从hibernate上理解mybatis

首先温习以下hibernate的结构：

hibernate.cfg.xml文件：

<?xml version='1.0' encoding='UTF-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<!-- Generated by MyEclipse Hibernate Tools. -->

<hibernate-configuration>

<session-factory>

<property name="connection.username">scott</property>

<property name="connection.url">

jdbc:oracle:thin:@127.0.0.1:1521:sinosoft

</property>

<property name="dialect">

org.hibernate.dialect.Oracle9Dialect

</property>

<property name="myeclipse.connection.profile">

myoracle2

</property>

<property name="connection.password">tiger</property>

<property name="connection.driver_class">

oracle.jdbc.driver.OracleDriver

</property>

<mapping resource="com/sina/domain/Users.hbm.xml" />

</session-factory>

</hibernate-configuration>

User.java实体：

public class Users implements java.io.Serializable {

// Fields

private Long id;

private String name;

private String passwd;

// Constructors

/** default constructor */

public Users4() {

}

/** minimal constructor */

public Users4(Long id, String passwd) {

this.id = id;

this.passwd = passwd;

}

/** full constructor */

public Users4(Long id, String name, String passwd) {

this.id = id;

this.name = name;

this.passwd = passwd;

}

// Property accessors

public Long getId() {

return this.id;

}

public void setId(Long id) {

this.id = id;

}

public String getName() {

return this.name;

}

public void setName(String name) {

this.name = name;

}

public String getPasswd() {

return this.passwd;

}

public void setPasswd(String passwd) {

this.passwd = passwd;

}

}

对应的xml文件：

<?xml version="1.0" encoding="utf-8"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<!--

Mapping file autogenerated by MyEclipse Persistence Tools

-->

<hibernate-mapping>

<class name="com.sina.domain.Users" table="USERS4" schema="SCOTT">

<id name="id" type="java.lang.Long">

<column name="ID" precision="22" scale="0" />

<generator class="assigned" />

</id>

<property name="name" type="java.lang.String">

<column name="NAME" length="64" unique="true" />

</property>

<property name="passwd" type="java.lang.String">

<column name="PASSWD" length="64" not-null="true" />

</property>

</class>

</hibernate-mapping>

上面时准备工作，对于如何通过hibernate对实体进行操作，看下面：

以验证是否合理为例：

Session session=null;

Transaction ts=null;

Users user=null;

try{

session=HibernateUtils.getCurrentSession();

ts=session.beginTransaction();

user=new Users();

List<Users> list=session.createQuery("from users where name="+user.getName()+"and passwd="+user.getPasswd()+"").list();

if(list.size()==1)

{

user=list.get(0);

}

else{

user=null;

}

ts.commit();

}catch(Exception e)

{

if(ts!=null)

{

ts.rollback();

}

throw new RuntimeException("wrong");

}finally

{

if(session!=null&&session.isOpen())

{

session.close();

}

}

return user;

}

}

那么我们来看看mybatis的：

mybatis的结构：

config.xml文件，相当于hibernate的hibernate.cfg.xml，在这里配置了连接池等重要的全局参数：

<?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>

<!-- 加载属性文件 -->

<properties resource="db.properties">

</properties>

<!-- 类别名定义 -->

<typeAliases>

<!--

<typeAlias type="com.mybatis.po.Student" alias="Student"/>

<typeAlias type="com.mybatis.po.User" alias="User"/> -->

<package name="com.mybatis.po"/>

</typeAliases>

<!-- 配置Mybatis的环境，事务及数据源等等 -->

<environments default="development">

<environment id="development">

<transactionManager type="JDBC" />

<dataSource type="POOLED">

<property name="driver" value="${jdbc.driver}" />

<property name="url" value="${jdbc.url}" />

<property name="username" value="${jdbc.username}" />

<property name="password" value="${jdbc.password}" />

</dataSource>

</environment>

</environments>

<!-- 指定映射文件或者映射类 -->

<mappers>

<!--

<mapper resource="com/mybatis/persistence/StudentMapper.xml" />

<mapper resource="com/mybatis/persistence/UserMapper.xml" /> -->

<!-- 通过mapper接口加载映射文件 -->

<!-- 映射单个 -->

<!-- <mapper class="com.mybatis.persistence"/> -->

<!-- 批量加载 -->

<package name="com.mybatis.persistence"/>

</mappers>

</configuration>

对于持久层框架而言，最终目的都是对实体数据库进行操作，而hibernate注重于实体类本身，把数据库表映射成对象，从每个实体类就有一个相应的xml文件中可以看出来

然而mybatis注重的是sql语句实体类的作用时接受执行sql语句返回的数据，关键在为sql语句服务，将增删改查的sql语句包装。

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.mybatis.persistence.UserMapper">

<sql id="query_user_where">

<if test="userCustom.username!=null and userCustom.username!=''">

and username like '%${userCustom.username}%'

</if>

<if test="ids!=null">

<foreach collection="ids" item="user_id" open="and id in (" close=")" separator=",">

#{user_id}

</foreach>

</if>

</sql>

<resultMap type="user" id="userresultMap">

<id column="id" property="id"/>

<result column="username" property="username"/>

</resultMap>

<select id="findUserByresultMap" parameterType="int" resultMap="userresultMap">

select id,username from user where id=#{id}

</select>

<select id="getUserCount" parameterType="UserQueryVo" resultType="int">

select count(*) from user where user.sex=#{userCustom.sex} and user.username like '%${userCustom.username}%'

</select>

<select id="findUserList" parameterType="UserQueryVo" resultType="UserCustom">

select id,username from user

<where>

<include refid="query_user_where"></include>

</where>

</select>

<select id="getUserById" parameterType="int" resultType="User">

select * from user where id = #{id}

</select>

<select id="findUserByName" parameterType="java.lang.String" resultType="User">

select * from user where username like #{username}

</select>

<insert id="insertUser" parameterType="User">

<selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">

select last_insert_id()

</selectKey>

insert into user(username,birthday,sex,address) values(#{username},#{birthday},#{sex},#{address})

</insert>

<update id="updateUser" parameterType="User">

update user set username=#{username},birthday=#{birthday},sex=#{sex},address=#{address} where id=#{id}

</update>

<delete id="deleteUser" parameterType="java.lang.Integer">

delete from user where id=#{id}

</delete>

</mapper>

上面的代码可以看出，mybatis对每个sql语句进行封装，如指定输入输出类型

使用mybatis：

package com.mybatis.test;

import java.io.Reader;

import java.util.ArrayList;

import java.util.List;

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.Before;

import org.junit.Test;

import com.mybatis.persistence.StudentMapper;

import com.mybatis.persistence.UserMapper;

import com.mybatis.po.Student;

import com.mybatis.po.User;

import com.mybatis.po.UserCustom;

import com.mybatis.po.UserQueryVo;

public class TestStudentMapper {

private SqlSession session=null;

@Before

public void setUp() throws Exception {

String resource = "config.xml";

Reader reader = Resources.getResourceAsReader(resource);

SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);

session = sqlMapper.openSession();

}

@Test

public void testSelectUser(){

UserMapper mapper=session.getMapper(UserMapper.class);

UserQueryVo userQueryVo=new UserQueryVo();

UserCustom userCustom=new UserCustom();

userCustom.setId(2);

userCustom.setUsername("aaa");

List<Integer> ids=new ArrayList<Integer>();

ids.add(1);

ids.add(2);

ids.add(3);

userQueryVo.setIds(ids);

userQueryVo.setUserCustom(userCustom);

List<UserCustom> list=mapper.findUserList(userQueryVo);

System.out.println(list.get(0).getUsername());

}

获得配置工厂，等等都跟hibernate思路一样。对于不懂的代码，自行百度吧，这里只是感受mybatis而已。