1.大家学习MyBatis时，可能会碰到实体类属性跟数据库字段不同的情况
如：数据库 ------ 实体类
stuname ----> name
即: 数据库中的stuname字段对应的事实体类里的name属性
如果这时，我们要用常规的查询方法时是不能正确查询到stuname的值的，它会显示为null
这时，我们可以使用我们的resultMap来解决这一问题。。。
源码介绍与对比:
1.Student.java (实体类)
package cn.zhang.entity; import java.util.Date; /**
* 学生实体类
*
*/
public class Student { private Integer stuno;
private String name;
private Integer stuage;
private Date studate; @Override
public String toString() {
return "Student [stuno=" + stuno + ", name=" + name + ", stuage="
+ stuage + ", studate=" + studate + "]";
} public Integer getStuno() {
return stuno;
} public void setStuno(Integer stuno) {
this.stuno = stuno;
} public String getName() {
return name;
} public void setName(String name) {
this.name = name;
} public Integer getStuage() {
return stuage;
} public void setStuage(Integer stuage) {
this.stuage = stuage;
} public Date getStudate() {
return studate;
} public void setStudate(Date studate) {
this.studate = studate;
} }
2.mybatis-config.xml (MyBatis的配置文件)
<?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>
<!-- 配置别名 -->
<typeAliases>
<!--方式一: 按类型名定制别名 -->
<typeAlias type="cn.zhang.entity.Student" alias="Student" />
<!--方式二: 拿当前指定包下的简单类名作为别名 -->
<!-- <package name="cn.zhang.entity"/> -->
</typeAliases>
<environments default="mysql">
<environment id="mysql">
<!-- 使用jdbc的事务 -->
<transactionManager type="JDBC" />
<!-- 使用自带的连接池 -->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/y2161" />
<property name="username" value="root" />
<property name="password" value="root" />
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="cn/zhang/dao/StudentDAO.xml" />
</mappers>
</configuration>
3.MybatisUtil.java (获得session的工具类)
package cn.zhang.util; import java.io.IOException;
import java.io.Reader; import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder; /**
* 获得session的工具类
*
*/
public class MybatisUtil { private static String config = "mybatis-config.xml";
static Reader reader;
static {
try {
reader = Resources.getResourceAsReader(config);
} catch (IOException e) {
e.printStackTrace();
}
}
private static SqlSessionFactory factory = new SqlSessionFactoryBuilder()
.build(reader); // 提供一个可以获取到session的方法
public static SqlSession getSession() throws IOException { SqlSession session = factory.openSession();
return session;
}
}
4.StudentDao.java (定义方法的接口)
package cn.zhang.dao; import java.io.IOException;
import java.util.List; import cn.zhang.entity.Student; public interface StudentDao { /**
* 查询所有记录
* @return
* @throws IOException
*/
public List<Student> findAll() throws IOException; }
5.StudentDaoImpl.java (实现接口方法的实现类)
package cn.zhang.dao.impl; import java.io.IOException;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import cn.zhang.dao.StudentDao;
import cn.zhang.entity.Student;
import cn.zhang.util.MybatisUtil; public class StudentDaoImpl implements StudentDao {
SqlSession session; public StudentDaoImpl() throws IOException {
session = MybatisUtil.getSession();
} /**
* 查询所有
*/
public java.util.List<Student> findAll() throws IOException {
List<Student> list = session.selectList("findAll");
session.close();
return list;
} }
6.StudentDAO.xml (对应的映射文件)
最常规的配法:
<?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="cn.zhang.dao"> <!-- 查询所有 -->
<select id="findAll" resultType="Student">
select * from student
</select> </mapper>
用resultMap的配法:
<?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="cn.zhang.dao"> <!-- 结果映射，指定了数据库和实体类中的对应值 -->
<resultMap type="Student" id="findstudent">
<result property="name" column="stuname" />
</resultMap> <!-- 查询所有 -->
<select id="findAll" resultMap="findstudent">
select * from student
</select> </mapper>
7.log4j.properties
### direct log messages to stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n ### direct messages to file mylog.log ###
log4j.appender.file=org.apache.log4j.FileAppender
log4j.appender.file.File=c\:mylog.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n ### set log levels - for more verbose logging change 'info' to 'debug' ### log4j.rootLogger=debug, stdout
8..MyTest.java (测试类)
package cn.zhang.test; import java.io.IOException;
import java.util.List;
import org.junit.Before;
import org.junit.Test;
import cn.zhang.dao.StudentDao;
import cn.zhang.dao.impl.StudentDaoImpl;
import cn.zhang.entity.Student; public class MyTest { StudentDao dao;
@Before
public void initData() throws IOException{
dao=new StudentDaoImpl();
} /**
* 查询所有学生
* @throws IOException
*/
@Test
public void findAll() throws IOException{
List<Student> list = dao.findAll();
for (Student student : list) {
System.out.println("编号: "+student.getStuno()+"姓名："+student.getName());
} } }
对应StudentDAO.xml中常规配法的结果:
对应StudentDAO.xml中resultMap配法的结果:
这样就可以成功的拿到值了，这就是resultMap的作用。
是不是很简单,这里只是记录一下。。