mybatis dao实现 || 接口代理方式实现

mybatis dao层实现1. 实现dao层接口
2. 接口代理方式实现dao代理开发要求：	Mapper接口开发方法只需要编写Mapper接口（相当于dao接口），由mybatis框架根据接口定义创建接口的动态代理对象，代理对象的方法体和dao方式实现的接口一样。1. mapper.xml 中namespace与mapper接口中全限定名相同
2. mapper接口方法名和mapper.xml中定义的每个statement的id相同
3. mapper接口方法入参类型，和 statement的paramType相同
4. mapper接口返回值类型，和statement的resultType相同

1、mybatis环境搭建

user-mapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="cn.bitqian.dao.UserMapper"><!-- resultType 引用别名user --><select id="queryAllUser" resultType="user">select * from users1</select><select id="queryUserByUserId" parameterType="int" resultType="user">select * from users1 where userid = #{id}</select></mapper>

mybatis-config.xml 核心配置文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><properties resource="jdbc.properties"></properties><!-- user别名 --><typeAliases><typeAlias type="cn.bitqian.entity.User" alias="user"></typeAlias></typeAliases><environments default="development"><environment id="development"><transactionManager type="JDBC"></transactionManager><dataSource type="POOLED"><property name="driver" value="${driver}"/><property name="url" value="${url}"/><property name="username" value="${username}"/><property name="password" value="${password}"/></dataSource></environment></environments><mappers><mapper resource="cn\bitqian\mapper\user-mapper.xml"></mapper></mappers></configuration>

2、mybatis dao接口实现

编写dao接口，同下面mapper接口

package cn.bitqian.dao;import cn.bitqian.entity.User;import java.io.IOException;
import java.util.List;/*** 注意 接口代理开发* 1. 接口类名与mapper中namespace对应* 2. 接口中方法名与statement中的id对应* 3. 接口中方法参数与statement中的parameterType对应* 4. 接口中方法返回值与statement中的resultType类型对应*/
public interface UserMapper {public List<User> queryAllUser() throws IOException;public User queryUserByUserId(int userId);}

dao接口实现

package cn.bitqian.dao.impl;import cn.bitqian.dao.UserMapper;
import cn.bitqian.entity.User;
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;/*** 传统实现dao层接口 模板api* @author echo lovely* @date 2020/9/11 9:23*/
public class UserMapperImpl implements UserMapper {@Overridepublic List<User> queryAllUser() throws IOException {InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);SqlSession sqlSession = sqlSessionFactory.openSession();// namespace.idList<User> userList = sqlSession.selectList("cn.bitqian.dao.UserMapper.queryAllUser");sqlSession.close();return userList;}@Overridepublic User queryUserByUserId(int userId) {return null;}
}

3、动态代理方式，只实现Mapper接口

UserMapper 接口同上

优点分析：1. 只需实现mapper接口，定义对应的业务方法，注意接口名，
方法名，入参，返回的参数和mappers的配置一致2. 无需实现mapper接口，mybatis通过动态代理的方式进行实现了
只需用UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
getMapper api 来创建对象，进行数据库操作

package cn.bitqian.service;import cn.bitqian.dao.UserMapper;
import cn.bitqian.dao.impl.UserMapperImpl;
import cn.bitqian.entity.User;
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;/*** @author echo lovely* @date 2020/9/11 9:29*/
public class DemoTest {public static void main(String[] args) {// 通过实现dao层接口UserMapper userMapper = new UserMapperImpl();try {System.out.println(userMapper.queryAllUser());} catch (IOException e) {e.printStackTrace();}// 编写mapper接口实现查询所有test1();// 根据id查询user对象test2();}private static UserMapper userMapper;static {try {InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);SqlSession sqlSession = build.openSession();// 使用getMapper api拿到接口对象，mybatis会通过动态代理进行底层实现userMapper = sqlSession.getMapper(UserMapper.class);} catch (IOException e) {e.printStackTrace();}}// 通过编写mapper接口实现查询static void test1() {try {List<User> userList = userMapper.queryAllUser();System.out.println(userList);} catch (IOException e) {e.printStackTrace();}}static void test2() {User user = userMapper.queryUserByUserId(1);System.out.println(user);}}