代理

此处使用的是JDK的动态代理方式，延迟加载使用的cglib动态代理方式

代理分为静态代理和动态代理。此处先不说静态代理，因为Mybatis中使用的代理方式是动态代理。
动态代理分为两种方式：
基于JDK的动态代理–针对有接口的类进行动态代理
基于CGLIB的动态代理–通过子类继承父类的方式去进行代理。

xml方式

开发方式
只需要开发Mapper接口（dao接口）和Mapper映射文件，不需要编写实现类。
开发规范
Mapper接口开发方式需要遵循以下规范：
1、 Mapper接口的类路径与Mapper.xml文件中的namespace相同。
2、 Mapper接口方法名称和Mapper.xml中定义的每个statement的id相同。
3、 Mapper接口方法的输入参数类型和mapper.xml中定义的每个sql 的parameterType的类型相同。
4、 Mapper接口方法的返回值类型和mapper.xml中定义的每个sql的resultType的类型相同。

UserMapper.java

package com.xd.mybatisdemo.mapper;

import com.xd.mybatisdemo.pojo.User;

public interface UserMapper {
    public User findUserById(int id) throws Exception;

}

User.java

package com.xd.mybatisdemo.pojo;

import java.util.Date;

public class User {
    private int id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    public int getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

db.properties

db.driver=com.mysql.cj.jdbc.Driver
db.url=jdbc:mysql://127.0.0.1:3306/mybatisdemo?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
db.username=root
db.password=root

SqlMapConfig.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>
    <properties resource="db.properties"></properties>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="${db.driver}" />
                <property name="url" value="${db.url}" />
                <property name="username" value="${db.username}" />
                <property name="password" value="${db.password}" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="UserMapper.xml" />
    </mappers>
</configuration>

UserMapper.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.xd.mybatisdemo.mapper.UserMapper">

    <!-- 根据id获取用户信息 -->
    <select id="findUserById" parameterType="int"
            resultType="com.xd.mybatisdemo.pojo.User">
        select * from user where id = #{id}
    </select>







</mapper>

UserMapperTest.java

package com.xd.mybatisdemo;

import com.xd.mybatisdemo.mapper.UserMapper;
import com.xd.mybatisdemo.pojo.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 org.junit.Before;
import org.junit.Test;

import java.io.InputStream;

public class UserMapperTest {
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void setUp() throws Exception {
//mybatis配置文件
        String resource = "SqlMapConfig.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
//使用SqlSessionFactoryBuilder创建sessionFactory
        sqlSessionFactory = new
                SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void testFindUserById() throws Exception {
//获取session
        SqlSession session = sqlSessionFactory.openSession();
//获取mapper接口的代理对象
        UserMapper userMapper = session.getMapper(UserMapper.class);
//调用代理对象方法
        User user = userMapper.findUserById(1);
        System.out.println(user.getUsername());
//关闭session
        session.close();
    }
}

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>org.example</groupId>
  <artifactId>mybatisdemo</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>mybatisdemo</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <!-- mybatis依赖 -->
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.4.6</version>
    </dependency>
    <!-- mysql依赖 -->
<!--    <dependency>-->
<!--      <groupId>mysql</groupId>-->
<!--      <artifactId>mysql-connector-java</artifactId>-->
<!--      <version>5.1.35</version>-->
<!--    </dependency>-->


    <dependency>
      <groupId>com.mysql</groupId>
      <artifactId>mysql-connector-j</artifactId>
      <version>8.0.32</version>
    </dependency>

    <!-- 单元测试 -->
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
    </dependency>
  </dependencies>
</project>