1、新建数据表

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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

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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

         
              
       
        org.mybatis
               
       
        mybatis
               
       
        3.4.6
           
          
              
       
        mysql
               
       
        mysql-connector-java
               
       
        5.1.47
           
      
     

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：

     
         
              select * from person where id = #{id}    
     

6、新建一个mybatis全局配置文件，详细信息见

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

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。

     
         
              select * from person where id = #{id}    
     

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'}