MyBatis系列：入门

Posted 2021-03-21 Tassdar

MyBatis无需我介绍，本系列文章是纯干货，没有一点废话。

1.创建一个maven项目，引入mysql的驱动和mybatis的maven引用

    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.3</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.18</version>
    </dependency>

2.编写mybatis配置文件放置于resources目录下，名字随意

<?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="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
   
  </mappers>
</configuration>

3.使用XML的方式创建SqlSessionFactory

//你的配置文件名称
   String source = "mybatis-config.xml";
//加载配置文件
        InputStream inputStream = Resources.getResourceAsStream(source);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

4.创建一个实体类完成一个基础的查询

创建JavaBean-Blog

public class Blog {

    private int id;

    private String name;

    private  String remark;

    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 String getRemark() {
        return remark;
    }

    public void setRemark(String remark) {
        this.remark = remark;
    }

    @Override
    public String toString()
    {
        return  this.name+this.remark;

    }
}

创建Blog对应的Mapper接口BlogMapper,接口内定义一个查询方法

public interface BlogMapper {

   public Blog selectBlog(int id);
   
}

创建BlogMapper对应的XML映射文件BlogMapper

namespace要与接口名称一致

select节点的id要和接口中定义的方法名字一样

resultType设置要返回的实体类型

<?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="BlogMapper">
    <select id="selectBlog" resultType="Blog">
        select * from Blog where id=#{id}
    </select>
</mapper>

然后我们需要在第一步设置的配置文件的mapper节点中加入我们新写的BlogMapper

    <mappers>
       <mapper resource="BlogMapper.xml"></mapper>
    </mappers>

5.在数据库中创建一个和上面Blog一样的表并且设置id为自增，添加一条测试数据

在main方法中编写如下代码，会从数据库中读取出相应的数据并且输出到控制台

    public static void main(String[] str) throws IOException {
        String source = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(source);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
        Blog blog = mapper.selectBlog(1);
        System.out.println( blog);
    }

本文介绍了Mybatis从创建工厂到从数据库读取出数据的基础流程，接下来将会详细的介绍各个节点的作用。