从hibernate上理解mybatis

痛定思痛。 2022-08-10 09:19 112阅读 0赞

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">  
  
<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">  
  
<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>    
     
   <properties resource="db.properties">  
   </properties>  
       
       
   <typeAliases>    
     
         <package name="com.mybatis.po"/>  
    </typeAliases>    
        
    <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>    
        
        
    <mappers>  
       
          
          
          
          
        <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。