MyBatis学习
接口代理开发
搭建环境架构
Maven导入包
POM.XML
<dependencies>
<!--mybatis-->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.5</version>
</dependency>
<!--mysql驱动-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.46</version>
</dependency>
<!--单元测试-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<!--mybatis日志配置-->
<!-- 添加slf4j日志api -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.20</version>
</dependency>
<!-- 添加logback-classic依赖 -->
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.3</version>
</dependency>
<!-- 添加logback-core依赖 -->
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-core</artifactId>
<version>1.2.3</version>
</dependency>
</dependencies>
搭建文件结构
映射文件对应的接口文件所在文件夹名称应相同
主文件结构
main.java
mapper: 映射接口包.反射获取调用sql语句
抽象方法接口
pojo: 主类包,数据库表的实现类
utils: 工具类包
main.resources
MyBatis-config配置文件
可以到MyBatis官网找到相关配置参数
<?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>
<!--配置数据库,命名驼峰对应-->
<setting name="mapUnderscoreToCamelCase" value="true"/>
<!--开启二级缓存,必须关掉上一个链接才有效-->
<setting name="cacheEnabled" value="true"/>
</settings>
<typeAliases>
<!--目标类,包扫描,扫描包中的所有类,取别名,别名就是类名-->
<package name="com.itheima.pojo"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<!--配置连接池需要的参数-->
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql:///exercise"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<!--包扫描,扫描包中的所有映射接口文件-->
<package name="com.itheima.mapper"/>
</mappers>
</configuration>
logback.xml是与日志相关配置文件
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<!--CONSOLE ：表示当前的日志信息是可以输出到控制台的。-->
<appender name="Console" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>[%level] %blue(%d{HH:mm:ss.SSS}) %cyan([%thread]) %boldGreen(%logger{15}) - %msg %n</pattern>
</encoder>
</appender>
<logger name="com.itheima" level="DEBUG" additivity="false">
<appender-ref ref="Console"/>
</logger>
<!--level:用来设置打印级别，大小写无关：TRACE, DEBUG, INFO, WARN, ERROR, ALL 和 OFF， 默认debug
<root>可以包含零个或多个<appender-ref>元素，标识这个输出位置将会被本日志级别控制。-->
<root level="DEBUG">
<appender-ref ref="Console"/>
</root>
</configuration>
Mapper.xml 映射文件
以User.Mapper为例子
<?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.itheima.mapper.UserMapper">
<resultMap id="UserInfoMap" type="UserInfo" autoMapping="true">
<id column="id" property="id"/>
<!--<result column="height" property="height"/>
<result column="weight" property="weight"/>
<result column="married" property="married"/>-->
</resultMap>
<resultMap id="OrderMap" type="Order" autoMapping="true">
<id column="oid" property="oId"/>
<!--<result column="user_id" property="userId"/>-->
<!--<result column="number" property="number"/>-->
<!--<result column="create_time" property="createTime"/>-->
<!--<result column="note" property="note"/>-->
</resultMap>
<resultMap id="UserMap" type="User" autoMapping="true">
<id column="id" property="id"/>
<!--<result column="username" property="username"/>
<result column="birthday" property="birthday"/>
<result column="sex" property="sex"/>
<result column="address" property="address"/>-->
<!--association: 配置一对一 property属性: 类中成员变量名-->
<association property="userInfo" resultMap="UserInfoMap"/>
<!--collection: 配置一对多 property属性: 类中成员变量名-->
<collection property="orders" resultMap="OrderMap"/>
<collection property="roles" javaType="List" ofType="Role">
<id column="role_id" property="roleId"/>
<result column="role_name" property="roleName"/>
<result column="role_detail" property="roleDetail"/>
</collection>
</resultMap>
<!--多表查询,查询结果有多张表的数据,需要使用resultMap,手动指定查询结果和类中成员变量的对应关系
注意: 多表查询表中字段名和类中成员变量相同的也要指定关系,
或者使用 autoMapping="true",但是主键相同也要配置
-->
<select id="findUserAndInfo" resultMap="UserMap">
SELECT * FROM USER INNER JOIN user_info ON user.`id`=user_info.`id` WHERE user.id=#{uid};
</select>
<!--一对多查询用户和多个订单-->
<select id="findUserAndOrders" resultMap="UserMap">
SELECT * FROM USER INNER JOIN `order` ON user.`id`=`order`.`user_id` WHERE user.`id`=#{uid};
</select>
<!--一个用户包含多个角色 (一对多)-->
<select id="findUserAndRoles" resultMap="UserMap">
SELECT * FROM USER INNER JOIN user_role ON user.`id`=user_role.`user_id` INNER JOIN role ON role.`role_id`=user_role.`role_id` WHERE user.`id`=#{uid};
</select>
<resultMap id="RoleMap" type="Role" autoMapping="true">
<id column="role_id" property="roleId"/>
<!--<result column="role_name" property="roleName"/>-->
<!--<result column="role_detail" property="roleDetail"/>-->
<collection property="users" javaType="List" ofType="User" autoMapping="true">
<id column="id" property="id"/>
<!--<result column="username" property="username"/>-->
<!--<result column="birthday" property="birthday"/>-->
<!--<result column="sex" property="sex"/>-->
<!--<result column="address" property="address"/>-->
</collection>
</resultMap>
<!--一个角色包含多个用户 (一对多)-->
<select id="findRoleAndUsers" resultMap="RoleMap">
SELECT * FROM USER INNER JOIN user_role ON user.`id`=user_role.`user_id` INNER JOIN role ON role.`role_id`=user_role.`role_id` WHERE role.`role_id`=#{rid};
</select>
</mapper>
有过报错
Cause: org.xml.sax.SAXParseException; lineNumber: 4; columnNumber: 45; 文档根元素 “mapper” 必须匹配 DOCTYPE 根 “null”。
解决:
原(自生成头文件):
<?xml version="1.0" encoding="utf-8" ?>
<mapper xmlns="http://mybatis.org/schema/mybatis-mapper"
namespace="*.mapper.UserMapper">
改为:
<?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="*.UserMapper">
main.test
test: 测试类
Utils:
public class SqlSessionFactoryUtils {
private SqlSessionFactoryUtils(){}
private static SqlSessionFactory sqlSessionFactory;
static {
String s="mybatis-config.xml";
try {
InputStream resourceAsStream = Resources.getResourceAsStream(s);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
} catch (IOException e) {
System.out.println("链接池初始化失败"+e.toString());
}
}
public static SqlSessionFactory getSqlSessionFactory(){
return sqlSessionFactory;
}
}
测试:
@Test
public void findSingleUserByID(){
SqlSession sqlSession = SqlSessionFactoryUtils.getSqlSessionFactory().openSession(true);
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
User userByID = mapper.findUserByID(1);
System.out.println(userByID);
}