mybatis之初见

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本文通过一个实战案例介绍了MyBatis的基本用法，包括搭建环境、配置文件解析、使用SqlSessionFactory构建连接、定义POJO及Mapper接口、实现增删改查操作等。

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一、简单介绍

这里从mybatis开始，一般的共识是有四个核心组件：

1. SqlSessionFactoryBuilder : (构造器)，采用Builder模式，根据配置或者代码生成SqlSessionFactory。

2. SqlSessionFactory：（工厂接口），使用工厂模式生成SqlSession。

3. SqlSession：（会话）：这个是核心接口，主要功能包括三个：

获取Mapper接口

发送SQL给数据库

控制数据库事务

4. SQL Mapper （映射器）：有Java接口和XML文件（或注解）组成，需要给出对应的SQL和映射规则，它负责发送SQL去执行，并返回结果。

二、栗子

下面是一个小例子，只有mybatis

1、需要的jar包如下：

2. 建立一个简单的maven项目，需要的类如图:

3. 建立日志文件 log4j.properties，日志配置如下：

log4j.rootLogger=DEBUG , stdout
log4j.logger.org.mybatis=DEBUG
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p %d %c: %m%n

4. 建立mybatis 配置文件mybatis-config.xml 如下：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://www.mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
   <typeAliases> <!-- 别名 -->
     <typeAlias alias="role" type="com.learn.ssn.chapter3.pojo.Role" />
   </typeAliases>
  
  <!-- 数据库环境 -->
  <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/mobile_bi" />
          <property name="username" value="root" />
          <property name="password" value="root" />
       </dataSource>
    </environment>
  </environments>
  
  <!-- 映射文件 -->
  <mappers>
  <mapper resource="com/learn/ssn/chapter3/mapper/RoleMapper.xml" />
  </mappers>
</configuration>

5. 根据mybatis-config.xml 通过SqlSessionFactoryBuilder 构建SqlSessionFactory,采用单例模式，如下：

package com.learn.ssn.chapter3.utils;

import java.io.IOException;
import java.io.InputStream;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class SqlSessionFactoryUtils {

	private final static Class<SqlSessionFactoryUtils> LOCK = SqlSessionFactoryUtils.class;
	
	private static SqlSessionFactory sqlSessionFactory = null;
	
	private SqlSessionFactoryUtils(){}
	
	public static SqlSessionFactory getSqlSessionFactory(){
		synchronized (LOCK){
			if(sqlSessionFactory != null){
				return sqlSessionFactory;
			}
			String resource = "mybatis-config.xml";
			InputStream inputStream;
			try{
				inputStream = Resources.getResourceAsStream(resource);
				sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
			}catch(IOException e){
				e.printStackTrace();
				return null;
			}
			return sqlSessionFactory;
		}
	}
	
	public static SqlSession openSqlSession(){
		if(sqlSessionFactory == null){
			getSqlSessionFactory();
		}
		return sqlSessionFactory.openSession();
	}
}

6. 定一个POJO, Role ,如下：

package com.learn.ssn.chapter3.pojo;

public class Role {

	private Long id;
	private String roleName;
	private String note;
	
	public long getId(){
		return id;
	}
	public void setId(long id){
		this.id = id;
	}
	public String getRoleName(){
		return roleName;
	}
	public void setRoleName(String roleName){
		this.roleName = roleName;
	}
	public String getNote(){
		return note;
	}
	public void setNote(String note){
		this.note = note;
	}
	
}

6. 采用XML方式构建映射器，包括一个借口和一个XML，接口如下：

package com.learn.ssn.chapter3.mapper;

import java.util.List;

import com.learn.ssn.chapter3.pojo.Role;

public interface RoleMapper {

	public int insertRole(Role role);
	public int deleteRole(Long id);
	public int updateRole(Role role);
	public Role getRole(Long id);
	public List<Role> findRoles(String roleName);
}

7. XML如下：

<?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.learn.ssn.chapter3.mapper.RoleMapper">
 <insert id="insertRole" parameterType="role">
   insert into t_role (role_name, note)  values ( #{roleName}, #{note})
 </insert>
 
 <delete id="deleteRole" parameterType="long">
  delete from t_role where id = #{id}
 </delete>
 
 <update id="updateRole" parameterType="role">
  update t_role set role_name = #{roleName}, note = #{note} where id = #{id}
 </update>
 
 <select id="getRole" parameterType="role" resultType="role">
  select id, role_name as roleName, note from t_role where id = #{id}
 </select>
 
 <select id="findRoles" parameterType="string" resultType="role">
 select id, role_name as roleName, note from t_role
 where role_name like concat('%', #{roleName}, '%' )
 </select>
</mapper>

8. 最后一个Main函数，

package com.learn.ssn.chapter3.main;

import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;

import com.learn.ssn.chapter3.mapper.RoleMapper;
import com.learn.ssn.chapter3.pojo.Role;
import com.learn.ssn.chapter3.utils.SqlSessionFactoryUtils;

public class Chapter3Main {

	public static void main(String[] args) {
		
		Logger logger = Logger.getLogger(Chapter3Main.class);
		SqlSession sqlSession = null;
		
		try{
			sqlSession = SqlSessionFactoryUtils.openSqlSession();
			RoleMapper rolemapper = sqlSession.getMapper(RoleMapper.class);
			Role role = rolemapper.getRole(1L);
			logger.info(role.getRoleName());
		}finally{
			if(sqlSession != null){
				sqlSession.close();
			}
		}

	}

}

9. 测试结果如下：

DEBUG 2018-05-15 17:11:37,951 org.apache.ibatis.logging.LogFactory: Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
DEBUG 2018-05-15 17:11:38,021 org.apache.ibatis.datasource.pooled.PooledDataSource: PooledDataSource forcefully closed/removed all connections.
DEBUG 2018-05-15 17:11:38,022 org.apache.ibatis.datasource.pooled.PooledDataSource: PooledDataSource forcefully closed/removed all connections.
DEBUG 2018-05-15 17:11:38,022 org.apache.ibatis.datasource.pooled.PooledDataSource: PooledDataSource forcefully closed/removed all connections.
DEBUG 2018-05-15 17:11:38,022 org.apache.ibatis.datasource.pooled.PooledDataSource: PooledDataSource forcefully closed/removed all connections.
DEBUG 2018-05-15 17:11:38,093 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
DEBUG 2018-05-15 17:11:38,268 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 967765295.
DEBUG 2018-05-15 17:11:38,268 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.Connection@39aeed2f]
DEBUG 2018-05-15 17:11:38,270 com.learn.ssn.chapter3.mapper.RoleMapper.getRole: ==>  Preparing: select id, role_name as roleName, note from t_role where id = ? 
DEBUG 2018-05-15 17:11:38,288 com.learn.ssn.chapter3.mapper.RoleMapper.getRole: ==> Parameters: 1(Long)
DEBUG 2018-05-15 17:11:38,300 com.learn.ssn.chapter3.mapper.RoleMapper.getRole: <==      Total: 1
 INFO 2018-05-15 17:11:38,301 com.learn.ssn.chapter3.main.Chapter3Main: name1
DEBUG 2018-05-15 17:11:38,301 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.Connection@39aeed2f]
DEBUG 2018-05-15 17:11:38,301 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Closing JDBC Connection [com.mysql.jdbc.Connection@39aeed2f]
DEBUG 2018-05-15 17:11:38,301 org.apache.ibatis.datasource.pooled.PooledDataSource: Returned connection 967765295 to pool.

这是只是初识mybatis的一小小栗子。