mybatis

1 要想使用mybatis 需要在maven的pom.xml中导入jar包和mysql的驱动包

    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.2.8</version>
    </dependency>

    <dependency>
      <groupId>Mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.38</version>
    </dependency>

2 每个基于 MyBatis 的应用都是以一个 SqlSessionFactory 的实例为中心的
SqlSessionFactory 的实例可以通过 SqlSessionFactoryBuilder 获得
SqlSessionFactoryBuilder 则可以从 XML 配置文件或一个预先定制的 Configuration 的实例构建出
SqlSessionFactory 的实例

    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

XML 配置文件（configuration XML）中包含了对 MyBatis 系统的核心设置，包含获取数据库连接实例的数据源（DataSource）和决定事务作用域和控制方式的事务管理器（TransactionManager）

3 配置文件

jdbc.properties

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://127.0.0.1:3306/数据库名?useUnicode=true&characterEncoding=utf-8
username=*****
password=*****

mybatis-config.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="jdbc.properties" />

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <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="BlogMapper.xml"/>
    </mappers>
</configuration>

BlogMapper.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.dsying.dao.BlogMapper">
    <select id="selectBlog" resultType="com.dsying.bean.Blog">
        select * from blog where id = #{id}
    </select>
</mapper>

#namespace:当前mapper.xml所对应的dao层接口类
#id:对应接口类中的方法(唯一)
#resultType:接口类中方法的返回值  

4 接口和实体类以及数据库表结构

dao层接口

package com.dsying.dao;

import com.dsying.bean.Blog;

public interface BlogMapper {
    Blog selectBlog(int id);

}

实体类

package com.dsying.bean;

public class Blog {
    private  int id;
    private String name;
    private int age;

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;

    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Blog{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

表结构

CREATE TABLE `blog` (
  `id` int(11) NOT NULL,
  `name` varchar(255) DEFAULT NULL,
  `age` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8

5 测试

 String resource = "mybatis-config.xml";
        InputStream inputStream =null;
        SqlSession sqlSession =null;
        try {
            inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
         
          //SqlSession 完全包含了面向数据库执行 SQL 命令所需的所有方法。
          //你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句
            sqlSession = sqlSessionFactory.openSession();

          //两个版本比较下 你会选择哪个版本（后者可以避免强转）
          //Blog blog = (Blog) session.selectOne("com.dsying.dao.BlogMapper.selectBlog", 1);
          /*
           BlogMapper.class = com.dsying.dao.BlogMapper = dao层接口类路径 = mapper.xml中的namespace
            selectBlog = select.id = 接口中要被实现的方法
          */
            BlogMapper blogMapper = sqlSession.getMapper(BlogMapper.class);
            Blog blog = blogMapper.selectBlog(1);

            System.out.println(blog.toString());
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            sqlSession.close();
        }

6 结果

屏幕快照 2018-02-06 10.49.14.png