01. MyBatis 接口式编程 Hello World

1.搭建环境

1.1 搭建数据库 MySQL

DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(30) DEFAULT NULL,
  `pwd` varchar(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


INSERT INTO `user`(`name`, `pwd`) VALUES ('hong', '123456');
INSERT INTO `user`(`name`, `pwd`) VALUES ('Tom', '123456');
INSERT INTO `user`(`name`, `pwd`) VALUES ('Jerry', '123456');

1.2 Maven

<dependencies>
    <!-- MySQL驱动 -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.47</version>
    </dependency>
    <!-- MyBatis -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.2</version>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.18</version>
    </dependency>
    <!-- 日志 -->
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>

    <!-- Junit -->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
</dependencies>

1.3 jdbc.properties

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?userSSL=true&useUnicode=true&characterEncoding=UTF-8
username=root
password=1234

1.4 log4j.properties

log4j.rootLogger=DEBUG,A1

log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=[%t] [%c]-[%p] %m%n

2.编写代码

2.1 实体类

package org.hong.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private Integer id;
    private String name;
    private String pwd;
}

2.2 Mapper 接口

package org.hong.mapper;

import org.hong.pojo.User;

import java.util.List;

public interface UserMapper {
    List<User> getAll();
}

2.3 Mapper.xml 文件

<?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">

<!--
    namespace:名称空间, 对应接口的全类名
 -->
<mapper namespace="org.hong.mapper.UserMapper">
    <!--
        select: 配置查询
        id: 唯一标识, 对应接口中的方法名
        resultType: 返回值类型, 类的全类名, 如果返回值是集合写集合中泛型的类型
     -->
    <select id="getAll" resultType="org.hong.pojo.User">
        select * from user
    </select>
</mapper>

2.4 MyBatis 核心配置文件

<?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: 核心配置文件 -->
<configuration>

    <!--
		properties: 引入外部properties文件 必须放在最前面,否则会报错
			resource: 类路径下
			url: 磁盘路径或网络路径
 	-->
    <properties resource="jdbc.properties"/>

    <!-- 设置日志输出, 方便观察sql语句和参数 -->
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>

    <!--
        environments配置项目的运行环境, 可以配置多个
        default: 启用的环境
     -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!-- 数据库连接信息 -->
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>

    <!-- 每一个Mapper.xml都需要在MyBatis核心配置文件中注册!!! -->
    <mappers>
        <mapper resource="org/hong/mapper/UserMapper.xml"/>
    </mappers>

</configuration>

3.测试用例

package org.hong.test;

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.hong.mapper.UserMapper;
import org.hong.pojo.User;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class HelloTest {
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        // MyBatis全局配置文件路径
        String resource = "mybatis-config.xml";
        // 获取MyBatis全局配置文件的输入流
        InputStream is = Resources.getResourceAsStream(resource);
        // 获取SqlSessionFactory对象
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
        return factory;
    }

    @Test
    public void testHello() throws IOException {
        // 1、获取SqlSessionFactory对象
        SqlSessionFactory factory = getSqlSessionFactory();

        // 2、获取SqlSession对象
        SqlSession openSession = factory.openSession();
        try {
            // 3、获取接口的实现类对象
            // 会为接口自动创建代理对象, 代理对象去执行增删改查方法, sql语句会从mapper.xml中获取
            UserMapper mapper = openSession.getMapper(UserMapper.class);
            List<User> list = mapper.getAll();
            list.forEach(System.out::println);
        } finally {
            // 4、SqlSession代表和数据库的一次对话, 用完必须关闭
            openSession.close();
        }
    }
}

4.控制台打印

## 发送的sql语句就是我们在mapper.xml中配置的sql语句
[org.hong.mapper.UserMapper.getAll]-==>  Preparing: select * from user
[org.hong.mapper.UserMapper.getAll]-==> Parameters:
[org.hong.mapper.UserMapper.getAll]-<==      Total: 4
User(id=1, name=hong, pwd=123456)
User(id=2, name=Tom, pwd=123456)
User(id=3, name=Jerry, pwd=123456)