1、新建数据表

本次测试使用mysql数据，数据库名称为mybatis,新建一张表person,建表语句如下:

CREATE TABLE `person` (

`id` INT ( 11 ) PRIMARY KEY auto_increment,

`first_name` VARCHAR ( 255 ),

`last_name` VARCHAR ( 255 ),

`age` INT ( 11 ),

`email` VARCHAR ( 255 ),

`address` VARCHAR ( 255 )

);

插入测试数据如下：

insert into person(first_name,last_name,age,email,address) VALUES('Schmitt', 'Carine',25,null,'beijing');

insert into person(first_name,last_name,age,email,address) VALUES('King', 'Jean',36,'Jean@163.com','beijing');

insert into person(first_name,last_name,age,email,address) VALUES('Ferguson', 'Schmitt',23,'88888@qq.com','shanghai');

insert into person(first_name,last_name,age,email,address) VALUES('Piestrzeniewicz', 'Nelson',55,null,'nanjing');

insert into person(first_name,last_name,age,email,address) VALUES('Jytte', 'Jean',22,'55555@qq.com','shenzhen');

insert into person(first_name,last_name,age,email,address) VALUES('Victorino', 'Diego',19,'Diego@163.com','shanghai');

insert into person(first_name,last_name,age,email,address) VALUES('Julie', 'Schmitt',56,null,'nanjing');

insert into person(first_name,last_name,age,email,address) VALUES('Gao', 'Diego',45,'66666@qq.com','beijing');

insert into person(first_name,last_name,age,email,address) VALUES('Piestrzeniewicz', 'Schmitt',36,'44444@qq.com','beijing');

insert into person(first_name,last_name,age,email,address) VALUES('Frdrique', 'Juri',25,'99999@qq.com','beijing');

结果如下：

2、mybatis入门

1、新建maven工程

本次演示使用IntelliJ IDEA社区版，新建一个maven工程，最终结果如下：

2、添加依赖，主要是mybatis和mysql

<dependencies>

    <dependency>

        <groupId>org.mybatis</groupId>

        <artifactId>mybatis</artifactId>

        <version>3.4.6</version>

    </dependency>

    <dependency>

        <groupId>mysql</groupId>

        <artifactId>mysql-connector-java</artifactId>

        <version>5.1.47</version>

    </dependency>

</dependencies>

3、编写数据库表person对应的实体。

package com.yefengyu.mybatis.entity;

public class Person

{

    private Integer id;

    private String firstName;

    private String lastName;

    private Integer age;

    private String email;

    private String address;

    public Integer getId()

    {

        return id;

    }

    public void setId(Integer id)

    {

        this.id = id;

    }

    public String getFirstName()

    {

        return firstName;

    }

    public void setFirstName(String firstName)

    {

        this.firstName = firstName;

    }

    public String getLastName()

    {

        return lastName;

    }

    public void setLastName(String lastName)

    {

        this.lastName = lastName;

    }

    public Integer getAge()

    {

        return age;

    }

    public void setAge(Integer age)

    {

        this.age = age;

    }

    public String getEmail()

    {

        return email;

    }

    public void setEmail(String email)

    {

        this.email = email;

    }

    public String getAddress()

    {

        return address;

    }

    public void setAddress(String address)

    {

        this.address = address;

    }

    @Override

    public String toString()

    {

        return "Person{" +

               "id=" + id +

               ", firstName='" + firstName + '\'' +

               ", lastName='" + lastName + '\'' +

               ", age=" + age +

               ", email='" + email + '\'' +

               ", address='" + address + '\'' +

               '}';

    }

}

4、编写mapper接口

package com.yefengyu.mybatis.mapper;

import com.yefengyu.mybatis.entity.Person;

public interface PersonMapper

{

    Person getPerson(Integer id);

}

5、编写mapper映射文件

在resources下面新建一个mapper文件夹，再在里面新建一个PersonMapper.xml文件，内容如下：

<?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.yefengyu.mybatis.mapper.PersonMapper">

    <select id="getPerson" resultType="com.yefengyu.mybatis.entity.Person">

        select * from person where id = #{id}

    </select>

</mapper>

6、新建一个mybatis全局配置文件，详细信息见官网

在resources下面新建mybatis-config.xml文件，内容如下：

<?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>

  <environments default="development">

    <environment id="development">

      <transactionManager type="JDBC"/>

      <dataSource type="POOLED">

        <property name="driver" value="com.mysql.jdbc.Driver"/>

        <property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis?characterEncoding=utf8"/>

        <property name="username" value="root"/>

        <property name="password" value="123456"/>

      </dataSource>

    </environment>

  </environments>

  <mappers>

    <mapper resource="mapper/PersonMapper.xml"/>

  </mappers>

</configuration>

7、测试

package com.yefengyu.mybatis;

import com.yefengyu.mybatis.mapper.PersonMapper;

import com.yefengyu.mybatis.entity.Person;

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;

public class Main

{

    public static void main(String[] args)

        throws IOException

    {

        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");

        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);

        SqlSession sqlSession = sqlSessionFactory.openSession();

        PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);

        Person person = mapper.getPerson(1);

        System.out.println(person);

        sqlSession.close();

    }

}

8、结果

Person{id=1, firstName='null', lastName='null', age=25, email='null', address='beijing'}

分析：这条查询的结果和数据库相比，firstName和lastName字段查询有问题，没有查询到结果，这个主要原因是数据库字段命名是使用下划线，而java实体使用驼峰法命名，导致mybatis无法自动匹配，解决方法有很多，此处使用最原始的一种：给查询语句中的字段添加别名的方式。

<?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.yefengyu.mybatis.mapper.PersonMapper">

    <select id="getPerson" resultType="com.yefengyu.mybatis.entity.Person">

        select * from person where id = #{id}

    </select>

</mapper>

中的查询语句由

select * from person where id = #{id}

改为下面这句

select id, first_name firstName, last_name lastName, age, email, address  from person where id = #{id}

这样就可以查询到我们需要看到的效果，是不是很神奇？

Person{id=1, firstName='Schmitt', lastName='Carine', age=25, email='null', address='beijing'}

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