mybatis的实例

mybatis的资源：链接：https://pan.baidu.com/s/1GxOKQJJrbbeJvAh8xQzShg
提取码：ib4g
mysql的驱动jar包：链接：https://pan.baidu.com/s/1GDqWknmwynDWOmtc35T1Vw
提取码：wfmp

文件	作用
chapterMain.java	程序入口，拥有main方法
RoleMapper.java	映射器接口
RoleMapper.xml	映射器XML文件，描述映射关系，SQL等内容
Role.java	POJO对象
SqlSessionFactoryUtils.java	一个工具类，用于创建SqlSessionFactory和SqlSession对象
log4j.propertoes	日志配置，让后台日志数据Mybatis运行的过程日志
mybatis-config.xml	MyBatis配置文件

log4j.properties

# Configure logging for testing: optionally with log file
log4j.rootLogger=DEBUG, stdout
# log4j.rootLogger=WARN, stdout, logfile
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=%d %p [%c] - %m%n

log4j.appender.logfile=org.apache.log4j.FileAppender
log4j.appender.logfile.File=target/spring.log
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=%d %p [%c] - %m%n

注意改为DEBUG
构造一个POJO对象，最终查询会映射到它上面或者将其存到数据库

package com.learn.ssm.chapter3.pojo;


public class Role {
    public Role(){};

    private int id;
    private String roleName;
    private String note;

    /** setter and getter **/
    public int getId() {
        return id;
    }

    public void setId(int 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;
    }

}

采用XML方式构建映射器，它包含一个接口和一个xml。这里要实现增删改查，所以要定义一个接口

package com.learn.ssm.chapter3.mapper;
import java.util.List;
import com.learn.ssm.chapter3.pojo.Role;
public interface RoleMapper {
    public int insertRole(Role role);
    public int deleteRole(int id);
    public int updateRole(Role role);
    public Role getRole(int id);
    public List<Role> findRoles(String roleName);
}

RoleMapper.xml文件

<?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}, #{note})
    </insert>

    <delete id="deleteRole" parameterType="int">
        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="int" 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>

这是一些比较简单的SQL语句，insert,delete,select,update元素表示增，删，改，查，而里面的元素id则标识了对应的SQL。parameterType标出了是什么类型的参数，resultType则代表结果映射成为什么类型。
其中insert,delete,和update返回的是影响的条数。
使用mybatis-config.xml构建SqlsessionFactory

<?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>
<!-- 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?characterEncoding=utf-8"/>
        <property name="username" value="root"/>
        <property name="password" value="123456"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
    <mapper resource="com/learn/ssm/chapter3/mapper/RoleMapper.xml"/>
    <!--构建SqlsessionFactory -->
     <mapper class="com.learn.ssm.chapter3.mapper.RoleMapper2"/> 
     <!-- 注解实现映射器 -->
  </mappers>
</configuration>

使用mybatis-config.xml文件。通过SQLSessionFactoryBUilder来构建SqlSessionFactory。由于SqlsessionFactory应该采用单例模式。所以使用单例模式

package com.learn.ssm.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 {
//使用单例模式创建SqlSessionFactory
    private final static Class<SqlSessionFactoryUtils> LOCK=SqlSessionFactoryUtils.class;
    private static SqlSessionFactory sqlSessionFactory=null;
    private SqlSessionFactoryUtils(){}
//  一定要声明无参构造方法，要不然会报错
    public static SqlSessionFactory  getSqlSessionFactory(){
        synchronized(LOCK){
            if(sqlSessionFactory!=null){
                return sqlSessionFactory;
            }
//          利用xml生成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();
//      返回sqlsession
    }

}

构造方法加入了private关键字，使得其他代码不能通过new的方式来创建它，而加入synchronized关键字加锁。主要是为了防止在多线程中多次实例化SqlsessionFactory对象，从而保证SqlsessionFactory的唯一性。
而openSqlSession方法的作用则是创建sqlsession

接下来是运行代码：

package com.learn.ssm.chapter3.main;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;

import com.learn.ssm.chapter3.mapper.RoleMapper;
import com.learn.ssm.chapter3.mapper.RoleMapper2;
import com.learn.ssm.chapter3.pojo.Role;
import com.learn.ssm.chapter3.utils.SqlSessionFactoryUtils;
public class chapter3Main {

    public static void main(String[] args) {
        testRoleMapper();
        
        
    }
    
    
    private static void testRoleMapper() {
        Logger log = Logger.getLogger(chapter3Main.class);
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
//                       静态方法返回sqlsession
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
//  sqlsession可以获取Mapper接口，通过Mapper接口发送SQL
            Role role = roleMapper.getRole(0);
            
            log.info(role.getRoleName());
            log.info(role.getId());
            log.info(role.getNote());
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }
    
    //注解SQL测试
//  private static void testRoleMapper2() {
//      Logger log = Logger.getLogger(chapter3Main.class);
//      SqlSession sqlSession = null;
//      try {
//          sqlSession = SqlSessionFactoryUtils.openSqlSession();
//          RoleMapper2 roleMapper2 = sqlSession.getMapper(RoleMapper2.class);
//          Role role = roleMapper2.getRole(1L);
//          log.info(role.getRoleName());
//      } finally {
//          if (sqlSession != null) {
//              sqlSession.close();
//          }
//      }
//  }
    
}

// sqlsession可以获取Mapper接口，通过Mapper接口发送SQL，
通过Sqlsession的getMapper的方法来获取一个Mapper接口，就可以调用他们的方法

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

通过SqlSession获取一个RoleMapper的对象，然后通过getRole的方法获取到Role的对象，最后正确关闭SqlSession对象。

运行结果.png mysql.png