使用注解开发，就可以删掉原本写MyBatis语句的xml文件了，注解只要在UserMapper.java接口上进行实现即可
增 @Insert("insert into user values(#{id}, #{username}, #{password}, #{birthday})")void save(User user); 删 @Delete("delete from user where id=#{id}")void delete(int id); 改 @Update("update user set username=#{username}, password=#{password}, birthday=#{birthday} where id=#{id}")void update(User user); 查 @Select("select * from user where id=#{id}")User findById(int id);@Select("select * from user")List<User> findAll(); 完整代码 package com.example.demo.mapper;import com.example.demo.domain.User;import org.apache.ibatis.annotations.Delete;import org.apache.ibatis.annotations.Insert;import org.apache.ibatis.annotations.Select;import org.apache.ibatis.annotations.Update;import java.util.List;public interface UserMapper {@Insert("insert into user values(#{id}, #{username}, #{password}, #{birthday})")void save(User user);@Delete("delete from user where id=#{id}")void delete(int id);@Update("update user set username=#{username}, password=#{password}, birthday=#{birthday} where id=#{id}")void update(User user);@Select("select * from user where id=#{id}")User findById(int id);@Select("select * from user")List<User> findAll();} 加载映射关系原本在sqlMapConfig.xml文件中的加载映射文件修改为加载映射关系：
<!-- 加载映射关系 --><mappers><package name="com.example.demo.mapper"/></mappers> 测试代码原本数据库中的内容：
package com.example.demo;import com.example.demo.domain.User;import com.example.demo.mapper.UserMapper;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;import java.io.InputStream;import java.util.Date;import java.util.List;public class DemoApplication {public static void main(String[] args) throws IOException {// 1. 创建SqlSessionFactoryBuilder对象SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();// 2. 加载SqlMapConfig.xml配置文件InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");// 3. 创建SqlSessionFactory对象SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);// 4. 获取SqlSessionSqlSession sqlSession = sqlSessionFactory.openSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);// 增加User信息User saveUser = new User();saveUser.setUsername("newUser");saveUser.setPassword("aaaaaa");saveUser.setBirthday(new Date());mapper.save(saveUser);// 删除User信息int deleteUserId = 3;mapper.delete(deleteUserId);// 修改User信息User updateUser = new User();updateUser.setId(2);updateUser.setUsername("ccc");updateUser.setPassword("1234567update");mapper.update(updateUser);// 根据Id查询UserUser user = mapper.findById(1);System.out.println(user);// 查询所有userList<User> userList = mapper.findAll();System.out.println(userList);sqlSession.commit();// 6. 释放资源sqlSession.close();}}打印的信息：
更新后的内容：
3. MyBatis的注解实现复杂映射开发此处对应于【Spring集成MyBatis】MyBatis的多表查询的内容，来写一下对应的注解实现。
一对一操作的实现原本基于配置是这么写的
<?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.example.demo.dao.OrderMapper"><resultMap id="orderMap" type="com.example.demo.domain.Order"><!-- 手动指定字段与实体属性的映射关系--><!-- column:数据表的字段名称--><!-- property:实体的属性名称--><id column="oid" property="id"></id><result column="ordertime" property="orderTime"></result><result column="total" property="total"></result><result column="uid" property="user.id"></result><result column="username" property="user.username"></result><result column="password" property="user.password"></result><result column="birthday" property="user.birthday"></result></resultMap><select id="findAll" resultMap="orderMap">SELECT *, o.id `orderid`, u.id `userid` FROM `order` o, `user` u WHERE o.uid=u.id</select></mapper>使用注解后如下修改
package com.example.demo.mapper;import com.example.demo.domain.Order;import org.apache.ibatis.annotations.Result;import org.apache.ibatis.annotations.Results;import org.apache.ibatis.annotations.Select;import java.util.List;public interface OrderMapper {@Select("select *, o.id oid from `order` o, user u where o.uid=u.id")@Results({@Result(column = "oid", property = "id"),@Result(column = "ordertime", property = "orderTime"),@Result(column = "total", property = "total"),@Result(column = "uid", property = "user.id"),@Result(column = "username", property = "user.username"),@Result(column = "password", property = "user.password")})List<Order> findAll();} 一对一操作实现的第二种方式其中，在要封装的User对象中，我们可以在@Result注解中写明属性名称、数据库查询到的值、要封装的实体类型等等等，有点类似于之前的注解中的那些属性，不同的事这里通过一个@One来指定通过哪个接口的方法来获得对应的数据，这时候会将column的值注入到这个方法中来获得具体的结果 也就是，首先使用
select * from `order`来查询出order下的所有信息，包括id、ordertime、total、uid，接着，我们需要根据里面的uid可以查出对应的User信息并封装到Order实体类下的user属性中
select * from `user` where id=(上面查询结果的所有uid)这里就需要在@Result注解中进一步指定property、column、javaType、one(由于是一对一所以使用one，一对多使用many)
package com.example.demo.mapper;import com.example.demo.domain.Order;import com.example.demo.domain.User;import org.apache.ibatis.annotations.One;import org.apache.ibatis.annotations.Result;import org.apache.ibatis.annotations.Results;import org.apache.ibatis.annotations.Select;import java.util.List;public interface OrderMapper {@Select("select * from `order`")@Results({@Result(column = "id", property = "id"),@Result(column = "ordertime", property = "orderTime"),@Result(column = "total", property = "total"),@Result(property = "user", // 要封装的属性名称column = "uid", // 根据哪个字段去查询user表的数值javaType = User.class, // 要封装的实体类型// select属性 代表查询哪个接口的方法获得数据one = @One(select = "com.example.demo.mapper.UserMapper.findById"))})List<Order> findAll();}以上两种一对一操作的测试代码：
package com.example.demo;import com.example.demo.domain.Order;import com.example.demo.domain.User;import com.example.demo.mapper.OrderMapper;import com.example.demo.mapper.UserMapper;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;import java.io.InputStream;import java.util.Date;import java.util.List;public class DemoApplication {public static void main(String[] args) throws IOException {// 1. 创建SqlSessionFactoryBuilder对象SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();// 2. 加载SqlMapConfig.xml配置文件InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");// 3. 创建SqlSessionFactory对象SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);// 4. 获取SqlSessionSqlSession sqlSession = sqlSessionFactory.openSession();OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);List<Order> orderList = orderMapper.findAll();for (Order order : orderList) {System.out.println(order);}// 6. 释放资源sqlSession.close();}}结果：
一对多操作的实现查询User对应的订单，和【Spring集成MyBatis】MyBatis的多表查询中一样，首先需要再User里面加上一个orderList属性，用于封装所有的订单，并写好对应的set、get方法以及对应的toString方法。 类似于一对一操作的第二种实现方式，我们需要在@Result里面指定property、column、javaType，由于返回的是List，就不用one而用many 首先查询出所有的用户，并在用户下面封装其订单列表。 通过
select * from user查出了用户的id,username,password,birthday的信息，我们需要根据里面的id到order表里查询对应的订单
select * from `order` where uid=(上面user查询出来的所有id)即再通过一个@Result注解指定根据uid查询订单的方法。目前Order类里还没有根据uid查询订单的方法，所以我们需要再去实现一下根据uid查询订单的方法 在OrderMapper里写：
@Select("select * from `order` where uid=#{id}")List<Order> findByUid(int id);在UserMapper里写根据userid查询指定订单
@Select("select * from user")@Results({@Result(column = "id", property = "id"),@Result(column = "username", property = "username"),@Result(column = "password", property = "password"),@Result(column = "birthday", property = "birthday"),@Result(property = "orderList",column = "id",javaType = List.class,many = @Many(select = "com.example.demo.OrderMapper.findByUid"))})List<User> findUserAndOrderAll();测试：
package com.example.demo;import com.example.demo.domain.User;import com.example.demo.mapper.UserMapper;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;import java.io.InputStream;import java.util.List;public class DemoApplication {public static void main(String[] args) throws IOException {// 1. 创建SqlSessionFactoryBuilder对象SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();// 2. 加载SqlMapConfig.xml配置文件InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");// 3. 创建SqlSessionFactory对象SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);// 4. 获取SqlSessionSqlSession sqlSession = sqlSessionFactory.openSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> userList = mapper.findUserAndOrderAll();for (User user : userList) {System.out.println(user);}// 6. 释放资源sqlSession.close();}}查询出来的结果如下：
多对多操作实现查询User对应的角色，和【Spring集成MyBatis】MyBatis的多表查询中一样，首先需要再User里面加上一个roleList属性，用于封装所有的角色，并写好对应的set、get方法以及对应的toString方法。 实现过程如下： 先查询所有的User信息
select * from USER根据userid查询所有的对应的role及其信息
select * from user_role ur, role r where ur.roleId=r.id and userid=(上面查出来的所有id)那么首先我们需要建立roleMapper，并在RoleMapper中写上对应的查询语句：
package com.example.demo.mapper;import com.example.demo.domain.Role;import org.apache.ibatis.annotations.Select;import java.util.List;public interface RoleMapper {@Select("select * from user_role ur, role r where ur.roleId=r.id and userid=#{id}")List<Role> findByUid(int id);}接着，在UserMapper中类似一对多一样补充如下方法：
@Select("select * from User")@Results({@Result(column = "id", property = "id"),@Result(column = "username", property = "username"),@Result(column = "password", property = "password"),@Result(column = "birthday", property = "birthday"),@Result(property = "roleList",column = "id",javaType = List.class,many = @Many(select = "com.example.demo.mapper.RoleMapper.findByUid"))})List<User> findUserAndRoleAll();最后测试：
package com.example.demo;import com.example.demo.domain.User;import com.example.demo.mapper.UserMapper;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;import java.io.InputStream;import java.util.List;public class DemoApplication {public static void main(String[] args) throws IOException {// 1. 创建SqlSessionFactoryBuilder对象SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();// 2. 加载SqlMapConfig.xml配置文件InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");// 3. 创建SqlSessionFactory对象SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);// 4. 获取SqlSessionSqlSession sqlSession = sqlSessionFactory.openSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> userList = mapper.findUserAndRoleAll();for (User user : userList) {System.out.println(user);}// 6. 释放资源sqlSession.close();}}结果如下：
