Mybatis Demo

分手后的思念是犯贱 2022-07-16 10:53 151阅读 0赞

***Mybatis Demo***

在分析Spring AOP的事务时，需要进行事务的配置，所以需要先对进行持久层的配置原理进行分析，这篇文章来分析下mybatis是如何使用的，通过一个简单的Demo并且分析它的原理：

**1.示例如下**

User.java

package com.company.user.entity;
    
    public class User {
    	
    	private Integer userId;
    	
    	private String userName;
    	
    	private String description;
    	
    	public Integer getUserId() {
    		return userId;
    	}
    	public void setUserId(Integer userId) {
    		this.userId = userId;
    	}
    	public String getUserName() {
    		return userName;
    	}
    	public void setUserName(String userName) {
    		this.userName = userName;
    	}
    	public String getDescription() {
    		return description;
    	}
    	public void setDescription(String description) {
    		this.description = description;
    	}
    	@Override
    	public String toString() {
    		return "User [userId=" + userId + ", userName=" + userName + ", description=" + description + "]";
    	}
    }

UserMapper.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.company.user.mapper.UserMapper">
    
    	<resultMap type="com.company.user.entity.User" id="resultMap_User">
    	<id column="user_id" property="userId" jdbcType="BIGINT"/>    
        <span style="white-space:pre">	</span><result column="user_name" property="userName" jdbcType="VARCHAR"/>
        <span style="white-space:pre">	</span><result column="description" property="description" jdbcType="VARCHAR"/>
    	</resultMap>
    	
    	<select id="findByUserId" parameterType="java.util.HashMap" resultMap="resultMap_User">
    	select A.user_id,A.user_name,A.description
    	from user A
    	where 1=1
    	and A.user_id = #{userId}
    	</select>
    
    </mapper>

UserMapper.java

package com.company.user.mapper;
    
    import java.util.Map;
    
    import com.company.user.entity.User;
    
    public interface UserMapper {
    	public User findByUserId(Map<String, Object> map);
    }

configuration.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>
          
      <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://localhost:3306/test"/>
            <property name="username" value="root"/>
            <property name="password" value="123456"/>
          </dataSource>
        </environment>
      </environments>
      
      
      <mappers>
        <mapper resource="com/company/user/mapper/UserMapper.xml"/>
      </mappers>
      
    </configuration>

userTest.java

package com.company.user.test;
    
    import java.io.IOException;
    import java.util.HashMap;
    import java.util.Map;
    
    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.junit.Test;
    
    import com.company.user.entity.User;
    import com.company.user.mapper.UserMapper;
    
    public class UserTest {
    	@Test
        public void findByUserId() {
            SqlSession sqlSession = getSessionFactory().openSession();  
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            Map<String, Object> map = new HashMap<String, Object>();
            map.put("userId","1");
            User user = userMapper.findByUserId(map); 
            System.out.println("UserTest.findByUserId():"+user.toString());
        }
    	    
        //Mybatis 通过SqlSessionFactory获取SqlSession, 然后才能通过SqlSession与数据库进行交互
        private static SqlSessionFactory getSessionFactory() {  
            SqlSessionFactory sessionFactory = null;  
            String resource = "configuration.xml";  
            try {  
                sessionFactory = new SqlSessionFactoryBuilder().build(Resources  
                        .getResourceAsReader(resource));
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
            return sessionFactory;  
        }  
    }

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
      <modelVersion>4.0.0</modelVersion>
      <groupId>com.mycompany.mytest</groupId>
      <artifactId>mytest</artifactId>
      <packaging>jar</packaging>
      <version>1.0-SNAPSHOT</version>
      <name>mytest</name>
      <url>http://maven.apache.org</url>
      <dependencies>
        <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>
          <version>4.10</version>
          <scope>test</scope>
        </dependency>
        
    
        <span style="white-space:pre">	</span><dependency>
    		<groupId>mysql</groupId>
    		<artifactId>mysql-connector-java</artifactId>
    		<version>5.1.39</version>
    	</dependency>
    		
    
    	<dependency>
    	    <groupId>org.mybatis</groupId>  
            <artifactId>mybatis</artifactId>  
            <version>3.4.0</version>  
     	</dependency>
    	 	
    
    	<dependency>
    		<groupId>org.mybatis</groupId>  
               <artifactId>mybatis-spring</artifactId>  
               <version>1.3.0</version>
    	</dependency>
        
      </dependencies>
    </project>

然后执行UserTest这个Junit即可~：

![Center][]

**2.分析它的原理：**

1）mybatis在执行时，会先分析它的配置文件，我们看UsetTest的getSessionFactory，它先指定配置文件configuration.xml，然后用SqlSessionFactoryBuilder来加载它，并且返回sessionFactory对象。其实加载的过程就是对configuration.xml配置文件进行分析的过程，看一下SqlSessionFactoryBuilder的实现就知道了：

![Center 1][]

它在分析完配置文件之后就会返回一个SqlSession的工厂，可以通过openSession从中得到SqlSession的一个句柄，也就是一个引用。

2）那如何得到userMapper的实现，并且使用其中的方法呢，只需要SqlSession.getMapper(UserMapper.class)即可。 那么为什么通过UserMapper.class就可以获得userMapper的方法呢； 我们一点点分析，现在看一下configuration.xml

A)首先是配置数据源 指定使用那个数据库和驱动。

B)然后就是指定UserMapper.xml

意思就是通过指定的数据源，来实现UserMapper.xml中的配置内容，那如何实现，其实就是通过指定的数据源来实现映射文件UserMapper中的sql语句，然后把namespace的值作为唯一标识。这个唯一标识会放入sqlSessionFactory中，接着得到SqlSession，然后使用SqlSession.getMapper(“nameSpace指定的唯一标识”)获得userMapper的实现，然后就可以执行其中的方法了。

上面就是Mybatis作用的大概原理，接着就可以分析，mybatis与Spring的集成和事物~

[Center]: /images/20220716/efe36f7fa9754fec9dc685988c045040.png
[Center 1]: /images/20220716/43c1ad9a7e264dc99d4233d0155bbad1.png