第 3 章 认识 MyBatis 核心组件

3.1 持久层的概念和 MyBatis 的特点

3.2 准备 MyBatis 的环境

jar包及其源码下载地址：https://github.com/mybatis/mybatis-3/releases
官方文档地址：http://www.mybatis.org/mybatis-3/zh/getting-started.html

3.3 MyBatis 的核心组件

• SqlSessionFactoryBuilder 构造器

• SqlSessionFactory 工厂接口

• SqlSession 会话

• SQL Mapper 映射器

3.4 SqlSessionFactory (工厂接口)

3.4.1 使用XML构建 SqlSessionFactory

代码清单3-1：MyBatis 的基础配置文件
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>
    <typeAliases><!-- 别名 -->
        <typeAlias alias="role" type="com.sinosoft.learn.ssm.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/ssm"/>
                <property name="username" value="root"/>
                <property name="password" value="12345"/>
            </dataSource>
        </environment>
    </environments>
    <!-- 映射文件 -->
    <mappers>
        <mapper resource="com/sinosoft/learn/mapper/RoleMapper.xml"/>
    </mappers>
</configuration>

解释：

• <ypeAliases> 元素定义了一个别名role 代表com.sinosoft.learn.ssm.pojo.Role这个类
• <environment> 数据库描述, <dataSource> 元素配置数据库 ，type=”POOLED” 代表采用MyBatis内部提供的连接池方式
• <mapper> 元素代表引入的一些映射器

代码清单3-2：通过 XML 构建 SqlSessionFactory

package com.sinosoft.learn.ssm;

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

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

/**
 * @author jue
 * @date 2018/9/2 1:10
 * @describe 通过 XML 构建 SqlSessionFactory
 */
public class XmlBuildSqlSessionFactory {

    public static void main(String[] args){
        SqlSessionFactory sqlSessionFactory = null;
        String resource = "mybatis-config.xml";
        InputStream inputStream;
        try {
            inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            System.out.println(sqlSessionFactory);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

打印结果：
org.apache.ibatis.session.defaults.DefaultSqlSessionFactory@3b81a1bc

3.4.2 使用代码构建 SqlSessionFactory

代码清单3-3：使用代码构建 SqlSessionFactory

package com.sinosoft.learn.ssm;

import com.sinosoft.learn.ssm.mapper.RoleMapper;
import com.sinosoft.learn.ssm.pojo.Role;
import org.apache.ibatis.datasource.pooled.PooledDataSource;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;

/**
 * @author jue
 * @date 2018/9/3 22:56
 * @describe
 */
public class CodeBuildSqlSessionFactory {

    public static void main(String[] args){
        //数据库连接池信息
        PooledDataSource dataSource = new PooledDataSource();
        dataSource.setDriver("com.mysql.jdbc.Driver");
        dataSource.setUsername("root");
        dataSource.setPassword("12345");
        dataSource.setUrl("jdbc:mysql://localhost:3306/ssm");
        dataSource.setDefaultAutoCommit(false);
        //采用MyBatis的JDBC事务方式
        JdbcTransactionFactory transactionFactory = new JdbcTransactionFactory();
        Environment environment = new Environment("development", transactionFactory, dataSource);
        //创建Configuration对象
        Configuration configuration = new Configuration(environment);
        //注册一个MyBatis上下文
        configuration.getTypeAliasRegistry().registerAlias("role", Role.class);
        //加入一个映射器
        configuration.addMapper(RoleMapper.class);
        //使用SqlSessionFactoryBuilder构建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
        System.out.println(sqlSessionFactory);
    }
}

3.5 SqlSession

代码清单3-4： 创建SqlSession

SqlSession sqlSession = SqlSessionFactory.openSession();

代码清单3-5：SqlSession 事务控制伪代码

//定义SqlSession
SqlSession sqlSession = null;
try {
    //打开 SqlSession 会话
    sqlSession = sqlSessionFactory.openSession();
    //some code
    //提交事务
    sqlSession.commit();
} catch (Exception e) {
    //回滚事务
    sqlSession.rollback();
} finally {
    //在 finally 语句中确保资源被顺利关闭
    if (sqlSession != null) {
        sqlSession.close();
    }
}

3.6 映射器

代码清单3-6： 定义角色的POJO

package com.sinosoft.learn.ssm.pojo;

/**
 * @author jue
 * @date 2018/9/2 1:20
 * @describe
 */
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;
    }
}

3.6.1 用XML实现映射器（推荐）

代码清单3-7：映射器接口

package com.sinosoft.learn.ssm.mapper;

import com.sinosoft.learn.ssm.pojo.Role;

/**
 * @author jue
 * @date 2018/9/4 0:12
 * @describe
 */
public interface RoleMapper {

    public Role getRole(Long id);
}

代码清单3-8：用XML的方式创建映射器

<?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.sinosoft.learn.ssm.pojo.Role">
    <select id="selectRole" parameterType="long" resultType="role">
        select * from role where id = #{id}
    </select>
</mapper>

解释：

• 属性namespace 所对应的是一个接口的全限定名，在MyBatis的上下文中就可以找到对应的接口
• select 表示这是一条查询语句 ，id=”selectRole” 唯一标识了这条语句，
  parameterType=”long” 说明传递给sql的是一个long类型的参数， resultType=”role” 之前配置文件中指定的别名，指的是com.sinosoft.learn.ssm.pojo.Role

3.6.2 注解实现映射器（不推荐）

代码清单3-9：通过注解实现映射器

package com.sinosoft.learn.ssm.mapper;

import com.sinosoft.learn.ssm.pojo.Role;
import org.apache.ibatis.annotations.Select;

/**
 * @author jue
 * @date 2018/9/4 22:02
 * @describe
 */
public interface RoleMapper2 {

    @Select(" select id, role_name as roleName, note from t_role where id=#{id} ")
    public Role getRole(Long id);
}

接着要把mybatis-config.xml配置文件中<mapper resource="com/sinosoft/learn/mapper/RoleMapper.xml"/> 改为
<mapper class="com.sinosoft.learn.ssm.mapper.RoleMapper2"/>

3.6.3 SqlSession 发送 SQL

Role role = (Role)sqlSession.selectOne("com.sinosoft.learn.ssm.mapper.RoleMapper.getRole", 1L);

这是MyBatis的前身iBatis留下的方式

3.6.4 用Mapper接口发送SQL

代码清单3-10：用SqlSession 获取Mapper接口，并发送SQL

RoleMapper mapper = sqlSession.getMapper(RoleMapper.class);
Role role = mapper.getRole(1L);

3.6.5 对比两种发送SQL的方式

推荐使用Mapper接口方式

3.7 生命周期

3.7.1 SqlSessionFactoryBuilder

SqlSessionFactoryBuilder的作用在于创建SqlSessionFactory，创建成功后就失去作用了，只存在于创建SqlSessionFactory的方法中，而不能长期存在

3.7.2 SqlSessionFactory

SqlSessionFactory可认为是一个数据库连接池，作用是创建SqlSession对象，SqlSessionFactory的生命周期等同于MyBatis的应用周期，一般以单例模式存在，可以被共享。

3.7.3 SqlSession

SqlSession相当于一个数据库连接（Connection 对象），可以在一个事务里面执行多条sql，只存在一个业务请求中，处理完整个请求后，应该关闭这条连接，把它归还给SqlSessionFactory。使用try..catch…finally..语句来保证正常关闭。

3.7.4 Mapper

它的最大生命周期至多和SqlSession保持一致，一般应小于SqlSession的生命周期，Mapper代表的是一个请求中的业务处理，一旦处理完可相关的业务，就应该废弃它。

3.8 实例

代码清单3-11：log4j.properties

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

代码清单3-12：Role.java

package com.learn.ssm.chapter3.pojo;

/**
 * @author jue
 * @date 2018/9/8 14:19
 * @describe
 */
public class Role {

    private Long id;
    private String roleName;
    private String noteInfo;

    public Role() {
    }

    public Role(Long id, String roleName, String noteInfo) {
        this.id = id;
        this.roleName = roleName;
        this.noteInfo = noteInfo;
    }

    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 getNoteInfo() {
        return noteInfo;
    }

    public void setNoteInfo(String noteInfo) {
        this.noteInfo = noteInfo;
    }

    @Override
    public String toString() {
        return "Role{" +
                "id=" + id +
                ", roleName='" + roleName + '\'' +
                ", noteInfo='" + noteInfo + '\'' +
                '}';
    }
}

代码清单3-13：RoleMapper.java

package com.learn.ssm.chapter3.mapper;

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

import java.util.List;

/**
 * @author jue
 * @date 2018/9/8 14:21
 * @describe
 */
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);
}

代码清单3-14：RoleMapper.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.learn.ssm.chapter3.mapper.RoleMapper">
    <insert id="insertRole" parameterType="role">
        insert into t_role(role_name, note) values (#{roleName}, #{noteInfo})
    </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 = #{noteInfo} where id = #{id}
    </update>

    <select id="getRole" parameterType="long" resultType="role">
        select id, role_name roleName, note as noteInfo from t_role where id=#{id}
    </select>

    <select id="findRoles" parameterType="string" resultType="role">
        select id,role_name roleName, note noteInfo from t_role
        where role_name like concat('%', #{roleName}, '%')
    </select>
</mapper>

代码清单3-15：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>
    <typeAliases>
        <typeAlias alias="role" type="com.learn.ssm.chapter3.pojo.Role" />
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/ssm"/>
                <property name="username" value="root"/>
                <property name="password" value="12345"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/learn/ssm/chapter3/mapper/RoleMapper.xml"/>
    </mappers>
</configuration>

代码清单3-16：构建SqlSessionFactory 工具类

package com.learn.ssm.chapter3.utils;

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

/**
 * @author jue
 * @date 2018/9/8 14:47
 * @describe
 */
public class SqlSessionFactoryUtils {

    private final static Class<SqlSessionFactoryUtils> LOCK = SqlSessionFactoryUtils.class;

    private static SqlSessionFactory sqlSessionFactory = null;

    public 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();
    }
}

代码清单3-17：Chapter3Main.java

package com.learn.ssm.chapter3.main;

import com.learn.ssm.chapter3.mapper.RoleMapper;
import com.learn.ssm.chapter3.pojo.Role;
import com.learn.ssm.chapter3.utils.SqlSessionFactoryUtils;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.Test;

import java.util.List;

/**
 * @author jue
 * @date 2018/9/8 14:59
 * @describe
 */
public class Chapter3Main {

    public static void main(String[] args){
        Logger log = Logger.getLogger(Chapter3Main.class);
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            Role role = roleMapper.getRole(5L);
//            log.info(role);
            System.out.println(role);
//            Role role1 = new Role();
//            role1.setRoleName("分公司管理员");
//            role1.setNote("fen发");
//            int insertNum = roleMapper.insertRole(role1);
//            System.out.println("新增个数：" + insertNum);

//            Role role2 = new Role(5L,"录单员", "绿单元");
//            int updateNum = roleMapper.updateRole(role2);
//            System.out.println("更新个数："+updateNum);
//            roleMapper.deleteRole(1L);
            sqlSession.commit();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }

    }

    @Test
    public void test1() {
        Logger log = Logger.getLogger(Chapter3Main.class);
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
//            Role role = roleMapper.getRole(5L);
            List<Role> roles = roleMapper.findRoles("经办人");
            roles.stream().forEach(System.out::println);
            sqlSession.commit();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }

    }


}