mybatis中Dao的三种实现方式

小咪咪 2022-06-12 12:28 604阅读 0赞

mybatis是继Hibernate后优秀的ORM框架之一，是支持自定义SQL，存储过程和高级映射的第一类持久化框架。本文将总结一下mybatis中Dao的三种实现方式。

1.Dao类调用映射文件：创建BaseDao，BaseDao中有sqlSession和对数据库的相关操作，其他Dao类继承BaseDao来实现使用sqlSession，其他的Dao类调用xml文件中定义的select中的id方法，返回相关结果或执行相关操作。这种方式是不被推荐的方法，仅了解即可，代码如下：

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>    
<settings>  
<setting name="useGeneratedKeys" value="true"></setting>  
<setting name="lazyLoadingEnabled" value="false"></setting>  
</settings>  
    <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/test" />    
                <property name="username" value="root" />    
                <property name="password" value="132566" />    
            </dataSource>    
        </environment>    
    </environments>    
        
        
        
    <mappers>    
        <mapper resource="xcg/model/TuserMapper.xml" />    
        <mapper resource="xcg/model/EmpMapper.xml" />    
        <mapper resource="xcg/model/EducationMapper.xml" />   
        <mapper resource="xcg/model/EmpMapperAndInterface.xml" />   
    </mappers>    
        
</configuration>

Tuser.java：

@Getter

@Setter

public class Tuser \{  
private Integer userid;  
private String loginname;  
private String userpwd;  
private String realname;

public Tuser() \{  
super();  
\}

BaseDao.java：

package xcg.dao;  
  
import java.io.IOException;  
import java.io.Reader;  
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;  
  
  
public class BaseDao \{  
public static SqlSession sqlSession=null;  
static\{  
String path = "mybatis-config.xml";  
Reader reader;  
try \{  
reader = Resources.getResourceAsReader(path);  
SqlSessionFactory factory = (SqlSessionFactory) new SqlSessionFactoryBuilder().build(reader);  
sqlSession = factory.openSession();  
\} catch (IOException e) \{  
// TODO Auto-generated catch block  
e.printStackTrace();  
\}  
\}  
  
/\*\*  
\*   
\* Discription:查询方法，不分页，直接返回结果集  
\*   
\* @param statement  
\*            SqlMapper配置文件中insert SQL语句对应的“命名空间.sqlId”  
\* @return  
\*/  
public List<?> selectList(String statement) \{  
return sqlSession.selectList(statement);  
\}  
  
  
/\*\*  
\*   
\* Discription:查询方法，不分页，直接返回结果集  
\*   
\* @param statement  
\*            SqlMapper配置文件中insert SQL语句对应的“命名空间.sqlId”  
\* @param parameter  
\*            持久化对象  
\* @return  
\*/  
public List<?> selectList(String statement, Object parameter) \{  
return sqlSession.selectList(statement, parameter);  
\}  
  
  
/\*\*  
\* 查询方法，查询单个对象  
\*   
\* @param statement  
\* @param parameter  
\* @return  
\*/  
public Object selectOne(String statement, Object parameter) \{  
return sqlSession.selectOne(statement, parameter);  
\}  
  
  
/\*\*  
\*   
\* Discription:新增操作  
\*   
\* @param statement  
\*            SqlMapper配置文件中insert SQL语句对应的“命名空间.sqlId”  
\* @param parameter  
\* @return  
\*/  
public <P> int insert(String statement, P parameter) \{  
return sqlSession.insert(statement, parameter);  
\}  
  
  
/\*\*  
\*   
\* Discription:修改操作  
\*   
\* @param statement  
\*            SqlMapper配置文件中update SQL语句对应的“命名空间.sqlId”  
\* @param parameter  
\*            持久化对象  
\* @return  
\*/  
public int update(String statement, Object parameter) \{  
return sqlSession.update(statement, parameter);  
\}  
  
  
/\*\*  
\*   
\* Discription:删除操作  
\*  
\* @param statement  
\* @param parameter  
\* @return  
\*/  
public int delete(String statement, Object parameter) \{  
return sqlSession.delete(statement, parameter);  
\}  
  
  
/\*\*  
\*   
\* Discription:插入多行数据  
\*  
\* @param <P>  
\* @param statement  
\* @param list  
\* @return  
\*/  
public <P> int insertMore(String statement, List<P> list) \{  
// TODO Auto-generated method stub  
return 0;  
\}  
  
public void close()\{  
sqlSession.close();  
\}  
  
\}

TuserDao.java：

package xcg.dao;  
  
  
import java.util.List;  
import java.util.Map;  
  
  
import xcg.model.Tuser;  
  
  
public class TuserDao extends BaseDao\{  
public List<Tuser> getAll()\{  
return (List<Tuser>) this.selectList("xcg.model.Tuser.getAll");  
\}   
public Tuser getOne(Tuser u)\{  
return (Tuser) this.selectOne("xcg.model.Tuser.getOne",u);  
\}  
public int insertOne(Tuser u)\{  
int i = this.insert("xcg.model.Tuser.insertOne",u);  
this.sqlSession.commit();  
return i;  
\}  
public int delete(Tuser u)\{  
int i = this.delete("xcg.model.Tuser.delete", u);  
this.sqlSession.commit();  
return i;  
\}  
  
//分页  
public List<Tuser> getPage(Map<String,?> map)\{  
return this.sqlSession.selectList("xcg.model.Tuser.selectPage", map);  
\}  
  
\}

TuserMapper.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="xcg.model.Tuser">  
  
<resultMap type="xcg.model.Tuser" id="UserInfoMap">  
<id column="userid" property="userid" />  
<result column="loginname" property="loginname" />  
<result column="userpwd" property="userpwd" />  
<result column="realname" property="realname" />  
</resultMap>  
<select id="getAll" parameterType="xcg.model.Tuser" resultMap="UserInfoMap">  
select   
userid,  
loginname,  
userpwd,  
realname  
from t\_user  
  
</select>  
  
<select id="getOne" parameterType="xcg.model.Tuser" resultMap="UserInfoMap">  
  
select   
userid,  
loginname,  
userpwd,  
realname  
from t\_user  
where 1=1   
<if test="userid!=null">  
and userid=\#\{userid\};  
</if>  
</select>  
  
<select id="insertOne" parameterType="xcg.model.Tuser">  
insert into t\_user set userid=\#\{userid\},loginname=\#\{loginname\},userpwd=\#\{userpwd\},realname=\#\{realname\}  
</select>  
  
<select id="delete" parameterType="xcg.model.Tuser">  
delete from t\_user where userid=\#\{userid\}  
</select>  
  
<select id="change" parameterType="xcg.model.Tuser">  
update t\_user set userid=\#\{userid\},loginname=\#\{loginname\},userpwd=\#\{userpwd\},realname=\#\{realname\}  
</select>  
  
<select id="selectPage" parameterType="map" resultType="xcg.model.Tuser">  
select \*from t\_user limit \#\{start\},\#\{size\}  
</select>  
</mapper>

测试：

package xcg.test;  
  
  
import java.util.List;  
import xcg.dao.TuserDao;  
import xcg.model.Tuser;  
  
  
public class Test \{  
public static void main(String\[\] args) throws Exception \{  
TuserDao userDao = new TuserDao();  
Tuser t = new Tuser();  
t.setUserid(2);  
//获取所有  
List<Tuser> list = userDao.getAll();  
for(Tuser u:list)\{  
System.out.println(u.toString());  
\}  
//获取单个  
System.out.println("\*\*\*\*\*\*\*\*\*\*");  
Tuser user = userDao.getOne(t);  
System.out.println(user.toString());  
System.out.println("\*\*\*\*\*\*\*\*\*\*");  
Tuser userinsert = new Tuser();  
userinsert.setUserid(null);  
userinsert.setLoginname("test");  
userinsert.setUserpwd("1325665");  
userinsert.setRealname("hehe");  
System.out.println(userDao.insertOne(userinsert));  
System.out.println("保存成功");  
System.out.println("\*\*\*\*\*\*\*\*\*\*");  
Tuser userdelete = new Tuser();  
userdelete.setUserid(136);  
System.out.println(userDao.delete(userdelete));  
System.out.println("删除成功！");  
\}  
\}  
  
//注意：测试最好使用junit或testng，输出尽量不要使用system.out，当需要测试的内容量大时，这个语句会占用很多资源。此类是早前写的，在这里描述一下，不做修改。

2.接口+注解方式：注解方式脱离了xml，使用与sql语句不复杂的情况，定义接口，在接口上使用mybatis注解声明sql语句，在mybatis的核心配置文件中mappers页签中声明注册包扫描：<package name=”xcg.dao”>声明接口所在位置，通过：

接口   dao类对象 =   sqlsession.getMapper(接口.class);

来获得相应的dao类的实例对象。代码如下：

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>    
<settings>  
<setting name="useGeneratedKeys" value="true"></setting>  
<setting name="lazyLoadingEnabled" value="false"></setting>  
</settings>  
    <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/test" />    
                <property name="username" value="root" />    
                <property name="password" value="132566" />    
            </dataSource>    
        </environment>    
    </environments>    
        
        
        
    <mappers>    
           
       <package name="xcg.dao"/>   
    </mappers>

</configuration>

TuserDaoAnno.java：

import java.util.List;  
import org.apache.ibatis.annotations.Insert;  
import org.apache.ibatis.annotations.Select;  
  
  
import xcg.model.Tuser;  
//使用注解方式使用mybatis  
public interface TuserDaoAnno \{  
@Insert("insert into t\_user values(null,\#\{loginname\},\#\{userpwd\},\#\{realname\})")  
public void save(Tuser u);  
@Select("select \*from t\_user")  
public List<Tuser> getAll();  
\}

TestAnn.java：  
package xcg.test;  
import java.util.List;  
import org.apache.ibatis.session.SqlSession;  
import xcg.dao.BaseDao;  
import xcg.dao.TuserDaoAnno;  
import xcg.model.Tuser;  
//使用注解的方式  
public class TestAnn\{  
public static void main(String\[\] args) \{  
SqlSession session = BaseDao.sqlSession;  
TuserDaoAnno t = session.getMapper(TuserDaoAnno.class);  
List<Tuser> list = t.getAll();  
for(Tuser tt:list)\{  
System.out.println(tt.toString());  
\}  
\}  
\}

//此类方法用的要多于第一种。

3.接口+xml方式：推荐，接口定义方法和2相同，将接口的sql语句写到xml文件中，并保证接口中的方法名和xml中的select的id相同，并在xml的namespace配置为接口的地址，然后在mybatis中的核心配置文件中配置xml的mapper，并且该方法获取dao的实例和第二种方法完全相同。推荐使用这种方法。这种方法配置在ssm环境中需要在spring配置文件中加入：

这句配置就是可以将Dao的接口实例化出Dao类。代码如下：

Emp.java：

package xcg.model;  
  
  
import java.util.Date;  
import java.util.HashSet;  
import java.util.Set;  
  
@Gettrer

@Setter  
public class Emp \{  
private Integer empno;  
private String empName;  
private String passWord;  
private Date birth;  
private String email;  
private Set<Education> set = new HashSet<Education>();

public Emp()\{

EmpDaoAnnoAndXml .java：

package xcg.model;  
import java.util.List;  
public interface EmpDaoAnnoAndXml \{  
public List<Emp> getAll();  
\}

EmpMapperAndInterface.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="xcg.model.EmpDaoAnnoAndXml">  
  
<resultMap type="xcg.model.Emp" id="userAndStuResultMap">  
<id column="EMPNO" property="empno" />  
<result column="EMPNAME" property="empName" />  
<result column="PASSWORD" property="passWord" />  
<result column="BIRTH" property="birth" />  
<result column="EMAIL" property="email" />  
<collection property="set" resultMap="EducationMap" />  
</resultMap>  
  
<resultMap type="xcg.model.Education" id="EducationMap">  
<id column="EDUNO" property="eduno" />  
<result column="XUELI" property="xueli" />  
<result column="SCHOOL" property="school" />  
<result column="MAGIR" property="magir" />  
<result column="STARTTIME" property="startTime" />  
<result column="ENDTIME" property="endTime" />  
  
</resultMap>  
  
<select id="getAll" resultMap="userAndStuResultMap">  
select  
e.empno,e.empname,e.password,e.birth,e.email,d.eduno,d.xueli,d.school,d.magir,d.starttime,d.endtime  
from emp e left join education d  
on e.empno=d.empno  
</select>  
</mapper>

TestEmpInterfAndXml .java：

package xcg.test;  
import java.util.List;  
import org.apache.ibatis.session.SqlSession;  
import xcg.dao.BaseDao;  
import xcg.model.Emp;  
import xcg.model.EmpDaoAnnoAndXml;  
  
  
//使用Interface和xml方式  
public class TestEmpInterfAndXml \{  
public static void main(String\[\] args) \{  
  
SqlSession session = BaseDao.sqlSession;  
EmpDaoAnnoAndXml t = session.getMapper(EmpDaoAnnoAndXml.class);  
List<Emp> list = t.getAll();  
for(Emp tt:list)\{  
System.out.println(tt.toString());  
\}  
\}  
\}

笔者推荐使用第三种方式，集成在SSM框架中能十分方便的进行持久层的操作。