put("allow", "");//默认就是允许所有访问
        initParams.put("deny", "192.168.15.21");
        bean.setInitParameters(initParams);

        return bean;
    }

    //2、配置一个web监控的filter
    @Bean
    public FilterRegistrationBean webStatFilter(){
        FilterRegistrationBean bean = new FilterRegistrationBean();
        bean.setFilter(new WebStatFilter());
        Map<String,String> initParams = new HashMap<>();
        //排除的请求
        initParams.put("exclusions","*.js,*.css,/druid/*");

        bean.setInitParameters(initParams);
        bean.setUrlPatterns(Arrays.asList("/*"));

        return bean;
    }
}

　　3、创建表

　　　　在配置文件中指定SQL脚本位置：

spring:
  datasource:
    username: root
    password: root
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/mybatis
    type: com.alibaba.druid.pool.DruidDataSource

#   数据源其他配置
    initialSize: 5
    minIdle: 5
    maxActive: 20
    maxWait: 60000
    timeBetweenEvictionRunsMillis: 60000
    minEvictableIdleTimeMillis: 300000
    validationQuery: SELECT 1 FROM DUAL
    testWhileIdle: true
    testOnBorrow: false
    testOnReturn: false
    poolPreparedStatements: true
    #   配置监控统计拦截的filters，去掉后监控界面sql无法统计，'wall'用于防火墙
    filters: stat,wall,log4j
    maxPoolPreparedStatementPerConnectionSize: 20
    useGlobalDataSourceStat: true
    connectionProperties: druid.stat.mergeSql=true;druid.stat.slowSqlMillis=500
    schema:
      - classpath:sql/department.sql
      - classpath:sql/employee.sql

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;

　　4、创建实体类

二、注解版 MyBatis

　　1、创建 Mapper 接口

//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") //使用自动生成的主键，keyProperty指定哪个属性与主键关联
    @Insert("insert into department(departmentName) values(#{departmentName})")
    public int insertDept(Department department);

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

　　　　使用注解版特别简单，只需要创建 Mapper 接口，使用注解写好 SQL 语句即可。

　　　　因为 SpringBoot 有 MybatisAutoConfiguration 自动配置类。

　　2、场景一

　　　　如果在数据库中某个字段是 last_name采用下划线方式，JavaBean 中属性是 lastName，怎么开启驼峰命名转换？

　　　　观察 MybatisAutoConfiguration 类在创建 SqlsessionFactory 是有一个 applyConfiguration方法：

　　会在容器中找到 configurationCustomizer 的组件，然后调用 customize() 方法。

  private void applyConfiguration(SqlSessionFactoryBean factory) {
    Configuration configuration = this.properties.getConfiguration();
    if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) {
      configuration = new Configuration();
    }
    if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
      for (ConfigurationCustomizer customizer : this.configurationCustomizers) {
        customizer.customize(configuration);
      }
    }
    factory.setConfiguration(configuration);
  }

　　　　如果想要自定义MyBatis的配置规则；给容器中添加一个ConfigurationCustomizer；

@org.springframework.context.annotation.Configuration
public class MyMybatisConfig {

    public ConfigurationCustomizer configurationCustomizer() {
        return new ConfigurationCustomizer(){

            @Override
            public void customize(Configuration configuration) {
                //MyBatis开启驼峰命名映射规则
                configuration.setMapUnderscoreToCamelCase(true);
            }
        };
    }
}

　　3、场景二

　　　　如果在某个包下都是 Mapper 接口，又不想在每个类上加 @Mapper 注解，可以使用包扫描规则。

　　　　在配置类上使用包扫描注解：

//使用MapperScan批量扫描所有的Mapper接口；
@MapperScan(value = "com.njf.springboot.mapper")
@SpringBootApplication
public class SpringBoot06DataMybatisApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBoot06DataMybatisApplication.class, args);
    }

}

三、配置版 Mybatis

　　1、创建接口

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

    public Employee getEmpById(Integer id);

    public void insertEmp(Employee emp);
}

　　2、创建 MyBatis 的全局配置文件

　　　　mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <settings>
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>
</configuration>

　　3、创建对应的 SQL 映射文件

　　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.njf.springboot.mapper.EmployeeMapper">

    <!-- public Employee getEmpById(Integer id); -->
    <select id="getEmpById" resultType="com.njf.springboot.bean.Employee">
        SELECT * FROM employee WHERE id=#{id}
    </select>

    <!-- public void insertEmp(Employee employee);-->
    <insert id="insertEmp">
        INSERT INTO employee(lastName,email,gender,d_id) VALUES (#{lastName},#{email},#{gender},#{dId})
    </insert>
</mapper>

　　4、在SpringBoot 的配置文件中指定MyBatis全局配置和SQL映射文件

mybatis:
  config-location: classpath:mybatis/mybatis-config.xml 指定全局配置文件的位置
  mapper-locations: classpath:mybatis/mapper/*.xml      指定 SQL 映射文件的位置