Mybatis Demo

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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;}@Overridepublic 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.descriptionfrom user Awhere 1=1and 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>    <!-- 映射文件，mybatis精髓， 后面才会细讲 -->  <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>    <!-- 添加数据库驱动 -->    <span style="white-space:pre"></span><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.39</version></dependency><!-- 添加Mybatis --><dependency>    <groupId>org.mybatis</groupId>          <artifactId>mybatis</artifactId>          <version>3.4.0</version>   </dependency> <!-- 添加mybatis-spring的依赖 --><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~：

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：

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~

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