MyBatis入门一
本人只是刚刚学习MyBatis,作为学习路程的记录,写的不好,不完善的地方请多多包涵;
首先,先比较一下Hibernate和MyBatis两种框架之间的区别:
两种都是ORM框架,但是Hibernate属于全自动化,而MaBatis则属于半自动化,也就是说Hibernate的SQL语句是会自动生产的,而MyBatis的话,需要在xml文件配置一个SQL的模板,这是全自动化和半自动化的含义;那么问题来了,为什么不用更方便的Hibernate呢?
这是因为在一些特殊的情况下,Hibernate反而不好用了:
有些数据来自现有的数据库,出于安全的考虑,只给出几条SQL语句或存储过程,具体表结构不予公开;
开发规范要求,所有牵涉到业务逻辑部分的数据库操作,必须在数据库层由存储过程来实现;
如果系统的数据处理量巨大,性能要求极为苛刻,而Hibernate自动生成的sql语句显然没有经过人工优化,不能高度优化;
总结以上就是:出于安全和性能的考虑,单纯的全自动不能满足行业的开发,因此MyBatis应运而生;
下面是MyBatis实现基本增删改查的基本步骤:
1,导入jar包:
2,编写POJO:
因为MyBatis的优化就是体现在以面对对象的编程机制去操纵数据库,所以,先要有一个POJO来映射相应数据库中的属性;
package org.fkit.domain; public class User { private Integer id; private String name; private String sex; private Integer age; public User(){ super(); } public User(String name,String sex,Integer age){ super(); this.name = name; this.sex = sex; this.age = age; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } }
3,配置MyBatis连接的数据库的相关参数属性;
这个地方就有个坑了,我调了一天的BUG,我们前面说过,MyBatis的优化就是体现在以面对对象的编程机制去操纵数据库,那么如何将这个POJO映射到MyBatis对应的数据库属性上呢?你需要这样一段代码:
<typeAliases> <typeAlias alias="user" type="org.fkit.domain.User"/> </typeAliases>
同时,要按照"(properties?,settings?,typeAliases?,typeHandlers?,objectFactory?,objectWrapperFactory?,reflectorFactory?,plugins?,environments?,databaseIdProvider?,mappers?)".
也就是说必须要先写settings标签之后,再写typeAliases标签;这是一个顺序的问题;
<?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> <settings> <setting name= "logImpl" value = "LOG4J"/> </settings> <typeAliases> <typeAlias alias="user" type="org.fkit.domain.User"/> </typeAliases> <environments default="mysql"> <environment id="mysql"> <transactionManager type = "JDBC"/> <dataSource type = "POOLED"> <property name = "driver" value="com.mysql.jdbc.Driver"/> <property name = "url" value = "jdbc:mysql://127.0.0.1:3306/mybatis"/> <property name = "username" value = "root"/> <property name = "password" value = "986532"/> </dataSource> </environment> </environments> <mappers> <mapper resource = "org/fkit/mapper/UserMapper.xml"/> </mappers> </configuration>
4,建立SQL语句模板;
前面提到,MyBatis的半自动化机制,就是要编写相应的SQL语句模板,所以我们需要这样一个文件;我想叫它做映射文件;
<?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 = "org.fkit.mapper.UserMapper"> <insert id = "save" parameterType ="user" useGeneratedKeys = "true"> INSERT INTO TB_USER(name,sex,age) VALUES(#{name},#{sex},#{age}) </insert> <select id = "selectUser" parameterType = "Integer" resultType = "user"> SELECT * FROM TB_USER WHERE id = #{id} </select> <update id = "modifyUser" parameterType = "user"> UPDATE TB_USER SET name = #{name},sex = #{sex},age = #{age} WHERE id = #{id} </update> <delete id = "removeUser" parameterType = "int"> delete from TB_USER WHERE id = #{id} </delete> </mapper>
5,编写测试类
做完上述配置之后,我们就可以开始做测试类来进行测试了。先上一段原始的;
package org.fkit.tst; 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; import org.fkit.domain.User; import org.fkit.factory.FKSqlSessionFactory; public class MyBatisTest { public static void main(String[] args) throws Exception{ InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession session = sqlSessionFactory.openSession(); User user = new User("admin","男",22); session.insert("org.fkit.mapper.UserMapper.save",user); session.commit(); session.close(); } }
其中,SqlSession是MyBatis中作为操纵数据库的重要对象,相当于JDBC中的connection;而以上代码我们可以进行再封装;代码如下:
package org.fkit.factory; 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 FKSqlSessionFactory { private static SqlSessionFactory sqlSessionFactory = null; static{ try{ InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml"); sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); }catch(Exception e){ e.printStackTrace(); } } public static SqlSession getSqlSession(){ return sqlSessionFactory.openSession(); } public static SqlSessionFactory getSqlSessionFactory(){ return sqlSessionFactory; } }
package org.fkit.tst; 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; import org.fkit.domain.User; import org.fkit.factory.FKSqlSessionFactory; public class MyBatisTest { public static void main(String[] args) throws Exception{ SqlSession session = FKSqlSessionFactory.getSqlSession(); User user = new User("admin","男",22); session.insert("org.fkit.mapper.UserMapper.save",user); session.commit(); session.close(); } }
将读取配置文件的操作封装在一个Factory类中,这样就可以更加简便。
6,顺便附上数据库表结构: