使用selectOne方法查询单条记录

1. 在接口StudentDao中新增一个方法

public Student findStuentById(int id);

完整源码：

package com.hbfu.dao;  
  
import com.hbfu.entity.Student;  
import java.util.List;  
  
public interface StudentDao {  
    public List<Student> findAllStudent();//查找全部学生  
    //新增方法
	public Student findStudentById(int id);  
}

2. 在映射文件StudentMapper.xml中新增一段select语句

<select id="findStudentById" parameterType="int" resultMap="studentResultMap">  
	 select * from student where id=#{id}  
</select>

完整源码：

<?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.hbfu.dao.StudentDao">  
  
	<!--  配置结果映射  -->  
	<resultMap id="studentResultMap" type="com.hbfu.entity.Student">  
		<result property="sgender" column="gender"></result>  
		<result property="sage" column="age"></result>  
	</resultMap>  
	<!-- 查询 -->  
	<select id="findall" resultMap="studentResultMap">  
		select * from student  
	</select>  
  
	<!-- 查询单条语句  -->  
	<select id="findStudentById" parameterType="int" resultMap="studentResultMap">  
		select * from student where id=#{id}  
	</select>  
	  
</mapper>

3. 在接口StudentDao的实现类StuedntDaoImpl中新增方法

@Override  
public Student findStudentById(int id) {  
    Student student = new Student();  
	try {  
        SqlSession session = MyBatisUtil.getSession();  
		student = session.selectOne("com.hbfu.dao.StuentDao.findStudentById",id);  
	}catch (Exception e){  
        e.printStackTrace();  
	}  
    return student;  
}

完整源码：

package com.hbfu.dao;  
  
import com.hbfu.entity.Student;  
import com.hbfu.util.MyBatisUtil;  
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 java.io.Reader;  
import java.util.ArrayList;  
import java.util.List;  
  
public class StudentDaoImpl implements StudentDao{  
  
    @Override  
	public List<Student> findAllStudent() {  
        SqlSession session = null;  
		List<Student> studentList=new ArrayList<Student>();  
		try {  
            session= MyBatisUtil.getSession();  
			studentList=session.selectList("com.hbfu.dao.StudentDao.findall");  
		}catch (Exception e){  
            e.printStackTrace();  
		}  
        return studentList;  
	}  
  
    //新增一个查询单条记录方法  
	@Override  
	public Student findStudentById(int id) {  
        Student student = new Student();  
		try {  
            SqlSession session = MyBatisUtil.getSession();  
		student = session.selectOne("com.hbfu.dao.StudentDao.findStudentById",id);  
		}catch (Exception e){  
            e.printStackTrace();  
		}  
        return student;  
	}  
}

4. 在测试类StuentTest中添加一个方法studentDao.findStudentById(int id)

System.out.println("通过id查询学生信息"+studentDao.findStudentById(2));

完整源码：

import com.hbfu.dao.StudentDao;  
import com.hbfu.dao.StudentDaoImpl;  
import com.hbfu.entity.Student;  
import org.junit.Test;  
  
public class StudentTest {  
    @Test//注解--测试方法，不需要写主方法就可以运行测试程序  
	public  void test(){  
        StudentDao studentDao = new StudentDaoImpl();  
		System.out.println(studentDao.findAllStudent());  
		//新增一个输出语句--查询单条记录方法，并传入id  
		System.out.println("通过id查询学生信息"+studentDao.findStudentById(2));  
	}  
}